Reliability and durability of equipment. further use of the object

Reliability – this is the property of an object to perform specified functions, maintaining over time the values ​​of established operational indicators within specified limits corresponding to specified modes and conditions of use, Maintenance, repair, storage and transportation. This is a quality that extends over time. Therefore, the concept of reliability is close to the concept of quality, and therefore the problems of quality management are directly reflected in the concept of reliability.

Reliability is an objective property of a product; reliability can be measured. To measure reliability, the concepts of “failure”, “probability of failure-free operation”, “failure rate”, etc. were introduced. The concepts of failure and reliability are among the basic ones in reliability theory. Usually under reliability understand the ability of products to remain operational for a long time. Refusal– this is a complete or partial loss of the product’s functionality.

American authors D. Lloyd and M. Lipov in the book “Reliability” write: “Reliability affects cost, time costs, psychologically - in the form of inconvenience, and in certain cases also threatens the safety of people and the nation. Typically, losses due to unreliability are not only the cost of the unit that fails, but also the cost of the associated equipment that deteriorates or is destroyed as a result of the failure... A classic example of the psychological effect of unreliability is the sad memory of the Avangard satellites, the United States, acutely experiencing the successes of Russia, which launched ". Sputnik-1" tried to enter the competition using for this purpose an almost untested rocket, which had to work almost to the limit of its capabilities. The failures and the ensuing despondency and loss of prestige were very serious."

American writer, poet and scientist of the 19th century. There is a poem by Oliver Holmes called "The Priest's Masterpiece, or the Wonderful One-Horse Carriage." It talks about a priest who built a carriage, remarkable in that all its parts had exactly the same strength. This stroller lasted exactly 100 years and fell apart right along the road. All parts broke at the same time.

A product that would be destroyed in this way is the dream of any engineer and quality management specialist. But real mechanisms are destroyed randomly and at random times. Therefore, statistical methods and the probabilistic apparatus of mathematics are used to assess reliability. The probability of failure-free operation is the probability that a product failure will not occur in a given time interval or within a given operating time.

There are many numerical characteristics to assess reliability. For example, availability factor is the probability that the product will be operational at specified or random moments, – the time during which the product is operational, referred to the time of its operation.

by the consumer means the time during which a product with a manufacturer's guarantee maintains its quality parameters expected by the consumer, and therefore this time is usually called the guaranteed service life of the product.

Product service life guaranteed by the manufacturer called the durability of the product. Durability depends on the possibility of repair, after which its quality parameters can be restored, i.e. on the maintainability of the product.

Based on the actual service life, the consumer judges mainly the quality of the product he purchased, which subsequently affects his attitude towards the corresponding manufacturer and, ultimately, the image of this manufacturer in the eyes of the consumer.

The most widely used indicator in reliability studies is failure rate (λ ):

Where n– number of failed products; N- total number

products; – average test time.

The average test time is determined by the formula

where is the number of products in the test group; – duration of the test for this group.

If the number of failed products exceeds 5-10%, then adjustments are made to the calculation:

(2.3)

where is the number of failed products in this group;

– number of failures during the same test time;

Duration of tests to disable the product.

To calculate the average failure rate, it is important to select the correct time interval, since failure density usually varies over time.

EXAMPLE 2.1

When testing a certain piece of electronic equipment, λ can be determined after 1000–2000 hours. Testing is carried out in 4 groups of 250 products for 2000 hours.

The test results are as follows:

Let's calculate:

In total, 20 products failed during the tests (7 + 5 + + 4 + 4).

Parts and assemblies may fail due to manufacturing defects and other reasons.

At a constant level of failure rate per unit time, the probability distribution of failure-free operation intervals is expressed by the exponential distribution law of operational durability.

The main quality parameters for products are:

• – functional characteristics – compliance of the product with its intended purpose;
• – reliability – the number of repairable failures over the service life;
• – durability (service life) – an indicator related to reliability;
• – defect-free – the number of defects detected by the consumer.

Reliability is a concept associated primarily with technology. It can be interpreted as failure-free-

ability, ability to perform specific task or howprobability of execution specific function or functions for a certain time and under certain conditions .

