Practice Problems on Fracture for the Mid term Determine what equations apply what the variables are in the equations and what they mean and solve for the requested information What is the magnitude of the maximum stress that exists at the tip of an internal crack having a radius of curvature of 2 5 10 4 mm and a crack length of 2 5 10 2 mm when a tensile stress of 170 MPa is applied Estimate the theoretical fracture strength of a brittle material if it is known that fracture occurs by the propagation of an elliptically shaped surface crack of length 0 25 mm and having a tip radius of curvature of 1 2 10 3 mm when a stress of 1200 MPa is applied A specimen of a 4340 steel alloy having a plane strain fracture toughness of 45 MPa m is exposed to a stress of 1000 MPa Will this specimen experience fracture if it is known that the largest surface crack is 0 75 mm long Why or why not Assume that the parameter Y has a value of 1 0 Some aircraft component is fabricated from an aluminum alloy that has a plane strain fracture toughness of 35 MPa m It has been determined that fracture results at a stress of 250 MPa when the maximum or critical internal crack length is 2 0 mm For this same component and alloy will fracture occur at a stress level of 325 MPa when the maximum internal crack length is 1 0 mm Why or why not Calculate the maximum internal crack length allowable for a 7075 T651 aluminum alloy component that is loaded to a stress one half of its yield strength Assume that the value of Y is 1 35 for the geometry and K Ic 24 MPa m y 495 MPa for the alloy Review all the homeworks and quizes Partial list of concepts to understand Bonding Types and their characteristics metallic covalent ionic van der Waals What is the relationship between the energy between atoms and their interatomic separation the force versus interatomic separation and the relationship between the energy and the force What is the meaning of the equilibrium separation separation distance between atoms How does the shape of the energy interatomic separation curve affect properties What are several properties we examined in class that are related to the energyinteratomic separation curve FCC and BCC know all about them atom positions lattice parameter in terms of atom radius density because different atoms weigh different amounts concept of atomic weight planar density linear density planes and directions identify construct spacing between planes in a given family of planes x ray diffraction how it works how it is related to all the above Stress and strain elastic and plastic deformation know how the atoms behave during these processes states of stress tensile test engineering stress and strain versis true stress and strain dislocations and slip in FCC and BCC slip systems relationship between applied stress axis and crystal orientation where can slip happen Strengthening mechanisms in metals what they are how they work how to create specific micostructures cold work recovery recrystallization and grain growth Fracture stress concentration at a crack tip fracture toughness plane strain fracture toughness
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