TABLE OF CONTENTS The variables of state for thermomechanical analysis are deformation (strain) and stress. The SI units of deformation are based on length (meter, m), volume, (cubic meter, m 3) and angle (radian, rad, or degree) as listed in Fig. 4.143 (see also Fig. 2.3). Stress is defined as force per unit area with the SI unit newton m ?2, also called by its own name pascal, Pa. Since these units are not quite as frequently used, some conversion factors are listed below. [1] The stress is always defined as force per area, while the strain is the fractional deformation, as is also shown in Fig. 4.143. The shear strain and tensile strain cause increasing strain with increasing stress. The volume strain is defined with a negative sign to account for the fact that increasing pressure causes always a decrease in volume. The derived function of the volume with respect to pressure is the compressibility, ?, as shown by the boxed equation in Fig. 4.143. The inverse of compressibility is the bulk modulus, also called the isothermal elasticity coefficient. The second equation in the box gives a general expression for three different isothermal elasticity coefficients, known as bulk modulus, B, tensile or Young's modulus, E, and shear modulus, G. They represent the differential coefficient of stress with respect to the three different types of strain sketched at the bottom of the figure. The bottom equation in Fig. 4.143...
