Study On The Method Of Sample Clamping Technology On Material Testing

Tensile test has been widely adopted as an experimental method for determiningthe material properties because of its high accuracy, controllability and economy. Theobtained data by a tensile test can be used to determine the elongation of the material,the amount of area reduction, the modulus of elasticity, elastic limit, proportional limit,tensile strength, yield point, tensile yield strength, and other performance indicators.From the high temperature tensile test can also get creep data. Due to constantlydevelop and research on a variety of new materials, in recent years, the requirementson material properties has become even more specialized. Thus, the geometricparameters specified of the clamp are more stringent. So the clamp as the standardconfiguration of the tensile testing machine, the important parameters, such as the sizeof its shape and the dimensions, the initial jaw clamping force size has also beenhighly concerned about the world.This topic starting from the clamping fixture issue, carried out the theoreticalanalysis and experimental demonstration of the problems of the minimum clampingforce required during the experiment, and also proposed a design concept of anelectric horizontal push clamping device.Firstly, established two different contacts models,they are:1,the clamp completelyelastic contact with the sample,2, plastic deformation occurs between the clamp blockand the sample. These two contact models are being heoretical analysis, to obtained afinal relationship between the minimum clamping force and the the tensile force, andderive two different expressions of the relationship between the minimum clampingforce and the tensile force.Secondly, analysis the clamping method of the cuneate clamps, to derive therelationship between cuneate angle of the clamp blocks, the tensile strength test andthe clamping force under the influence of friction of the test. Since this relational expression is only consider the impact of the friction factor, thus the theoreticalclamping force is relatively larger than actual clamping force value. According to thisfeature of relational expression, calculate an estimate of the clamping force,substituted the same parameter values into the two general formula for the clampingforce. compared the estimated values with the theoretical value, supported by aconcluded: under the same experimental conditions, the clamping force of the secondset of formula is smaller than clamping force value obtained by the method of friction.Thus, preliminary proved that the second group of the general formula about theclamping force is correct.Thirdly, tensile test was performed to low-carbon steel samples, and theindentation depth of the sample surface to be measured with laser sensor. through theformula given by Johnson, size of the clamping force would be calculated by thedepth of the indentation, compared this value with the theoretical value, supported bya concluded: under the same experimental conditions, the clamping force of thesecond set of formula is bigger than clamping force value obtained by the test. Andthis can further demonstrate the feasibility of clamping force formulas.Finally, invented an electric horizontal push clamping device, Structural selectionand design of its clamping device and transmission device was carried out. Use DCgeared motor as drive system of the electric horizontal push clamping device.The topic raised about the minimum clamping force in the process of tensile test,derive the relevant formulas to theoretical and experimental verification, and apply itto a calculation of a new level electric horizontal push clamping device, thus, canmakes the structure more simple, more stable performance.