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This thesis utilized a linear analytical approach to explore the damage tolerance or residual strength as a function of increasing damage in traditional single and hybrid-grid IsoTruss® structures. Residual strength was studied for structures subjected to axial compression, torsion and flexural bending, independently. Carbon/epoxy material properties were applied in all load cases, and fiberglass/epoxy material properties were also applied in the flexural bending case. Prior to imposing damage conditions, the IsoTruss® structures were parametrically optimized to achieve the highest strength-to-weight ratios. Typical compression strut, driveshaft, and utility pole specifications governed the design strength dimensions and boundary conditions. Damage growth was achieved by removing members from IsoTruss® structures progressively about the circumference in a symmetrical manner. The sequence of member removal, beginning with primary or secondary members, was examined, and is described as primary and secondary analyses. ABAQUS finite element analysis was employed to quantify the residual strength of each IsoTruss® configuration. Reduction in residual strength trends are compared to net section strength, which assumes a linear relationship between damage size and residual strength. Results indicate that the 6-node IsoTruss® configuration is the most damage tolerant structure in the sense that the 6-node configuration deviates the least from the net section strength. As more nodes are added, IsoTruss® structures behave more like a composite tube, exhibiting a brittle behavior characterized by an increase in strength reduction for a given damage size. Bending results reveal that carbon fiber IsoTruss® structures are more damage tolerant under primary bending conditions than fiberglass poles. On the other hand, fiberglass IsoTruss® poles prove to be more damage tolerant under secondary bending conditions than carbon fiber structures. Most importantly, however, hybrid-grid IsoTruss® poles are definitively more optimal structures than single-grid poles in terms of both strength-to-weight ratio and damage tolerance. The results and conclusions from this thesis provide benchmark capacities for mechanically manufactured IsoTruss® structures. Also included in this thesis is documentation of a special program written to analyze IsoTruss® structures.

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<p dir="ltr">During agricultural production, grain damage is a persistent problem that reduces grain quality. The goal of this study is to develop mechanics-based models that can accurately predict grain damage caused by mechanical handling processes and validate the models with lab-scale and industrial-scale test systems.</p><p dir="ltr">A discrete element method (DEM) simulation was developed to predict the impact damage of corn kernels in a Stein breakage tester. The DEM model relied on an empirically generated, three-parameter Weibull distribution describing the damage probability of repeated impacts. It was found that the DEM model was able to give good predictions on the kernel damage fraction for different sample sizes and operating times. The root-mean-square deviation between the damage fractions acquired from the simulation and experiment is 0.05. A sensitivity analysis was performed to study the effects of material and interaction properties on damage fraction. It was found that damage resistance parameters, coefficients of restitution, and particle shape representation had a significant effect on damage fraction. The statistics of the number of contacts and impact velocity were collected in the simulation to interpret the results of sensitivity analysis at the contact level. The locations where the damage occurs on the particle and in the operating device were also predicted by the model.</p><p dir="ltr">In addition to impact damage, another major type of grain damage is compression damage caused by mechanical harvesting and handling processes. A mechanistic model was developed to predict the compression damage of corn kernels using the DEM. The critical model input parameters were determined using a combination of single kernel direct measurements and bulk kernel calibration tests. The Young's modulus was measured with a single kernel compression test and verified with a bulk kernel compression test. An innovative approach was proposed to calibrate the average failure stress using a bulk kernel compression test. After implementation of the model, a validation test was performed using a Victoria mill. Comparing the simulation and the experimental results demonstrated that the simulation gave a good prediction of the damage fraction and the location of the damage when the von Mises stress damage criterion with a variable damage threshold was used. A sensitivity analysis was conducted to study the effects of selected model input parameters, including particle shape, Young's modulus, particle-particle coefficient of friction, particle-boundary coefficient of friction, particle-boundary coefficient of restitution, and damage criterion.</p><p dir="ltr">An industrial-scale handling system was designed and built to validate the DEM-based grain impact damage model. The low moisture content corn and soybean samples were handled through the system at three impeller speed levels and two feed rate levels, and the amount of damage caused by handling was evaluated. DEM simulations with the impact damage model were constructed and run under the corresponding test conditions. The experimental results showed that grain damage increased with increasing impeller speed and decreasing feed rate, which aligned with the model predictions. The simulated damage fraction values were larger than the experimental measurements when the experimentally-measured DEM input parameters were used. The simulation predictions can be significantly improved by decreasing the particle-boundary coefficient of restitution (PB COR). The mean absolute error between the simulation and experimental results decreased from 0.14 to 0.02 for the corn tests and from 0.05 to 0.01 for the soybean tests after the reduction of PB COR.</p><p dir="ltr">The developed damage models can accurately predict the amount of grain damage and the locations where the damage occur within a grain handling system. The models are expected to be useful in providing guidance on designing and operating grain handling processes to minimize kernel damage and, thus, improve grain quality. To further improve the performance of the model, the methods that accurately and efficiently determine the model input parameters need to be explored. In addition, in this work, the models were only applied to corn and soybeans at specific conditions. The applicability of the model to other types of grain, such as rice, or other grain conditions, such as wet corn, should be investigated.</p>

Yes / This study established a dynamic damage constitutive model for ultra-high performance concrete (UHPC) with nanofillers, based on a viscoelastic dynamic constitutive model and a damage evolution equation. Ten types of nanofillers, including particle, tube and flake nanofillers, were incorporated to modify UHPC. The split Hopkinson pressure bar was used to obtain the relationship between stress and strain of UHPC specimens at a strain rate of 200/s-800/s. The experimental results indicated that the dynamic compressive strength of UHPC with nanofillers at strain rates of approximately 200/s, 500/s, and 800/s can reach 172.8 MPa, 219.6 MPa, and 275.9 MPa, respectively, reflecting an increase of 85.2 %, 76.5 %, and 53.9 % compared with the blank UHPC. The established dynamic damage constitutive model considered the damage accumulation with strains under dynamic loading. The fitting coefficients of the dynamic damage constitutive model, when compared against experimental results, range from 0.8796 to 0.9963, showing a higher accuracy compared with traditional Zhu-Wang-Tang (ZWT) viscoelastic model, especially at a strain rate of approximately 200/s. / National Science Foundation of China (52178118 and 52308236), and the China Postdoctoral Science Foundation (2022M720648 and 2022M710973)

