Fatigue temperature

Initial design considerations require a knowledge of the chemical and physical properties of both adhesive and adherends. Furthermore, an adhesive joint is expected to perform satisfactorily under the expected service conditions, for the planned lifetime of the structure. Thus the change in the properties of the materials involved as a function of the effects of environment, fatigue, temperature, loading rate, and age must also be known, or be predicted. ... 

Thermal cycling, tensile, shear, and mechanical fatigue tests of solder joints of several alloys, including Sn-37Pb, Sn-0.7Cu, and Sn-3.5Ag-0.5Cu, attached to ENIG and Cu pads, in a flip chip test vehicle without underfill were conducted (Ref 101, 102). The thermal fatigue temperature profiles were 0 to 100 C (32 to 212 °F), and -40 to 125 (-40 to 257 °E), both... 

The magnitude and nature of the load are considered in formulating the design. The load may be essentially quasistatic, cycHc, or impact. Many stmctural failures, for example, have been caused by supposedly innocuous stmctural details welded in place without any consideration given to their effect on fatigue properties. The service temperatures are also important, since they affect the fracture resistance of a material. 

Division 2. With the advent of higher design pressures the ASME recognized the need for alternative rules permitting thinner walls with adequate safety factors. Division 2 provides for these alternative rules it is more restrictive in both materials and methods of analysis, but it makes use of higher allowable stresses than does Division 1. The maximum allowable stresses were increased from one-fourth to one-third of the ultimate tensile stress or two-thkds of the yield stress, whichever is least for materials at any temperature. Division 2 requkes an analysis of combined stress, stress concentration factors, fatigue stresses, and thermal stress. The same type of materials are covered as in Division 1. 

Fatigue. Engineering components often experience repeated cycles of load or deflection during their service fives. Under repetitive loading most metallic materials fracture at stresses well below their ultimate tensile strengths, by a process known as fatigue. The actual lifetime of the part depends on service conditions, eg, magnitude of stress or strain, temperature, environment, surface condition of the part, as well as on the microstmcture. 

The constant, C, is proportional to the ductility of the material in tension the exponent, b, is near 0.5 for most materials over a wide temperature range. This equation applies usually in the range 1—10 cycles, and typical data are shown in Figure 4a (5). The exponent rises when creep or environmental interactions affect fatigue behavior. 

Fig. 4. Fatigue data for high temperature alloys (a) As vs cycles to failure for various alloys tested under strain control. (°) = testing at RT in air ...

High temperature materials which exhibit the greatest resistance to high cycle fatigue on a strength basis, ie, fatigue limit/tensile strength vs are... 

High temperature fatigue and fretting fatigue behavior has also been improved by implantation (113,114). This has been achieved by using species that inhibit oxidation or harden the surface. It is generally accepted that fretting behavior is closely coimected to oxidation resistance, perhaps due to third party effects of oxidation products. Oxidation resistance alone has also been improved by ion implantation (118—120). 

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