As a technical concept, "reliability" is the probability (in a mathematical sense) of satisfactorily performing a specified function. Since reliability is a probability, statistical characteristics are used to evaluate it. The results of reliability measurements should include data on sample sizes, confidence limits, sampling procedures, etc.

In technology, the concept of “satisfactory performance” is also used. The precise definition of this concept is related to the definition of its opposite - “unsatisfactory performance” or “refusal”.

The general concept of “reliability” is opposed to the concept of “reliability itself” of a sample of equipment, which is the probability of failure-free operation in accordance with specified technical conditions under specified verification tests for the required period of time. Reliability testing measures the actual reliability. It essentially represents the “operational reliability” of the equipment and is a consequence of two factors: actual reliability and operational reliability. Operational reliability, in turn, is determined by the compliance of the equipment with its use, the procedure and method of operational use and maintenance, the qualifications of personnel, the ability to repair various parts, factors environment and etc.

For each characteristic to be measured, in technical conditions a tolerance is specified, the violation of which is considered as a “failure”. The tolerance defining a failure must be optimal with the necessary allowance for wear of parts, i.e. it must be wider than the normal factory tolerance. Therefore, factory tolerances are set taking into account the fact that parts wear out over time.

Let us characterize the basic concepts related to reliability.

• 1. Serviceability – the state of the product in which it is in this moment time meets all the requirements established both in relation to the main parameters characterizing the normal performance of specified functions, and in relation to secondary parameters characterizing ease of use, appearance and so on.
• 2. Malfunction – the state of a product in which it does not currently meet at least one of the requirements characterizing the normal performance of specified functions.
• 3. Performance – the state of the product in which it currently meets all the requirements established in relation to the basic parameters characterizing the normal performance of specified functions.
• 4. Refusal – an event consisting in the complete or partial loss of a product’s functionality.
• 5. Complete refusal – a failure, until the elimination of which the use of the product for its intended purpose becomes impossible.
• 6. Partial failure – failure, until elimination of which partial use of the product remains possible.
• 7. Reliability – the property of a product to continuously maintain performance over a certain period of time.
• 8. Durability – the property of a product to maintain operability (with possible interruptions for maintenance and repair) until destruction or another limiting state. The limit state can be set based on changes in parameters, safety conditions, etc.
• 9. Maintainability – property of a product, expressed in its suitability for carrying out maintenance and repair operations, i.e. to the prevention, detection and elimination of malfunctions and failures.
• 10. Reliability (in a broad sense) – property of a product due to the reliability, durability and maintainability of the product itself and its parts and ensuring

ensuring the preservation of the performance characteristics of the product under specified conditions.

• 11. Recoverability – the ability of a product to restore the initial values ​​of parameters as a result of eliminating failures and malfunctions, as well as restore the technical life as a result of repairs.
• 12. Storability – the property of a product to maintain serviceability and reliability under certain conditions and transportation.

For some products that are relatively simple in design, the concept of “failure” can be introduced quite clearly. For example, a light bulb either lights up or doesn’t light up.

In practice, sometimes special attention is paid to improving the main components of the product, losing sight of the fact that the cause of unreliability and subsequent accidents may be structural components that are of an auxiliary nature.

To measure (estimate) reliability, it is necessary to test an apparatus that would describe random events or random processes. We are talking about probability theory and mathematical disciplines. The main quantitative indicator of reliability is the probability of failure-free operation of a product for a given period of time.

Probability of failure-free operation is the probability that a product failure will not occur within a given time interval or within a given operating time. With the introduction of this concept, it becomes possible to measure reliability and compare the reliability of a product according to this indicator. The probability of failure-free operation of the same product is not the same at different moments of its operation.

To assess reliability, there are many characteristics, in particular: probability of failure-free operation; availability factor(the probability that the product will be operational at a given or random moment); time utilization ratio(the time during which the product is operational, referred to the time of its operation).

Time of trouble-free operation of the product consumer refers to the time during which a product with a manufacturer's guarantee maintains its quality parameters expected by the consumer, and therefore this time is usually called guaranteed product service life.

Guaranteed product service life, as a rule, less than its actual service life, which is characterized by the durability of the product.

