The objective of this study was to evaluate the effects of sex, loading rate, and age on the compressive and tensile material properties of human costal cartilage over a wide range of subject ages and sexes. Cylindrical compression samples and dog-bone shaped tension samples were tested to failure on a material testing system using target strain rates of 0.005 strain/s and 0.5 strain/s. Compression data were obtained from forty (n = 40) subjects (M = 26, F = 14) ranging in age from 11 – 69 years (Avg. = 39.1 ± 18.2 yrs.), and matched loading rate data were obtained for thirty-four (n = 34) samples. Tension data were obtained from forty-one (n = 41) subjects (M = 30, F = 11) ranging in age from 10 – 59 years (Avg. = 32.9 ± 14.9 yrs.), and matched loading rate data were obtained for seventeen (n = 17) samples. For both compression and tension, load and sample deflection data were collected and used to calculate stress and strain. For the compression data, the toe region was fit using a second-order polynomial, and the toe transition stress, toe transition strain, second-order polynomial coefficient A, and second-order polynomial coefficient B were calculated. In addition, the elastic modulus, ultimate stress, ultimate strain, and strain energy density (SED) were also calculated for each test. For the tension data, only the elastic modulus, ultimate stress, ultimate strain, and SED were calculated for each test. There were no effects of sex on the material properties for either method of loading or strain rate. Therefore, male and female data were combined for the age and loading rate analyses. For compression, toe transition stress, toe transition strain, A, elastic modulus, ultimate stress, and SED were all found to be significantly higher at 0.5 strain/s compared to 0.005 strain/s. For tension, no material properties were found to differ with respect to loading rate. Regarding the effects of age, toe transition stress, toe transition strain, A, B, ultimate stress, ultimate strain and SED were found to significantly decrease with advancing age for the 0.005 strain/s compression data. At 0.5 strain/s, toe transition stress, toe transition strain, elastic modulus, ultimate stress, ultimate strain, and SED all significantly decreased with advancing age. For tension, ultimate stress, ultimate strain, and SED were found to significantly decrease with advancing age at 0.005 strain/s and 0.5 strain/s. Comparing the two loading modes, the ultimate stress, elastic modulus, and SED were significantly higher in compression than in tension. For the compression samples, sample density and percent calcification were also obtained for each sample using physical measurements and micro-CT scans, respectively. However, since there were only a few samples with large calcifications, no meaningful trends were found. This is the first study of its kind to analyze the effects of sex, loading rate, and age on both the compressive and tensile material properties on human costal cartilage from such a wide range of subject ages. The results from this study can be used to develop more accurate finite element models of the human body, which will allow researchers to better evaluate human occupant response and injury risk in motor vehicle collisions for both young and old individuals. / Master of Science / Serious thorax injuries are often observed in motor vehicle collisions. Although a considerable amount of research has investigated the material and structural properties of rib cortical bone and whole rib sections, only a limited number of studies have focused on characterizing the material properties of costal cartilage, which comprises a substantial portion of the anterior region of the thorax. The studies that do exist include small subject pools and/or are limited to sub-failure indentation tests. Indentation tests are limited to low deflections and focal loading and are unable to obtain the failure material properties of costal cartilage. Therefore, the purpose of this study was to quantify the compressive and tensile material properties of human costal cartilage at two loading rates for a wide range of subject demographics. These properties were then evaluated with respect to sex, loading rate, and age. Cylindrical compression samples and dog-bone shaped tension samples were tested to failure on a material testing system at target strain rates of 0.005 strain/s and 0.5 strain/s. Compression data were obtained from forty (n = 40) subjects ranging in age from 11 – 69 years, and tension data were obtained from twenty-eight (n = 28) subjects ranging in age from 10 – 59 years. For both compression and tension, load and sample deflection data were collected and used to calculate stress and strain. For the compression data, the magnitude and shape of the initial loading region (i.e., the toe region), elastic modulus, ultimate stress, ultimate strain, and strain energy density (SED) were quantified for each test. For the tension data, the elastic modulus, ultimate stress, ultimate strain, and SED were calculated for each test. There were no significant effects of sex on the material properties for either method of loading or strain rate. Therefore, male and female data were combined for the age and loading rate analyses. For compression, the toe region transition point (i.e., stress and strain), toe region shape coefficient A, elastic modulus, ultimate stress, and SED were all found to be significantly higher at 0.5 strain/s compared to 0.005 strain/s. For tension, no material properties were found to differ with respect to loading rate. Regarding the effects of age, toe region transition point (i.e., stress and strain), toe region shape coefficients A and B, ultimate stress, ultimate strain, and SED were found to significantly decrease with advancing age for the 0.005 strain/s compression data. For the 0.5 strain/s compression data, toe transition stress, toe transition strain, elastic modulus, ultimate stress, ultimate strain, and SED all significantly decreased with age. For tension, ultimate stress, ultimate strain, and SED were found to significantly decrease with advancing age at 0.005 strain/s and 0.5 strain/s. The ultimate stress, elastic modulus, and SED were higher in compression than in tension. Overall, this is the first study to evaluate the effects of sex, loading rate and age on the compressive and tensile material properties of human costal cartilage from a wide range of ages. These data can be used to assess differences in the response and tolerance of the human rib cage for occupants of various age in motor vehicle collisions.

