A two-section extension ladder, made from 6061-T6 aluminum alloy extrusions and stampings that were riveted together at each rung location and at the ends of side rails, broke in service after having been used at the sites of several fires by the fire department of a large city. The fracture surfaces were examined visually and by optical (light) stereomicroscopy. Material testing showed a sample to be within the specified material limits for aluminum alloy 6061. Microscopic examination showed no significant differences in microstructure or grain size among the four T-sections, and thickness measurements at various locations indicated that thicknesses were well within standard industry tolerances for aluminum extrusions in this size range. However, hardness testing of the four T-sections showed that in two, hardness was considerably lower than the acceptable hardness for the T6 temper and were within the range for 6061-T4 (acceptable hardness, 19 to 45 HRB). This indicated they had been naturally aged at room temperature after solution heat treatment instead of artificially aged as per specs. Edge cracking in two of the T-sections was the result of improper conditions during extrusion of the T-sections; however, this condition was not a primary cause of failure.

A Marine Corps helicopter crash was investigated. Efforts were directed to the failure of one of the main rotor blades that had apparently separated in the air. The apparent failure of a blade integrity monitor (BIM) system was also considered. The rotor blade comprised a long, hollow 6061-T651 aluminum alloy extrusion and 26 fiberglass “pockets” that provided the trailing-edge airfoil shape. Visual examination of the fracture surface of the aluminum extrusion indicated fatigue crack growth followed by ductile overload separation. Examination of the fatigue fracture region revealed several pits that appeared to have acted as fracture origin sites. Time to failure was determined using fracture mechanics. It was concluded that failure was caused by a fatigue crack that grew to critical length without detection. The crack originated at pits that resulted from the use of an improperly designed heating element used to cure fiberglass repairs.

Several 6063-T6 aluminum alloy extension ladders of the same size and type collapsed in service in the same manner; the extruded aluminum alloy 6063-T6 side rails buckled, but the rungs and hardware remained firmly in place. The ladders had a maximum extended length of 6.4 m (21 ft) with a recommended maximum angle of inclination of 75 deg (15 deg from vertical). Investigation (visual inspection, hardness testing, metallographic examination, stress analysis, and tensile tests) supported the conclusion that the side rails of the ladders buckled when subjected to loads that produced stresses beyond the yield strength of the alloy. Recommendations included increasing the thickness of the flange and web of the side-rail extrusion.

Aluminum alloy BS.1476-HE.15 by virtue of its high strength and low density finds application in the form of bars or sections for cranes, bridges, and other such structures where a reduction in dead weight load and inertia stresses is advantageous. Bars and sections in H.15 alloy are mostly produced by extrusion. Some material processed this way has been prone to exfoliation corrosion. Extended aging for 24 h at a temperature of 185 deg C (365 deg F) virtually suppresses the tendency for exfoliation corrosion to develop. Also, the use of a sprayed coating, either of aluminum or Al-1Zn alloy, was effective in halting and preventing this form of attack. While alarming, the appearance of exfoliation corrosion provides a valuable warning to the engineer or inspector before a severe weakening of the particular sections has occurred.

A recurring piston shaft failure problem on the billet-loading tray of an extrusion press was investigated. Two shafts fractured within a period of 10 days. The shaft was machined from normalized EN3 (AISI C1022) steel stock without further treatment. Visual, microstructural, chemical, and mechanical (hardness and tensile properties) analyses of failed shaft specimens were conducted. The examinations showed that the shafts had failed by fatigue. It was recommended that a low-alloy steel (e.g., 3% Ni-Cr) in the hardened and tempered condition and subjected to shot-peening surface-hardening treatment be used. The provision of a stop to reduce bending stresses was also recommended.

