MAT E202 Lecture Notes - Lecture 7: Stress Concentration, Thermal Expansion, Heat Flux

• School: University of Alberta
• Department: Materials Engineering
• Course: MAT E202
• Professor: Thomas Etsell

Document Summary

Under cyclic loading, metals fail at stresses well below ys. Must avoid possible points of stress concentration like surface flaws, bolt holes, and sharp bends which can initiate a crack. Fortunately, some materials like steel exhibit an endurance limit. The stress below which fatigue will not occur. If fatigue is a potential problem, this becomes new design stress. Expressed generally by linear expansion coefficient, defined by. Relates temperature of material (level of thermal activity), to the heat content (thermal energy) Molar heat capacity is change in heat content/mole. Heat capacity (c) is the change in hear content / oc. Thermal expansion ( ) causes greater atomic vibrations at high temperature. If the material is restrained form expanding or contracting, this becomes mechanical strain. Stress can be great since e is huge. Tensile stresses are positive, compressive stresses are negative. Thermal conductivity (k) is the proportionality constant relating the heat flux q and the thermal gradient in a material.