Apparent Strain Research Articles

Frost heaving strain monitoring for lining structure in extreme cold and high-altitude area with FBG strain sensors

Due to the extreme temperature with significant variation in the alpine region, the tunnels in this area are subjected to intense freeze–thaw cycles and frost heaves, which leads to the cracking of the second lining structure. We propose an approach to monitor the frost heaving strain of the second lining and simultaneously measure the thermal strain and applied stress strain of the structure. The Fiber Bragg Grating (FBG) strain sensors are installed on the structure surface to measure the strains caused by the thermal strain and loaded stress. Meanwhile, one FBG temperature sensor is installed on the structure surface to measure the local temperature. Then, the structure thermal strain and applied stress strain are simultaneously measured based on the sensitivity difference for temperature and strain response of the above two measurement methods. The proposed approach is implemented in an alpine region tunnel. The results show that the local temperature is inversely proportional to the total strain and the thermal apparent strain of the second lining. The applied stress–strain of the lining fluctuates in a small range, and the thermal strain from the daily temperature difference incremental demodulation is very close to the daily strain difference. Therefore, the main cause of lining frost damage is the thermal strain due to the local temperature variation, and there is no frost heave occurred in the surrounding rock. Thus, the method is offered to monitor the freeze–thaw cycles and freeze-swelling effects in the extreme cold and high-altitude tunnels.

Research on Apparent Strain Measurement of Ankle Joint in Taekwondo Sports Using Data Mining Algorithm

As a sport, Taekwondo has always attracted everyone’s attention and love, but it is a very common phenomenon to have ankle injuries during sports. Therefore, the detection of ankle injuries has become a concern theme of scholars. It is of great significance to realize the ankle apparent strain measurement quickly and in colleges and universities. In this paper, a data mining algorithm-based approach to measuring the apparent strain of the ankle joint in Taekwondo sports is proposed. This paper first analyzes and integrates the research results of scholars, and then expounds from the two aspects of data mining and ankle apparent strain measurement. The method is introduced in detail, and the principle of apparent strain measurement is explained by the formula. The feasibility and robustness of the research scheme are then demonstrated through specific experimental data. The data showed that there was a difference between the boy group and the girl group in the time of jumping, kicking, and reaching the ground.

Insights into the roles of intergranular carbides in the initiation of intergranular stress corrosion cracking of alloy 690 in simulated PWR primary water

The effect of intergranular carbides on the stress corrosion crack (SCC) initiation of alloy 690 in high-temperature hydrogenated water was systematically studied. Irrespective of the aging temperature, the resistance to SCC initiation continuously increases with increasing carbide coverage. The understanding of carbide effects was further advanced. Mechanically, the carbide mitigates the breach of surface oxide film over the grain boundary by suppressing the local apparent plastic strain. The carbide also greatly diminishes grain boundary migration by retarding the diffusion of Cr. More importantly, it decomposes when exposed to the environment and serves as Cr source for forming protective oxide film.

Ontogeny of Pediatric Pharmacogenetics: Celebrating the Past and Vision for the Future.

Ontogeny of Pediatric Pharmacogenetics: Celebrating the Past and Vision for the Future.

Deformation and fracture behavior of granite by the short core in compression method with 3D digital image correlation

AbstractBased on three‐dimensional digital image correlation (3D‐DIC) technique, the deformation behavior, damage and fracture characteristics of the granite specimens have been tested and observed by the short core in compression (SCC) method. The test results show that (1) the damage degree of rock in the region of interest (ROI) increases with axial stress. Before peak stress, damage factor based on apparent principal strain increases slowly, then rises rapidly; (2) relative displacements in both horizontal and vertical directions are observed, indicating that the fracture mode for SCC specimens subjected to uniaxial compression is the tensile‐shear mixed mode fracture; (3) new fracture initiates from the middle part of the expected shear fracture band (ESFB) then propagates along the loading direction. A dominant macro‐fracture, linking up the tips of two notches, eventually forms. Meanwhile, a calculation method based on the energy conservation law for the fracture energy of SCC specimens is proposed. The fracture energy of granite is estimated as 1760.4 J/m2.

