Institute of Fundamental Technological Research

Needle-like twins are observed experimentally within the transition layer at the martensite–twinned martensite interface. We utilize a phase-field approach to investigate this microstructure. Our goal is to simulate the morphology of the transition layer and to perform a detailed analysis to characterize its interfacial and elastic micro-strain energy. To illustrate the micromechanical framework developed for that purpose, sample computations are carried out for a CuAlNi shape memory alloy undergoing a cubic-to-orthorhombic martensitic transformation. A particular focus of the study is on size-dependent morphology through examining the impact of twin spacing. Additionally, our results reveal that certain twin volume fractions lead to the emergence of twin branching as a way to minimize the total free energy stored in the microstructure.

Microstructure,Martensitic transformation,Transition layer,Phase-field method,Size effects

In this comment, it is shown that there are some non-negligible big mistakes in the analyses and stability proof of the proposed controller in the quoted paper, which makes the main results of this paper to be incorrect. The main unavoidable mistakes in the stability analysis of the main theorem (Theorem 1) are stated and some remarks are also mentioned to fix some of them.

finite-time convergence, fractional-order controllers, lower-limb exoskeleton, robustadaptive control, terminal sliding mode control

Researchers have a special fondness for continuum robots (CRs) due to their various applications. CRs have been modeled in different ways. One of these methods is called lumped model. Although the lumped modeling of CRs needs multiple degrees of freedom, researchers have considered only a few degrees of freedom. But considering such structures led to some issues in the accuracy of the controller. Therefore, in this paper, the dynamic modeling of a CR which is based on the lumped model is developed in a general form. Additionally, a control strategy based on sliding mode back-stepping control is proposed after introducing the first and second Lyapunov functions for stability proof. Moreover, a new function in the control law is used to avoid chattering phenomena. The proposed controller can reduce the settling time, which is one of the most important factors in controlling such robots. To demonstrate the efficiency of the proposed method, three different case studies are conducted for a planar 8-DOF continuum manipulator and the simulations are compared with the feedback linearization method (FL). The simulations show the effectiveness of the proposed method for controlling the continuum robot.

microstructure, martensitic phase transformation, transition layer, phase-field method, size effects

shape memory alloys, branched microstructures, free energy, continuum model

Shape memory alloys, Branched microstructures, Energy minimization, Continuum framework