Typical Metal Material Yield Strength Of The Static Pressure Experiments

Under high pressures, to accurately measure yield strength of solid materials is an important issue for both equation of state (EOS) and constitutive equation. The traditional pressure gradient method under diamond anvil cell (DAC) loading is one of three major techniques in this issue. A good agreement has been achieved in other two methods; the pressure gradient method was thus questioned because a systemic difference was found between the results determined by this method and the other two methods. In this work, a systemic analysis on the stress balance equation which the pressure gradient method relied on and the experimental requirements have been discussed in detail. Accordingly modifications to the traditional pressure gradient method are made. By measuring the yield strength of molybdenum, the modified technique is verified and the main goals obtained can be concluded as follows:(1) In the traditional radial pressure gradient method, a gasket made by other materials was normally used, and the strength of the gasket will effect the accurately measurement on pressure distribution. In our modified method, the sample was used as a gasket; the effect concerned above is thus eliminated. The measured pressure distribution is good enough to accurately determine the maximum pressure gradient and its location.(2) In the traditional pressure gradient method, the thickness of the sample was corrected by an EOS correction method; it produces an error of above 30%. In our modified method, a technique to in-situ measure the thickness of sample under high pressures is developed. By use this technique, the repetitive error is less than 3 urn and the maximum relative error is reduced to～16%.(3) The yield strength of molybdenum obtained in three samples with different initial thicknesses of 100μm, 250μm and 500μm (denoted as Mo-100, Mo-250 and Mo-500, respectively) is identical above a certain pressure (～8 GPa). The yield strength of molybdenum is thus independent with their initial thickness of samples and their plastic deformation history.(4) The obtained yield strength of molybdenum can be described as Y= 0.48+0.14P and agree well with Y= 0.46+0.13P measured by Duffy by using radial X-ray diffraction technique. Also our experimental results are consistent with the tensile value of 0.7 GPa determined by Bridgman at ambient conditions and shock data at a relative low pressure. The consistency of different methods proves that our results are reasonable and the modified technique is valid.In summary, by measuring the yield strength of molybdenum this work shows a consistency of the three major techniques under diamond anvil cell (DAC) loading although the detailed explanation of this conclusion needs a further experimental and theoretical study.