A number of failures involving carbon and alloy steels were analyzed to assess the effects of inclusions and their influence on mechanical properties. Inclusions, including brittle oxides and more ductile manganese sulfides (MnS), affect fatigue endurance limit, fatigue crack propagation rates, fracture toughness, notch toughness, and transverse tensile properties, and do so in an anisotropic manner with respect to rolling direction. Significant property anisotropy has been documented in the failures investigated, providing evidence that designers failed to account for it. Typical fracture morphologies observed in such cases and metallographic appearances of MnS-containing materials are illustrated.

This article briefly introduces some commonly used methods for mechanical testing. It describes the test methods and provides comparative data for the mechanical property tests. In addition, creep testing and dynamic mechanical analyses of viscoelastic plastics are also briefly described. The article discusses the processes involved in the short-term and long-term tensile testing of plastics. Information on the strength/modulus and deflection tests, impact toughness, hardness testing, and fatigue testing of plastics is also provided. The article describes tension testing of elastomers and fibers. It covers two basic methods to test the mechanical properties of fibers, namely the single-filament tension test and the tensile test of a yarn or a group of fibers.

Mechanical testing is an evaluative tool used by the failure analyst to collect data regarding the macro- and micromechanical properties of the materials being examined. This article provides information on a few important considerations regarding mechanical testing that the failure analyst must keep in mind. These considerations include the test location and orientation, the use of raw material certifications, the certifications potentially not representing the hardware, and the determination of valid test results. The article introduces the concepts of various mechanical testing techniques and discusses the advantages and limitations of each technique when used in failure analysis. The focus is on various types of static load testing, hardness testing, and impact testing. The testing types covered include uniaxial tension testing, uniaxial compression testing, bend testing, hardness testing, macroindentation hardness, microindentation hardness, and the impact toughness test.

A missile detached from a Navy fighter jet during a routine landing on an aircraft carrier deck because of a faulty missile launcher detent spring. Visual inspection of Inconel 718 detent spring assembly revealed that four of the nine spring leafs comprising the assembly were plastically deformed while two of the deformed leafs did not meet minimal hardness or tensile requirements. Liquid penetrant testing revealed no cracks or other surface discontinuities on the leaf springs. Material sectioned from the soft spring leafs was heat-treated according to specifications in the laboratory. The resultant increase in mechanical properties of the re-heat-treated material indicated that the original heat treatment was not performed correctly. The failure was attributed to improper heat treatment. Recommendations focused on more stringent quality control of the heat-treat operations.

Numerous flaws were detected in a steam turbine rotor during a scheduled inspection and maintenance outage. A fracture-mechanics-based analysis of the flaws showed that the rotor could not be safely returned to service. Material, samples from the bore were analyzed to evaluate the actual mechanical properties and to determine the metallurgical cause of the observed indications. Samples were examined in a scanning electron microscope and subjected to chemical analysis and several mechanical property tests, including tensile, Charpy V-notch impact, and fracture toughness. The material was found to be a typical Cr-Mo-V steel, and it met the property requirements. No evidence of temper embrittlement was found. The analyses showed that the observed flaws were present in the original forging and attributed them to lack of ingot consolidation. A series of actions, including overboring of the rotor to remove indications close to the surface and revision of starting procedures, were implemented to extend the remaining life of the rotor and ensure its fitness for continued service.

The U-0.8wt%Ti alloy is often used in weapon applications where high strength and fairly good ductility are necessary. Components are immersion quenched in water from the gamma phase to produce a martensitic structure that is amenable to aging. Undesirable conditions occur when a component occasionally cracks during the quenching process, and when tensile specimens fail prematurely during mechanical testing. These two failures prompted an investigative analysis and a series of studies to determine the causes of the cracking and erratic behavior observed in this alloy. Quench-related failures whereby components that cracked either during or immediately after the heat treatment/quenching operation were sectioned for metallographic examination of the microstructure to examine the degree of phase transformation. Examination of premature tensile specimen failures by scanning electron microscopy and X-ray imaging of fracture surfaces revealed pockets of inclusions at the crack origins. In addition, tests were conducted to evaluate the detrimental effects of internal hydrogen on ductility and crack initiation in this alloy.

The article commences with an overview of short-term and long-term mechanical properties of polymeric materials. It discusses plasticization, solvation, and swelling in rubber products. The article further describes environmental stress cracking and degradation of polymers. It illustrates how surface degradation of a plain strain tension specimen alters the ductile brittle transition in polyethylene creep rupture. The article concludes with information on the effects of temperature on polymer performance.

Mechanical properties of wire ropes, their chemical composition, and the failure analysis process for them are described. The wires are manufactured from high-carbon, plain carbon steel, with high-strength ropes most often manufactured from AISI Grade 1074. During visual failure examination, the rope, strand, and wire diameters should all be measured. Examination should also address the presence or absence of lubricant, corrosion evidence, and gross mechanical damage. Failed wires can exhibit classic cup-and-cone ductile features, flat fatigue features, and various appearances in-between. However, wires are often mechanically damaged after failure. Most nondestructive evaluation (NDE) techniques are not applicable to wire rope failures. Electron microscope fractography of fracture surfaces is essential in failure analysis. Fatigue is the most important fracture mode in wire ropes. Metallographic features of wire ropes that failed because of ductile overload and fatigue are described.

