Method and apparatus for testing coiled materials

A curved sample of material is tested for ultimate tensile stress and elongation without prestraightening or premarking of the length of the sample. The sample is gripped at its ends and positioned to extend over convex surfaces mounted adjacent to the grippers on a pair of longitudinally moveable members. The members are moved apart and incremental data of the relative distances between the convex surfaces, representing the length of the sample, are stored. With each of the distance measurements, tensile stress measurements in the wire are made and stored. After the wire breaks, the data is analyzed. The stress versus distance ratios and rates of changes are analyzed to determine the end points of the stress versus length curve for the elastic deformation region, which is taken to begin when the wire has been pulled straight as is detected by a sudden increase in ratio of the tensile force versus sample length, and to end by a decrease the ratio, at the yield point where plastic deformation or permanent elongation of the sample begins. The permanent elongation of the sample ends at the break point of the sample, when it is at its total elongation.