Durability depends on the possibilities of repair, after which the quality parameters of the product are restored, i.e. depends on maintainability. Durability characterizes the actual service life of a product. Based on the actual service life, the consumer judges the quality of the purchased product, which subsequently affects his attitude towards the manufacturer and, ultimately, the image of this manufacturer in the eyes of the consumer.

At the same time, the guaranteed service life of a product is of significant importance at the time of its purchase in comparison with a similar product from competitors, and the strictness of the subsequent fulfillment of all pre-agreed conditions and guarantees when purchasing a product determines the consumer’s attitude towards the reliability of not only the supplier (seller), but also the manufacturer .

If during the guaranteed service life the value of the quality parameters does not meet the consumer’s expectations, which are guaranteed by the manufacturer, then the responsibility for this lies with the manufacturer of the product (supplier), who must carry out repairs at his own expense, and if repairs are impossible, replace defective goods for quality.

The manufacturer must guarantee the quality of the product both during its storage and during its operation.

To predict failures in the future, actual data on the frequency of failures during the period of use of the equipment for its intended purpose is necessary.

When processing information, the inverse of the failure rate is used "mean time between failures".

Quite complex analytical techniques are used to study reliability. For example, when researching electronic systems the engineer selects a number of key characteristics, selects the most important one, selects options for action and one of these options, studies the operating conditions and evaluates them.

Due to the high pace of modern scientific and technological progress, it is important to choose the optimal moment for the transition from scientific research and preparatory work to production. In a competitive environment, the timing of production launch is an important factor, acting in two directions: launching production “too early” can lead to the same negative consequences as launching “too late”.

The reasons for manufacturing unreliable products may be:

• – lack of regular verification of compliance with standards;
• – errors in the use of materials and improper control of materials during production;
• – incorrect accounting and reporting of controls, including information on technology improvements;
• – sampling schemes that do not meet the standards;
• – lack of testing of materials for their compliance;
• – failure to comply with acceptance testing standards;
• – lack of instructional materials and instructions for conducting control;
• – irregular use of control reports for improvement technological process.

The mathematical models used to quantify reliability depend on the “type” of reliability. Modern theory identifies three types.

• 1. Instant Reliability(eg fuses).
• 2. Reliability with normal service life(for example, computer technology). In normal serviceability studies, the unit of measurement is "mean time between failures". The range recommended in practice is from 100 to 2000 hours.
• 3. Extremely long-term operational reliability(For example, spaceships). If service life requirements exceed 10 years, they are classified as extremely long service reliability.

Under normal operational reliability, technical prediction of reliability can be theoretical, empirical and experimental.

At theoretical testing means develop a scheme for this operation and check the compliance of the scheme using mathematical model. If the diagram does not correspond to the operation, clarifications are made until compliance is achieved. This is the so-called scientific research.

Empirical approach consists of performing the necessary measurements on the actual products produced and drawing conclusions about reliability.

Experimental approach occupies an intermediate position between theoretical and empirical. The experimental approach uses both theory and measurements. At the same time, methods of mathematical modeling of processes are widely used, creating experimental data on this basis. After this, the information is subjected to statistical analysis using modern means computer technology, which ensures the reliability and validity of the conclusions.

Any type of test is preceded by an experimental plan.

Because reliability is a probabilistic characteristic, quantitative ratings are used to estimate the “average reliability” calculated from samples of the entire population, as well as to predict future reliability. Reliability is examined using statistical methods and can be refined with their help.

It should be noted that service life is not the only indicator of performance properties.

In some cases, other indicators are used (mileage, duration of active use, etc.); The service life of products depends on both manufacturing conditions and operating conditions.

The reliability of many products can be revealed in the conditions of their consumption. A scientifically based system for monitoring the operation of products makes it possible to identify defects caused by violations of the manufacturer’s technological process.

The manufacturer must:

apply statistical quality control;

• – check the controllability state of processes at certain intervals;
• – strive to improve the quality and reliability of manufactured equipment;
• – ensure a correct understanding of customer requirements and their satisfaction.

An analysis of various definitions of reliability available in the literature leads to a generalized conclusion that reliability is understood as the failure-free operation of products under regulated operating conditions for a certain period of time.

