Course summary

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Machine Design 1. Design Criteria Mechanical Failure : any change in size, shape or mechanical propertie s of a structure, machine or components that renders it incapable of satisfactory performing its intended function. Failure : omission of occurrence or performance; specifically: a failing to perform a duty or expected action. A state of inability to perform a normal fu nction. Failure Mechanisms : force, time, temperature, reactive environment. Failure modes of interest : yielding, ductile rupture, brittle fracture, fatigue. Aeronautical certification : aircrafts must satisfy the structural requirement s described in the Certification Specification (CS) standards to obtain the authorization to flight. Two different analyses are required: - static analysis: components must guarantee the oper ation of the system under limit loads (the maximum loads to be expected in service) and ultimate loads (limit loads multiplied by a prescribed safety factor). Preventing the static fr acture and high plasticization is the aim of the static design. High safety factors are used. Tools for static analysis: identification of load conditions, structural equilibrium and internal loa ds, state of stress on critical zones, geometry variations and notch effects, static properties of the material, static strength analysis and safety factors. - fatigue analysis (variable loads): Three main fatig ue design philosophies are available in aeronautics: safe life, fail safe and damage tolerance (flow tolerance). Safe life approach: the structure is designed to su stain the loads for the whole system life. The component is replaced at the end of the aircraft li fe. Main features of safe-life components are high thicknesses, low stresses and structural integ rity during life (no damages allowed).…