Chinese name: failure rate English name: failure rate Definition 1: the ratio of the total number of failures of a group of a product in the specified time of use to the total working time of the group of products in that time of use. Applied disciplines: aviation science and technology (first-level disciplines); aircraft maintenance engineering (second-level disciplines) Definition 2: work to a certain moment has not yet failed the product, in the moment after the unit of time after the occurrence of the probability of failure. Applied disciplines: mechanical engineering (first-level disciplines); reliability (second-level disciplines); reliability of general terms (third-level disciplines) The above content by the National Science and Technology Nomenclature Validation Committee validation and publication
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Failure rate refers to work up to a certain moment of the product has not yet failed, after the moment, the probability of failure in a unit of time. Generally recognized as λ, it is also a function of time t, so also known as λ (t), known as the failure rate function, sometimes also known as the failure rate function or risk function.
Contents
Definitions
CategorizationEarly Failure Periods
Incidental Failure Periods
Consumptive Failure Periods
Calculation of Failure Rates
Failure Modes and Effects Analysis (FMEA) Basic Terminology
History
Implementation
Application of FMEA in Design Work
Preparation
Step 1: Severity
Step 2: Frequency of Occurrence
Step 3: Inspection
Risk Prioritization
Timing of FMEA
Use of FMEA
Benefits
Limitations
Definitions
Classification Early Failure Periods
Incidental Failure Periods
Depletion Failure Periods
Calculation of Failure Rates
Failure Modes and Impact Analysis Basic Terminology
History
Implementation
Application of FMEA to Design Work
Preparation
Step 1: Severity Levels
Step 2: Frequency of Occurrence
Step 3: Inspection
Risk Prioritization Number
Timing of FMEA
Use of FMEA
Advantages
Limitations
Expand Edit Definition
In Extreme Value Theory, the failure rate is called the "intensity function"; in economics, its reciprocal is called the "Mill rate"; in life insurance accidents, it is called the "mortality intensity". Failure rate is the work to a certain moment has not yet failed the product, after the moment the probability of failure per unit of time. Generally referred to as λ, it is also a function of time t, so also referred to as λ (t), known as the failure rate function, sometimes also known as the failure rate function or risk function. According to the above definition, the failure rate is at the moment t has not yet failed in t + △ t of the conditional probability of failure of the product in the unit of time. That is, it reflects the rate of failure at time t, also known as instantaneous failure rate.
Edit this paragraph classification
Failure rate of the observed value of the failure rate is in a moment after the number of products failing per unit of time with the work to that moment has not yet failed the number of products, that is, the failure rate curve: a typical failure rate curve failure rate (or failure rate) curve reflects the overall life of the product failure rate situation. The figure shows the typical failure rate curve, sometimes figuratively called the bathtub curve. Failure rate over time can be divided into three periods:
Early failure period
Early failure period, the failure rate curve is decreasing. The product is submitted for use in the early days, the failure rate is high and decreases very quickly. Mainly due to the design, manufacture, storage, transportation and other defects, as well as debugging, running, starting improper human factors. When these so-called innate bad failure and operation is gradually normal, the failure rate tends to stabilize, to t0 when the failure rate curve has begun to flatten. t0 before the early failure period called. For the early failure period of the cause of failure, should try to avoid, and strive for low failure rate and t0 short.
Incidental failure period
Incidental failure period, the failure rate curve is constant, that is, t0 to ti between the failure rate is approximately constant. Failure is mainly caused by unintended overload, misoperation, accidental acts of God, as well as some unknown accidental factors. Since the cause of failure is mostly accidental, it is called the accidental failure period. The incidental failure period is a period of time that can work effectively, and this period of time is called the effective life. In order to reduce the failure rate of the incidental failure period and increase the effective life, attention should be paid to improve the quality of the product, careful use and maintenance. Increase the size of the cross-section of the part can make the resistance to unintended overdyeing ability to increase, so that the failure rate decreased significantly, but too much increase, will make the product bulky and heavy, not in order to help, and often do not allow.
Depletion failure period
Depletion failure period, the failure rate is increasing. In t1 after the failure rate rise faster, this is due to the product has been aging, fatigue, wear and tear, creep, corrosion and other so-called wear and tear caused by the reason, it is called wear and tear failure period. For the reasons of wear and tear failure, should pay attention to check, monitor, predict the time of the beginning of wear and tear, repair in advance, so that the failure rate still does not rise, as shown by the dotted line in the figure to extend the life of not much. Of course, repair if you need to spend a lot of money and not much life extension, it is better to scrap more economical.
