A Contribution to Time-Dependent Damage Modeling of Composite Structures
The paper presents a new damage model for predicting stiffness loss due to creep loading and cyclic fatigue. The model, developed within a continuum damage mechanics framework, is based on the idea of a time-dependent damage spectrum, some elements of which occur rapidly and others slowly. The use of this spectrum allows a single damage kinematic to model creep and fatigue damage and to take into account the effect of stress amplitude, R ratio, and frequency. The evolution equations are based on similar equation than the one describing the viscoelasticity model and are relatively easy to implement. The new model is compared to the experimental results on carbon fiber/epoxy tubes. Quasi-static, creep and fatigue tests are performed on filament-wound tubular specimens to characterize the elastic, viscoelastic and plastic behavior of the composite material. Varying amounts of damage are observed and discussed depending on stress level and R ratio. The experimental work aims to develop and validate the damage model for predicting stiffness loss due to creep loading and cyclic fatigue.
Influence of time-dependent damage on creep of multidirectional polymer composite laminates
An experimental study (Birur et al., 2006 [1]) on time-dependent evolution of various damage modes under constant load was extended; specifically, time-dependent evolution and influence of transverse cracks, in ±45° and 90° plies, on the creep of [±45/902]S multidirectional laminate of a polymer composite (Hexcel F263-7/Toho G30-500) was studied and modeled. The damage evolved with time in both ply groups sequentially and/or simultaneously depending on the test conditions. For the latter case, the two ply groups influenced each other’s damage evolution. The creep of the laminate was due to both the viscoelasticity of the plies and the time-dependent damage. A damaged ply was modeled using an equivalent undamaged ply with an apparent compliance, which was determined as a function of time-dependent transverse crack density. This was used along with a model frame work, based on lamination theory, to predict the creep compliance of the [±45/902]S laminate. The model predictions compared well with experimental results.
Evaluation of buckling load and dynamic performance of steel shear wall retrofitted with strips made of shape memory alloy
One of the most imperfections of the steel shear wall is out of plane displacements that cause severe damage in both structural and non-structural elements. In this paper, the effects of shape-memory alloys on steel shear walls are investigated. First, a numerical analysis using the finite element method in ABAQUS software has been carried out according to an experimental test. The results of the numerical analysis have been verified with experimental results. Next, shape-memory alloy fibers have been added vertically and horizontally to various parts of the steel shear wall. The results show that retrofitting with the shape-memory alloy reduces the out-of-plane displacement of the steel shear wall under both cyclic and seismic loadings. Besides, the buckling load in the steel shear wall increases when it is retrofitted with the shape-memory alloy. Also, the total out-of-plane movement (accumulated absolute displacements) of the steel shear wall and non-structural damage are controlled by the characteristic of a shape-memory alloy material called “super-elastic”.