As the use of polymer matrix composites for structures increases, there is a growing need for monitoring these structures. Distributed strain sensing using optical fibers shows promise for monitoring composite structures due to optical fiber's small size, light weight, and ability to obtain continuously distributed strain data. This study investigates the feasibility of using embedded optical fibers using two case studies: embedding the fibers in the adhesive layer of double lap shear composite specimens, and within composite end-notched flexure specimens to locate a growing crack front. To establish a repeatable fabrication methodology, manufacturing techniques for embedding the optical fibers were investigated. The measured strain distribution from the optical fibers compares well with data obtained from finite element analyses for both the double lap shear and end-notch flexure specimens. Additionally, the embedded optical fibers do not seem to impact the failure loads or fracture behavior of the specimens.

An investigation of the microstructure-mechanical property relationships for gray cast iron and a vintage ASTM A7 steel are presented herein. Gray cast iron was shown to have a moderate sensitivity to strain rate and a large disparity in behavior between compression, tension, and torsion. ASTM A7 steel was shown to behave in a more complex manor with the strain rate sensitivity having a negative relationship in tension and positive relationship in compression and torsion, the tensile stress-state producing the highest stress response, and the material producing a higher stress response when exposed to elevated temperatures. The counterintuitive behavior observed in A7 steel was attributed to dynamic strain aging. The Mississippi State University Internal State Variable Plasticity-Damage model was updated to accurately capture negative strain rate sensitivity and DSA embrittlement by developing kinematic, thermodynamic, and kinetic constitutive relationships for dynamic strain aging. A parametric study was performed to elucidate the behavior of the new internal state variable for dynamic strain aging. Gray cast iron was successfully calibrated to a pre-DSA version of the plasticity-damage model and A7 steel was successfully calibrated to the updated plasticity-damage model.

Gels and hydrogels have attracted a great attention for potential applications in tissue engineering, drug delivery, actuators, and soft robots. There has been a significant progress to engineer hydrogels from both synthetic and natural precursors to be as tough as a solid and as stretchable as a rubbery material while maintaining high water/solvent content. Despite considerable advances in rationally designing hydrogels, our understanding of their complex nonlinear mechanical deformation behavior is incomplete. This is partially due to the difficulty in conducting mechanical characterization on slippery, soft and swollen gels. Thus, it is required to develop new experimental techniques in order to better characterize them. Further, analyzing the experimental observations and link it with the molecular networks is an important factor. With this perspective, in this dissertation, nonlinear mechanical properties of different gel like materials have been investigated. We chose different gels with varied molecular structure, from molecular gel to self-assembled copolymer gels with flexible chains, to semiflexible polysaccharide based polymers. By developing suitable experimental protocols, strain-stiffening behavior of these materials, similar to that observed in biological materials, have been captured. Chain flexibility is a dominant factor in mechanical behavior of gels. For example, gels with flexible chains dilate orthogonal to an external shear load, whereas gels with semilexible chains contract similar to biological gel-like materials. In order to investigate the failure mechanism in our gels, cavitation rheology technique was also applied. We found that cavitation phenomenon in gels is related to the molecular architecture of the gels. The present work provides a better understanding of the deformation behavior of soft gels when subjected to a large load.