Edit the calculation of the failure rate
The reliability of the computer system is the system from the beginning of its operation (t = 0) to a certain moment t the probability of this period of time can be normal operation, expressed in R (t). The so-called failure rate refers to the number of failed components per unit of time and the proportion of the total number of components, expressed as λ, when λ is a constant, reliability and failure rate of the relationship between: R (λ) = e - λu (λu for the sub-party) between two failures of the system is able to work normally the average of the time is called the average for the time to failure (MTBF) such as: the same type of 1,000 units of computers, working under the specified conditions 1000 hours, of which 10 units failed , computer failure rate: λ = 10 / (1000 * 1000) = 1 * 10-5 (5 as a sub-party) Thousands of hours of reliability: R (t) = e - λt = e (-10-5 * 10^3 (3 times) = 0.99 Mean Time Between Failures MTBF = 1 / λ = 1 / 10-5 = 10^5 hours.
Edit Failure mode and effects analysis
Failure mode and effects analysis (English: Failure mode and effects analysis, FMEA), also known as failure mode and consequence analysis, failure mode and effects analysis, failure mode and consequences analysis, failure mode and consequences analysis, or failure modes and effects analysis, etc., is an operational procedure designed to FMEA, also known as Failure Modes and Effects Analysis, FMEA or FMEA, is an operational procedure designed to analyze potential system-wide failure modes in order to categorize them in terms of severity or to determine the impact of a failure on the system.FMEA is widely used in the manufacturing industry in all phases of the product lifecycle; and, increasingly, it is being used in the service industry as well. Causes of failure are any errors or defects in processing, design, or the item itself, especially those that will have an impact on consumers; they can be categorized as potential or actual. Impact analysis refers to the investigation of these failures.
Basic Terminology
Failure Mode (also known as Failure Mode) The manner in which a failure is observed; generally refers to the way in which a failure occurs. Failure effects (also known as consequences of failure, consequences of failure) The direct consequences of a failure on the operation, function, or functionality of an item, or the state of an object/project (English: item). Engagement level (also known as engagement level) An identifier representing the complexity of an item/project. Complexity increases as the level approaches 1. Localized Impact A failure impact that accrues only to the item/item being analyzed. Upper Order Impact Accumulates the failure impact of the previous engagement level. Final Impact Accumulates the failure impact of the highest engagement level or the entire system. Cause of Failure (also known as Cause of Failure) Defects in design, processing, quality, or component application that are the root cause of the failure, or that initiate the process leading to the failure Severity (also known as Severity) The consequence of a failure. Severity considers the worst potential consequences of a failure as determined by the degree of damage, property loss, or system damage that may eventually occur.
History
Learning lessons from each failure/failure is a costly and time-consuming endeavor, and FMEA is a much more systematic methodology used to study failures/failures. Again, it is best to conduct some thought experiments first. FMEA was formally adopted by the U.S. Air Force in the late 1940s [2]. Later, the space technology/rocket manufacturing field used FMEA to avoid errors in costly rocket technology in small sample situations. One example of this is the Apollo space program. In the 1960s, FMEA received initial impetus and development while developing the means to send astronauts to the Moon and return them safely to Earth. In the late 1970s, Ford Motor Company adopted FMEA in the automotive industry for safety and regulatory reasons following the Pinto incident (see English entry: Pinto), and they also used FMEA to improve production and design. Although originally established by the military, FMEA methodologies are now used in a wide variety of industries, including semiconductor processing, food service, plastics manufacturing, software, and healthcare [3][4]. FMEA has been integrated into Advanced Product Quality Planning (APQP) in both design and processing formats to provide basic risk mitigation and timing of prevention strategies. The Automotive Industry Action Group (AIAG) requires the use of the FMEA methodology in the APQP process for automobiles and has published a detailed manual on how to apply this methodology [5]. Each potential cause must be considered in terms of its impact on the product or process, and based on the corresponding risk, the action to be taken is determined and the risk is reassessed after the action has been completed. [Toyota has further integrated this approach with its own Design Review Based on Failure Mode (DRBFM) methodology. This approach is now also supported by the American Society for Quality (ASQ). The American Society for Quality provides several detailed guidelines for applying this approach.
Implementation
In an FMEA, failures are prioritized based on how serious their consequences are, how often they occur, and how easily they can be detected, and the FMEA documents the current understanding of the risk of failure and the actions to be taken for continuous improvement. During the design phase, FMEA is applied to avoid future failures. Later, FMEA is used in process control and before and during the ongoing operation of the respective process, ideally from the earliest conceptual design stage and continues to be used throughout the entire life cycle of the product or service. The purpose of an FMEA is to eliminate or reduce failures by taking action on the highest priority failures, FMEA can also be used to evaluate risk management priorities in order to mitigate weaknesses that are known to pose a threat, and FMEA can help in the selection of remedial measures to reduce the cumulative effect of several life-cycle consequences (risks) due to a system failure (malfunction). FMEA is currently used in many formal quality systems, such as QS-9000 or ISO/TS 16949.
