Mechanical properties testing creep analysis

The above-mentioned thermomechanical models only consider the elastic behavior of materials. Boyd et al. [13] reported on compression creep rapture tests performed on unidirectional laminates of E-glass/vinylester composites subjected to a combined compressive load and one-sided heating. Models were developed to describe the thermoviscoelasticity of the material as a function of time and temperature. In their work, the temperature-dependent mechanical properties were determined by fitting the Ramberg-Osgood equations and the temperature profiles were estimated by a transient 2D thermal analysis in ANSYS 9.0. 

Macroscopic properties, alternatively referred to as bulk properties or simply performance , are of the utmost importance in material selection. For any application it is essential that the material provides the properties desired, under the conditions of use. In addition, it is wise to characterise the material more fully in order to understand what the effect might be, for example, of changing the temperature. Consideration should also be given to time-related phenomena, such as creep or stress relaxation. What are the consequences of dimensional instability Techniques that can provide this type of information directly include mechanical testing, rheology and thermal analysis. In cases where knowledge of the relationship between structure and properties is desirable, then obviously the techniques described here must be used in combination with those which follow. 

The test methodologies, whether tension/ compression tests on bulk solders or shear tests on solder joints, have their merits for specific study objectives. Tension and compression tests on bulk solder provide critical input data for constitutive models. The finite element analysis within those models can account for geometric effects on creep deformation in an actual joint configuration (included spatially varying stress state). However, length-scale effects of small joints, or elemental contamination that alters the intrinsic mechanical and physical properties of the solder, require an entirely new set of constitutive equations because finite element analysis cannot account for these effects. Thus, in the latter circumstance, the most accurate creep data would be results obtained from tests on actual joints. 

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