Rheology is defined as the study of the flow and deformation of matter. This article begins with an examination of flow behavior. It describes the geometries and methods employed for rheological testing of polymers in their molten state. It also discusses materials that are predominantly in the solid state and the methods employed for solids testing. Examples of unidirectional and dynamic oscillatory testing are provided for different mechanical behaviors.

Over a period of 2 or 3 years, 40 to 50 premature failures of drawn high-tensile, pearlitic high-carbon (0.8 wt% C) steel wires used as cables for towing targets behind aircraft occurred. Six service failures were examined in detail. Four types of failure characteristics were noted. A close examination of wire that had been flown several times without failure was also made, and dynamic tests were conducted to investigate the fracture characteristics of wire subjected to dynamic loading. It was concluded that dynamic shock loading transmitted by the target during unsteady flight conditions was the major cause of failure. Recommendations emphasized the need for a suitable shock absorber to be fitted at the constant-tensioning device of the winch system.

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.

Shaft misalignment and rotor unbalance contribute to the premature failure of many machine components. To understand how these failures occur and quantify the effects, investigators developed a model of a rotating assembly, including a motor, flexible coupling, driveshaft, and bearings. Equations of motion accounting for misalignment and unbalance were then derived using finite elements. A spectral method for resolving these equations was also developed, making it possible to obtain and analyze dynamic system response and identify misalignment and unbalance conditions.

This article reviews the impact response of plastic components and the various methods used to evaluate it.. It describes the effects of loading rate on polymer deformation and the influence of temperature and strain rate on failure mode. It discusses the advantages and limitations of standard impact tests, the use of puncture tests for assessing material behavior under extreme strain, and the application of fracture mechanics for analyzing impact failures. It also develops and demonstrates the theory involved in the design and analysis of thin-walled, injection-molded plastic components.

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.

Six transformer brackets failed in service, sending a group of three pole-mounted transformers to the ground below. The brackets were made from acrylonitrile-butadiene-styrene (ABS) resin and had been in service for more than 30 years. Remnants of the fractured brackets were analyzed using optical and scanning electron microscopy, Fourier transform infrared spectroscopy (FTIR), and thermogravimetric analysis (TGA). The exterior surfaces of all six brackets were alike and shared similar features, including witness marks, discoloration, mechanical deformation, and secondary cracking, along with crack networks. Both FTIR and TGA analyses indicated that the surface material was in a highly degraded state, likely due to weathering and thermal and ultraviolet exposure. This, in turn, led to the formation of cracks that propagated under the cyclic forces of vibration and wind. As the cracks grew larger, the weight of the transformer eventually overloaded the brackets, resulting in failure.

This article addresses some established protocols for characterizing thermoplastics and whether they are homogeneous resins, alloyed, or blended compositions or highly modified thermoplastic composites. It begins with a discussion on characterizing mechanical, rheological, and thermal properties of polymer. This is followed by a section describing molecular weight determination using viscosity measurements. Next, the article discusses the use of cone and plate and parallel plate geometries in melt rheology. It then reviews the processes involved in the analysis of thermoplastic resins by chromatography. Finally, the article covers three operations of thermoanalysis, namely differential scanning calorimetry, thermogravimetric analysis, and thermomechanical testing.

In 1979, during a routine bridge inspection, a fatigue crack was discovered in the top flange plate of one tie girder in a tied arch bridge crossing the Mississippi River. Metallographic analysis indicated a banding or segregation problem in the middle of the plate, where the carbon content was twice what it should have been. Based on this and results of ultrasonic testing, which revealed that the banding occurred in 24-ft lengths, it was decided to close the bridge and replace the defective steel. The steel used in the construction of this bridge was specified as ASTM A441, commonly used in structural applications. Testing showed an increase in hardness and weight percent carbon and manganese in the banded region. Further testing revealed that the area containing the segregation and coarse grain structure had a lower than expected toughness and a transition temperature 90 deg F higher than specified by the ASTM standards. The fatigue crack growth rate through this area was much faster than expected. All of these property changes resulted from increased carbon levels, higher yield strength, and larger than normal grain size.

