This research was directed toward quantitatively characterizing the effects of arterial mechanical treatment procedures on the stress and strain energy states of the artery wall. Finite element simulations of percutaneous transluminal angioplasty (PTA) and orbital atherectomy (OA) were performed on arterial lesion models with various extents and types of plaque. Stress fields in the artery were calculated and strain energy density was used as an explicit description of potential damage to the artery. The research also included numerical simulations of changes in arterial compliance due to orbital atherectomy. The angioplasty simulations show that the damage energy fields in the media and adventitia are predominant in regions of the lesion that are not protected by a layer of calcification. In addition, it was observed that softening the plaque components leads to a lower peak stress and therefore lesser damage energy in the media and adventitia under the action of a semicompliant balloon. Orbital atherectomy simulations revealed that the major portion of strain energy dissipated is concentrated in the plaque components in contact with the spinning tool. The damage and peak stress fields in the media and adventitia components of the vessel were significantly less. This observation suggests less mechanically induced trauma during a localized procedure like orbital atherectomy. Artery compliance was calculated pre- and post-treatment and an increase was observed after the orbital atherectomy procedure. The localized plaque disruption produced in atherectomy suggests that the undesirable stress states in angioplasty can be mitigated by a combination of procedures such as atherectomy followed by angioplasty.

Previously it was shown that including smaller inset regions of less stiff material in the larger O-ring section at locations of high stress results in lower strain energy density in the section. This lower energy content is expected to lead to improved long-term seal performance due to less permanent material deformation and so less loss of seal-housing contact pressure. The shape of the inset region, the time-dependent change in material properties, and hence change in seal behavior over time in use were not considered. In this research experimental and numerical simulation studies were conducted to characterize the time-dependent performance of O-ring section designs with small inset regions of different mechanical behaviors than the larger surrounding section. Seal performance in terms of the rate of loss of contact pressure of modified designs and a baseline elastic, one-material design was calculated in finite element models using experimentally measured time-dependent material behavior. The elastic strain energy fields in O-ring sections were calculated under applied pressure and applied displacement loadings. The highest stress, strain, and strain energy regions in O-rings are near seal-gland surface contacts with significantly lower stress in regions of applied pressure. If the size of the modified region of the seal is comparable to the size of the highest energy density region, the shape of the inset is not a major factor in determining overall seal section behavior. The rate of loss of seal-housing contact pressure over time was less for the modified design O-ring sections compared with the baseline seal design. The time-dependent performance of elastomeric seals can be improved by designing seals based on variation of mechanical behavior of the seal over the seal section. Improvement in retention of sealing contact pressure is expected for seal designs with less stiff material in regions of high strain energy density.

The performance of elastomeric seals degrades over time in use due to the development of permanent material deformation. The existence of localized high stress regions below seal-housing contact areas led to consideration of improving O-ring design by modifying material behavior to decrease strain energy, and so permanent deformation, in these regions. Photoelastic stress analysis was used to experimentally characterize the stress and strain fields in O-ring sections and to validate finite element models used in design studies. O-ring section designs that included small inset regions of different material behavior than the larger surrounding section were investigated with the intent of manipulating and reducing the strain energy content. Finite element models of O-rings were used to characterize the strain energy content and distribution for inset materials with various stress-strain behaviors. Measurements of permanent deformation and load-deflection behavior of specimens held under applied compression over time showed dependence of the amount of permanent deformation on strain energy. Design rules were extracted from results of studies in which inset region material stiffness, stress-strain behavior, size, and location in the larger section were varied. O-ring sections with regions of less stiff material result in lower strain energy and more uniform strain energy density distribution than the typical one-material seal. Inclusion of less stiff softening stress-strain behavior material insets in the larger O-ring section produced reduction in strain energy level and favorable redistribution of the high strain energy density regions compared with the conventional one-material one-material-behavior design. Similar concepts will apply to the design of other elastomeric structures in which permanent material deformation affects structure performance.

A review of research results demonstrating that magnetic fields applied to machining processes and mechanically manufactured parts can have beneficial effects is presented, an explanatory mechanistic model is described, and the model is used to interpret some results. The magnetic field-material interaction model shows an exponential dependence of material behavior and mechanical property changes on applied field strength and material magnetostrictive characteristics. Implications for use of magnetic fields to manipulate tribological processes, control machining processes, and alter material properties are that low field strengths can be useful for treating materials that have large magnetostrictive stain and high magnetic saturation level.

A numerical simulation system was developed to predict local part-mold forces and local and total ejection forces in injection molding. Local reaction forces between the part and mold surfaces are calculated first using numerical molding process and structural simulations. Using experimentally obtained coefficients of friction the friction force and ejection force are calculated. Ring moldings were used to measure the coefficient of friction. Box moldings were used to validate predictions of local and total ejection forces and to demonstrate the use of the system in mold design. Calculated ejection force was maximum at the beginning of ejection and differed by 10%–16% from experimental values, with the difference being much less over the main part of the ejection process. The maximum number of ejector pins for failed ejection was predicted. The difference between the predicted and observed number of ejector pins was at most four pins for a twenty ejector pin system.