The Instability of Testing Machines

Abstract

The paper is concerned with the stability of compression- and tension-testing machines. It is demonstrated that the buckling of a simple testing machine may be treated as an elementary problem in elastic stability. The case of a simple compression machine is first studied; it is found that machines of this type may be highly unstable if the length of a ball-ended compression specimen is short in relation to the length of the connecting ties. This adverse feature of compression machines is confirmed by general experience in compression testing. The theory of instability presented is in good agreement with the results of tests on both model and full-size compression-testing machines. In the case of tension-testing machines it is found that for most practical test conditions the length of the tension specimen is not a critical factor.