This article describes the general root causes of failure associated with wrought metals and metalworking. This includes a brief review of the discontinuities or imperfections that may be the common sources of failure-inducing defects in bulk working of wrought products. The article discusses the types of imperfections that can be traced to the original ingot product. These include chemical segregation; ingot pipe, porosity, and centerline shrinkage; high hydrogen content; nonmetallic inclusions; unmelted electrodes and shelf; and cracks, laminations, seams, pits, blisters, and scabs. The article provides a discussion on the imperfections found in steel forgings. The problems encountered in sheet metal forming are also discussed. The article concludes with information on the causes of failure in cold formed parts.

A longeron assembly constructed of Alclad 2024, some parts being in the T3 condition, others in the T42 condition, failed at a rivet hole. Plastic deformation at the crack site was found, but no plastic deformation was found in similar failed components. It was concluded that the numerous hairline cracks in the Alclad layer adjacent to the main fracture were fatigue cracks. In another case, bonded samples of 2024-T3 sheet were fatigue tested at various stress levels. Failures could be separated into three groups: those that failed in the adhesive bond, those that failed in the base material, and those that exhibited a dual failure. The last category failed in the adhesive bond and also showed a type of pitting on one face of the base material. In a third case, a 2024-T4 extrusion section was found to exhibit blistering after chemical milling. The presence of interconnecting microcracks between adjacent discontinuities supported a hydrogen blistering diagnosis.

A 230 mm (9 in.) thick casing, fabricated from ASTM 235-55 low-carbon steel, of a 450 Mg (500 ton) extrusion press failed after 27 years of service. Initial visual examination revealed an area that exhibited multiple origins and classic beach marks radiating out approximately 75 mm (3 in.) from the origin along the wall of a hydraulic-oil bleed hole. Investigation with a SEM showed corrosion pits along the bleed hole wall, but oxidation and corrosion prevented review of microfractographic details. Vacuum epoxy encapsulation, sectioning of the bleed hole, and metallographic examination revealed a basic microstructure of pearlite and ferrite with bands of slightly finer pearlite, with a large concentration of inclusion stringers in the area of the fracture origin. Further investigation using an energy-dispersive x-ray analyzer showed high concentrations of sulfur and manganese. Thus, the failure appeared to have resulted from corrosion-assisted fatigue, and the inclusion concentration in the fracture-initiated area indicated that the chemical-composition limits for sulfur and manganese would have greatly exceeded material specifications. A higher quality steel was recommended for the replacement unit to lessen the possibility of such gross inclusion segregation and to improve the fracture toughness of the cylinder.

Several failed dies were analyzed and the results were used to evaluate fatigue damage models that have been developed to predict die life and aid in design and process optimization. The dies used in the investigation were made of H13 steels and fractured during the hot extrusion of Al-6063 billet material. They were examined to identify critical fatigue failure locations, determine corresponding stresses and strains, and uncover correlations with process parameters, design features, and life cycle data. The fatigue damage models are based on Morrow’s stress and strain-life models for flat extrusion die and account for bearing length, fillet radius, temperature, and strain rate. They were shown to provide useful information for the analysis and prevention of die failures.

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.

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.

Materials selection is closely related to the objectives of failure analysis and prevention. This article briefly reviews the general aspects of materials selection as a concern in both proactive failure prevention during design and as a possible root cause of failed parts. Coverage is more conceptual, with general discussions on the following topics: design and failure prevention, materials selection in design, materials selection for failure prevention, and materials selection and failure analysis. Because materials selection is just one part of the design process, the overall concept of design is discussed. The article also describes the role of the materials engineer in the design and materials selection process. It provides information on the significance of materials selection in both the prevention and analysis of failures.

Materials selection is an important engineering function in both the design and failure analysis of components. This article briefly reviews the general aspects of materials selection as a concern in proactive failure prevention during design and as a possible root cause of failed parts. It discusses the overall concept of design and describes the role of the materials engineer in the design and materials selection process. The article highlights the significance of materials selection in both the prevention and analysis of failures.

