Tension–Compression Asymmetry in the Off-Axis Nonlinear Rate-Dependent Behavior of a Unidirectional Carbon/Epoxy Laminate at High Temperature and Incorporation into Viscoplasticity Modeling
Abstract:Off-axis compressive deformation behavior of a unidirectional CFRP laminate at high temperature and its strain-rate dependence in a quasi-static range are examined for various fiber orientations. By comparing the off-axis compressive and tensile behaviors at an equal strain rate, the effect of different loading modes on the flow stress level, rate-dependence and nonlinearity of the off-axis inelastic deformation is elucidated. The experimental results indicate that the compressive flow stress levels for relatively larger off-axis angles of 30°,45° and 90° are about 50 percent larger than in tension for the same fiber orientations, respectively. The nonlinear deformations under off-axis tensile and compressive loading conditions exhibit significant strain-rate dependence. Similar features are observed in the fiber-orientation dependence of the off-axis flow stress levels under tension and compression and in the off-axis flow stress differential in tension and compression, regardless of the strain rate. A phenomenological theory of viscoplasticity is then developed which can describe the tension–compression asymmetry as well as the rate dependence, nonlinearity and fiber orientation dependence of the off-axis tensile and compressive behaviors of unidirectional composites in a unified manner. It is demonstrated by comparing with experimental results that the proposed viscoplastic constitutive model can be applied with reasonable accuracy to predict the different, nonlinear and rate-dependent behaviors of the unidirectional composite under off-axis tensile and compressive loading conditions.
Keywords: CARBON FIBER; EPOXY; HIGH TEMPERATURE; NONLINEAR BEHAVIOR; OFF-AXIS COMPRESSION; OFF-AXIS TENSION; RATE DEPENDENCE; TENSION-COMPRESSION ASYMMETRY; UNIDIRECTIONAL COMPOSITES; VISCOPLASTIC CONSTITUTIVE MODEL
Document Type: Research Article
Affiliations: 1: Department of Engineering Mechanics and Energy, University of Tsukuba, Tsukuba 305-8573, Japan 2: Graduate School of Systems and Information Engineering, University of Tsukuba, Tsukuba 305-8573, Japan 3: Aerospace Research and Development Directorate, Japan Aerospace Exploration Agency, Mitaka 181-0015, Japan 4: Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, Sagamihara 229-8510, Japan
Publication date: August 1, 2009