Cam crack failures are a common occurrence in cam-follower systems often caused by excessive loading or inappropriate operating conditions. An investigation into such a failure was conducted to assess the effect of cam crack damage on the dynamic behavior of cam-follower systems. It was shown both theoretically and experimentally that a cracked cam causes an overall reduction in stiffness. To further probe the effect, investigators derived an analytical formula expressing the time varying stiffness of a cam-follower system. They also succeeded in quantifying the relationship between crack size and stiffness, showing that cracks have an amplitude modulating effect.

Following three similar failures of load chains on manually operated geared pulley-blocks of 1-ton capacity, a portion of one of the chains was obtained for examination. The chain was made of mild steel and the links had been electrically butt-welded at one side. In the case of the sample obtained, the failure in service had resulted from fracture of one of the links in the plane of the weld. Six of the other links in the vicinity showed cracks in the welds in various stages of development. Microscope examination showed a crack in an early stage of development and also from an apparently sound link, the prepared surfaces lying in the planes of the links. This examination revealed that the welds were initially defective. Discontinuities were present in both cases adjacent to the insides of the links, of a type indicative of either inadequate fusion or incomplete expulsion of oxide, etc., at the time of the upset, i.e. the pressing together of the ends of the links to complete the welding. It was evident from the examination that the service failures were due to the use of chain that was initially defective.

There are many different types of polymeric materials, ranging from glassy to semicrystalline polymers and even blends. Their mechanical properties range from pure elastic with very high strains to fracture (elastomers) to almost pure linear elastic (Hookian behavior) with low strains to fracture (glassy polymers). This article provides an overview of historical development of fracture behavior in polymers. It discusses the processes involved in three fracture test methods for polymers, namely linear elastic fracture mechanics, elastic-plastic fracture mechanics, and post-yield fracture mechanics.

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.

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.

Two type 316L stainless steel orthopedic screws broke approximately 6 weeks after surgical implant. The screws had been used to fasten a seven-hole narrow dynamic compression plate to a patient's spine. The broken screws and screws of the same vintage and source were examined using macrofractography, SEM fractography, and hardness testing. Fractography established that fracture was by fatigue and that the fatigue cracking originated at corrosion pits. Hardness while below specification, still indicated that the screws were in the cold-worked condition and notch sensitive during fatigue loading. Use of a steel with a higher molybdenum content (317L) in the annealed condition was recommended.

The plate used to treat a pseudarthrosis in the proximal femur was investigated for reasons of non-progress of healing. Fatigue cracks were revealed on the top surface of the small section of the plate at the fifth screw hole. The plate was found to be heavily loaded by comparison of intensity of these structures, compared to results of systematic crack-initiation experiments. It was revealed by fatigue bending tests that the fatigue life of plates with asymmetrically arranged holes is at least as long as for plates with holes situated in the center. Fatigue began at the large section only after a fatigue crack begins to propagate into the small plate section. A large secondary crack which had developed parallel to the main crack in the center of the surface was revealed. The fifth hole was situated at the transition between the supporting bone and the defect and hence stress concentration was revealed to be high.

An agricultural tine, which is a relatively large double torsion spring with outer legs that are used to sweep through hay or other crops and turn them over, had failed. It was made hard-drawn carbon steel. Bending fatigue was revealed by visual examination to be almost certainly the cause of failure. The fatigue fracture origin was found on the inside surface of the legs at the point where they joined the coiled body of the spring. It was established that the tines after being wound up by loading with hay, sprung back through the neutral unloaded position and into the unwind direction. This movement into the unwind direction was concluded to be happening often enough to initiate fatigue. The stress relieving temperature was recommended to be increased to reduce the residual stresses from coiling and hence improve fatigue performance.

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.