Critic-based design systems are systems whose architecture consists of a central synthesis module responsible for initiating design decisions and a set of independent asynchronous modules, called critics, responsible for providing feedback on these decisions. Critics can signal flaws in the design and provide evaluations that can guide the synthesis module in making additional design decisions. Critics form a modular, expandable library that is particularly suited for distributed design environments. This paper describes the structure and operation of a mechanical strength critic. The critic is part of an Automated Simultaneous Engineering (ASE) environment whose initial domain is the design of window regulators. We describe the architecture of the system and show its performance on some typical mechanical parts from a car window regulator assembly.