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What is Reliability?
- A Performance
• Ability of an item to perform its intended function for a specified interval under stated conditions • Reliability as a performance 9 Degradation in functional/parametric performance 9 Service life and warranty claim 9 Number of field failures and product return 9 Requirement on maintenance and repair
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What is Reliability?
- The Quantitative Measure
• The probability that an item can perform its intended function for a specified interval under stated conditions. • Reliability as the measure 9 Failure probability/reliability
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What is Reliability?
- A Practice
• • • • • • IQC: incoming quality control SPC: statistical process control ORT: on-going reliability test Corrective and preventive actions Auditing Specifications on product and component reliability and reliability testing • FA (failure analysis)/FMEA (failure mode and effect analysis)/ FMECA (failure mode, effect, and criticality analysis) and troubleshooting • Customer service • 所有可靠性工程的手段、技术和方法
• Failure is defined by failure criteria
9 Failure is not necessarily “permanent” or “catastrophic”; 9 Reliability is dependent upon the definition of failure 9 Failure criteria are determined based on required function and/or application.
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Failure Distribution
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A Failure Mechanism Hypothesis
• 产品缺陷部位的过应力损毁（失效的时间来源于失效失稳过程 的时间以及载荷发生的不确定性） 9 Early failure: 产品的早期失效由产品中的“非正常”缺陷所 决定，所谓“非正常”是指这些缺陷来源于制造工艺、流 程、来料以及设计中较为的严重问题，且一般来说缺陷会 有明确的宏观特征，如尺寸大、数量多、部位集中等特 点，而且问题可以通过调整产品的制造参数、优化工艺流 程和强化产品质量管理等手段来解决。 9 Random failure: 偶然失效是由产品中 “固有的”缺陷所决 定，在工程上被认为是一种“不可避免的”、某种意义上 说是“正常的”失效。它们在产品中的尺寸更为微观，且 数量和分布都有一定的分散性，所以，造成最终产品功能 的失效也体现为一种偶然性。 • 强度范围内随时间累计的应力损伤 9 Wearout failure: 除“先天”的缺陷外，还有“后天”带来的损伤
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Verification, Qualification and Reliability Assessment
• Verification: “Verification and Validation: In engineering or a quality management system, "verification" is the act of reviewing, inspecting, testing, etc. to establish and document that a product, service, or system meets the regulatory, standard, or specification requirements. By contrast, validation refers to meeting the needs of the intended end-user or customer.” • Qualification: “Product certification or product qualification is the process of certifying that a certain product has passed performance and quality assurance tests or qualification requirements stipulated in regulations such as a building code and nationally accredited test standards, or that it complies with a set of regulations governing quality and minimum performance requirements.” • Reliability Assessment: “Assessment is the process of documenting, usually in measurable terms, knowledge, skills, attitudes and beliefs. … It is important to notice that the final purposes and assessment practices depends on the theoretical framework of the practitioners and researchers, their assumptions and beliefs about the nature of human mind, the origin of knowledge and the process of learning.”
• Failure mode: observable way of failure • Failure site: location of failure • Failure mechanisms: the physical, chemical, electrical, thermal or other processes that results in failure • Root cause of failure: cause of failure that can lead to corrective or preventive actions
• Reliability issues
9 与产品实际使用环境和条件相关的产品性能和寿命 问题
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Concept of Quality and Reliability
• Quality 9 产品验证(validation and verification)和评价 (assessment)体系：产品的质量检验是一个 验证体系(qualification)。 • Reliability 9 而产品可靠性则是一个评价体系(reliability assessment)。 9 需要在失效物理这样的理论构架之上才能 完成
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关于寿命和可靠性
• 何为“长寿命”和“高可靠”？ • “可靠度”是“可靠性”唯一的一个 “充分” 的度量 • “寿命”是失效分布的随机变量；“可靠度” 则是“寿命”的随机函数
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Concept of Intrinsic and Extrinsic Reliability
• Early failure is a “Quality failure”, is of an extrinsic failure mechanism; • Random failure is of an intrinsic failure mechanism; • This directly implies that manufacturing quality cannot increase the inherent reliability of a design in a given use environment; however, inadequate manufacturing quality can reduce this inherent designed-in reliability by increasing infant mortality failures. • 国内的“固有可靠性/固有质量”和“使用可靠性”概念 和问题
Reliability Physics – Theory and Application
(Day 2 Concepts)
141303 可靠性物理
谢劲松 北京航空航天大学工程系统工程系 (Fall 2009)ຫໍສະໝຸດ bout Failure2
About Failure
• Failure: the event, or inoperable state, in which any item or part of an item does not, or would not, perform as previously specified