Harvey Donald Solomon

Fatigue of 60/40 Solder

Plastic strain versus fatigue life data are presented for tests run at -- 50, 35, 125, and 150°C. It was found that these data could be correlated by the Coffin-Manson fatigue law, with an exponent of approximately 0.5 for the tests run at -35°C to 125°C. At 150°C the exponent was reduced to 0.37. These results were obtained for plastic strain limited tests. Different results are obtained when total strain limits are employed. This difference is discussed. The influence of cycling frequency and temperature changes are also discussed. A model is presented which describes the influence of plastic strain and cycling frequency. Corrections to the model predicted fatigue life, which account for temperature changes, cycling waveshape, and joint geometries, are also discussed.

Load relaxation studies of polycrystalline high purity aluminium

Abstract Load relaxation studies were carried out to test for the existence of a plastic equation of state in high purity polycrystalline aluminium. The tests verified that such an equation of state held at room temperature. The hardness states that were demonstrated were stable against static recovery up to at least 0.45 T m . The hardness curves of stress-strain rate satisfied a scaling relationship with respect to different states of hardness. Accumulated plastic strain is not a good state variable. Transient behavior could be readily distinguished from the time independent state behavior.

Mössbauer effect study of ‘475°c embrittlement’ of duplex and ferritic stainless steels

Abstract The phenomenon of ‘475°C embrittlement’ of a duplex stainless steel and seven single phase ferritic alloys was studied with Mossbauer spectroscopy and transmission electron microscopy. The alloys studied included two binary Fe-Cr alloys and multicomponent alloys containing Ni, Mo and Cu as well as Fe and Cr. There is a hyperfine field shift with aging at 475°C in all of the alloys. In addition, paramagnetic peaks and precipitates are observed only in the alloys containing Ni. These results are described in terms of Cr and Fe separation via spinodal decomposition. Furthermore, in the Ni containing alloys, the peak local Cr level is estimated as being higher than 78 at.% whereas in the Ni free alloys, after similar heat treatments, the peak local Cr level is estimated as being only about 45 at%.

Solute effects in micro and macroyielding of iron at low temperatures

Abstract The temperature dependences of the micro and macroplastic behavior following a prestrain have been studied in an Fe-0.15 wt. % Ti alloy, two vacuum melted irons containing 0.005 and 0.035 wt. % carbon, respectively, and an Fe-3.1 wt. % Si alloy. The results are consistent with a previously proposed model which ascribed the low temperature microplastic deformation to motion of edge and other non-screw dislocations and macroscopic flow to the motion of screw dislocations. Interstitial impurities were found to influence the motion of the former, whereas the screw dislocation motion was not similarly affected. The results are also consistent with those theories which ascribe the temperature dependence of macroscopic flow to the nature of the b.c.c. lattice. The microstrain behavior of the Fe-3.1 % Si alloy was found to be considerably different from that of the other alloys. Caution is necessary in using experimental results obtained on this alloy as a model for the yielding of other b.c.c. metals and alloys.

Low cycle fatigue of surface-mounted chip-carrier/printed wiring board joints

Chip-barrier/printed-wiring-board joints have been tested isothermally, at 35 degrees C, in shear. The joints were subjected to fully reversed cycling with fixed plastic displacement limit. The fatigue life was correlated with this displacement by a pseudo Coffin-Manson law. The fatigue life was defined in terms of 25%, 50%, 90%, and 100% drop in the load required to produce a given displacement. The resistance of each of 22 joints was also measured and the fatigue life, N/sub f/, defined in terms of the first joint to increase by 0.02%, 0.05%, 0.1%, 1%, 10%, 100%, and 10*. The results were found to be in general agreement with those obtained previously on single, larger, solder joints. Some variations were noted in the Coffin-Manson exponent, depending on how the displacement and fatigue lives were defined. This is discussed along with a model describing the process of joint failure. A set of displacement versus fatigue life curves which can be used to estimate the joint life on the basis of a variety of criteria is provided.<<ETX>>

Slow Strain-Rate Testing in High Temperature Water

The apparatus and technique employed in slow strain-rate testing of stainless steels in high temperature high purity water are described and discussed. Typical results from work in progress on the influence of heat treatment and surface treatment on the intergranular stress corrosion cracking of Types 304 and 308 stainless steel and Alloy XM-19 are described. The correspondence between strain-rate tests varies from alloy to alloy. The minimum strain rate required to cause intergranular cracking varied significantly with the alloy and with the surface treatment. It is suggested that reduction of area and observation of the fracture mode provide better measures of environmental interactions than measures of tensile parameters obtained from the test records.

Influence of Mean Stress on the Fatigue Behavior of 304L SS in Air and PWR Water

Load-controlled experiments on 304L stainless steel were run in Air and PWR water, at 150°C and 300°C, with and without a mean stress of 100MPa. These experiments were run to determine the influence of temperature, environment, and mean stress on the 107 Cycle Fatigue Limit stress amplitude. A 100MPa mean stress was found to have different effects at the different temperatures and environments. In contrast to all the conventional models used to describe the effects of mean stress, when the testing was done at 300°C (for both air and PWR water), a 100MPa mean stress was found to raise the 107 Cycle Fatigue Limit relative to that observed without a mean stress. This was ascribed to the effect of the hardening due to the initial straining and to secondary hardening, both of which are more pronounced at 300°C than at 150°C. The increased initial and secondary hardening resulted in the development of less non-elastic strain, thereby improving the fatigue behavior. In PWR water at 150°C, a 100MPa mean stress reduced the 107 Cycle Fatigue Limit by more than that predicted by conventional mean stress models, but in air at 150°C, the decrease in the endurance limit was more in keeping with the predictions of these models. This difference was ascribed to the effect of the PWR water, in the absence of significant initial straining and secondary hardening.Copyright

Crack initiation in low alloy steel in high temperature water

This paper describes a study of fatigue crack initiation in WB36, a German low alloy steel, tested in high temperature, high purity, water. Flat un-notched, tensile specimens were cycled under load control, with R=0.1, and with a saw-tooth wave form (with a loading time of 30 seconds and an unloading time of 3 seconds). Crack initiation was followed by periodically stopping the test and replicating the surface. The tests were performed at 177°C, in water containing 8ppm O 2 H 2 SO 4 additions were also made in some tests to raise the conductivity of the water from 0.06 μS/cm to 0.4-0.5μS/cm. The crack initiation and growth data are correlated with the water chemistry of the test.