The effects of the temperature in the testing system on the measurements of thermal rock strain with clip-on extensometers

The present work was aimed to identify and quantify the offsets biasing the thermal rock strain as measured with clip-on extensometers at a mechanical testing system (MTS) so as to increase the reliability of such measured strain. We conducted an experiment via cycling the temperature of a sample of aluminum alloy between ambient temperature and 90 °C under the hydrostatic confining pressure as maintained at 2 MPa. Thereby, the readouts of the extensometers appeared to be irreversible subsequent to the temperature cycle mimicking residual deformation in the sample. The numerically simulated temperature in the setup of the testing system was heterogeneous throughout such temperature cycling test showing an irreversible plug-in temperature in particular. These temperatures resulted in the apparent amplification of the circuit as constituted by the extensometer and the amplifiers as well as the relevant reading offset. Such induced offset biased the actual sample strain besides the expansion (contraction) in the metal parts of the extensometers yielding the apparent irreversible strain in the sample. We presented a workflow for quantifying the amplification- and the metal part-related offsets. The validity of the workflow was demonstrated via rectifying the strain in a rock sample that was monitored throughout a temperature cycle between 30 °C and 40 °C. Our present work would be referable for experimental researches on thermal rock strain with similar setup of measurement. The amplification- and the metal part-related offsets could be likewise estimated and excluded from the measurements conducted elsewhere before the strain in a tested sample could be obtained.

The Symmpact: A Direct-Impact Hopkinson Bar Setup Suitable for Investigating Dynamic Equilibrium in Low-Impedance Materials

BackgroundMeasuring the dynamic behavior of low-impedance materials such as foams is challenging. Their low acoustic impedance means that sensitive force measurement is required. The porous structure of foams also gives rise to dynamic compaction waves, which can result in unusual behavior, in particular if the foam material is so thick, that dynamic force equilibrium is not reached.ObjectiveThis work investigates comparatively large polyurethane foam specimens with densities in the range of 80 – 240 kg/m3 to deliberately achieve a state away from force equilibrium during high-rate compaction. The aim is to understand how an increase in strain rate leads to a reduction in strength for such materials.MethodsA specialized direct-impact Hopkinson bar is employed. It uses polycarbonate bars to achieve the required long pulse duration of 2.6 ms to compress the large specimens into the densification regime. In contrast to existing setups, both striker and output bar are instrumented with strain gauges to monitor force equilibrium. The absence of an input bar allows monitoring force equilibrium more accurately. Special attention is paid to the calibration of strain gauges, taking non-linear effects, wave dispersion and attenuation into account. Digital Image Correlation is employed to analyze elastic and plastic compaction waves by means of Lagrange diagrams.ResultsDepending on density, the specimens show saturation of dynamic strength increase at high rates of strain approx 500 /s, or even negative strain rate sensitivity in case of the lowest density. The occurrence of apparent negative strain rate sensitivity is accompanied by a localized structural collapse front, moving at a low velocity of approx 10 m/s through the material. This apparent strain rate sensitivity is a structural effect which is related to the thickness of the specimen.ConclusionsThe primary aim of material characterization using Hopkinson bars is to achieve a state of force equilibrium. For this reason, very thin specimens are usually employed. However, data gathered in this way is not representative for thick foam layers. Here, an increase of strain rate can lead to a decrease of strength if homogeneous deformation is replaced by a dynamic compaction wave. This behavior can occur at strain rates encountered under conditions such as automotive crash.

Perspective error reduction in 2D Digital Image Correlation measurements by combination with Defocused Speckle Imaging

2D Digital Image Correlation (2D DIC) enables full-field in-plane displacement measurement by tracking the physical surface texture in the recorded images. However, because camera magnification is inversely proportional to object distance, points along the imaged surface can have different scales and appear to move at different rates. Surface curvature and out-of-plane motions may thus lead to perspective errors that manifest as apparent strains, limiting the method suitable only for flat objects that move purely in-plane. Defocused Speckle Imaging (DSI) is a related optical method where the movements of a laser-illuminated surface are determined by tracking the scattered interference speckle pattern. When the camera is in focus, the speckles appear to move at the same rate with the physical surface. However, camera defocus causes the speckle motion to deviate from the actual surface motion. Interestingly, the observed speckle motion magnitude increases with positive defocus distance, which is contrary to the perspective effects inherent to 2D DIC. Remarkably, with optimized geometric arrangement, 2D DIC and DSI have perspective errors that are equal in magnitude but with opposite signs. It is thus possible to compensate perspective errors by performing DIC and DSI measurements simultaneously and simply calculating the average of the two signals. This article derives the proposed compensation principle analytically using simple geometric framework. An experimental demonstration shows that the combination of DIC and DSI reduces magnification-dependent perspective errors by 73%, and errors due to object rigid-body rotation by 86%.

