Search Results for Motor vehicles

This article focuses on the general methods and approaches from the perspective of a reconstruction analyst and includes discussions relevant to materials failure analysts at the incident scene. The elements of accident reconstruction are described. These have conceptual similarity with the principles for failure analysis of material incidents that are less complex than a large-scale accident. The article provides a brief review of some general concepts on the use of modeling which can be a very powerful tool for information pertaining to the reconstruction of an accident where the model can be a physical, mathematical, or logical representation of a physical system or process.

A welded vessel made of acid resistant 18-8 steel used in a derusting operation started to leak after a long period due to the formation of cracks. The vessel was heated from the outside and did not come into direct contact with the flame. It was surrounded by a casing of unalloyed steel. Where the cracks had not eroded away, it was clear they ran transcrystalline, indicative of stress-corrosion cracking. Because the cracks propagated from the outer surface of the vessel, they were not caused by the derusting agent but by the external atmosphere in conjunction with welding stresses. The narrow gap between vessel and mild steel casing may have aggravated the situation in that it hindered ventilation and evaporation of condensation and favored the absorption and concentration of acids and salts. Contact and crevice corrosion due to deposition of rust from the mild steel casing may have contributed.

Failure analysis is generally defined as the investigation and analysis of parts or structures that have failed or appeared to have failed to perform their intended duty. Methods of field inspection and initial examination are also critical factors for both reconstruction analysts and materials failure analysts. This article focuses on the general methods and approaches from the perspective of a reconstruction analyst. It describes the elements of accident reconstruction, which have conceptual similarity with the principles for failure analysis of material incidents that are less complex than a large-scale accident. The approach presented is that the analysis and reconstruction is based on the physical evidence. The article provides a brief review of some general concepts on the use and limitations of advanced data acquisition tools and computer modeling. Legal implications of destructive testing are discussed in detail.

A sand-cast LM6M aluminum alloy sprocket drive wheel in an all-terrain vehicle failed. Extensive cracking had occurred around each of the six bolt holes in the wheel. Evidence of considerable deformation in this area was also noted. Examination indicated that the part failed because of gross overload. Use of an alloy with a much higher yield strength and improvement in design were recommended.

Distortion failure occurs when a structure or component is deformed so that it can no longer support the load it was intended to carry. Every structure has a load limit beyond which it is considered unsafe or unreliable. Estimation of load limits is an important aspect of design and is commonly computed by classical design or limit analysis. This article discusses the common aspects of failure by distortion with suitable examples. Analysis of a distortion failure often must be thorough and rigorous to determine the root cause of failure and to specify proper corrective action. The article summarizes the general process of distortion failure analysis. It also discusses three types of distortion failures that provide useful insights into the problems of analyzing unusual mechanisms of distortion. These include elastic distortion, ratcheting, and inelastic cyclic buckling.

Distortion often is observed in the analysis of other types of failures, and consideration of the distortion can be an important part of the analysis. This article first considers that true distortion occurs when it was unexpected and in which the distortion is associated with a functional failure. Then, a more general consideration of distortion in failure analysis is introduced. Several common aspects of failure by distortion are discussed and suitable examples of distortion failures are presented for illustration. The article provides information on methods to compute load limits, errors in the specification of the material, and faulty process and their corrective measures to meet specifications. It discusses the general process of material failure analysis and special types of distortion and deformation failure.

This article provides assistance to a failure analyst in broadening the initial scope of the investigation of a physical engineering failure in order to identify the root cause of a problem. The engineering design process, including task clarification, conceptual design, embodiment design, and detail design, is reviewed. The article discusses the design process at the personal and project levels but takes into consideration the effects of some higher level influences and interfaces often found to contribute to engineering failures.

In this study, the failure modes of cartwheel and mechanical properties of materials have been analyzed. The results show that rim cracking is always initiated from stringer-type alumina cluster and driven by a combination effect of mechanical and thermal load. The strength, toughness, and ductility are mainly determined by the carbon content of wheel steels. The fatigue crack growth resistance is insensitive to composition and microstructure, while the fatigue crack initiation life increases with the decrease of austenite grain size and pearlite colony size. The dynamic fracture toughness, KID, is obviously lower than static fracture toughness, KIC, and has the same trend as KIC. The ratio of KID/sigma YD is the most reasonable parameter to evaluate the fracture resistance of wheel steels with different composition and yield strength. Decreasing carbon content is beneficial to the performance of cartwheel.

The intent of this article is to assist the failure analyst in understanding the underlying engineering design process embodied in a failed component or system. It begins with a description of the mode of failure. This is followed by a section providing information on the root cause of failure. Next, the article discusses the steps involved in the engineering design process and explains the importance of considering the engineering design process. Information on failure modes and effects analysis is also provided. The article ends with a discussion on the consequence of management actions on failures.

This paper presents a failure analysis of a reverse shaft in the transmission system of an all-terrain vehicle (ATV). The reverse shaft with splines fractured into two pieces during operation. Visual examination of the fractured surface clearly showed cracks initiated from the roots of spline teeth. To find out the cause of fracture of the shaft, a finite element analysis was carried out to predict the stress state of the shaft under steady loading and shock loading, respectively. The steady loading was produced under normal operation, while the shock loading could be generated by an abrupt change of operation such as start-up or sudden braking during working. Results of stress analysis reveal that the highest stressed area coincided with the fractured regions of the failed shaft. The maximum stress predicted under shock loading exceeded the yield strength and was believed to be the stimulant for crack initiation and propagation at this weak region. The failure analysis thus showed that the premature fatigue fracture of the shaft was caused by abnormal operation. Finally, some suggestions to enhance service durability of the transmission system of ATV are discussed.

