Bending fatigue of hybrid composite rods
The flexural fatigue behavior of hybrid composite rods comprised of unidirectional carbon and glass fibers was investigated. Damage was evaluated by monitoring stiffness loss as a function of cycles, and bending fatigue failure was defined in terms of strength retention. The acoustic emission technique and microscopic examination were used to characterize damage progression and failure mechanisms. The number of cycles to failure depended on applied stress level, and a two-parameter Weibull analysis was used to incorporate probability of failure to the S–N curve. Damage initiated and propagated as a result of matrix cracking and fiber bundle failures within the GF shell. Bending fatigue damage only initiated when the hybrid was exposed to a deflection in excess of 42% of flexural strength, which does not occur in actual conductor field use. Damage reached a saturation point along the GF/CF interface because of the stress concentration that existed between the two material systems, resulting in asymptotic behavior of the stiffness loss. Because damage did not extend into the CF core, static mechanical properties were retained to ∼85% or more.
Water Absorption and Distribution in a Pultruded Unidirectional Carbon/Glass Hybrid Rod under Hydraulic Pressure and Elevated Temperatures
A pultruded unidirectional carbon/glass reinforced epoxy hybrid FRP rod with 19 mm of diameter was developed for a sucker rod and lifting oil wells. The rod possesses a 12-mm diameter carbon fiber core and a 3.5-mm thick outer shell. The rod was exposed to high-temperature immersion in water under hydraulic pressure. To understand the long-term service performance of the rod, immersions in water at 20 °C, 40 °C, or 60 °C under 20 MPa of pressure for 1 year were conducted on the water uptake and distribution in the rod. The water uptake data were fitted by Fickian diffusion law, and the diffusion coefficient and the maximum water uptake were derived. Water distribution in the rod as a function of the immersion time, temperature, and hydraulic pressure was analyzed theoretically. This study revealed the accelerating effects of the elevated temperatures and the hydraulic pressure on the water diffusion in the hybrid rod.
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”.