Evolution of fluid pathways during eclogitization and their impact on formation and deformation of eclogite: A microstructural and petrological investigation at the type locality (Koralpe, Eastern Alps, Austria)

Eclogites representing three strain stages from the type locality (Saualpe-Koralpe Complex, Eastern Alps, Austria) have been analyzed with regard to their microstructural, petrological and mechanical evolution during the gabbro-eclogite transformation and subsequent deformation. Thermodynamic forward models suggest the presence of a H2O dominated fluid phase during eclogitization and following deformation. While all three eclogite types show the same mineral paragenesis composed of garnet, omphacitic clinopyroxene, quartz and a fine grained polyphase aggregate of kyanite, clinozoisite, quartz and retrograde plagioclase, we do observe a microstructural and mechanical evolution with strain.Eclogitization is controlled by dissolution of metastable gabbro and precipitation of the stable finer grained eclogitic mineral paragenesis. This induces a micro-porosity which allows fluids to migrate in an unchannelized way. Distributed eclogitization results in strain weakening, where both transformational and volumetric strain are accommodated by dissolution-precipitation creep. Subsequent deformation of eclogite results in the development of pronounced eclogitic foliation accompanied by grain coarsening and reduction of porosity. The latter results in a reduced efficiency of dissolution-reprecipitation possibly causing apparent strain hardening. Based on our observations we suggest a model for the rheological evolution during the transformation of a dry mafic rock into an eclogite where the combination of volumetric and transformational strain at the onset of eclogitization assisted by fluid induces rapid weakening followed by apparent hardening once eclogitization is completed and steady state deformation of the eclogite mineral paragenesis sets in.

Dynamic mechanical properties and microstructure evolution of AlCoCrFeNi2.1 eutectic high-entropy alloy at different temperatures

The dynamic mechanical properties of the AlCoCrFeNi2.1 eutectic high-entropy alloy (EHEA) fabricated by drop-casting (DC) and suction-assisted casting (SC) are investigated under different strain rates and temperatures using Split Hopkinson Pressure Bar (SHPB) system. Microstructure analysis is conducted through SEM, EBSD and TEM to reveal the deformation and fracture mechanisms of the present EHEA. The yield strength and flow stresses for both the DC alloy and SC alloy increase with increasing strain rate, but decrease with increasing temperature. A mixture of ductile and brittle fracture morphologies exists in both the DC and SC EHEAs. Moreover, the SC alloy displays more shear dimples on the fracture surface, while brittle fracture features become dominant for the DC alloy. Abundant accumulation of dislocations in the quasi-static test produces slip traces in the FCC lamellar phase which further enhances the plasticity of the SC alloy. Meanwhile, the dislocation cells formed by high-density dislocation tangles at high strain rates, leading to apparent work hardening and strain rate sensitivity of the SC alloy. The adiabatic shear band (ASB) forms in the SC alloy before shear failure and the adjacent twisted and curved lamellar structures play a significant role in preventing shear localization. Overall, the SC alloy exhibits a stronger strain rate effect and better ductility than the DC alloy.