Selective control. Characteristic feature control when studying reliability is that the possibilities of compiling samples are limited by the small number of pieces of equipment in the early stages of its development. As a rule, the number of units for testing is chosen by the customer. Moreover, the level of reliability of the test results varies depending on the number of units tested. The duration of the expected operating time and the degree of wear of the samples during testing have the same effect.

In practice, sampling for reliability testing is carried out in accordance with a plan that initially (and then each time a sampled product is characterized by a reduced mean time between failures) provides for a 10% consumer risk at an acceptable quality level corresponding to 10% of the units. with reliability below normal. Let us note some differences between statistical quality control and random checks in connection with technical support reliability. In the latter case, in addition to questions of sample representativeness, the question of the required test time arises.

Naturally, 100% testing of batches until the samples are completely worn out is impossible. Therefore, sampling schemes used in reliability studies provide for ongoing random testing of manufactured products with a weakened control regime until products with characteristics below the standard are detected. In other words, the weakened control procedure continues until a defective specimen appears in the sample. If a unit of manufactured products is detected with a characteristic lower than the norm, the normal control mode is restored, which can switch to an enhanced control mode depending on the number of defects identified in the sample. Typically, such sampling plans are developed taking into account a given mean time between failures and monthly production volumes.

When studying reliability, the method of sequential analysis is often used to decide whether to accept or reject a batch. First of all, it is determined that the mean time between failures under given conditions is at or above the established minimum. Such tests are planned after the specimens and test apparatus to be tested have been properly verified. Testing stops as soon as a decision on acceptance is made. But they do not stop if the decision is made to reject the batch. In the latter case, they continue in accordance with a precisely defined statistical control plan.

Refusal means the appearance of the first signs malfunction or equipment malfunctions. Each failure is characterized by a certain time of its occurrence.

The results of reliability research are important for the certification of products and quality systems Mazur I. I., Shapiro V. D. Quality management: textbook. allowance. M.: Omega-L, 2011.

One of the main characteristics of complex technical systems is their reliability. Reliability theory has received significant development and practical application in technology.

Reliability- this is the property of an object to preserve over time, within established limits, the values ​​of all parameters that allow it to perform the required functions. To quantify reliability, probabilistic values ​​are used. Those changes that occur over time in any technical system and lead to the loss of its performance are associated with external and internal influences to which it is exposed. During operation, the system is affected by all types of energy, which can lead to changes in the parameters of individual elements, mechanisms and the system as a whole. There are three main sources of influence:

• - the effect of environmental energy, including a person performing the functions of an operator or repairman;
• - internal energy sources associated both with the work processes occurring in the technical system and with the operation of individual elements of the system;
• - potential energy that is accumulated in materials and parts of system components during their manufacture (internal stresses in the casting, installation stresses).

During the operation of a technical object, the following main types of energy are observed, affecting its performance and reliability (Fig. 6.4).

Mechanical energy which is not only transmitted through all elements of the system during operation, but also affects it in the form of static or dynamic loads from interaction with the external environment.

Thermal energy affects the system and its parts during fluctuations in ambient temperature, during the work process (especially strong thermal effects occur during the operation of engines and a number of technological machines), during the operation of drive mechanisms, electrical and hydraulic devices.

Chemical energy also affects the operation of the system. For example, moisture contained in the air can cause corrosion of individual system components. If the system equipment operates in aggressive environments (equipment chemical industry, ships, etc.), then chemical influences cause processes leading to the destruction of individual elements and components of the system.

Nuclear (atomic) energy, released during the transformation of atomic nuclei, can affect materials (especially in space), changing their properties.

Electromagnetic energy in the form of radio waves ( electromagnetic vibrations) permeates the entire space around the object and can affect the operation of electronic equipment.

Biological factors can also affect the performance of the system in the form of microorganisms, which not only destroy some types of plastics, but can even affect metal.

Rice. 6.4.

Thus, all types of energy act on a technical system and its mechanisms, cause a number of undesirable processes in it, and create conditions for the deterioration of its technical characteristics.

Normal operation of an ergotechnical system is characterized by a certain degree of reliability, which is a complex probabilistic characteristic of the system’s successful performance of the required target functions while maintaining its performance indicators within specified limits for the required time. Reliability theory allows us to estimate the service life, at the end of which technical means is exhausting its resource and must undergo major renovation, modernization or replacement. One of the basic concepts of reliability theory is failure.

