Peter A. Gustafson

Measurement of the state of stress in silicon with micro-Raman spectroscopy

Micro-Raman spectroscopy has been widely used to measure local stresses in silicon and other cubic materials. However, a single (scalar) line position measurement cannot determine the complete stress state unless it has a very simple form such as uniaxial. Previously published micro-Raman strategies designed to determine additional elements of the stress tensor take advantage of the polarization and intensity of the Raman-scattered light, but these strategies have not been validated experimentally. In this work, we test one such stategy [S. Narayanan, S. Kalidindi, and L. Schadler, J. Appl. Phys. 82, 2595 (1997)] for rectangular (110)- and (111)-orientated silicon wafers. The wafers are subjected to a bending stress using a custom-designed apparatus, and the state of (plane) stress is modeled with ABAQUS. The Raman shifts are calculated using previously published values for silicon phonon deformation potentials. The experimentally measured values for σxx, σyy, and τxy at the silicon surface are in good ag...

Efficient and Robust Traction Laws for the Modeling of Adhesively Bonded Joints

A discrete cohesive zone method finite element is used to evaluate traction law eciency and robustness in predicting decohesion in a finite element model. Three traction laws are reported and are compared from the perspective of their computational eciency and robustness. The smooth traction laws (based on the beta distribution and sine functions) are found to have greater computational eciency than the trapezoidal traction law. Eciency gains are due to the elimination of the stiness discontinuities associated with the generalized trapezoidal traction law. The sinusoidal traction law is found to be more robust and ecient than the other traction laws.

The effect of clavicle malunion on shoulder biomechanics; A computational study

BACKGROUND Clavicle malunion affects the biomechanics of the shoulder joint. The purpose of this study is to establish the abduction, flexion, and internal (medial) rotation biomechanics of the shoulder after clavicle malunion. METHODS A computational study was performed utilizing a three-dimensional, validated computational model of the upper extremity. Sequential shortening of the clavicle up to 20% was simulated. Muscle forces, moment arms, and moments were calculated for the surrounding musculature through a range of flexion, abduction, and internal rotation during the simulated shortening. FINDINGS Shortening of the clavicle decreases the shoulder elevation moments of the upper extremity muscles during abduction. Internal rotation moments are also decreased with shortening. Flexion moments were affected less through physiologic range of motion. The observed effects are due to a combination of changes in moment arms of the individual muscles as well as a decrease in the force generating capacity of the muscles. Additionally, shortening of the clavicle increases coronal angulation of the clavicle at the sternoclavicular joint. INTERPRETATION Shortening causes a decrease in the moment generating capacity as well as the total force generating capacity of the shoulder girdle muscles. The clinical significance of these computational results, which are consistent with recent clinical studies, is validation of the proposed functional deficit caused by clavicle malunion.

The subtalar joint: Biomechanics and functional representations in the literature

The subtalar joint is important for gait and function of the foot and ankle. With few external landmarks, the joint is difficult to conceptualize and study in vivo. There have been several functional representations put forth in the literature which can be combined to give a broader understanding of the overall function and mechanics of the subtalar joint. This understanding is clinically important when considering the impact that disease has on the subtalar joint as well as how treatment of the subtalar joint impacts on the surrounding structures.

T650/AFR-PE-4/FM680-1 Mode I Critical Energy Release Rate at High Temperatures: Experiments and Numerical Models

An experimental program to determine the mode I critical energy release rate (GIc) of the T650/AFR-PE-4/FM680-1 material system is reported. Two forms of GIc are determined over the range of 20 to 350 C, the area method critical energy release rate G a and the inverse method critical energy release rate (G i). The value of GIc was found to increase with increasing temperature. The inverse method is determined to be a very effective method of determining GIc over the entire range of temperatures. Inverse modeling was completed using the finite element method, coupled with a novel Discrete Cohesive Zone Element, to determine G i over the range of crack advance in a given specimen. The element is described in detail, as well as the metrics used by the inverse algorithm. The FE models, subsequent to inverse modeling, accurately reproduce the experimental load-displacement curves. They therefore provide a capable analysis method, as well as a material system constitutive relation that contains a range of appropriate properties for use in the design and analysis of T650/AFR-PE-4/FM680-1 joints. Nomenclature GI Energy release rate, J/m 2 GIc Critical energy release rate, J/m 2 G a Area method critical energy release rate, J/m 2 G i Inverse method critical energy release rate, J/m 2 c Cohesive strength of the adhesive system, N/m 2

Measurement of Biaxial Stress States in Silicon Using Micro-Raman Spectroscopy

Micro-Raman spectroscopy is used to determine the multiaxial stress state in silicon wafers using a strategy proposed by Narayanan, et al. (J. Appl. Phys. 82, 2595-2602 (1997)) Previously, this strategy was validated when silicon was subjected to uniaxial stress in the laboratory frame (Harris, et al. J. Appl. Phys. 96, 7195-7201 (2004)). In the present work, silicon wafers have been analyzed that were subjected to biaxial stress states in the laboratory frame. The predicted curves for the initially degenerate F 2g peaks were found to fall within the variability of the measured curves. Stress ratios were found to be predictable. Stress magnitudes were also found to be predictable, but are subject to uncertainty greater than 25%. To perform these tests, an apparatus has been developed which can provide controlled ratios of biaxial stress in a simple and compact test geometry. This fixture was used under a microscope, enabling in situ measurement of biaxial stress states.

