Stress-Strain State and Damage in Polymer Parts of Instruments Aboard Artificial Satellites

Abstract

The paper presents a method for determination of the stress-strain state and the level of accumulated damage in polymer parts of the devices aboard artificial satellites orbiting the Earth. A mathematical statement of the creep problem is put forward using the Lagrange approach. The methods involves the use of constitutive equations that include elastic, thermoelastic, and creep strains and damage due to cyclic actions of temperature fields and space radiation. Different types of damage are allowed for through the Yokobory hypothesis, and the equivalent stress is chosen by the Pisarenko–Lebedev criterion. The intensification of creep and the damage accumulation due to period changes in temperature stresses are taken into account by means of special constitutive equations derived by the methods of asymptotic expansion and averaging over the period of stress variation. A transient heat conduction problem is pre-solved in order to determine the temperature field. At each time step the boundary-value problem is solved by the finite-element method using a 3D eight-node element and a three-node element of a solid of revolution. The initial boundary value problem is solved by the finite-difference predictor-corrector method. By way of example, the thermal fields, stress state and damage accumulation are computed for a polypropylene component of a fiber-optic gyroscope. Based on the thermoelastic problem computations, the time dependence of the equivalent stress has been found, which is allowed for in the constitutive equations during the strain and damage calculations for the polypropylene component. The calculated data on the stress redistribution, the increase in stress and damage are discussed for various cases of protection against space radiation.