Application of FMEA to design
FMEA provides a means of analysis when dealing with failure modes and their associated causes. When considering possible failures in a design, such as safety, cost, performance, quality, and reliability, engineers can use FMEA to gain a wealth of information about how to change the development/manufacturing process in order to avoid these failures. before it actually occurs, and to take action to avoid it. The preparation of these specifications will ensure that the product meets the intended requirements.
Preparation
The FMEA process is simple and straightforward, and is divided into three main phases. Within these phases, appropriate action steps need to be identified. However, before the FMEA can begin, it is important to complete some preparatory work to confirm that the analysis is robust and that it includes past history. Robustness analysis can be accomplished using interface matrices, boundary diagrams, and parametric plots. Many failure problems tend to be caused by noise factors and ****-enjoyed interfaces with other components and/or systems, as engineers tend to focus on what they have direct control over. First, it is necessary to describe the current system and its function. A thorough understanding will simplify further analysis. In this way, the engineer will be able to understand exactly which uses of the system are desired and which are not. It is important to consider both intended and unintended uses. Unintended usage is a form of unfavorable environment. Next, a block diagram of the system needs to be created. This diagram is used to describe in general terms the major components or process steps and how they relate to each other. These are known as logical relationships, and it is around these relationships that the FMEA proceeds. Establishing a coding system will help to identify the different system elements, and the block diagram should always be included in the FMEA. Before starting the actual FMEA, a worksheet should be created that contains important information about the current system, such as revision dates or component names. In this worksheet, all items or functions of the analyzed object should be listed in a logical manner based on the above block diagram. FMEA Worksheet Example Function Failure Mode Impact S
(Severity Rating) Cause O
(Frequency of Occurrence Rating) Current Control Measures D
(Inspection Rating) CRIT
(Critical Characteristics) RPN
(Risk Prioritization Number) Recommended Action Steps Responsibility and Target Completion Dates Action Steps Taken
Fill bath tub Error in high water level sensor Liquid spilled onto customer's floor 8 Water level sensor has failed
Water level sensor disconnected 2 Fill timeout based on time taken to fill to low water level sensor 5 N 80 Perform a cost analysis for the addition of an additional sensor halfway between the high and low water level sensors John
October 10, 2010
Step 1: Severity
Determine all failure modes based on functional requirements and their impact. Examples of failure modes are: shorted circuits, corrosion or deformation. It is important to note that a failure mode in one component can lead to a failure mode in another component. Therefore, for each failure mode, the technical terminology should be used and listed by function. Thereafter, it is the ultimate impact of each failure mode that needs to be considered. The impact of failure is defined as the result of the failure mode's effect on the function of the system as perceived by the user. This makes it easier to characterize these impacts in terms of what the user is likely to see or experience. Examples of failure effects are: performance degradation, noise, or even harm to the user. For each effect, a severity value between 1 (no risk) and 10 (critical) is assigned. Such values help engineers prioritize failure modes and their effects. If an effect has a severity value of 9 or 10, consideration should be given to taking action to change the design by eliminating the failure mode if possible, or protecting the user from its effects. Severity ratings of 9 or 10 are generally reserved for impacts that could cause harm to users or otherwise give rise to litigation.
Step 2: Frequency
In this step, the cause of the failure and how often it occurs are considered. This can be done by examining similar products or processes and the associated failures that have been documented. The cause of failure is considered a design flaw. All potential causes of failure modes should be identified and documented. Again, technical terminology should be used here to describe them. Examples of causes are: faulty algorithms, excessive voltages, or improper operating/operating conditions. Similarly, a probability value (O) ranging from 1 to 10 can be assigned to each failure mode. If the frequency of occurrence is high (referring to non-safety failure modes with a probability value of >4 and when the severity value from step 1 is 9 or 10 with a probability value of >1), action steps need to be identified. This step is called the refinement part of the FMEA process. Alternatively, the frequency of occurrence can be defined as a percentage (%). If a non-safety issue occurs less than 1% of the time, then it can be assigned a value of 1. This depends on your product and customer specifications.