The purpose of this investigation was to provide quality dynamic strength properties for a solid grade severe-weather (SW) brick material and to illustrate the need for careful evaluation of the strain-rate effects on geomaterials. A split Hopkinson pressure bar (SHPB) was used to perform a series of tests on specimens from a solid grade SW brick to determine the mechanical response of this material at high strain-rates. Both classical and modified SHPB tests were performed. The results from the classical SHPB tests provided evidence that modifications to the SHPB are necessary when testing geomaterials such as brick. To modify the SHPB, a small copper disk was placed at the impact end of the SHPB incident bar to increase the rise time of the initial pulse. The material response from the modified SHPB tests provided an average compressive strength of 104 MPa, which resulted in a dynamic increase factor of 1.42.

Understanding the mechanisms governing left ventricular function and dysfunction is critical to analyze cardiovascular disorders and gaining insights into possible therapies. Left ventricular function can be evaluated using Magnetic Resonance Imaging (MRI). Cardiac displacements and corresponding strains are then computed from the imaging data. In measuring and assessing the left ventricle’s motion, images are taken either in the short axis (top-down) or long axis (side) views. In this project, we will use DENSE MRI data, which measures the displacements of individual tissue voxels during the cardiac cycle. After extracting the myocardial tissue by segmenting the MR images, strains are computed by differentiating the displacement field in the radial direction (across the thickness of the heart wall), longitudinal direction (along the left ventricle long axis), and in the circumferential direction. Current approaches focus mainly on evaluating cardiac motion and strains during ventricular systole, when the ventricles contract and blood is pumped out of the heart ~\cite{srichai2009cardiovascular}. Our aim is to characterize strains during atrial systole, which corresponds to the late filling of the ventricles before the next contraction occurs. Understanding the deformation of the left ventricle during late filling is particularly important to evaluate the passive response of the myocardium, which is related to several cardiac diseases, such as heart failure with preserved ejection fraction and diabetic cardiomyopathy. During this study we will use preclinical data already acquired in healthy swine subjects. Our goal is to evaluate inter subject variability at peak atrial systole and how different segmentations (intra and inter observer variability) affect the computed strains.

The mechanical properties of pure Aluminium, Al-0.2%Cu and Al-0.4%Cu at large strains were studied by channel-die compression at three different temperatures: 77K, 200K and 300K. The results were interpreted in terms of work hardening rate versus stress (0/r) diagrams. The evolution of the structure was studied on a range of scales from macroscopic to microscopic, by optical study of slip lines, X-ray diffraction for texture measurements, Electron Back-Scattering Kikuchi Patterns for local texture measurements, and by Transmission Electron Microscopy for microstructural information. Intense shear banding was observed at large strains in all alloys at all temperatures. The texture evolution was shown to be consistent with this change in deformation mode. At low temperatures, stage HI of deformation was shown to be represented by a straight line in the 6lr diagram. Increasing the temperature lead to a dramatic decrease in work hardening rate and to an increasing concavity of the 0lr plots. The addition of solutes to pure Aluminium was shown to result in an increase of the work hardening rate, which could be represented by a simple translation of the 0/r plots on the stress axis. At large strains, all three materials experienced a stage (stage IV) of constant work hardening at low rate. The stage IV work hardening rate decreased with increasing temperature, and was not influenced by solute content. The stage Ill-Stage IV transition was very sharp at 77K and smoother at higher testing temperatures. Phenomenological models were developed for the prediction of the influence of temperature and solute content on work hardening. Moderate strains were modelled taking into account the evolution of the dislocation density into two different populations during the deformation. The influence of solutes on work hardening was modelled by considering how segregation of solute atoms at the dislocation cores influences dynamic recovery. Stage IV work hardening was considered to arise from the accumulation of dislocation debris resulting from the dynamic recovery events. / Thesis / Master of Engineering (ME)