Refusal- this is a malfunction technical device due to cessation of operation or due to a sudden change in its parameters. In reliability theory, the probability of failure is estimated, that is, the probability that a technical device will fail within a given operating time. The study of the reasons that cause failures of objects, the determination of the patterns to which they obey, the development of a method for checking the reliability of products and methods for monitoring reliability, methods of calculation and testing, finding ways and means to improve reliability are the subject of reliability research. When studying reliability issues, a wide variety of objects are considered - products, structures, systems with their subsystems. The reliability of a product depends on the reliability of its elements, and the higher their reliability, the higher the reliability of the entire product.

Ensuring system reliability covers a variety of aspects of human activity. Reliability is one of the most important characteristics taken into account at the stages of development, design and operation of a wide variety of technical systems (Fig. 6.5).

Insufficient reliability of the facility leads to huge costs for its repair, downtime of machines, cessation of supply of electricity, water, gas to the population, vehicles, failure to fulfill important tasks, sometimes to accidents associated with large economic losses, destruction of large objects and human casualties.

As follows from the above definition of reliability, the most significant thing for the successful operation of any technical system and the performance of its specified functions is the preservation of its functionality.

Rice. 6.5.

Performance as the state of a system means the ability to perform the required functions with given operating parameters. In turn, the availability of system operability throughout the entire period of its operation presupposes the reliability of its functioning, and is also indirectly related to other properties of operational reliability. The reliability (operability) of an object is complex property, it is assessed by four quantitative indicators - reliability, durability, maintainability and storability, or a combination of these properties.

Reliability- the property of an object to maintain its functionality for a given time without failures or forced interruptions.

Durability- the property of an object to save operational state to the limit state with the necessary breaks for routine maintenance and repairs.

Maintainability- the property of an object’s adaptability to preventing, identifying and eliminating failures in its performance by carrying out routine maintenance and repairs.

Storability- the property of an object to maintain the required performance indicators during and after the established period of its storage or transportation.

Objects are divided into unrecoverable, which cannot be repaired by the consumer and must be replaced (for example, light bulbs, bearings, resistors, etc.), and recoverable, which can be restored by the consumer (for example, a TV, a car, a tractor, a machine, etc.).

A classification of failures has been developed from the standpoint of studying the nature and nature of failures, the influence of various factors on their occurrence (Fig. 6.6).

• 1. According to the conditions of occurrence, they divide failures in normal And abnormal (extreme) conditions. Abnormal conditions occur due to human error, natural disasters or other emergency situations.
• 2. According to the reasons for their occurrence, they distinguish failures not associated with destruction and caused by the destruction of the object.
• 3. By the nature of occurrence: sudden failures associated with a sharp change in basic parameters, and gradual failures under the influence of random factors, caused by slowly occurring irreversible processes
• 4. According to the degree of influence on performance: complete and partial failures. The latter are associated with a “partial” loss of system functionality, i.e., with a reduced level of functioning. Such failures occur in systems that have a large number of autonomous elements. If some fail, most elements remain operational.
• 5. According to signs of manifestation: explicit and implicit failures. The occurrence of an obvious failure is detected by organoleptic methods. In case of implicit failures, their detection requires the use of special instruments or devices or significant experience and skill of personnel.
• 6. In relation to each other: independent and dependent failures, when the occurrence of one failure entails the occurrence of others. The interconnection of failures can lead to their avalanche-like growth.
• 7. According to the consequences, they are distinguished: dangerous and safe failures for the health and life of personnel and for the environment; severe failures leading to significant material, financial and other costs and losses; easy failures almost no losses.
• 8. According to the method of elimination, there are: Failures to be eliminated replacing elements, adjusting, cleaning and self-correcting failures or failures.
• 9. By complexity of elimination: simple and complex failures, requiring highly qualified specialists and significant labor costs.

