Multiaxial Fatigue Testing Machines: A Critical Review of Architectures, Control, and Applications

Fatigue failure remains a key design concern in many mechanical components, particularly in applications where cyclic loading is unavoidable. In experimental practice, uniaxial fatigue testing is still the most widely used approach, mainly because it is simple, cost-effective, and supported by long-established standards. However, many components in service are subjected to combined axial, bending, and torsional loads, for which single-axis tests provide only limited insight. This discrepancy between laboratory testing and real operating conditions has driven the development of multiaxial fatigue testing systems. Existing review studies on multiaxial fatigue largely focus on failure criteria and life prediction models, while the experimental machines required to generate multiaxial loading are seldom examined in a systematic and comparative manner. In this paper, uniaxial and multiaxial fatigue testing machines reported in the literature are reviewed from an experimental perspective, with attention given to mechanical layout, actuation principles, load control, and synchronization. The discussion highlights the trade-offs between loading realism, system complexity, and cost, and illustrates industrial relevance through examples from aerospace and automotive engineering. Recent developments in control, automation, and data analysis are briefly discussed in relation to future experimental fatigue testing strategies.