Failure Definitions. In the general sense of the word, a failure is defined as an undesirable event or condition. For the purposes of discussion related to failure analysis and prevention, it is a general term used to imply that a component is unable to adequately perform its intended function. The intended function of a component and therefore the definition of failure may range greatly. For instance, discoloration of an architectural feature is a failure of its intended aesthetic but does not perform its intended function(Ref 13). This is considered a loss of function. A jeteomponent that smut can Failure can be defined on several different levels. The simplest form of a failure is a system or component that operates only produce partial thrust(insufficient to enable an aircraft to take off)is an example of a loss of function The next level of failure involves a system or component that performs its function but is unreliable or unsafe(Ref 13).In this form of failure, the system or component has sustained a loss of service life. For example, a wire rope for an elevator has lost its service life when it has sustained fatigue fractures of some of the individual wires, due to irregularities in the wrapping over the sheave. Even though the wire rope continues to function, the presence of fatigue fractures of some of the wires results in an unsafe condition and is therefore considered a failure. Another example of such a failure is the inability of an integrated circuit to function reliably In the next level of severity of failure, a system or component is inoperable(Ref 13), such as a pump shaft fracture that causes the impeller to seize or a loss of load-carrying capability of a structural bolt in-service due to fracture Failure and Failure Analysis. A logical failure analysis approach first requires a clear understanding of the failure definition and the distinction between an indicator (i.e, symptom), a cause, a failure mechanism, and a consequence Although it may be considered by some to be an exercise in semantics, a clear understanding of each piece of the situation associated with a failure greatly enhances the ability to understand causes and mitigating options and to specify appropriate corrective action Consider the example of a butterfly valve that fails in service in a cooling water system at a manufacturing facility ( table 1). Recognizing the indicators, causes, mechanisms, and consequences helps to focus investigative actions Indicators(s): Monitor these as precursors and symptoms of failures Cause(s): Focus mitigating actions on these Failure mechanism(s): These describe how the material failed according to the engineering textbook definitions If the analysis is correct, the mechanism will be consistent with the cause(s). If the mechanism is not properl understood, then all true cause(s) will not be identified and corrective action will not be fully effective Consequence(): This is what we are trying to avoid Table 1 Example--Failure of a butterfly valve in a manufacturing plant cooling water system Item Description Indicators Cause Throttling of valve by the operator outside of the design Flow gages and records Low-strength copper nickel alloy construction Material specifications Flow-induced cavitation Rumbling noise in system Failure Erosion-fatigue damage Laboratory examination of disk, nInn Inability to manufacture at normal production rates Life-Cycle Management Concepts. The concept of life-cycle management refers to the idea of managing the service life of a system, structure, or component. There is a cost associated with extending the service life of a component, for example, higher research costs, design costs, material and fabrication costs, and higher maintenance costs With regard to product failures, it must be understood that failures cannot be totally avoided, but must be better understood, anticipated, and controlled. Nothing lasts and functions forever. For some products, consumers may prefer a shorter life at a more modest cost. In contrast, the useful service life of a product such as an aircraft part may be carefull planned in advance and managed accordingly with routine inspections and maintenance, which may increase in frequency over time. In many cases, avoiding failures beyond a certain predetermined desired life provides no benefit, such as is the when a surgical implant is designed to far outlive the human recipient. There is also a point of diminishing return on stments related to extending the life of a component. a life-cycle management study of a component would look at issues as well as other factors such as the issue of obsolescence. How long will it be before the product is obsolete? Thefileisdownloadedfromwww.bzfxw.comFailure Definitions. In the general sense of the word, a failure is defined as an undesirable event or condition. For the purposes of discussion related to failure analysis and prevention, it is a general term used to imply that a component is unable to adequately perform its intended function. The intended function of a component and therefore the definition of failure may range greatly. For instance, discoloration of an architectural feature is a failure of its intended aesthetic function. Failure can be defined on several different levels. The simplest form of a failure is a system or component that operates, but does not perform its intended function (Ref 13). This is considered a loss of function. A jet engine that runs but can only produce partial thrust (insufficient to enable an aircraft to take off) is an example of a loss of function. The next level of failure involves a system or component that performs its function but is unreliable or unsafe (Ref 13). In this form of failure, the system or component has sustained a loss of service life. For example, a wire rope for an elevator has lost its service life when it has sustained fatigue fractures of some of the individual wires, due to irregularities in the wrapping over the sheave. Even though the wire rope continues to function, the presence of fatigue fractures of some of the wires results in an unsafe condition and is therefore considered a failure. Another example of such a failure is the inability of an integrated circuit to function reliably. In the next level of severity of failure, a system or component is inoperable (Ref 13), such as a pump shaft fracture that causes the impeller to seize or a loss of load-carrying capability of a structural bolt in-service due to fracture. Failure and Failure Analysis. A logical failure analysis approach first requires a clear understanding of the failure definition and the distinction between an indicator (i.e., symptom), a cause, a failure mechanism, and a consequence. Although it may be considered by some to be an exercise in semantics, a clear understanding of each piece of the situation associated with a failure greatly enhances the ability to understand causes and mitigating options and to specify appropriate corrective action. Consider the example of a butterfly valve that fails in service in a cooling water system at a manufacturing facility (Table 1). Recognizing the indicators, causes, mechanisms, and consequences helps to focus investigative actions: · Indicators(s): Monitor these as precursors and symptoms of failures. · Cause(s): Focus mitigating actions on these. · Failure mechanism(s): These describe how the material failed according to the engineering textbook definitions. If the analysis is correct, the mechanism will be consistent with the cause(s). If the mechanism is not properly understood, then all true cause(s) will not be identified and corrective action will not be fully effective. · Consequence(s): This is what we are trying to avoid. Table 1 Example—Failure of a butterfly valve in a manufacturing plant cooling water system Item Description Indicators Throttling of valve by the operator outside of the design parameters Flow gages and records Operator logs Low-strength copper nickel alloy construction Material specifications Laboratory analysis Cause Flow-induced cavitation Rumbling noise in system Vibration of system Failure mechanism Erosion-fatigue damage Laboratory examination of disk, thinning Consequences Inability to manufacture at normal production rates Life-Cycle Management Concepts. The concept of life-cycle management refers to the idea of managing the service life of a system, structure, or component. There is a cost associated with extending the service life of a component, for example, higher research costs, design costs, material and fabrication costs, and higher maintenance costs. With regard to product failures, it must be understood that failures cannot be totally avoided, but must be better understood, anticipated, and controlled. Nothing lasts and functions forever. For some products, consumers may prefer a shorter life at a more modest cost. In contrast, the useful service life of a product such as an aircraft part may be carefully planned in advance and managed accordingly with routine inspections and maintenance, which may increase in frequency over time. In many cases, avoiding failures beyond a certain predetermined desired life provides no benefit, such as is the case when a surgical implant is designed to far outlive the human recipient. There is also a point of diminishing return on investments related to extending the life of a component. A life-cycle management study of a component would look at these issues as well as other factors such as the issue of obsolescence. How long will it be before the product is obsolete? The file is downloaded from www.bzfxw.com