Strain fatigue

Increasing temperature decreases the modulus of elasticity of elastomers at the same time that accelerated chemical effects occur. In our constant strain fatigue tests it has been found that the effect on the modulus (lower stress at the same strain) is significantly more important than chemical degradation effects, as shown in Figure 2. Thus, failure occurred much more rapidly at 4°C than at 37°C or 60°C. This may be one manner in which fatigue... 

Figure 1. Cumulative distribution function for a step-increasing strain fatigue test cycled at 120 cpm in distilled water at 37° C using cut-initiated specimens.

Figure 3. Oxygen influences upon uncut specimens from step-increasing strain fatigue tests cycled...

Fatigue is the decay of mechanical properties after repeated application of stress and strain. Fatigue tests given information about the ability of a material to resist the development of cracks or crazes resulting from a large number of deformation cycles. 

There are also applications of quantum theory for instance in the onset of a failure in a material. The failure starts on the atomic scale when an interatomic bonding is stressed beyond its yield-stress threshold and breaks. The initiation and diffusion of point defects in crystal lattice turn out to be a starting point of many failures. These events occur in a stress field at certain temperatures. The phenomena of strain, fatigue crack initiation and propagation, wear, and high-temperature creep are of particular interest The processes of nucleation and diffusion of vacancies in the crystal lattice determines the material behavior at many operation conditions. 

The presence of vibrations can be detrimental to the performance of mental and physical tasks by humans. Low-frequency and large-amplitude vibrations contribute to problems such as headaches, motion sickness, eye strain, fatigue, and interference with the ability to read and interpret instruments [29]. These symptoms become less pronoimced as the frequency of vibration increases and the amplitude decreases. However, high-frequency and low-amplitude vibrations can also be quite fatiguing. 

Work effort framework of stress, strain, fatigue and injury... 

The work effort framework can be thought of as four parts - stress, strain, fatigue and injury. If we are thinking about the musculoskeletal system, the stress as noted earlier... 

Notes T is temperature Ep refers to prior plastic strain, especially cyclic plastic strain (fatigue) (these are qualitative indicators here exceptions are possible)... 

An important step in local strain fatigue analysis under irregular variation of load with time, as schematized in Fig. 6.16a, is the knowledge of the local notch strain-stress history, as shown in Fig. 6.16c. This, in turn, necessitates the knowledge of the cyclic stress-strain characteristic of the material (see Sect. 1.3.1). Advanced elastic-plastic analysis technique such as finite element computer code is needed or it can be used a simplified Neuber s rule as described in the next section. 

Tavernelli, J.F., Coffin Jr, L.F. A compilation and interpretation of cyclic strain fatigue tests on metals. Trans. ASM 51, 438 (1959)... 

While this may seem a rather flippant example, the cracial point is that if the machine expects its driver to be shaped like the genetically modified version in Figure 3.1 but inreahty the driver is normal, then the likelihood of errors increases. This inerease is both in direct errors (for example, the inability to easily reach and operate controls) and in indirect ones (by, for example, increasing musculoskeletal strain, fatigue etc.). 

A. Kapoor, A re-evaluation of the life to rupture of ductile metals by cyclic plastic strain. Fatigue and Fracture of Engineering Materials and Structures 17 (1994) 201-219. 

---