Akademik Veri Yönetim Sistemi
Yükseköğretim Kurumları Destekli Proje, 2019 - 2020
"As far as we know and experience in everyday life, static events, especially in Mechanical Engineering domain, occur so slowly. For this, they can be considered independent of time called time-independent phenomena. On the other hand, dynamic events relate to time and change by that. These phenomena are a function of two main concepts, the rate at which our observed event changes and the fact that information is propagated at a finite speed. These two facts imply the strain rate and wave propagation, respectively. This sometimes means that the motion of the rigid body is a net result of many, many wave reflections. Wave propagation in a solid material is a function of the sample geometry as well as its material’s constitution (mechanical properties). In this regard, two prevalent geometries, rods, and plates are really practical due to their simplicities. Rods exposed to uniaxial stresses cause the samples to bear elastic longitudinal, shear and torsional waves. The elastic wave propagation runs inside the material up to elastic limit and then it continues in both elastic and plastic forms. The magnitude of moving stress is governed by plasticity and material failure. In rod-likeshaped samples changes in the stress wave propagation speed, as a result of loading speed, can be remedied by changing the deformation rate of the samples. In other words, the deformation rate of the sample keeps the pace of the speed of stress wave propagation up to a point where the stress can be considered 1D due to the uniform deformations of the sample. This situation begins to change after a while when the material enters the instability section of its deformation, at which the deformations are non-uniform which causes the sample experience 3D stresses. The non-uniformity of the deformation can easily be observed after the initiation of metal instability, results in a phenomenon called necking. This feature of the different materials can be a characteristic of that material due to its indicatory nature, by which the transition of the stress from 1D to 3D is appropriately accessible. This transition procedure imposes the material behave differently in different situations of loading. This project refers to a novel concept about materials behavior and the mechanism by which a metallic material convey some different waves through itself. This research improves the knowledge about this behavior or response of material enduring loading both in tensile and compression forms with respect to several sorts of loading speed. As an outcome from similar studies, it is certain that the speed of loading affects the place of samples necking or rupture, especially in high speed loading, in which high rate of imposing the load or corresponding displacement causes the samples be failed in a place near the loading location. This can be explained by the fact that loading a specimen with high speed force the stress wave in a speed higher than the speed of sound in that material, which results in creating shock waves. In such a case that a primary loading wave or shock wave can be superposed by another unloading (rarefaction) wave reflected from the free edges of the sample, a reinforced wave will propagate through the sample, which is powerful enough to damage or even explode the structure in superposed locations. Materials under huge loading pass the elastic domain and tolerate plastic eternal deformations, including necking and rupture. With the knowledge that the place of potential necking phenomena and its mode is of importance in the prediction of the failure of specimens, investigating the causes and facts, by which an almost perfect procedure of estimation or some powerful relations governing the wave propagation inside the materials, is necessitated. This study includes a literature review comprising all concepts, theories and relations published previously as well as some introduced new correlations justified by simulations performed using ABAQUS commercial finite element package. In addition, some experiments may be done to indicate the accuracy of the finite element analyses."