A helicopter tail rotor blade spar failed in fatigue, allowing the outer section of the blade to separate in flight. The 7075-T7351 aluminum alloy blade had fiberglass pockets. The blade spar was a hollow “D” shape, and corrosion pits were present on the inner surface of the hollow spar A single corrosion pit, 0.38 mm (0.015 in.) deep, led to a fatigue failure of the spar The failure initiated on the pylon side of the blade. Dimensional analysis of the spar near the failure revealed measurements within engineering drawing tolerances. Though corrosion pitting was present, there was an absence of significant amounts of corrosion product and all of the pits were filled with corrosion-preventative primer. This indicated that the pitting occurred during spar manufacture, prior to the application of the primer The pitting resulted from multiple nickel plating and defective plating removal by acid etching. Post-plating baking operations subsequently reduced the fatigue strength of the spar.

Cluster bomb tailcone assemblies each containing two aluminum die-cast components were rejected because of the poor surface condition of the die castings. Numerous heat checks were found on the surfaces of the tailcones and radiographic inspection revealed inclusions, gas holes, and shrinkage defects in the castings. Most of the components failed to meet required mechanical properties because of these casting defects.

The upper frame from a large cone crusher failed in severe service after an unspecified service duration. The ductile iron casting was identified as grade 80-55-06, signifying minimum properties of 552 MPa (80 ksi) tensile strength, 379 MPa (55 ksi) yield strength, and 6% elongation. Investigation (visual inspection, chemical analysis, unetched 30x images, and 2% nital etched 30x images) was difficult because the fracture surface of the frame section was obliterated by postfracture corrosion. Repeated attempts at cleaning using progressively stronger chemicals revealed that no telltale fracture morphology remained. However, the investigation supported the conclusion that the crusher frame failed via brittle overload fracture, likely due to excessive service stresses and substandard mechanical properties. Recommendations included additional quality-control measures to provide better spheroidal graphite morphology at the frame surface.

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 failure of a boiler operating at 540 °C and 9.4 MPa was investigated by examining material samples from the near-failure region and by thermodynamic analysis. A scanning Auger microprobe, SEM, and commercial thermodynamic software codes were used in the investigation. Results indicated that the boiler failure was caused by grain-boundary segregation of phosphorous, tin, and nitrogen and the in-service formation of carbide films and granules on the grain boundaries.

This article describes the viscoelastic behavior of plastics in their solid state only, from the standpoint of the material deforming without fracturing. The consequences of viscoelasticity on the mechanical properties of plastics are described, especially in terms of time-dependencies, as well as the dependence of the viscoelastic character of a plastic on chemical, physical, and compositional variables. By examining the viscoelastic behavior of plastics, the information obtained are then applied in situations in which it may be important to anticipate the long-term properties of a material. This includes assessing the extent of stress decay in materials that are pre-stressed, the noise and vibration transmission characteristics of a material, the amount of heat build-up in a material subjected to cyclic deformation, and the extent a material can recover from any prior deformation. Several qualitative graphs are presented, which highlights the possible differences in the viscoelastic behavior that can exist among plastics.

Engineering plastics, as a general class of materials, are prone to the development of internal stresses which arise during processing or during servicing when parts are exposed to environments that impose deformation and/or temperature extremes. Thermal stresses are largely a consequence of high coefficients of thermal expansion and low thermal diffusivities. Although time-consuming techniques can be used to analyze thermal stresses, several useful qualitative tests are described in this article. The classification of internal stresses in plastic parts is covered. The article describes the effects of low thermal diffusivity and high thermal expansion properties, and the variation of mechanical properties with temperature. It discusses the combined effects of thermal stresses and orientation that result from processing conditions. The article also describes the effect of aging on properties of plastics. It explains the use of high-modulus graphite fibers in amorphous polymers.

Plastics or polymers are used in a variety of engineering and nonengineering applications where they are subjected to surface damage and wear. This article discusses the classification of polymer wear mechanisms based on the methodologies of defining the types of wear. The first classification is based on the two-term model that divides wear mechanisms into interfacial and bulk or cohesive. The second is based on the perceived wear mechanism. The third classification is specific to polymers and draws the distinction based on mechanical properties of polymers. In this classification, wear study is separated as elastomers, thermosets, glassy thermoplastics, and semicrystalline thermoplastics. The article describes the effects of environment and lubricant on the wear failures of polymers. It presents a case study on nylon as a tribological material. The article explains the wear failure of an antifriction bearing, a nylon driving gear, and a polyoxymethylene gear wheel.

Two sand-cast low-alloy steel equalizer beams (ASTM A 148, grade 105-85) designed to distribute the load to the axles of a highway truck broke after an unreported length of service. Normal service life would have been about 805,000 km (500,000 mi) of truck operation. Investigation (visual inspection, chemical analysis, tensile testing, unetched 65x and 1% nital etched 65x magnification) supported the conclusions that the steel was too soft for the application – probably due to improper heat treatment. Fracture of the equalizer beams resulted from growth of mechanical cracks that were formed before the castings were heat treated. Recommendations included the following changes in processing: better gating and risering in the foundry to achieve sounder castings; better shakeout practice to avoid mechanical damage; better inspection to detect imperfections; and normalizing and tempering to achieve better mechanical properties.

Polymer materials are key building blocks of the modern world, commonly used in packaging, automobiles, building materials, electronics, telecommunications, and many other industries. These commercial applications of polymeric materials would not be possible without the use of additives. This article is divided into five sections: mechanical property modifiers, physical property modifiers, biological function modifiers, processing aids, and colorants. It describes three classes of additives that are used to inhibit biological activity, six classes of mechanical property modifiers, three classes of physical property modifiers, and two classes of both colorants and processing aids.