Determination of the constants of material models at high strain rates and elevated temperatures using shot impact test

The Journal of Strain Analysis for Engineering Design

Fariba

Pipelzadeh

et al. 2014

Self Cite

The true stress–strain curve has a significant role in the analysis of deformation in theoretical plasticity and numerical simulations. Because of the triaxial state of stress in the neck zone, the relationship that is normally obtained from the engineering stress–strain curve is no longer valid and must be corrected. Various correction techniques have been proposed and can be found in the literature. In this study, a new semi analytical approach for the correction of the stress–strain curve for circular cross-section specimens (axisymmetric) is introduced and a relation for a correction factor is derived based on the theory of plasticity. The relation requires only a few experimental surface strain measurements which can easily be made using an image processing technique. In the new method, the neck zone is divided into a number of thin walled toroidal elements. The algorithm for the correction factor is obtained in terms of the initial specimen radius, the neck radius and the z-strain on the neck surface. In this work, the true stress–strain curve, that is obtained using the image processing, follows a power law trend before the onset of necking and a linear trend after necking. However, the method is not limited by the trend of the stress–strain curve and can accommodate any trend describing the stress–strain relationship. The proposed approach is compared with methods proposed by Bridgman–Leroy, Bridgman, Davidenkov and Spiridonova, Siebel and Schwaigere and also numerical simulations. The number of simplifying assumptions in the present work is less than that of the Bridgman approach and some of the other methods.

Section: Validation Of the Methodsmentioning

confidence: 99%

A new approach for the correction of stress–strain curves after necking in metals

The Journal of Strain Analysis for Engineering Design

Fariba

Pipelzadeh

et al. 2014

Self Cite

“…Johnson–Cook model is a well-known model which has been proved to be a proper choice for describing the behaviour of most of metals. The model is defined as follows 1…”

Section: Johnson–cook Materials Modelmentioning

confidence: 99%

“…During the past decade, attempts have been made to invent new devices or to develop new methods for dynamic stress–strain measurement. The shot impact test introduced by Majzoobi et al 1 is one of the most recent developments in this regard. The indentation test has drawn much attention in recent years due to the development of new test equipment.…”

Section: Introductionmentioning

confidence: 99%

Determination of stress–strain curves of materials at high strain rates using dynamic indentation technique

Pourolajal

The Journal of Strain Analysis for Engineering Design

2020

Determination of dynamic behaviour of materials is a serious challenge in mechanics of materials. In this investigation, a new approach is proposed to obtain stress–strain curves of metals from dynamic indentation test. This approach is based on a combined experiment, simulation, and optimization techniques. In the experiment side, a conical penetrator is shot against the material as the target. The load–indentation depth curve is obtained from the dynamic indentation test. The indentation test is simulated using Ls-dyna and the numerical load–indentation depth is obtained from the simulation. The stress–strain curves are defined by Johnson–Cook material model. From optimization of the difference between the experimental and numerical load–indentation depth curves, the constants of the material model are identified. The material model is validated also by stress–strain curves obtained from quasi-static test conducted using Instron and dynamic tests conducted using Split Hopkinson Bar. The results show a close agreement between the model prediction and the experimental stress–strain curves for different strain rates.

“…This is while, in some deformation processes, the strain can be greater than 1. In shot impact method, high strength shots are impacted on specimens at high impact velocities and at elevated temperatures using a gas gun [18]. The section of the shot inside a crater is illustrated in Fig.…”

Section: Shot Impact Testmentioning

confidence: 99%

A comparative study on the restrictions of dynamic test methods

Lahmi

2015

EPJ Web of Conferences

Abstract. Dynamic behavior of materials is investigated using different devices. Each of the devices has some restrictions. For instance, the stress-strain curve of the materials can be captured at high strain rates only with Hopkinson bar. However, by using a new approach some of the other techniques could be used to obtain the constants of material models such as Johnson-Cook model too. In this work, the restrictions of some devices such as drop hammer, Taylor test, Flying wedge, Shot impact test, dynamic tensile extrusion and Hopkinson bars which are used to characterize the material properties at high strain rates are described. The level of strain and strain rate and their restrictions are very important in examining the efficiency of each of the devices. For instance, necking or bulging in tensile and compressive Hopkinson bars, fragmentation in dynamic tensile extrusion and petaling in Taylor test are restricting issues in the level of strain rate attainable in the devices.