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Principles of Plastic Design of Statically Indeterminate Structures
Published in A.I. Rusakov, Fundamentals of Structural Mechanics, Dynamics, and Stability, 2020
In Chapter 11, we introduced the concept of the quasistatic process in a mechanical system. Quasistatic loading of a structure is a slow change of loads from zero magnitudes to given values. As a rule, we shall consider the quasistatic one-step process. This means that a given system of loads is achieved through uniform and proportional increase of loads during the extended period of time T. Thus, at any time t in the period of load increase [0, T], each exerted load is represented in the form: Pi(t)=k(t)Pi(T);k(t)≡tT.
Development of a Strain-Rate Dependent Model for Uniaxial Loading of SMA Wires
Published in Norman M. Wereley, Inderjit Chopra, Darryll J. Pines, Twelfth International Conference on Adaptive Structures and Technologies, 2017
Harsha Prahlad, Inderjit Chopra
Experimental investigations previously reported by the authors [5] demonstrated a number of deviations of the SMA response between quasistatic and non-quasistatic loading. These included : The transformation stresses increased significantly as function of the strain rates above rates of 5 × 10−4/s. Below this strain rate, there was no appreciable change in the mechanical properties of the material at different strain rates. In this paper, strain rates below this value are referred to as “quasistatic”, and strain rates above this as “non-quasistatic”. The increase in transformational stresses during non-quasistatic loading was accompanied by a change in the path followed by the transformation, and also significant changes in the instantaneous temperature of the material.When the material was loaded under non-quasistatic loading, the stresses reached an instantaneous value which was higher than the those reached during quasistatic loading for the same final strains. However, when the strain was subsequently held constant, the material returned to lower values of stress consistent with quasistatic loading. This phenomenon, known as “stress-relaxation”, has also been reported before in different SMA alloy systems [18]. The magnitude of the decrease in stress due to the stress-relaxation was found to be significant (of the order of 30% of original stress).The phenomenon of stress relaxation was also observed during loading patterns that combine quasistatic and non-quasistatic loading. When the material was loaded under non-quasistatic loading, stresses instantaneously reached high values, and returned to values consistent with quasistatic loading when the strain rate was stepped down to quasistatic values.
Modeling the role of phase boundaries on the pullout response of shape memory wire reinforced composites
Published in Mechanics of Advanced Materials and Structures, 2023
Venkatesh Ananchaperumal, Srikanth Vedantam
A SMA wire of aspect ratio is considered to be embedded in a square matrix of side L as shown in Figure 3a such that the width of the wire represented is 0.5 mm. The domain size then corresponds to 5 mm × 5 mm in this case. The matrix and wire are taken to be separated by an interface of 0.01 L. This domain is discretized into about 3200 particles in the wire and the interface and about 300 particles in the matrix as shown in Figure 3b. Discretization refinement was carried out to ensure that this particle distribution was sufficient to give mesh independent results. The loading is performed in incremental load steps and the system is allowed to equilibrate between load increments in order to simulate quasistatic loading.
Dynamic behavior of carbon nanofiber-modified epoxy with the effect of polydopamine-coated interface
Published in Mechanics of Advanced Materials and Structures, 2020
Pengfei Wang, Jinglei Yang, Xin Zhang, He Zhang, Lijiang Zhou, Wanshuang Liu, Hang Zheng, Ming Zhang, Junfang Shang, Songlin Xu
Numerous researchers provide valuable insight into the nanoparticle constituent, such as carbon nanotube, graphene and nano-clay [1–6], for improving the mechanical properties of epoxy. The nanofiller’s reinforcing efficiency largely depends on their dispersibility and the interfacial adhesion between fillers and epoxies. Carbon nanofibers (CNFs) [7–9] were characterized in an outer diameter larger than 50 nm, which were regarded as an ideal candidate for enhancing epoxy resins owing to their lower cost and abundant sacrificial bonds [8, 10, 11]. However, nanocomposites as promising engineering materials are inevitable in encounter accidents such as impacting by foreign objects, striking by birds, and hailstones, in which the materials are substantially subjected to dynamic loading. The quasi-static loading implies the materials deform very slowly under a lower strain rate in which the inertia force can be neglected. However, the materials deform very quickly under dynamic loading at a high impact velocity, where the strain rate effect and inertia effect are both important in influencing the material’s mechanical property [12, 13]. It could be regarded that the dynamic behaviors of composites are not only related to their components, but also attributed by their complicated interface behaviors. However, uncovering the dynamic compressive behaviors of nano-composites with the effect of different interface states remain a great challenge.
Experimental and numerical investigations on the failure behavior of metal skin and carbon fiber-reinforced polymer core structures considering layup and manufacturing process conditions
Published in Advanced Composite Materials, 2022
Sewon Jang, Luca Quagliato, Naksoo Kim
Both tensile and 3-point bending tests have been carried out in room temperature conditions and utilizing a test speed of 2 mm/min to achieve quasi-static loading conditions. For each one of the 12 tested combinations of temperatures and cutting directions, six test repetitions have been carried out and, among them, the two extreme curves ones, considered as those with the highest and the lowest load integral over stroke, until the failure stroke, have been considered for the comparison with the FE simulation results, reported in section 5 of the paper. This approach allows accounting for the accuracy of the implemented finite element (FE) simulation model in accounting for the unavoidable experimental scattering and provides a more accurate insight into its real performances.