• 0 - element failure,
• 1- primary failure;
• 2- secondary failures;
• 3 - erroneous commands,
• 4-elements in specified operating modes,
• 5 - excess voltage;
• 6- erroneous commands;
• 7- natural aging;
• 8- adjacent elements,
• 9- environment;
• 10 - enterprise personnel

Rice. 6.6. Failure characteristics of technical system elements

• 10. By frequency of occurrence: on random(single) and non-random(systematic) failures. Random failures are caused by unforeseen loads, hidden defects in materials, manufacturing errors, and maintenance personnel errors. Non-random failures are natural phenomena that cause a gradual accumulation of damage associated with the influence of the environment, time, temperature, radiation, etc.
• 11. But possible solutions: Recoverable and unrecoverable failures, in the event of which restoring the system’s functionality is technically impossible or economically unjustified.
• 12. By origin: constructivefailures caused by design flaws; technological failures- shortcomings in the technological process of manufacturing and assembling parts and assemblies and operational failures, related only to operating conditions.

Depending on the ability to predict the moment of failure, all failures are divided into sudden(breakdowns, jamming, shutdowns) and gradual(wear, aging, corrosion). Failures leading to severe consequences are classified as “ critical».

TO accidents include all failures, the occurrence of which is associated with a threat to people and the environment, as well as serious economic and moral damage. The reliability of technical systems is influenced by three groups of factors: structural, technological and operational.

TO design factors include: schematic diagram of the machine, quality of materials, shape and dimensions of parts, safety factor, applied methods of strength calculations, structural stress concentrators in parts

Technological factors- factors associated with the process of obtaining stable properties of materials, ensuring stability of structure, physical and mechanical properties, strength; factors associated with workpiece shaping, processing and assembly methods; methods and modes of mechanical, thermal, chemical-thermal treatment; cutting tool geometry; organization of technical control at stages of the technological process.

Operational Factors- nature of loading, speed, pressure, ambient temperature, environmental humidity, types and methods of lubrication, compliance with technical operation rules, maintenance, quality of repairs, qualifications of repair and operational personnel, technical equipment of repair services, etc.

TO category:

Blacksmithing

Reliability and durability of equipment

Durability and reliability are the most important performance characteristics of the equipment. Reliability is the property of equipment to perform its functions, maintaining performance within specified limits for the required period of time. Reliability is the most important operational indicator of a machine’s operation, characterizing its quality.

One of the elements of reliability is non-failure operation, i.e. the ability of a machine to remain operational without forced interruptions. Reliability is determined by the time of continuous operation of the machine without downtime associated with adjustments and repairs. Different machine parts naturally have different service lives. The reliability characteristic is taken to be a period close to the shortest service life of the parts.

However, the concept of non-failure operation does not fully reveal the operational qualities of the equipment. Let, for example, one press have high reliability, that is, it works for a long time without adjustments, but then requires lengthy repairs. And when operating another press, frequent short-term adjustments are required, but there is no need for lengthy repairs. In some cases, the second press, despite its lower reliability, has advantages associated with its greater durability.

The property of a machine to remain operational to its limiting state with the necessary breaks for maintenance and repair is called durability.

Over time, the properties of materials, including the strength of parts, as well as their geometry, change. Consequently, reliability indicators do not remain constant. Nevertheless, the machine must remain operational, which is ensured not only by its quality, but also proper organization maintenance and repair.

Durability is determined by the time and money spent on repairs and adjustments of the machine over the entire period of its operation. This means that the machine that, other than that, equal conditions produces more products over a long period of time and has greater durability. In other words, the concept of durability is also related to equipment performance.

Wear of a part is the result of a gradual change in its dimensions due to friction under the action of various loads under the conditions in which the machine is operated.

Wear and damage that occur during operation are divided into normal (acceptable) and unacceptable (emergency). Acceptable conditions that occur under normal operating conditions include abrasive wear, crushing of surface layers, etc. These damages cannot be completely excluded. However, it is necessary to reduce them to a minimum so that negative consequences manifest themselves over the longest possible period of time. Acceptable wear and damage are repaired during scheduled maintenance.

In case of unacceptable wear and damage, either the destruction of the part occurs or its deformation is such that it completely prevents the normal operation of the machine. Inadmissible (emergency) damage is eliminated when emergency repairs because they appear suddenly.

The durability of parts depends on the correct selection of materials for the rubbing pair. In this case, the operating conditions of the equipment should be taken into account, since the same pair can be wear-resistant in some conditions, and wear out quickly in others.

