A finite element method for thermo-mechanical coupling analysis of shape memory alloys

Due to strong thermo-mechanical coupling in shape memory alloys (SMAs), heat generation/absorption during forward/reverse phase transformation can cause temperature variations in the material; influencing its mechanical behaviour. It is usually assumed that this coupling is only affected by the loading rate. But, recently studies have shown that the size of the structure and the boundary conditions are also important. Therefore, only the definition of quasistatic or slow loading rate can not guarantee an isothermal process and so further considerations need to be made. Based on the powerful model, proposed by Lagoudas et al. [1] and later improved for computer programming using the return mapping algorithm by Qidwai and Lagoudas [2], this contribution presents a three-dimensional thermo-mechanically coupled extension which describes two important typical phenomena of material model of SMAs: superelasticity and superplasticity (shape memory effect). An algorithm is then proposed to implement the coupled model into a finite element code. Performed simulations with different boundary conditions demonstrate that the both loading rate and the size dependency can be captured within the proposed framework. The results are in good agreement with available data in the literature

Design of Finite-Length Irregular Protograph Codes with Low Error Floors over the Binary-Input AWGN Channel Using Cyclic Liftings

We propose a technique to design finite-length irregular low-density parity-check (LDPC) codes over the binary-input additive white Gaussian noise (AWGN) channel with good performance in both the waterfall and the error floor region. The design process starts from a protograph which embodies a desirable degree distribution. This protograph is then lifted cyclically to a certain block length of interest. The lift is designed carefully to satisfy a certain approximate cycle extrinsic message degree (ACE) spectrum. The target ACE spectrum is one with extremal properties, implying a good error floor performance for the designed code. The proposed construction results in quasi-cyclic codes which are attractive in practice due to simple encoder and decoder implementation. Simulation results are provided to demonstrate the effectiveness of the proposed construction in comparison with similar existing constructions.Comment: Submitted to IEEE Trans. Communication