Quasi-static models of a four-bar quick-release hook

Quick-Release Hooks (QRHs) are connection devices for chains or metal ropes, which can be unfastened under full-load conditions by using a limited opening force. Despite their widespread use, the scientific literature about the mechanical behaviour of QRHs is rather limited. This paper deals with the kinematic and quasi-static analysis of a class of QRHs, based on a spring-loaded four-bar mechanism operating in the proximity of a singularity configuration. The quasi-static analysis allows to estimate the opening force as a function of the mechanism geometry and of the safety spring's features. At last, a multibody model of the system is developed, in order to validate the analytical model and to evaluate the influence of friction in revolute joints.