Erosion occurs as the result of a number of different mechanisms, depending on the composition, size, and shape of the eroding particles; their velocity and angle of impact; and the composition of the surface being eroded. This article describes the erosion of ductile and brittle materials with the aid of models and equations. It presents three examples of erosive wear failures, namely, abrasive erosion, erosion-corrosion, and cavitation erosion.

The Advanced Photon Source (APS) is a state-of-the-art synchrotron light source. The storage ring vacuum chamber is fabricated from 6061 extruded aluminum. Water connections to the vacuum chambers that were fabricated from 3003 aluminum had developed water leaks, which were subsequently remedied after considerable investigations.

New aircraft wing panels extruded from 7075-T6 aluminum exhibited an unusual pattern of circular black interrupted lines, which could not be removed by scouring or light sanding. The panels, subsequent to profiling and machining, were required to be penetrated inspected, shot peened, H2SO4 anodized, and coated with MIL-C-27725 integral fuel tank coating on the rib side. Scanning electron microscopy and microprobe analysis (both conventional energy-dispersive and Auger analyzers) showed that the anodic coating was applied over an improperly cleaned and contaminated surface. The expanding corrosion product had cracked and, in some places, had flaked away the anodized coating. The corrodent had penetrated the base aluminum in the form of subsurface intergranular attack to a depth of 0.035 mm (0.0014 in.). It was recommended that a vapor degreaser be used during cleaning prior to anodizing. A hot inhibited alkaline cleaner was also recommended during cleaning prior to anodizing. The panels should be dichromate sealed after anodizing. The use of deionized water was also recommended during the dichromate sealing operation. In addition, the use of an epoxy primer prior to shipment of the panels was endorsed. Most importantly, surveillance of the anodizing process itself was emphasized.

The primary purpose of this article is to describe general root causes of failure that are associated with wrought metals and metalworking. This includes a brief review of the discontinuities or imperfections that may be common sources of failure-inducing defects in the bulk working of wrought products. The article addresses the types of flaws or defects that can be introduced during the steel forging process itself, including defects originating in the ingot-casting process. Defects found in nonferrous forgings—titanium, aluminum, and copper and copper alloys—also are covered.

An AMS 4126 (7075-T6) aluminum alloy impeller from a radial inflow turbine fractured during commissioning. Initial examination showed that two adjacent vanes had fractured through airfoils in the vicinity of the vane leading edges, and one vane fractured through an airfoil near the hub in the vicinity of the vane trailing edge. Some remaining vanes exhibited radial and transverse cracks in similar locations. Binocular and scanning electron microscope examinations showed that the cracks had been caused by high-cycle fatigue and had progressed from multiple origins on the vane surface. Structural analysis indicated that the fatigue loading probably had been caused by forced excitation, resulting in the impeller vibrating at its resonant frequency. It was recommended that the impeller design, control systems, and material of construction be changed.

An aluminum bronze propeller tap bolt from a twin-screw vessel fractured just below the bolt head. Liquid penetrant testing revealed a large network of cracks that extended radially from sites in and just below the bolthead. Metallographic analysis indicated that the tap bolt failed by stress-corrosion cracking. It was surmised that seawater or some other corrosive substance was present in sufficient quantity to induce intergranular cracking at regions of high stress concentration. It was recommended that all tap bolts be replaced with new bolts made from an alloy with a higher copper content and at least the same yield strength. Steps to exclude seawater and any possible source of ammonia from the bolt shank were also suggested.

Erosion is the progressive loss of original material from a solid surface due to mechanical interaction between that surface and a fluid, a multicomponent fluid, an impinging liquid, or impinging solid particles. The detrimental effects of erosion have caused problems in a number of industries. This article describes the processes involved in erosion of ductile materials, brittle materials, and elastomers. Some examples of erosive wear failures are given on abrasive erosion, liquid impingement erosion, cavitation, and erosion-corrosion. In addition, the article provides information on the selection of materials for applications in which erosive wear failures can occur.