Single-crystal silicon is an excellent infrared window material and is often used as light filter, infrared window and
substrate material in an optical system. At the same time single-crystal silicon is typical brittle material. Therefore
thermal stress damage has possibly occurred before melting when it is irradiated by laser. In order to investigate on the
laser-induced thermal stress damage problem in single-crystal silicon, a spatial axisymmetric finite element model is
established to solve the thermal stress problem which a single-crystal silicon substrate is heated by a Nd:YAG laser beam
with wavelength of 1064nm and pulse width of the millisecond order. After the temperature and stress fields are obtained, the relevant analysis is carried out. The calculational results are in reasonable agreement with the reported experiment results. It found that the stress value in the central zone of the laser spot exceeds the fracture strength of single-crystal silicon, which can explain the damage of cleavage fracture of the material.
During laser heating of a metal material, the continuity of material confines its free expansion, thermal stresses arise. On
one hand the thermal expansion of the heated zone of the material increases with the increase of temperature, the
thermal stress level increases correspondingly; on the other hand the mechanical properties of the material will change
with the increase of temperature, especially the elastic modulus, yield strength and tensile strength drop significantly,
which is the so-called thermal softening problem. Due to the effect of the two factors, as the heating time or the intensity
of the laser beam increases, it is possible that the stress levels of the heated zone of the material exceed the yield
strength, which leads the material to come into a plastic stage. Thus, a thermal plastic problem occurs. In this study,
thermal elasto-plastic stresses during laser heating of a metal plate are computed by the finite element method (FEM)
based on thermal elasto-plastic constitutive theory. The mechanical behaviors of the metal material during the laser
heating are analyzed. By the analysis of the results, it is found that thermal expansion leads to the increase of stress level
early during the laser irradiating, and thermal softening causes the decrease of stress levels in the plastic zone and the
slow growth and even decrease of stress levels in elastic zone later. The radial stresses are all compressive stresses, and
the hoop stresses are compressive stresses within about the laser spot and are tensile stresses at other place. This work
may be beneficial to the laser processing of metal materials.
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