Nondestructive testing (NDT), also known as nondestructive evaluation (NDE), includes various techniques to characterize materials without damage. This article focuses on the typical NDE techniques that may be considered when conducting a failure investigation. The article begins with discussion about the concept of the probability of detection (POD), on which the statistical reliability of crack detection is based. The coverage includes the various methods of surface inspection, including visual-examination tools, scanning technology in dimensional metrology, and the common methods of detecting surface discontinuities by magnetic-particle inspection, liquid penetrant inspection, and eddy-current testing. The major NDE methods for internal (volumetric) inspection in failure analysis also are described.

A material is flammable if it is subject to easy ignition and rapidly flaming combustion. The plastics that are most widely used are the least expensive and tend to be the most flammable. This article describes the two basic approaches to improving the fire resistance of a polymeric material: modifying or substituting the basic polymer so that exposure to heat and oxygen will not produce rapid combustion, and using flame-retardant additives. It also provides an overview of the burning process and presents two flammability test methods.

Rolling-element bearings use rolling elements interposed between two raceways, and relative motion is permitted by the rotation of these elements. This article presents an overview of bearing materials, bearing-load ratings, and an examination of failed bearings. Rolling-element bearings are designed on the principle of rolling contact rather than sliding contact; frictional effects, although low, are not negligible, and lubrication is essential. The article lists the typical characteristics and causes of several types of failures. It describes failure by wear, failure by fretting, failure by corrosion, failure by plastic flow, failure by rolling-contact fatigue, and failure by damage. The article discusses the effects of fabrication practices, heat treatment and hardness of bearing components, and lubrication of rolling-element bearings with a few examples.

This article provides information on the development of finite element analysis (FEA) and describes the general-purpose applications of FEA software programs in structural and thermal, static and transient, and linear and nonlinear analyses. It discusses special-purpose finite element applications in piping and pressure vessel analysis, impact analysis, and microelectronics. The article describes the steps involved in the design process using the FEA. It concludes with two case histories that involve the use of FEA in failure analysis.

When complex designs, transient loadings, and nonlinear material behavior must be evaluated, computer-based techniques are used. This is where the finite-element analysis (FEA) is most applicable and provides considerable assistance in design analysis as well as failure analysis. This article provides a general view on the applicability of finite-element modeling in conducting analyses of failed components. It highlights the uses of finite-element modeling in the area of failure analysis and design, with emphasis on structural analysis. The discussion covers the general development and both general- and special-purpose applications of FEA. The special-purpose applications of FEA covered are piping and pressure vessel analysis, impact analysis, and microelectronic and microelectromechanical systems analysis. The article provides case histories that involved the use of FEA in failure analysis.

This article discusses technologies focused on processing plastic materials or producing direct tools used in plastics processing. The article focuses on extrusion and injection molding, covering applications, materials and their properties, equipment, processing details, part design guidelines, and special processes. It also covers the functions of the extruder, webline handling, mixing and compounding operations, and process troubleshooting. Thermoforming and mold design are covered. Various other technologies for polymer processing covered in this article are blow molding, rotational molding, compression molding, transfer molding, hand lay-up process, casting, and additive manufacturing.

This article is dedicated to the fields of mechanical engineering and machine design. It also intends to give a nonexhaustive view of the preventive side of the failure analysis of rolling-element bearings (REBs) and of some of the developments in terms of materials and surface engineering. The article presents the nomenclature, numbering systems, and worldwide market of REBs as well as provides description of REBs as high-tech machine components. It discusses heat treatments, performance, and properties of bearing materials. The processes involved in the examination of failed bearings are also explained. Finally, the article discusses in detail the characteristics and prevention of the various types of failures of REBs: wear, fretting, corrosion, plastic flow, rolling-contact fatigue, and damage. The article includes an Appendix, which lists REB-related abbreviations, association websites, and ISO standards.

This article briefly introduces the concepts of failure analysis, including root-cause analysis (RCA), and the role of failure analysis as a general engineering tool for enhancing product quality and failure prevention. It initially provides definitions of failure on several different levels, followed by a discussion on the role of failure analysis and the appreciation of quality assurance and user expectations. Systematic analysis of equipment failures reveals physical root causes that fall into one of four fundamental categories: design, manufacturing/installation, service, and material, which are discussed in the following sections along with examples. The tools available for failure analysis are then covered. Further, the article describes the categories of mode of failure: distortion or undesired deformation, fracture, corrosion, and wear. It provides information on the processes involved in RCA and the charting methods that may be useful in RCA and ends with a description of various factors associated with failure prevention.

This article outlines the basic steps to be followed and the range of techniques available for failure analysis, namely, background data assembling, visual examination, microfractography, chemical analysis, metallographic examination, electron microscopy, electron microprobe analysis, X-ray techniques, and simulations. It also describes the steps for analyzing the data, preparing the report, preservation of evidence, and follow-up on recommendations.