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EVALUATION THE NITROGEN NEEDS AND EFFICIENCY OF RHIZOBIA STRAINS TO PROVIDE NITROGEN TO CHIPILIN (Crotalaria Longirostrata HOOK. AND ARN.) FEBRUARY OF 2013 FATIMA DEL ROSARIO CAMARILLO CASTILLO, B.A., AUTONOMOUS UNIVERSITY OF CHAPINGO M.A., UNIVERSITY OF MASSACHUSETTS AMHERST Directed by: Professor Francis X. Mangan Chipilin (Crotalaria Longirostrata) is a leguminous plant native to Central America and Southern Mexico and used in the preparation of traditional dishes in this region. Starting in 2009, farmers in Massachusetts have been growing chipilin with a weekly production of 800 kg∙ha-1. However, as much as 300 kg∙ha-1 of nitrogen has been necessary to apply to the soil in order to obtain a marketable leaf quality. With the goal to determine the nitrogen requirements of chipilín and to quantify the capacity of selected stains to infect and provide nitrogen for this crop, two-field experiments were conducted at the UMass Research farm at Deerfield, Massachusetts, in an occum fine sandy loam soil (coarse-loamy, mixed, mesic Fluventic Dystrudept) soil as a randomized complete bock design with five replications. For the field trial in 2011, nitrogen rates were (kg∙ha-1): 40, 80, 120, 160, 200 and 240 and 0, 40, 80, 120, 160, 200, 240 and 280 in 2012 in combination with four Rhizobia strains: Bradyrhizobium sp. (Vigna), Rhizobium leguminosarum biovar, Bradyrhizobium USDA 3384 and no Rhizobia were the treatments. Based on the results obtained, nitrogen fertilizer application of 80 kg∙ha-1 was economically sufficient for chipilin to reach optimum yield. However higher nitrogen rates are needed to obtain marketable leaf color and quality. Additionally a greenhouse experiment set up as a factorial experiment with five replications was conducted with seven nitrogen concentrations (mg N∙L-1)-; 0, 26.25, 52.5, 105, 157.5, 210 and 262.5 mg∙L1 and the three Rhizobia strain for the previous experiment plus Bradyrhizobium USDA 2370 as treatments. Results suggest from Bradyrhizobium USDA 3384 is not an efficient strain for chipilin, and Rhizobium leguminosarum biovar potentially may provide the most nitrogen of the strains evaluated. In the greenhouse trial, nodules number per plant decreased with the increase in nitrogen applications, but this was not the case in the field trial in 2012. Nodules were found on the root of chipilin plants in the control. This is suspected to be due to one of the following possibilities: Rhizobia inoculum presence in the seed, Rhizobia in the soil (in the field trial) or contamination during the setup of the experiment.

High entropy alloys (HEAs) are a relatively new class of solid solution alloys that contain multiple principal elements to take advantage of their high configurational entropy, sluggish diffusion, lattice distortion, and the cocktail effect. In recent development, work hardening mechanisms known as twinning induced plasticity (TWIP) and transformation induced plasticity (TRIP) have been found active in Al0.3CoCrFeNi (molar fraction) and Fe50Mn30Co10Cr10 (at %) HEA compositions. Friction-stir processing was done to increase the mechanical properties and improve the microstructure of the alloys for the purpose of high strain rate performance. Quasi-static tensile tests as well as top-hat geometry Split-Hopkinson pressure bar tests were conducted to view the mechanical properties as well as view the microstructural evolution at dynamic strain rates. Overall, the Al0.3CoCrFeNi condition after friction-stir processing and heat treatment has proved to have the best mechanical properties, and selecting from the conditions in this study, Al0.3CoCrFeNi has better shear localization resistance.