A novel flexure-based biaxial compression/shear apparatus has been designed, built, and utilized to conduct tribological studies of interfaces relevant to MEMS. Aspects of our new apparatus are detailed and its capabilities are demonstrated by an investigation of two interfaces for MEMS applications. Tribological tests may be performed with normal and tangential forces in the µN to N range and relative sliding displacements in the nm to mm range. In this testing range, the new experimental apparatus represents an improvement over existing techniques for tribological studies at the small scale. / Singapore-MIT Alliance (SMA)

"The presence of moisture can lead to serious damage in Hot Mix Asphalt mixes and failures of HMA pavements. This is of an even greater concern for Warm Mix Asphalt (WMA) due to the use of much lower production temperatures which may not be high enough to completely dry the aggregates. In this Maine DOT study, the use of fracture energy parameters was evaluated to determine the influence of incomplete drying of mixes on their mechanical properties. Fracture energy based parameters (ER: energy ratio; RER: ratio of energy ratio) were determined from the following indirect tensile testing on mixes with fully and partially dried aggregates, some of which were subjected to moisture conditioning: Resilient modulus (Mr), creep compliance, and indirect tensile strength (ITS) strength at 5oC. The results indicate that: i. resilient modulus, creep compliance, and indirect tensile strength were all affected by the presence of moisture in mixes; ii. the trend and degree of influence by moisture for the different mechanical parameters are different; iii. The moisture conditioning process has caused larger decreases in resilient modulus and ITS values than incomplete drying of aggregates; however, the same moisture conditioning process has caused much larger decreases in modulus and ITS in asphalt mixes prepared with incompletely dried aggregates than the counterparts prepared with fully dried aggregates; and iv. fracture energy-based parameters (ER and RER) appear to be more distinctive moisture effect/damage indicators than the other parameters. "

acase@tulane.edu / The application of continuum mechanics principles to biological tissues is paramount to understanding (patho)physiological changes in tissue structure and function. Experimental and mathematical approaches can be utilized to quantify tissue mechanical behavior. In particular, planar biaxial mechanical testing of soft tissues (i.e. applying loads or deformation along two axes in the same plane) has proven to mimic physiologically relevant conditions for most soft tissues. Constitutive relations can then be formulated based on biaxial data to describe and predict soft tissue mechanical behavior. These mathematical tools could aid in delineating underlying mechanisms of and evaluating treatments for various clinically relevant issues. Therefore, the overall objective of this thesis is to build a custom planar biaxial mechanical testing device to characterize the mechanical properties of soft biological tissues to identify appropriate constitutive relations. A custom planar biaxial mechanical testing device was successfully built and validated. A LabVIEW program was written to interface with the stepper motors and load cells of the device to control their movements. A mechanical testing protocol was developed and incorporated to enable the characterization of a variety of soft tissue structure-function relationships. Foundations were laid for studies using the planar biaxial device for research in a tissue-engineered nipple-areolar complex (NAC), pelvic floor disorders, and age-specific tendinopathy. The planar biaxial device has the potential to impact many areas of clinical research. / 1 / Taylor McCrady

The current thesis takes a step forward into understanding the intergranular stress corrosion cracking (IGSCC) by applying a relatively new micro-mechanical technique to look at the crack growth rate of individual grain boundaries in 304 stainless steel (SS) and to measure fracture toughness for different grain boundaries in Ni Alloy 600. In addition, a model is tested and proposed that could predict crack initiation in 304 SS. Pentagonal cross-section cantilevers 5 μm wide by 25 μm long were milled at individual grain boundaries in both 304 SS and Ni Alloy 600. The cantilevers milled in 304 SS were tested in-situ in a customised stage, using the nanoindenter. Crack growth rate was measured for two different cantilevers to be approximately 40 μm/s (K = 1.1 MPa(m)^(1/2)) and 120 μm/s (K = 1.7 MPa(m)^(1/2)). Cantilevers were milled in Ni Alloy 600 for three different samples: samples that were exposed to simulated pressurized water reactors (PWR) environment for 4500 h, for 1500 h and un-oxidised samples. The fracture toughness calculated for the fractured cantilevers in samples that were exposed for 4500 h was measured to be between 0.73 and 1.82 MPa(m)^(1/2). No intergranular fracture occurred in the samples that were exposed for 1500 h and in the un-oxidised samples. The grain boundary misorientation was measured for the tested cantilevers but no direct correlation was observed between the misorientation angle and the fracture toughness. A Schmid-modified grain boundary stress (SMGBS) model previously used to study the intergranular behaviour of irradiated 316L steel in supercritical water was applied to predict crack initiation in 304 stainless steel. The model was successfully applied and accurately predicted crack initiation. To extend the model, sensitisation was also included. In addition, different areas of the specimen, including the initiation site were analysed using High resolution electron backscatter diffraction (HR-EBSD) technique to measure the geometrically necessary dislocations (GNDs) density. It was observed that the boundary average GNDs is lower for the intact boundaries and higher for the cracked grain boundaries.

International Telemetering Conference Proceedings / October 22-25, 2001 / Riviera Hotel and Convention Center, Las Vegas, Nevada / The objective of any data acquisition system is to make accurate measurements of physical phenomena. Many of the phenomena to be characterized contain data that is in the audio-frequency range between 0 and 50,000 Hertz. Examples include structural vibration, wind-tunnel measurements, turbine engines and acoustics in air and water. These tests often require a large number of channels and may be very expensive. In some cases, there may be only one opportunity to acquire the data. This paper describes a testing/measurement philosophy and the use of advances in available hardware/software systems to implement the requirements. Primary emphasis is on robustness (assurance that critical data is properly recorded), measurement/characterization of unexpected results (generated by accidents or unexpected behavior), and test safety (for both the test article and the facility). Finally, a data acquisition system that encompasses the features discussed is described.

