A cysteine-containing elastin-like polypeptide (ELP2cys) was successfully synthesized and purified, and was shown to behave in a similar fashion to other well-characterized ELPs. Incorporating the ELP2cys as a crosslinking agent into a solution of sulphated hyaluronan (CMHA-S) not only decreased the gelation time of the solution but also increased the crosslinking density of the resultant hydrogel, in turn increasing both the resiliency and stiffness of the construct. Preliminary in vitro work involved culture of human disc cells, followed by their encapsulation within the hydrogel. Unfortunately the results were inconclusive, although it appeared as though the addition of ELP2cys to the matrix did not negatively affect the viability of the cells, as compared to hydrogels with CMHA-S only. This study showed that ELP2cys is a valuable addition to the family of recombinant elastin-like polypeptides, and shows promise as a crosslinking agent in the formation of hyaluronan hydrogels.

The purpose of this randomized controlled trial was to investigate temporal skeletal responses to short-term high intensity physical activity. Twenty-eight normal active females [age: 20.7 +/- 2.1 yr (mean +/- SD)] were randomized into exercise (EX, n = 15) or control (CN, n = 13) groups. The exercise group trained 6 days/wk for 6 wk, which consisted of maximal isokinetic knee flexion/extension 3 days/wk, combined with 3 days/wk running. The purpose was to expose the tibiae to a period of abruptly increased loading forces. Tibial bending stiffness (EIMRTA), and serum concentrations of biochemical markers of bone formation [osteocalcin (OC)], and bone resorption [n-telopeptide of type I collagen (NTx)] were measured at baseline, 2 wks, 4 wks, and 6 wks. Isokinetic concentric knee extension/flexion peak torque, as well as total body and site-specific bone mineral density (BMD) were measured at baseline and 6 wk. After training, the exercise group significantly increased (p < 0.05) isokinetic concentric peak torque for the dominant (13.6%) and non-dominant (5.7%) quadriceps, as well as dominant (7.7%) and non-dominant (9.5%) hamstrings, compared to the controls. No differences for total body or site-specific BMD were noted. A two-way multivariate repeated measures ANOVA revealed no timeâ ¢group interactions for composite tibial bending stiffness [(EIMRTA); p = 0.57] or the biochemical markers of bone turnover [(OC and NTx); p = 0.15] across the four sampling periods. While there were no main effects for group, a trend for time (p = 0.051) for composite EIMRTA was observed. The exercise group demonstrated a 20% increase in EIMRTA from baseline (74.8 +/- 22.3 Nm2) to 6 wk (89.8 +/- 24 Nm2), compared to controls who demonstrated a 4% increase (Baseline 86.5 +/- 23.8 Nm2; 6 wk 90 +/- 23.7 Nm2). Significant group differences (p = 0.05) were noted for OC, but not NTx. Differences (p < 0.05) for OC were observed at baseline [13.2 +/- 2.4 ng/ml (CN), 15.6 +/- 2.7 ng/ml (EX)], and follow-up ANCOVA revealed no differences for subsequent sampling periods. Main effects for time were found for OC and NTx (p < 0.001). Main effects for time in OC were attributable to changes in the exercise group (p < 0.01) and NTx (p < 0.01), but not the control group. / Ph. D.

No description available.

