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In solid mechanics, the Johnson–Holmquist damage model is used to model the mechanical behavior of damaged brittle materials, such as ceramics, rocks, and concrete, over a range of strain rates. Such materials usually have high compressive strength but low tensile strength and tend to exhibit progressive damage under load due to the growth of microfractures. There are two variations of the Johnson-Holmquist model that are used to model the impact performance of ceramics under ballistically delivered loads.〔Walker, James D. ''Turning Bullets into Baseballs'', SwRI Technology Today, Spring 1998 http://www.swri.edu/3pubs/ttoday/spring98/bullet.htm〕 These models were developed by Gordon R. Johnson and Timothy J. Holmquist in the 1990s with the aim of facilitating predictive numerical simulations of ballistic armor penetration. The first version of the model is called the 1992 Johnson-Holmquist 1 (JH-1) model.〔Johnson, G. R. and Holmquist, T. J., 1992, ''A computational constitutive model for brittle materials subjected to large strains'', Shock-wave and High Strain-rate Phenomena in Materials, ed. M. A. Meyers, L. E. Murr and K. P. Staudhammer, Marcel Dekker Inc. , New York, pp. 1075-1081.〕 This original version was developed to account for large deformations but did not take into consideration progressive damage with increasing deformation; though the multi-segment stress-strain curves in the model can be interpreted as incorporating damage implicitly. The second version, developed in 1994, incorporated a damage evolution rule and is called the Johnson-Holmquist 2 (JH-2) model〔Johnson, G. R. and Holmquist, T. J., 1994, ''An improved computational constitutive model for brittle materials'', High-Pressure Science and Technology, American Institute of Physics.〕 or, more accurately, the Johnson-Holmquist damage material model. == Johnson-Holmquist 2 (JH-2) material model == The Johnson-Holmquist material model (JH-2), with damage, is useful when modeling brittle materials, such as ceramics, subjected to large pressures, shear strain and high strain rates. The model attempts to include the phenomena encountered when brittle materials are subjected to load and damage, and is one of the most widely used models when dealing with ballistic impact on ceramics. The model simulates the increase in strength shown by ceramics subjected to hydrostatic pressure as well as the reduction in strength shown by damaged ceramics. This is done by basing the model on two sets of curves that plot the yield stress against the pressure. The first set of curves accounts for the intact material, while the second one accounts for the failed material. Each curve set depends on the plastic strain and plastic strain rate. A damage variable D accounts for the level of fracture. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Johnson–Holmquist damage model」の詳細全文を読む スポンサード リンク
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