The main objective of this study is to design titanium alloy femoral stems with cubic porous structures that will be able to reduce stress shielding and promote stem stability. These porous structure designs were introduced into titanium alloy femoral stems as homogeneous and functionally graded porous structures. First, the cubic cellular structures were simulated under compressive loading to measure the yield and modulus of elasticity for various porosity ranges. Based on the selected porosity range, fifteen different arrangements of radial geometrical functionally graded (FG) designs were developed with average porosities of 30, 50, and 70% respectively. Finite element models were developed with physiological loads presenting three different walking speeds (1, 3, and 5 km/h), where the average human body weight was assumed. Stresses at the bone Gruen zones were measured to check the percentage of stress transfer to the bone for each porous stem design and were compared with the bulk stem. Several FG stem designs were shortlisted for further investigation as candidates for hip implants.

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High-temperature bulge forming of AA5083 aluminum sheet was simulated with the commercial finite element (FE) code ABAQUSä. A material model that is strain rate sensitive and accounts for strain hardening and softening was used. Results were compared with data from AA5083 bulge forming experiments at 450°C where the gas pressure was a prescribed constant value. The results show that the material model is capable of predicting the deformation and thinning behavior at different constant pressure levels. In ancillary simulations, time-varying pressure profiles were computed (rather than prescribed) with an internal ABAQUSä routine that attempts to maintain the strain rate at the bulge dome pole within a specified range. The time-varying profiles, for which no experimental AA5083 bulge forming data exist, can be programmed into existing bulge testing instrumentation to validate the associated predictions of bulge dome height and thinning. The present effort represents a necessary step toward predicting gas pressure profiles by coupling the pressure profile with a desired sheet deformation rate.

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This paper studies the effects of interfacial friction distribution on the integrity of superplastic formed parts. For that purpose, the deformation of AA5083 superplastic aluminum alloy into a long rectangular box is investigated. The die surface is divided into five regions for local application of friction coefficients. The commercial finite element code, ABAQUSTM, is used to carry out the forming simulations and calculate the thickness distribution, forming time, and forming pressure profile for different combinations of friction coefficients. It is found that friction distribution at the die-sheet interface strongly affects the metal flow during the forming process, which has a direct impact on deformation stability and strain localization. With the proposed optimal variable friction distribution, the quality of the formed parts has been enhanced, while reducing the required forming time.

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