<p>  </p> <p>The fundamental theory of the glass transition and the glassy state does not exist. Instead, over the years of research there have accumulated a vast number of experimental observations and phenomenological models developed in order to rationalize these observations. A case in point is the stress-strain behavior of a polymer glass during large constant strain rate deformation; for every feature of the stress-strain curve, such as yield, post-yield softening and post-yield hardening, a new mechanism is postulated. But do these mechanisms have a physical basis or are they merely curve-fits? The experiments included in this dissertation are purposefully designed to challenge the prevailing model assumptions. Four specific areas have been chosen: (1) the linear viscoelastic behavior above the glass transition temperature, Tg, (2) the effect of physical aging on the relaxation response of the glassy polymers well below Tg, (3) the behavior of the glassy polymers during a multi-step non-linear deformation, and (4) the effect of the large deformation of the glassy polymer on the enthalpy relaxation as measured by the DSC.</p> <p>(1) Linear viscoelastic isotherms were analyzed by performing dynamic mechanical analysis on a thermoset epoxy, EPON1009F-MDA (Tg: 102.5°C). Storage and loss moduli for the material were investigated for isotherms ranging from 90°C (Tg-12°C) to 180°C (Tg+78°C) for frequencies ranging from 10-2 Hz to 101.7 Hz. This linear viscoelastic dataset was augmented by performing stress relaxation experiments on the same material for temperatures ranging from 90°C (Tg-12°C) to 112.5°C (Tg+10.5°C). The transient results from the stress relaxation (SR) were converted to frequency domain. The resulting augmented dataset spanned 6 order of magnitude in frequency. The wide frequency window showed that the material is thermo-rheologically complex, precluding the creation of a master curve via horizontal shifting of the isotherms. This renders impossible the use of time-temperature superposition, and thus highlights the need for reevaluating its prominent use in glass studies.</p> <p>(2) Existing beliefs on the diminishing effects of physical aging at low temperatures were studied. Linear viscoelastic isotherms of EPON825-MDA (Tg: 182°C) that have been annealed for 2 to 600 hours at temperature ranging from -100°C (Tg-282°C) to 185°C (Tg+3°C) were investigated. At temperatures near Tg, no tangible effects of annealing were identified. At the lowest temperature of -100°C, no differences could be identified between 2 hour and 6 hour annealed specimens; however, annealing effects could possibly be observed at longer aging times based on the results of other isotherms. For all other isotherms between -50°C to 170°C, clear differences could be observed between 2 hour and 6 hour annealed specimens, where the storage moduli increased while the loss moduli decreased. In addition, the effects of annealing were unidentifiable when the material went through a temperature up-jump, but persisted when the material went through a temperature down-jump. The results of this study show that contrary to popular belief, annealing effects are not frozen and persist deep in the glass state and is observable even within experimental limits. Additionally, deep glass aging is fundamentally different from physical aging in that no master curve can be achieved via horizontal shifting along the frequency axis unlike physical aging, due to the change in shape and magnitude of the isotherms.</p> <p>(3) Many constitutive models that target prediction of mechanical behaviors are drawn from the results of single step deformation experiments. Multi-step non-linear deformation experiments were performed on a copolymer of PBMA and PMMA, to challenge the existing models, where the last step is a constant-strain-rate loading step that shows the effects of previous deformation histories on the stress overshoot. Various multi-step deformation histories were investigated, one being a sequence of constrain-strain-rate-loading/unload/creep/constant-strain-rate-loading. Contrary to previous literature reports, the results showed a dependence on the creep stress level of the last overshoot, which initially increased in peak magnitude with creep stress, reached a maximum, and decreased for further increase in creep stress. These results are not qualitatively predicted by any of the existing constitutive models, illustrating the need to rethink how the mechanisms behind stress-strain behaviors are approached. A new toy model is also discussed that can qualitatively predict these results as well as the results of other multi-step deformation histories that are discussed.</p> <p>(4) A new methodology for analysis of the differential scanning calorimetry (DSC) traces was proposed. The DSC trace is known to be sensitive to the thermo-mechanical history a material is subjected to prior to the DSC test; but, the true effects are convoluted with the experimental scatter. The conventional method consists in shifting of the data obtained for different thermo-mechanical histories to the same glassy asymptote, but this has no physical basis. In fact, we argue that this misses the actual effects. We propose that the shifting must be to match the liquid, i.e., equilibrium, asymptote as it is in the equilibrium state which is independent of the history. The new methodology was used to confirm literature reports on the effects of aging. DSC scans of deformed specimens were also studied, where the results showed a systematic effect in the heat capacity traces of deformed specimens, where an endothermic peak followed by an exothermic peak is observed. The peaks are not present in the case of an undeformed material, where a larger degree of strain led to a larger endothermic peak. The results indicate the possibility of a systematic effect where the magnitudes of the additional endothermic and exothermic peaks are controlled by the amount of mechanical work performed during the deformation.</p>

This work analyzes the design and implementation of waveguides used to measure stress waves in solid mechanics via explicit finite element analysis and experimentation. Many areas of physics use waveguides where control of timing, location, or frequency of waves is imperative to functionality of a system. Split Hopkinson pressure bars (Kolsky bars) traditionally utilize straight waveguides during testing. Prior research produced the first bent wave guide for use in such an application, the coaxially embedded serpentine bar (CESB). Explicit finite element analysis (FEA) provides a modeling approach to understand the effects of pass and joint geometry and boundary conditions on the functionality of solid-mechanic waveguides like the CESB. FEA and experimentation also contrasts the functionality of welded joints and threaded joints. Novel waveguide designs that do not feature tubes are also detailed for use in dynamic mechanical testing and dynamic hardness indentation experiments. These designs feature acoustic lengths up to two orders of magnitude greater than their physical lengths.