Compression properties and impact energy release characteristics of TiZrNbV high-entropy alloy

To explore the potential of high-entropy alloys (HEAs) as energetic structural materials (ESMs), the compression behaviors and impact energy release characteristics of TiZrNbV HEA were investigated. Mechanical experiments at strain rates from 1 × 10−3 s−1 to 1 × 104 s−1 showed that TiZrNbV HEA exhibits clear dynamic brittle fracture behavior under dynamic compression loading, which is diametrically opposite to its behavior under quasi-static compression loading. A Johnson–Cook constitutive model for TiZrNbV HEA was obtained by fitting the experimental data, which demonstrated an apparent strain rate effect. Numerical simulation and microstructure results revealed the role of an adiabatic shear band (ASB) in the brittle fracture. The crack profiles that evolved from the ASB exhibited the typical characteristic for high temperatures. The degree and rate of the chemical reaction and recycled products of direct ballistic tests indicated that severe oxidation reactions induced by the high-temperature profiles resulted in chemical energy release under impact loading. The relationship between the material microstructure and macromechanical behavior of TiZrNbV HEA, which is important in the use of HEAs as ESMs, was revealed in this study through mechanical and material methods and finite element numerical simulation.

Mapping local mechanical properties of human healthy and osteoporotic femoral heads

The complexity of bone tissue, its hierarchical multi-scale structure and the delicate mechanobiological equilibrium that regulates its architecture make the analysis of bone local mechanical characteristics highly challenging. The strong dependence between bone's mechanical properties and meso- and micro-architectural arrangement is particularly evident in the human femur, where loads are transmitted from the pelvis along the stress trajectories. An alteration in loads distribution generates a consequent deterioration in the structural pattern of trabecular groups, that worsen in presence of pathologies such as osteoporosis. Considering this complexity, it is crucial to map femur's local strength values, in order to capture their variability and to evaluate the possible causes of fragility and fracture. For this purpose, a portable micro-compression device compatible with a synchrotron is designed and realized: it allows to test millimetric samples cut along the stress trajectories from three healthy and three osteoporotic femoral heads and to real-time monitor the apparent stress-apparent strain curves. Intra-patients variability shows increased resistance to compression in the proximal sub-region, anatomically close to the acetabulum, where the loads are transmitted from the pelvis to the femur. Inter-patients variability show an interesting trend: non-osteoporotic femoral heads are characterized by a more uniform distribution in terms of Young moduli in the whole head, while non-uniform values are present in osteoporotic subjects.

Rapid Consolidation of WC-ZrSiO4 Hard Materials by Spark Plasma Sintering: Microstructure, Densification, and Mechanical Properties

Densely consolidated WC-based hard materials with 5–20 vol% ZrSiO4 was fabricated by spark plasma sintering at 1400 ℃ at a constant heating rate of 70 ℃/min−1. To achieve mechanical alloying of WC-ZrSiO4, planetary ball milling was carried out for 12 h, during which the brittle-brittle components (WC-ZrSiO4) became fragmented and their particles became refined. It was observed that certain, specific, non-isothermal sintering kinetics, such as apparent activation energy, sintering exponents, and densification strain, affected the densification behavior. The evolution of phase structure from powder to compact was found to be related the lattice distortion and micro-strain in the basal planes of WC. By examining the mechanical properties of the samples, it was that the added zircon content leads to enhanced fracture toughness (12.9 MPa m1/2) owing to the presence of WC-ZrSiO4 in the cemented carbide. In fact, the microcrack propagation of the fracture passed through zircon from a transgranular to a ductile component (fcc) where the crack tips could be absorbed.Graphic

Deformation behavior and microstructure evolution of as-cast Ti2ZrMo0.5Nb0.5 high entropy alloy

Abstract A high entropy alloy (HEA) with a composition of Ti2ZrMo0.5Nb0.5 was prepared by vacuum induction melting technology. The mechanical properties at room temperature and elevated temperature (900 °C–1150 °C), microstructure evolution and hot deformation behavior during hot deformation are studied. The as-cast alloy is composed of equiaxed grains with the yield strength, the apparent plastic strain of 1306 MPa and 44%, respectively. By TEM analysis, the ZrTi2 Laves C15 phase is found corresponding the precipitation strengthening effect accompanied with the solid solution strengthening as a ramification of the high-entropy alloy. Then the hot compression tests were carried out. The deformed alloy still maintains the same single BCC structure as the as-cast state. It is noted that when the temperature is 900 °C, the structure of the alloy mainly exhibits dynamic recovery (DRV) characteristics, and when the temperature reaches 1000 °C, there are clear dynamic recrystallization (DRX) characteristics in the structure, which are analyzed as the features of continuous dynamic recrystallization (CDRX). Keeping the temperature at 1150 °C, when the strain rate is 0.1 s−1, the characteristics of discontinuous dynamic recrystallization (DDRX) appear, and as the strain rate decreases, CDRX becomes the main recrystallization mechanism again.