The materials used for guides must have high wear resistance, a low coefficient of friction, and be able to withstand significant mechanical loads without changing properties. Bronze and plastics are used as antifriction materials. Low-load gears are also made from plastic, which makes them not only wear-resistant, but also silent in operation.

Materials for parts of braking devices and controls, such as brake discs and clutches, must, on the contrary, have friction properties, that is, have a high coefficient of friction.

Special attention You should pay attention to the wear of the following parts of forging and pressing machines: bearings, guides of hydraulic presses and crank machines, plungers, seals, disks friction clutches and brakes, etc. Since wear affects the accuracy of equipment, wear rates are determined by accuracy standards.

Basic concepts of reliability. classification of failures. Components of reliability

The terms and definitions used in reliability theory are regulated by GOST 27.002-89 "Reliability in technology. Terms and definitions."

1. Basic concepts

Reliability– the property of an object to perform specified functions, maintaining the values ​​of established operational indicators over time and within specified limits.
An object– a technical product for a specific purpose, considered during the periods of design, production, testing and operation.
Objects can be various systems and their elements.
An element is the simplest component of a product; in reliability problems, it can consist of many parts.
A system is a set of jointly operating elements designed to independently perform specified functions.
The concepts of element and system are transformed depending on the task at hand. For example, a machine tool, when establishing its own reliability, is considered as a system consisting of individual elements - mechanisms, parts, etc., and when studying the reliability of a production line - as an element.
The reliability of an object is characterized by the following main states and events.
Serviceability– the state of the object in which it meets all the requirements established by the normative and technical documentation (NTD).
Performance– the state of an object in which it is capable of performing specified functions, maintaining the values ​​of the main parameters established by the normative and technical documentation.
The main parameters characterize the functioning of the object when performing assigned tasks.
Concept serviceability broader than the concept performance. An operational object must satisfy only those requirements of the technical documentation, the fulfillment of which ensures the normal use of the object for its intended purpose. Thus, if an object is inoperative, then this indicates its malfunction. On the other hand, if an object is faulty, this does not mean that it is inoperable.
Limit state– the state of an object in which its intended use is unacceptable or impractical.
The use (use) of the object for its intended purpose is terminated in the following cases:

in case of an unrecoverable security breach;

in case of irreparable deviation of the values ​​of the specified parameters;

with an unacceptable increase in operating costs.

For some objects, the limit state is the last in its operation, i.e. the facility is decommissioned; for others, it is a certain phase in the operational schedule that requires repair and restoration work.
In this regard, objects can be:

unrecoverable, for which operability in the event of a failure cannot be restored;

recoverable, the functionality of which can be restored, including by replacement.

Non-recoverable objects include, for example: rolling bearings, semiconductor products, gears, etc. Objects consisting of many elements, for example, a machine tool, a car, electronic equipment, are recoverable, since their failures are associated with damage to one or a few elements that can be replaced.
In some cases, the same object, depending on its characteristics, stages of operation or purpose, can be considered recoverable or non-recoverable.
Refusal– an event consisting in a violation of the operational state of an object.
Failure criterion is a distinctive feature or set of features according to which the fact of a failure is established.

2. Classification and characteristics of failures

By type, failures are divided into:

operational failures(the performance of the main functions of the object stops, for example, the breakdown of gear teeth);

parametric failures(some object parameters change within unacceptable limits, for example, loss of machine accuracy).

By their nature, failures can be:

random, caused by unforeseen overloads, material defects, personnel errors or control system failures, etc.;

systematic, caused by natural and inevitable phenomena that cause gradual accumulation of damage: fatigue, wear, aging, corrosion, etc.

Main characteristics of failure classification:

nature of occurrence;

cause of occurrence;

nature of elimination;

consequences of failures;

further use of the object;

ease of detection;

time of occurrence.