Mechanical Response Tissue Analysis (MRTA) is an emerging technology for assessing maximal bending stiffness (EI) of human long bones in vivo. The MRTA variable, EI, is the product of Young's modulus of elasticity (E) and cross-sectional moment of inertia (I). EI quantifies material and architectural/geometric properties of bone. Published human research using MRTA to measure EI has been limited to the ulna; however, the tibia requires further investigation due to its central involvement in many human activities and exercise-related clinical problems, e.g. stress fracture of the lower leg. To evaluate the inter- and intra-reliability of tibial EI, 22 healthy women (X + SD: 20.8 + 1.8 yr) were assessed twice daily for three non-consecutive days. Each daily session consisted of five repeated trials. The ulnar EI protocol of McCabe et al. [J Bone and Mineral Res. 1991;6(1):53-59] was adapted to assess tibial EI via MRTA. A significant difference was not found in scores for five repeated trials taken consecutively on the same day. Mean scores for EI were higher on day 1 (59.1 &#177; 35.5 N&#183;m², p < 0.05), compared to day 2 (46.9 &#177; 22.3) and day 3 (49.9 &#177; 18.3). Individual trial mean scores for EI on each day (mean of 5 trials) were highly correlated, R² = 0.84, 0.62, and 0.79 (set 1 vs. 2, for day 1,2,3, respectively) and the average percent change between sets 1 and 2 on each day was 5.3. The inter-test (between day) reproducibility was found to be low and unacceptable, 11.7, 18.3, and 1.3%, for day 1 vs. 2, 1 vs. 3, and 2 vs. 3. Poor inter-day reliability may be a result of the inability, at the time of this study, to apply the best computational EI model. It is concluded that tibial bone stiffness measurements with the MRTA are in the range of acceptability for same day inter- and intra-trial reliability when the 7-parameter analytic model of vibratory properties developed by McCabe et al. is used. / Master of Science

This study relates the sensitization process microstructural changes of 5083-H116 to its resulting corrosion resistance and mechanical performance. Alcoa 5083-H116 was sensitized in an environmental chamber at 100°C for up to ~1500 hours and 150°C up to ~2000 hours, revealing different degrees of sensitization based on exposure times. Microstructural characterization was conducted on etched sensitized samples. Additionally, samples were subjected to accelerated corrosion scenarios for subsequent microstructural examination and subsequent mechanical (tension and tensile creep) testing. To connect the laboratory studies to the field exposure, Novelis 5083-H116 was sensitized at 100°C; dog bone samples were created and exposed for two years in a beach environment to investigate possible sensitization and corrosion effects. It was found that the sensitization at 100°C and 150°C of Alcoa 5083-H116 led to recrystallization from the asreceived (AR) state of the material (3 mg/cm²). The degree of sensitization of 61 mg/cm² recrystallized the grain size the most from the AR state. The higher sensitization temperature of 150°C caused higher thickness loss and mass-loss rates (MR) for the intergranular corrosion (IGC) susceptible sensitization levels. Accelerated corrosion on different surface orientations led to different corrosion mechanisms (parallel IGC vs. perpendicular IGC). While 5083-H116 material corroded on the rolled surface led to a uniform exfoliation damage on 150°C sensitization exposure, the 100°C rolled surface only exhibited pitting corrosion damage. The through plate thickness corrosion damage, however, exhibited a corrosion susceptible-resistant-susceptible (CSRS) pattern. Mechanical properties were assessed for the various conditions in terms of room temperature tension testing and elevated temperature creep tests. Sensitization affected yield strength but did not play a role in ultimate tensile strength. The presence of corrosion damage lowered yield strength and ultimate tensile strength of the IGC susceptible sensitized 5083-H116, with the through thickness corrosion damage reducing the properties more than corrosion of the rolled surface. Material sensitized at 150°C and then corroded had a greater reduction in room temperature mechanical properties. Creep testing was performed at elevated temperatures, and it was found the solely sensitized 5083-H116 at 100°C or 150°C behaved the same as as-received 5083-H116. When corrosion damage was introduced, creep rupture times and secondary creep rates were changed. Once the corroded section area was accounted for, no significant difference in Larson-Miller parameters was observed. / Ph. D. / Aluminum is frequently replacing steel in the hulls of U.S. and Australians naval ships. It is preferred because of its lower density than steel and higher corrosion resistance which reduces the need to paint topside surfaces. However, when aluminum alloys that are used in ship construction are exposed to elevated temperatures, the corrosion resistance ca be considerably decreased. Furthermore, fire resistance is always a concern on naval ships. Accordingly, we are interested in predicting how aluminum ships that may have previously corroded respond to fires. In this study, a laboratory technique was used to speed up the corrosion process of these ship hull aluminum alloys. Some samples were thermally exposed in the laboratory for microscopic analysis, corrosion testing, and subsequent mechanical testing. To connect the laboratory studies to the field exposure, thermally exposed samples were placed on a beach for two years to investigate further environmental damages. It was found that the laboratory thermal exposure weakened the aluminum alloy. The thermally exposed alloys were weakened to the corrosion process. Different surfaces of the thermally exposed plates had different corrosion damage mechanisms. Mechanical properties were assessed for the various conditions in terms of room temperature tension testing and elevated temperature creep tests. Thermal exposure affected yield strength (the ability of the material to stretch) but did not play a role in ultimate tensile strength (maximum strength prior to breaking). The presence of corrosion damage lowered yield strength and ultimate tensile strength of the corrosion susceptible thermally exposed alloy. Creep testing (constant applied stress testing) was performed at elevated temperatures (representative of fire damage scenarios), and it was found that the solely thermally exposed alloy behaved the same as as-received alloy in terms of failure mechanisms. When corrosion damage was introduced, creep rupture times (time until material fails by breaking into two pieces) was reduced. Once the corrosion damage was accounted for, mechanical properties could be more accurately represented, and failure times (conditions in the alloy needs to be replaced on ships) were predicted for the alloy.

