The effects of cementite particles and subgrain boundaries on workhardening behavior of spheroidized carbon steels vere investigated by making direct measurements of residual internal stresses. These internal stresses developed due to plastic incompatabilitiesbetween elastic particles and an elastic-plastic matrix. A continuum analysis of these internal stress fields, based upon a multiple slip model, is presented and is found to be in good accord with the experiments. The internal stresses appear to saturate in the plastic strain range of 3 -5% where a transition in strain-hardening behavior was observed ("double-n" behavior), and to contribute approximately 20% to total work-hardening. The cementite-particle-pinned-subgrain-boundaries, formed during a post-quench annealing treatment, were found to lower the internal stress, thus indicating that they assisted the relaxation processes of entrapped Orowan loops by acting as sources of dislocations. The flow stress increment in dispersion hardened alloys due to work-hardening consisted of internal stress, forest stress, and source-shortening stress.The flow stress curves of spheroidized carbon steels were found to be described by a modified mean-square-root addition law of the form
The effect of through-thickness reinforcement by composite pins (Z-pins) on the static tensile strength and failure mechanisms of the joints made from ceramic matrix composite (CMC) is investigated. Overlap length of the single lap joint is 15 mm, 20 mm, 23 mm, 37 mm, and 60 mm, respectively. The experimental results indicate that the final failure modes of the joints can be divided into two groups, (a) the bond-line stops debonding until crack encounters Z-pins; and then the adherends break at the location of Z-pins, when overlap length is more than 20 mm; (b) the bond-line detaches entirely and Z-pins are drawn from adherends, when overlap length is equal to 15 mm. A simple efficient computational approach is presented for analyzing the benefit of through-thickness pins for restricting failure in the single lap joints. Here, the mechanics problem is simplified by representing the effect of the pins by tractions acting on the fracture surfaces of the cracked bond-line. The tractions are prescribed as functions of the crack displacement, which are available in simple forms that summarize the complex deformations to a reasonable accuracy. The resulting model can be used to track the evolution of complete failure mechanisms, for example, bond-line initial delamination and ultimate failure associated with Z-pin pullout, ultimate failure of the adherends. The paper simulates connecting performance of the single lap joints with different Z-pins' diameter, spacing and overlap length; the numerical results agree with the experimental results; the numerical results indicate enlarging diameter and decreasing spacing of Z-pins are in favor of improving the connecting performance of the joints. By numerical analysis method, the critical overlap length that lies between two final failure modes is between 18 mm and 19 mm, when Z-pins' diameter and spacing are 0.4 mm, 5 mm, respectively.
A micromechanical model for elastic behavior analysis of angle-interlock woven ceramic composites is proposed in this paper. This model takes into account the actual fabric structure by considering the fiber undulation and continuity in space, the cavities between adjacent yarns and the actual cross-section geometry of the yarn. Based on the laminate theory, the elastic properties of 3D angle-interlock woven ceramic composites are predicted. Different numbers of interlaced wefts have almost the same elastic moduli. The thickness of ceramic matrix has little effect on elastic moduli. When the undulation ratio increases longitudinal modulus decreases and the other Young's moduli increase. Good agreement between theoretical predictions and experimental results demonstrates the feasibility of the proposed model in analyzing the elastic properties of 3D angle-interlock woven ceramic composites. The results of this paper verify the fact that the method of analyzing polyester matrix composites is suitable for woven ceramic composites.
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