Step 3: Check
Once the appropriate action steps have been identified, one of the things that needs to be done is to test their effectiveness. Also, design validation needs to be done. And, the right inspection method needs to be chosen. First, engineers should focus on the controls currently in place for the system, that is, those that prevent failure modes from occurring or detect failures before they reach customers. Then, test, analysis, monitoring, and other techniques that can be or have been used on similar systems to detect failures should be identified. Based on these controls, engineers can see how likely it is that a failure problem will be recognized or detected. Each combination of the first two steps results in a discovery index (D). This index indicates the ability of the intended test or inspection effort to eliminate defects or detect failure modes. After completing these 3 basic steps, it is the Risk Priority Numbers (English: RPN) that are calculated.
Risk Priority Numbers
RPNs do not play a significant role in the selection of actions to prevent failure modes. They belong more to the thresholds in terms of evaluating these action measures. After grading severity, frequency of occurrence, and ease of detection, the RPN can be obtained by simply multiplying these three values: RPN = S x O x D This is a mandatory task for the entire process and/or design. Once completed, the determination of the Maximum Scope of Concern is easy. In terms of corrective action, the failure mode with the highest RPN should receive the highest priority level. This means that the failure modes with the highest severity values should not necessarily be addressed first. It may be that failures of lower severity that are more frequent and less easy to detect should be dealt with first, and after these values have been assigned, recommendations for action with objectives, responsibilities, and implementation dates are documented. These actions may include specific inspections, testing or quality procedures, redesign (e.g., selecting new components), adding more redundancy, and limiting environmental stresses or work ranges. Once these action steps have been implemented in the design/process, the new RPN should be checked to confirm improvements. These tests are often presented graphically for ease of visualization. Whenever there is a change in the design or process, the FMEA should be updated. The logical and important points are: Efforts to eliminate failure modes (some failures are easier to prevent than others) Minimizing the severity of failures Reducing the frequency of failure modes Improving inspection discovery.
Timing of the FMEA
The FMEA should be updated whenever: - at the beginning of each cycle (new products/processes) - changes are made to operating conditions - changes are made to the design - new laws or regulations are established - consumer feedback indicates that there is some kind of problem
Purpose of the FMEA
To establish a system that minimizes the likelihood of failure. System requirements that minimize the likelihood of failure. Establish system design and test methods to ensure that corresponding failures are eliminated. Evaluate consumer requirements to ensure that they do not contribute to potential failures. Identify certain design features that contribute to failure and minimize or eliminate the corresponding effects. Track and manage potential risks in the design. This helps to avoid encountering the same failures in future projects. Ensure that any failures that may occur do not harm consumers or severely impact the system.
Benefits
Improve product/process quality, reliability, and safety Improve company image and competitiveness Improve user satisfaction Reduce time and cost of system development efforts Gather information to mitigate future failures and gain knowledge of the engineering design Reduce the likelihood of billable problems Early detection, identification, and elimination of potential failure modes Prevention of critical problems Minimize the impact of late changes and their associated costs Facilitate teamwork and collaboration Minimize late changes and their associated costs Facilitate teamwork and the exchange of ideas between different functions
Limitations
Since the FMEA is really dependent on the members of the committee who are responsible for investigating the failure of the product, their experience with past failures governs the FMEA. If a failure mode cannot be identified, then external assistance is needed from consultants who know many different types of product failure problems. Thus, FMEA is part of a larger quality control system in which documentation is critical to implementation. General articles and detailed publications are available in the areas of forensic engineering and failure analysis (or fault analysis). The application of FMEA in product integrity assessment is now a general requirement of many specific national and international standards. As a top-down tool, FMEA may only be able to identify major failure modes in a system. Fault tree analysis (FTA) is more suitable for top-down analysis. If used as a "bottom-up" tool, FMEA can augment or complement FTA by discovering and identifying many more causes and failure modes that lead to symptoms at the top level, but FMEA is unable to detect complex failure modes that involve multiple failures within the same subsystem or to report on the suitability of a particular failure mode for a higher-level subsystem or system expectation. expected failure intervals for the parent subsystem or system. In addition, the multiplication of severity, frequency of occurrence, and difficulty of discovery ratings may result in a level reversal phenomenon, whereby failure modes of lesser severity receive higher RPNs than more severe failure modes. The reason for this phenomenon is that these ratings are ordinal scale numbers for which multiplication is not a valid operation. The ordinal scale simply means that one scale is better or worse than the other, but it does not say to what extent. For example, a rank of "2" does not mean that it is twice as bad as a rank of "1", or a rank of "8" does not mean that it is twice as bad as a rank of or "8" does not mean that it is twice as bad as when the rank is "4". However, the above multiplication treats them as such. For further discussion, see Level of measurement.