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As shown in the formula above, compressive stress is typically represented by negative values to indicate that there is compression of an object, however, in geotechnical engineering compressive stress is conventionally represented by positive values. [2]
The "strain" is the relative change in length under applied stress; positive strain characterizes an object under tension load which tends to lengthen it, and a compressive stress that shortens an object gives negative strain.
Restated, the gas receives positive heat from the environment. If the system rejects heat, then Q < 0. That is, during isobaric compression/cooling, negative heat is added to the gas, or equivalently, the environment receives positive heat. Restated, the environment receives positive heat from the gas.
In the physical-space sign convention, positive normal stresses are outward to the plane of action (tension), and negative normal stresses are inward to the plane of action (compression) (Figure 5). In the physical-space sign convention, positive shear stresses act on positive faces of the material element in the positive direction of an axis.
For ordinary materials, the bulk compressibility (sum of the linear compressibilities on the three axes) is positive, that is, an increase in pressure squeezes the material to a smaller volume. This condition is required for mechanical stability. [8] However, under very specific conditions, materials can exhibit a compressibility that can be ...
The non-mechanical work of force fields can have either positive or negative sign, work being done by the system on the surroundings, or vice versa. Work done by force fields can be done indefinitely slowly, so as to approach the fictive reversible quasi-static ideal, in which entropy is not created in the system by the process.
The vector T may be regarded as the sum of two components: the normal stress (compression or tension) perpendicular to the surface, and the shear stress that is parallel to the surface. If the normal unit vector n of the surface (pointing from Q towards P) is assumed fixed, the normal component can be expressed by a single number, the dot ...
The bulk modulus (which is usually positive) can be formally defined by the equation K = − V d P d V , {\displaystyle K=-V{\frac {dP}{dV}},} where P {\displaystyle P} is pressure, V {\displaystyle V} is the initial volume of the substance, and d P / d V {\displaystyle dP/dV} denotes the derivative of pressure with respect to volume.