Furthermore, the irreversible axial strain
, the material stiffness degradation, and the energy dissipation have been used to quantitatively investigate the damage characteristics of rocks to evaluate the stability of underground excavations (Zhou et al., 2015; Liu et al., 2016; Munoz and Taheri, 2017).
The effects of various geometric parameters, the size and thickness of the printed circuit board and component and solder interconnect dimensions on the fundamental resonant frequency of the assembly and the axial strain
of the most critical solder joint were thoroughly investigated.
According to Corigliano (2007), the axial force, which may induce tensile stresses in the tunnel lining, can be assessed reliably through a free-field analysis, knowing the free-field axial displacement along the tunnel upon the evaluation of the axial strain
[[sigma].sub.a] is the stress value of the beginning point of the linear segment on the stress-strain relation curve (MPa); [[sigma].sub.b] is the stress value of the end of the linear segment on the stress-strain relation curve (MPa); [[epsilon].sub.la] is the axial strain
value when the stress is [[sigma].sub.a], and [[epsilon].sub.lb] is the axial strain
value when the stress is [[sigma].sub.b].
The axial stress and strain are recorded, and the peak strength ([q.sub.u]), strength of axial strain
15% ([q.sub.a]), residual strength ([q.sub.r]), axial strain
of failure ([[epsilon].sub.f]), elasticity modulus (E), and failure modulus ([E.sub.f]) are measured.
An axial strain
in the grating alters not only the grating spatial period but also the effective refractive index and changes the Bragg wavelength as a result of the elastic behavior and the elastooptical effect.
Figures 1(a), 1(b), and 1(c) show the stress ([sigma]) versus axial strain
([[epsilon].sub.a]) curves at different temperatures for slow, moderate, and fast monotonic tests, respectively.
The axial strain
of the rod and cable elements in the unit can be written as follows:
In terms of triaxial compression tests, Gray and Alrefeai  carried out triaxial tests on the stress-strain performance of fiber-reinforced sand with nondiscrete distribution, and the test results show that the fiber increases the axial strain
of reinforced sand when it is destroyed, and reduces the loss of postpeak strength.
In elastic mechanics using Poisson's ratio and axial strain
to calculate volume strain is the most common method for brittle rock.
In these procedures the inclination of neutral axis is kept constant and the unknown represents either the depth of neutral axis or axial strain
. These parameters are determined iteratively such that the equilibrium of the axial force to be satisfied (Charalampakis, Koumousis 2008; Marmo et al.