Requirements for the Permitted Size of the Alignment Errors of Load Frames for Fatigue Testing and a Proposal for a Relevant Measuring Method

Abstract

This paper covers the activities of the working party on Requirements for Fatigue Testing Machines [3]. Requirements and recommendations are specified with respect to the alignment of load frames for fatigue testing, including load cell and (hydraulic) actuator. Subsequently, a method is proposed to measure the alignment errors. Calculations are made and a series of alignment specimens are designed for load frames of different capacities to check whether or not the bending stresses under load, due to misalignment, correlate with the off-load measured alignment errors. Designs for clamping the alignment specimens are given and applied for the measurements as well. The alignment errors to be specified, defined, and measured include: 1. Eccentricity. 2. Angular deflection. 3. Alignment error. Although a literature survey was carried out, there appeared to be no specific requirements for the alignment accuracy of load frames. International standards mainly set out requirements concerning the accuracy of the load cell and the maximum allowable specimen bending at zero load. These standards, however, have omitted the effect of the alignment errors as defined in this paper. Results of measurements obtained with the described method lead to a recommendation for its application, either in part or in total.