Although nondestructive evaluation techniques have been implemented in many industry fields and proved to be useful, they are generally expensive, time consuming, and the results may not always be reliable. To overcome these drawbacks, structural health monitoring (SHM) systems has received significant attention in the past two decades. As structural systems are becoming more complicated and new materials are being developed, new methodologies, theories, and approaches in SHM have been developed for damage detection, diagnosis, and prognosis. Among the methods developed, the guided Lamb wave based SHM can be a promising technique for damage evaluation since it provides reliable damage information through signals propagating over large distance with little loss of amplitude. While this method is effective for damage assessment, the guided Lamb wave contains complicated mode characteristics, i.e. an infinite number of wave modes exist and these modes are generally dispersive. For this reason, a minimum number of wave modes and various signal processing algorithms are implemented to obtain better signal interpretations. Phased array beamsteering is an effective means for damage detection in guided Lamb wave SHM systems. Using this method, the wave energy can be focused at localized directions or areas by controlled excitation time delay of each array element. In this research, two types of transducers are utilized as phased array elements to compare beamsteering characteristics. Monolithic piezoceramic (PZT) transducers are investigated for beamsteering by assuming omnidirectional point sources for each actuator. MacroFiber Composite (MFC) transducers with anisotropic actuation are also studied, considering the wave main lobe width, main lobe magnitude, and side lobe levels. Analysis results demonstrate that the MFC phased arrays perform better than the PZT phased arrays for a range of beamsteering angles and have reduced main lobe width and side lobe levels. Experiments using the PZT and MFC phased arrays on an aluminum plate are also performed and compared to the analysis results. A time-frequency signal processing algorithm coupled with a machine learning method can form a robust damage diagnostic system. Four types of such algorithms, i.e. short time Fourier transform, Wigner-Ville distribution, wavelet transform, and matching pursuit, are investigated to select an appropriate algorithm for damage classification, and a spectrogram based on short time Fourier transform is adopted for its suitability. A machine learning algorithm called Adaboost is chosen due to its effectiveness and high accuracy performance. The classification is preformed using spectrograms and Adaboost for crack and corrosion damages. Artificial cracks and corrosions are created in Abaqus® to obtain the training samples consist of spectrograms. Several beam experiments in laboratory and additional simulations are also performed to get the testing samples for Adaboost. The analysis results show that not only correct damage classification is possible, but the confidence levels of each sample are acquired. / Ph. D.

No / In recent years, two techniques for detecting genetic damage in the whole genome have gained importance: the alkaline comet assay, to detect DNA damage such as strand breaks and alkali-labile sites, and a multicolour FISH method, spectral karyotyping (SKY), to identify chromosomal aberrations simultaneously in all metaphase chromosomes. In the present study, the induction of DNA damage in human sperm and lymphocytes in vitro has been studied employing an anticancer drug, doxorubicin (DX). An increase in DNA damage was observed with the comet assay as the median per cent head DNA of sperm significantly decreased from 82.07 and 85.14% in the untreated control groups to 63.48 and 72.52% at doses of 0.8 µM DX. At 1.6 µM the percentage declined to 60.96% (the corresponding tail moment increased from 4.42 to 12.19). In stimulated lymphocytes, a significant increase was observed in tail moment, from 0.72 and 0.53 in controls to 15.17 and 12.10 at 0.2 µM DX, continuing at the same level to a final concentration of 1.6 µM. Structural aberrations found in the parallel SKY study in stimulated lymphocytes at 0.2 µM DX consisted of 14% chromatid-type and 2% chromosome-type aberrations; none were found in controls. The SKY results correlate very well with the findings of the comet assay in lymphocytes where DNA damage was observed at similar doses. This study is the first reporting use of the comet assay and SKY analysis in parallel after chemical treatment. The potential of the two techniques together is evident, as they represent a set of assays feasible for evaluating damage in human somatic and germ cells after chemical treatment (i) by direct observation of two different end-points, detecting general DNA damage and chromosomal aberrations and (ii) by extrapolation from lymphocytes to sperm, which provides a `parallelogram¿ approach in human cells.

Yes / The DNA Damage Response (DDR) pathways sense DNA damage and coordinate robust DNA repair and bypass mechanisms. A series of repair proteins are recruited depending on the type of breaks and lesions to ensure overall survival. An increase in glucose levels was shown to induce genome instability, yet the links between DDR and glucose are still not well investigated. In this study, we aimed to identify dysregulation in the transcriptome of normal and cancerous breast cell lines upon changing glucose levels. We first performed bioinformatics analysis using a microarray dataset containing the triple-negative breast cancer (TNBC) MDA-MB-231 and the normal human mammary epithelium MCF10A cell lines grown in high glucose (HG) or in the presence of the glycolysis inhibitor 2-deoxyglucose (2DG). Interestingly, multiple DDR genes were significantly upregulated in both cell lines grown in HG. In the wet lab, we remarkably found that HG results in severe DNA damage to TNBC cells as observed using the comet assay. In addition, several DDR genes were confirmed to be upregulated using qPCR analysis in the same cell line. Our results propose a strong need for DDR pathways in the presence of HG to oppose the severe DNA damage induced in cells. / Wellcome Trust