Bone mineral content (BMC) and bone mineral density (BMD), measured by dual x-ray absorptiometry are used clinically to diagnose osteoporosis and estimate risk for fragility fractures. Bone mineral explains up to 70% of bone strength; however, it does not take into account bone geometry. Mechanical Response Tissue Analysis is a method of non-invasively measuring the bending stiffness (EI) of bone which is determined by the product of Young's modulus of elasticity (E) and the areal cross sectional moment of inertia (I). The aim of the current study was to determine if high intensity strength training will increase ulnar bending stiffness in young women. Forty-nine women aged 19.9 ± 1.7 yrs, trained their nondominant arm either concentrically or eccentrically in the Isokinetic modality on the Biodex® system III 3d/wk for 32 wks. The dominant arm served as the control limb (untrained). Analysis of all subjects regardless of training mode demonstrated a significant increase in ulnar EI (22% ↑, P=0.01) with no significant difference in the untrained arm. When EI results were assessed by training mode, subjects who trained eccentrically showed a significant increase for ulnar EI in the trained limb (40% ↑, P=0.01) with no significant effect on the untrained limb while concentric training demonstrated no significant gain in either the trained or untrained arm. There was no effect of time x mode of training interaction for either the trained or untrained limb. Bone mineral density and bone mineral content of the ulna increased significantly in the trained arm in both concentric and eccentric training modes (P<0.05). These findings suggest support for the hypothesis that a critical threshold of mechanical bending loads may be necessary to effect an adaptation in bone strength and thus, eccentric training may be a novel approach to increase ulnar EI in young women. / Master of Science

<p>  </p> <p>Molecular crystals are used in a wide variety of applications, from pharmaceuticals and sweeteners to energetic materials. Understanding their chemical and mechanical properties provides insight into their performance and use. These properties are especially critical for energetic material systems, which may be sensitive to impact and require specific handling and storage practices. The mechanical properties of energetic molecular crystals are typically determined using nanoindentation by measuring elastic modulus, hardness, yield point, and fracture behavior. Reports of the properties and mechanical behavior of as-grown molecular crystals are limited due to the relative difficulty of performing good quality measurements. This work’s contributions include the first known measurements of elastic and plastic properties for crystals of DAAF, CL-20, NTO, ETN, and R-salt.</p> <p>When studying molecular crystalline systems, some important assumptions and behaviors typical to metallic and ionic systems begin to break down. The energetic material diaminoazoxyfurazan (DAAF) exhibits highly irregular mechanical behavior, which is likely explained by a complex combination of chemical and material attributes. This work investigates and compares the irregular mechanical response in DAAF—including high variance in mechanical properties, broad range of load-depth behavior, and non-conforming indentation impression geometries—to other energetic molecular crystals. The yield points (i.e., onset of plasticity) for several energetic materials, whose elastic modulus values range from 9.6 to 25.5 GPa, are also compared to identify the parameters that govern the onset of plasticity. This includes an investigation into yield point dependence on (or independence from) elastic modulus, hardness, near-neighbor spacing, and activation volume. When these materials reach the onset of plasticity, the maximum shear stress in each material ranges from 2-7% of their elastic modulus value. Analysis of the yield behavior in these materials suggests that there is not a strong correlation between yield stress and hardness, thus establishing that the mechanisms governing dislocation nucleation are not controlled by hardness, and vice-versa. By recognizing and accounting for the added complexities associated with inherently non-spherical molecules in a crystal lattice, this work advances the comprehension of mechanical response in molecular crystal systems.</p>

No description available.