DEFINING IMPACT

摘要

Describing impact in terms of sonic velocity provides a dissection tool for this complex event. Impact velocity induces a proportional stress in the colliding objects. For flapper valves we also have viscous fluids at the interface, inviting stiction and cavitations. Stress in the reed develops at the speed of impact, while fluid layer dilation may take somewhat longer. Viscosity alters anchoring of the reed membrane just long enough for the stress to develop. A wider seat increases the clamping force in proportion to the area and the ambient viscosity. With the valve temporarily held down, reverse bending stress develops under gas/air pressure and inertia force. Regression of the test data supports this scenario. In the presence of any fluid, stiction effects match impact, and both participate equally in the outcome recorded as impact failure. There may be no such thing as pure impact in the micro world of flapper valves.