Non-Destructive Pressure Pulse Examination for Fatigue Crack Detection in Hydraulic Components

The growth of fatigue cracks in hydraulic components limits their lifetime. In consequence, many components are oversized for their operating life to prevent crack growth and premature component failures. As an alternative, condition monitoring prevents machine downtime by closely monitoring the components’ state of life. However, due to the harsh operating conditions of hydraulic components, detecting fatigue cracks is difficult. We propose a new approach for non-destructive crack detection that employs a pressure pulse with a high drop rate while measuring the component’s deformation. The oil has to flow out for a fatigue crack to close, which delays the closing of the crack. In consequence, an existing crack causes an offset between the load pressure and the mechanical strain. The offset is measured in order to detect possible cracks. We demonstrate the approach on a test specimen with single-grid linear strain gauges. In our experiments, the offset reached up to 5%. The magnitude of the offset increases with the crack length and can be used as an indicator or threshold in condition monitoring. In addition to a possible online assessment, the proposed approach can be utilized on test rigs as an inspection method or for trial runs.