c88 D 3 Design 2 自 gg 2 Anticipated service condition Premature failure I Prototype Increasing service life Intended life Fig. 5 Application-life diagram comparing the severity of a service condition with the service lives of products having a variable characteristic. This diagram is utilized in specific examples in text. By varying the characteristics, a family of curves is generated, contrasting the lives of components with the various characteristics and service conditions with the intended service life. Each of the curves represents a different design/configuration characteristic, with increasing degrees of durability as the curves move up the ordinate. Failures can be prevented when the curve for a specific design/configuration lies above the severity of service line, and to the left of the intended service life line. However, if the severity of service conditions increases (either intentionally during operation or as a result of some other change in the system), the propensity for failure may increase, since the characteristics curves intersect the severity of service condition line to the left,that is, at an earlier point in the service Design Deficiencies Root causes of failures that stem from design deficiencies refer to unacceptable features of a product or system that are a result of the design process. This process encompasses the original concept development, the general configuration definition, and the detail design, including selection and specification of materials and manufacturing processes. Design involves identifying and defining a need for the product or system, followed by definition of the performance requirements, anticipated service conditions in the application(s), the constraints on the design, and the criticality or risks associated with failure(Ref 31). Discussion of the design process as it relates to failure analysis and prevention is provided in the article"Design Review for Failure Analysis and Prevention"in this Section Some examples of design deficiencies include unintended stress raisers due to excessively sharp notches(Ref 32)(e.g,in keyways on shafts)or insufficient radii(e.g, on shafts at bearing journals). Other examples include unanticipated residual stresses associated with heat treating configurations designed with complex geometries, or assembly stresses from configurations that contain unwanted interference. Inappropriate surface treatments could result in failures, such as the use of cadmium plating on an A286 superalloy fastener, subjected to service temperatures above 315C(600F)(the elting temperature of cadmium is 320C, or 610F). Two metals specified for use in a wear application could sustain galling if the metals are incompatible, such as sliding wear of components made from 300 series stainless steels Selection of a material that is incapable of providing adequate mechanical properties for the application(including strength, fatigue resistance, fracture toughness, corrosion resistance, elevated temperature resistance, etc )is also a type of design deficiency. Materials can exhibit anisotropy, or variability in properties within a product, such as between the thickFig. 5 Application-life diagram comparing the severity of a service condition with the service lives of products having a variable characteristic. This diagram is utilized in specific examples in text. By varying the characteristics, a family of curves is generated, contrasting the lives of components with the various characteristics and service conditions with the intended service life. Each of the curves represents a different design/configuration characteristic, with increasing degrees of durability as the curves move up the ordinate. Failures can be prevented when the curve for a specific design/configuration lies above the severity of service line, and to the left of the intended service life line. However, if the severity of service conditions increases (either intentionally during operation or as a result of some other change in the system), the propensity for failure may increase, since the characteristics curves intersect the severity of service condition line “to the left,” that is, at an earlier point in the service life. Design Deficiencies Root causes of failures that stem from design deficiencies refer to unacceptable features of a product or system that are a result of the design process. This process encompasses the original concept development, the general configuration definition, and the detail design, including selection and specification of materials and manufacturing processes. Design involves identifying and defining a need for the product or system, followed by definition of the performance requirements, anticipated service conditions in the application(s), the constraints on the design, and the criticality or risks associated with failure (Ref 31). Discussion of the design process as it relates to failure analysis and prevention is provided in the article “Design Review for Failure Analysis and Prevention” in this Section. Some examples of design deficiencies include unintended stress raisers due to excessively sharp notches (Ref 32) (e.g., in keyways on shafts) or insufficient radii (e.g., on shafts at bearing journals). Other examples include unanticipated residual stresses associated with heat treating configurations designed with complex geometries, or assembly stresses from configurations that contain unwanted interference. Inappropriate surface treatments could result in failures, such as the use of cadmium plating on an A286 superalloy fastener, subjected to service temperatures above 315 °C (600 °F) (the melting temperature of cadmium is 320 °C, or 610 °F). Two metals specified for use in a wear application could sustain galling if the metals are incompatible, such as sliding wear of components made from 300 series stainless steels. Selection of a material that is incapable of providing adequate mechanical properties for the application (including strength, fatigue resistance, fracture toughness, corrosion resistance, elevated temperature resistance, etc.) is also a type of design deficiency. Materials can exhibit anisotropy, or variability in properties within a product, such as between the thick