We have developed a new digital image correlation (DIC) algorithm for non-contact, two-dimensional, whole-field displacement and strain measurement. Relative to existing algorithms, our algorithm substantially reduces the calculation expense by using neighborhood information while processing the data to determine the displacement field in a sub-region of interest. The new algorithm also uses higher-order interpolations of the displacement field, allowing for better accuracy in estimating strain distributions when the deformation field is non-homogeneous. Numerically-generated digital images are used to show that the new algorithm accurately reproduces the imposed displacement fields. The algorithm is also tested on actual images from deformed specimens from a variety of experiments, and shown to perform satisfactorily. / Singapore-MIT Alliance (SMA)

Bone quality and the conditions that affect it make up a large field of study. One specific area of interest is the loss in bone strength during exposure to microgravity. The femoral neck (FN) region in particular is an important region of study since a FN failure has such a detrimental effect on mobility. The objective of this study was to characterize the effects of microgravity and recovery on the FN in the adult male hindlimb unloaded (HU) rat model. This was done through peripheral quantitative computed tomography (pQCT), mechanical testing in two different loading conditions, and estimated strength indices. Adult male Sprague-Dawley rats (6-mo) were grouped into baseline (BL), ambulatory cage control (CC) and hindlimb unloaded (HU); HU and CC animals were further divided into sub-groups (n=15 each): HU euthanized after 28 days of suspension, and HU euthanized after 28, 56, and 84 days of recovery with CC groups being euthanized at each of these time points. The excised right and left femoral necks were both scanned ex vivo using pQCT. Quasi-static mechanical testing was performed with the right femurs positioned vertically and the left femurs positioned laterally at a -10 degree angle. A series of strength indices was used to attempt to predict the mechanical testing results, including a compression index, a bending index and an alternative combination of the two. HU exposure led to 6.3 percent lower bone mineral content (BMC), compared to BL and 7.8 percent lower total volumetric bone mineral density (vBMD) at the FN. The vertical or axial loading showed a 17.1 percent drop in mechanical strength due to HU exposure. The lateral loading test revealed a 5.4 percent drop in strength, showing that HU had a greater effect on the axial loading configuration. Also, after just 28 days of recovery, the axial loading test revealed a complete recovery of strength. None of the strength indexes completely predicted the mechanical behavior of the FN. In the right femur, the combined index had the highest correlation with an R value of 0.94. The bending strength index had the highest correlation in the left lateral testing with an R value of 0.98. However, in all the cases, the strength indexes failed to predict the mechanical behavior at all the time points. In general, the strength indexes provide valuable input, but fail to replace mechanical testing.

No description available.

Mechanical unloading with microgravity exposure during spaceflight induces bone loss in weight bearing bones. Combined with loss of bone due to aging, this disuse bone loss puts astronauts at increased risk of fracture upon returning to 1G conditions. It is important to study countermeasures, such as exercise, to mitigate or prevent this bone loss. This study utilized the hindlimb unloaded (HU) rat model to characterize the effects of resistance exercise on recovery dynamics in-between two bouts of HU. In the larger project adult male Sprague-Dawley rats, six months of age, were divided into the following groups: baseline (sacrificed at 6 months of age); aging cage controls (did not undergo any treatment, sacrificed at 7, 8, 9, 10, and 12 months of age); 1HU7 (one month of HU at 6 months of age followed by three months of ambulatory recovery); 2HU10 (one month of HU at 6 months of age, ambulatory recovery for two months, one month HU at 9 months of age, and final two month ambulatory recovery); 1HU10 (one month HU at 9 months of age and two month ambulatory recovery); and 2HU+Ex (One month HU at 6 months of age, two month resistance exercise recovery, and a 2nd bout of HU at 9 months of age). This thesis focused on the 2HU+Ex data, while utilizing data from other groups for comparisons. The data in this thesis includes ex vivo densitometric and biomechanical properties at the femoral neck (FN), femur midshaft diaphysis (FD), and distal femur metaphysis (DFM). All compartments of BMC increased following exercise recovery above AC at the FN and DFM. Ambulatory recovery values revealed incomplete recovery in total and cortical BMC at the DFM and full recovery in other parameters. DFM and FD vBMD data indicated there were further benefits of exercise during recovery. Geometric data revealed periosteal apposition at the DFM and FN following exercise recovery. FD mechanical properties did not produce benefits of exercise. However, FN maximum force increased above all other groups after exercise recovery. Elastic modulus of the DFM showed benefits of exercise recovery in the response to the 2nd HU.

Developing a multi-scale math-based model for powder metallurgy (PM) component design and performance prediction requires experimental calibration and validation. Monotonic tension, compression and torsion tests were performed at various porosity and temperatures to obtain the set of plasticity and damage constants required for model calibration. Uniaxial fatigue experiments were performed to determine the constants required for capturing the low cycle and high cycle fatigue characteristics of a PM steel. Tension tests on two different Bridgman notched specimens were undertaken to study the damage-triaxiality dependence for model validation. Validation of the model is further being performed by monotonic component testing using PM bearing caps. Fracture surface analysis was performed using Scanning Electron Microscopy (SEM) to quantify the void nucleation and void sizes of the different specimens. The developed model will be used for optimizing component performance and design for PM parts.