Cyclic deformation behavior of an epoxy polymer. Part I: Experimental investigation

Abstract

A series of uniaxial cyclic tests were carried out on solid cylindrical specimens of an epoxy resin, Epon 826/Epi-Cure Curing Agent 9551. The focus of the study was to investigate time-dependent viscoelastic behavior of this thermosetting polymer material under cyclic loading and to develop a constitutive model with the capabilities to simulate the observed deformation response. The tests include stress-controlled or strain-controlled cyclic loading with/without mean stress or mean strain at various amplitudes and loading rates. It was found that the cyclic stress-strain response of this material is amplitude-dependent and rate-dependent, and the response to axial tension is different from that in compression. The stress-strain loops exhibit more pronounced nonlinearity with high amplitudes or low loading rates. For stress-controlled cyclic loading with mean stress, ratcheting strain is accumulated, which is of viscoelastic nature, and this is confirmed by its full recovery after load removal. For strain-controlled cyclic loading with mean strain, the mean stress relaxation occurs, which contributes to the observed longer life in comparison to the stress-controlled cyclic loading with mean stress. Polym. Eng. Sci

Monitoring the early stiffness development in epoxy adhesives for structural strengthening

“…16b. This process of a continuous increase in strain is called cyclic creep (or ratcheting strain) [18] and it confirms that epoxy resin shows a typical visco-elastic behaviour. Therefore, the high visco-elasticity that epoxy exhibited at very early ages may have influenced the measurement of elastic modulus through tensile tests, leading to lower values.…”

“…This initial stretch of testing was performed under displacement control by reason of the machine operation and as to ensure the respect of the targeted stress limits. It is further remarked that the choice of a load rate of 20 N/s for the all ages of testing was based on the fatigue tests carried out by Shen et al [18] and was related to the intent of matching the strain rate of the standard tensile tests for an intermediate value of stiffness of 4 GPa (1/2 of the expected ultimate value in the studied mix).…”

Nonlinear numerical predictions of three-dimensional orthogonal woven composite under low-cycle tension using multiscale repeating unit cells

“…Note that when R ¼ 1, then equation (7) reduces to the von Mises equivalent stress, eq ¼ ffiffiffiffiffiffiffi 3J 2 p . Based on the uniaxial creep curves at different stress levels following a routine procedure as described in Hu et al (2003) and Shen et al (2004), the values of constants (E, , , 1 , R) and the functional form of E i ¼ E 1 ð eq Þ can be obtained from experimental tests in Table 1.…”

A large deformation framework for compressible viscoelastic materials: Constitutive equations and finite element implementation

“…In an investigation by Shen et al (2004) and Xia et al (2005a), a series of uniaxial cyclic tests were carried out on an epoxy resin, Epon 826/EpiCure 9551. The data were used to evaluate the performance of two nonlinear viscoelastic constitutive models (Xia et al, 2005b), where a general loading/unloading criterion and a 'switch rule' was proposed.…”