Subtalar Arthrodesis Alignment The Effect on Ankle Biomechanics

Background: The position, axis, and control of each lower extremity joint intimately affect adjacent joint function as well as whole-limb performance. A review of the literature finds little describing the biomechanics of subtalar arthrodesis and the effect on ankle biomechanics. The purpose of the current study was to establish this effect on sagittal plane ankle biomechanics. Methods: A study was performed using a 3-dimensional, validated, computational model of the lower extremity. A subtalar arthrodesis was simulated from 20 degrees of varus to 20 degrees of valgus. At each arthrodesis position, the ankle dorsiflexor and plantarflexor muscles’ fiber force, moment arm, and moments were calculated throughout a physiologic range of motion. Results: Throughout ankle range of motion, plantarflexion and dorsiflexion strength varied with subtalar arthrodesis position. When the ankle joint was in neutral sagittal alignment, plantarflexion strength was maximized in 10 degrees of subtalar valgus, and strength varied by a maximum of 2.6% from the peak 221 Nm. In a similar manner, with the ankle joint in neutral position, dorsiflexion strength was maximized with a subtalar joint arthrodesis in 5 degrees of valgus, and strength varied by a maximum of 7.5% from the peak 46.8 Nm. The change in strength was due to affected muscle fiber force generating capacities and muscle moment arms. Conclusion: The significance of this study is that subtalar arthrodesis in a position of 5 to 10 degrees of subtalar valgus has a biomechanical advantage. Clinical Relevance: This supports previous clinical outcome studies and offers a biomechanical rationale for their generally favorable outcomes.

Pectoralis major transfer for subscapularis deficiency: a computational study

Background Clinical studies purport an increase in internal rotation strength after transfer in subscapularis deficient patients. The present study aimed to establish the internal rotation biomechanics of a pectoralis major muscle transfer for the treatment of subscapularis muscle insufficiency. Methods A computational study was performed utilizing a three-dimensional, validated, computational model of the upper extremity. The pectoralis major was modeled as three distinct components. Moments were calculated from combined force (active and passive) as well as muscle moment arms for each of the internal rotators throughout a physiologic range of motion. The results were compared to both normal and subscapularis deficient simulations. Results A deficient subscapularis decreases the internal rotation moment by a maximum of 55% (16.9Nm). Transfer of the clavicular component in isolation and transfer of both the clavicular and sternal components decrease the sum internal rotation moment about the shoulder in a subscapularis deficient patient by a maximum of 5.3% (1.6Nm) and 10.6% (3.2Nm) respectively. Conclusion The clinical significance of this study is that the strength improvement demonstrated in clinical studies is likely a dynamic stabilizing effect of the transfer. This affirms the concept that the glenohumeral joint must have stability before the surrounding musculature can act effectively.

Three-Dimensional Printing and Surgical Simulation for Preoperative Planning of Deformity Correction in Foot and Ankle Surgery

A paucity of published data is available describing the methods for the integration of 3-dimensional (3D) printing technology and surgical simulation into orthopedic surgery. The cost of this technology has decreased and the ease of use has increased, making routine use of 3D printed models and surgical simulation for difficult orthopedic problems a realistic option. We report the use of 3D printed models and surgical simulation for preoperative planning and patient education in the case of deformity correction in foot and ankle surgery using open source, free software.

Experiments and Cohesive Zone Model Parameters for T650/AFR-PE-4/FM680-1 at High Temperatures

This paper reports an experimental program to establish a cohesive zone model for the T650/AFR-PE-4 (laminate) and FM680-1 (adhesive) system. The cohesive zone model is based on a four parameter characterization: in each mode, a range of values for the critical energy release rate and cohesive strength are computed from a set of experimental results. Values of each parameter are determined over the temperature range of 20–350°C. Owing to experimental limitations, two methods for determining the Mode I critical energy release rate are reported from the double cantilever beam test: the area method and the inverse method. The Mode I strength is determined from a button peel stress test. The values of the Mode II parameters are determined by using a mapping procedure that accounts for multiparameter dependence in models of the end notch flexure and single lap joint tests.