Let's take a closer look at each of the classification features:

Sudden failures usually manifest themselves in the form of mechanical damage to elements (cracks - brittle fracture, insulation breakdowns, breaks, etc.) and are not accompanied by preliminary visible signs of their approach. Sudden failure is characterized by the independence of the moment of occurrence from the time of previous operation.
Gradual failures are associated with wear of parts and aging of materials.

cause:	structural failure caused by deficiencies and poor design of the facility;
	production failure associated with errors in the manufacture of an object due to imperfections or violations of technology;
	operational failure caused by violation of operating rules.
nature of elimination:	sustained failure;
	intermittent failure (appearing/disappearing).
	consequences of failure: easy failure (easily remedied);
	average failure (not causing failures of adjacent nodes - secondary failures);
severe failure (causing secondary failures or leading to a threat to human life and health).	further use of the object:
	complete failures that prevent the facility from operating until they are eliminated;
partial failures, in which the object can be partially used.	ease of detection:
	obvious (explicit) failures;
hidden (implicit) failures.	time of occurrence:
	running-in failures that occur during the initial period of operation;
	failures during normal operation;

wear failures caused by irreversible processes of wear of parts, aging of materials, etc.

3. Components of reliability

Reliability is a complex property that includes, depending on the purpose of the object or its operating conditions, a number of simple properties:

reliability;

durability;

maintainability;

Reliability preservation.
– the property of an object to continuously maintain operability for some operating time or for some time.
Durability– the property of an object to maintain operability until a limit state occurs with an established system of maintenance and repairs.
Maintainability– a property of an object, which consists in its adaptability to preventing and detecting the causes of failures, maintaining and restoring operability through repairs and maintenance.
Storability– the property of an object to continuously maintain the required performance indicators during (and after) storage and transportation.
Depending on the object, reliability can be determined by all of the listed properties or part of them. For example, the reliability of a gear wheel and bearings is determined by their durability, and the reliability of a machine tool is determined by its durability, reliability and maintainability.

4. Main reliability indicators

Reliability indicator quantitatively characterizes the extent to which a given object has certain properties that determine reliability. Some reliability indicators (for example, technical resource, service life) may have a dimension, a number of others (for example, the probability of failure-free operation, availability factor) are dimensionless.
Let's consider the indicators of the reliability component - durability.
Technical resource– operating time of an object from the start of its operation or resumption of operation after repair until the onset of the limit state. Strictly speaking, the technical resource can be regulated as follows: up to average, capital, from capital to the nearest average repair, etc. If there is no regulation, then we mean the resource from the start of operation until reaching the limit state after all types of repairs.
For non-repairable objects, the concepts of technical resource and time to failure coincide.
Assigned resource– the total operating time of an object, upon reaching which operation must be stopped, regardless of its condition.
Life time– calendar duration of operation (including storage, repair, etc.) from its beginning until the onset of the limit state.
In Fig. a graphical interpretation of the listed indicators is given, with:

t0 = 0 – start of operation;
t1, t5 – shutdown moments for technological reasons;
t2, t4, t6, t8 – moments of switching on the object;
t3, t7 – moments when the object is taken out for repairs, medium and major, respectively;
t9 – moment of termination of operation;
t10 – moment of object failure.

Technical resource (time to failure)Main concepts theories of rights... in finished product. Concept And classification transaction costs, ways... economics, it components To transactional... determines_rationally justified refusal 0T rights to... ruler less reliable. Eventually...

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Cheat sheet >> Sociology

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Lecture >> State and law

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If the child begins to get up and move more actively, then it’s time to limit access to some cabinets and drawers for his safety.

In principle, we were not going to choose, because... IKEA locks inspired the greatest confidence. But the presence of 2 large chests of drawers (and that’s already 11 drawers) and besides them 12 other important and dangerous doors forced us to take a closer look and evaluate other cheaper analogues. We sampled different manufacturers and almost all of them had to be replaced with IKEA ones.

About the advantages (and no disadvantages other than cost were found)

They have been serving for a year without any complaints. Sticks to any surface. The main thing is to degrease it before gluing it.

There is an adjustment for different doors in terms of the width of the lock - we installed it on a cabinet in the bathroom,

where the distance is small, and on the drawer under the crib, where the maximum length of the lock was required. Adjustable by cutting the tape. The truth is already irrevocable))

The lock is quite difficult to open. With long nails, I think it’s more difficult; with small nails, opening and closing takes seconds. The main thing is to get used to it. Well, of course, a child can’t do it at all. Unlike other locks we've tried.

The color is only white. We were more than satisfied with this, because... in the room everything is mostly bright, but where things don’t match is not scary for us - safety comes first.