Experimental and analytical study on the behavior of RC beams with externally bonded carbon-FRCM composites

This paper presents both experimental and analytical study results for predicting the flexural capacity of reinforced concrete (RC) beams with externally bonded carbon fabric reinforced cementitious matrix (carbon-FRCM). Firstly, the available prediction approaches for FRCM-strengthened RC in flexure were summarized. The prediction formulas were deficient in the fabric slippage failure. Nine carbon-FRCM specimens with different layers of carbon fabric (CF) were tested under uniaxial tensile loading. Four RC beams were strengthened in flexure with carbon-FRCM having different layers of CF, which were tested under four-point bending. From the tensile test results, the apparent strain of CF was derived from the global strain of carbon-FRCM, and the two-layer carbon-FRCM was an optimized selection in the design of multilayer carbon-FRCM. From the bending test results, the utilization efficiency of CF was slightly higher in the fabric slippage failure than that in the peeling-off of concrete cover, and the failure mode was differentiated as the layers of CF increased. Additionally, a new procedure of prediction formulas in flexure for carbon-FRCM-strengthened beams was proposed, using the apparent strain of CF to assess the strengthening performance of beams at different load-carrying scenarios. The prediction of the proposed formulas agreed well with the experimental results.

Effect of fiber orientation on the tensile properties of cross-ply laminates of PP reinforced continuous carbon fiber

This paper presents an experimental study of tensile properties, using a carbon–polypropylene uni-directional sheet with a thickness of 0.15 mm, which shows that highly non-linear stress–strain curves can be achieved with cross-angle-ply laminates. Generally, these properties are studied from the scanning electronic microscope and X-ray computed tomography. Cross-ply laminates with fiber orientation angles from 15 to 60° are investigated and it is found that there are the pseudo-ductile behavior with the fiber rotation, especially at fiber orientation angles from 30° to 60°.The Pseudo-ductile behavior is a phenomenon in which the apparent strain increases after yielding with strain hardening. It is greatly affected by the fiber reorientation in the loading direction. The fiber reorientation is allowed the plasticity of the polypropylene and thickness of each layer.

Proximal Tibia Bone Stiffness and Strength in HR-pQCT- and QCT-Based Finite Element Models.

Injury to the ACL significantly increases the risk of developing post-traumatic osteoarthritis. Following injury, considerable focus is placed on visualizing soft tissue changes using MRI, but there is less emphasis on the alterations to the underlying bone. It has recently been shown using high-resolution peripheral quantitative computed tomography (HR-pQCT) that significant reductions in bone quality occur in the knee post ACL-injury. Despite the ability of HR-pQCT to show these changes, the availability of scanners and computational time requirements required to assess bone stiffness and strength with HR-pQCT limit its widespread clinical use. As such, the objective of this study was to determine if clinical quantitative CT (QCT) finite element models (QCT-FEMs) can accurately replicate HR-pQCT FEM proximal tibial stiffness and strength. From FEMs of 30 participants who underwent both QCT and HR-pQCT bilateral imaging, QCT-FEMs were strongly correlated with HR-pQCT FEM stiffness (R2 = 0.79). When QCT-FEM bone strength was estimated using the reaction force at 1% apparent strain, strong correlations were observed (R2 = 0.81), with no bias between HR-pQCT FEMs and non-linear QCT-FEMs. These results indicate that QCT-FEMs can accurately replicate HR-pQCT FEM stiffness and strength in the proximal tibia. Although these models are not able to replicate the trabecular structure or tissue-level strains, they require significantly reduced computational time and use widely available clinical-CT images as input, which make them an attractive choice to monitor bone density, stiffness and strength alterations, such as those that occur post ACL-injury.

Effects of Osteoporosis on Bone Morphometry and Material Properties of Individual Human Trabeculae in the Femoral Head.

ABSTRACTOsteoporosis is the most common bone disease and is conventionally classified as a decrease of total bone mass. Current diagnosis of osteoporosis is based on clinical risk factors and dual energy X‐ray absorptiometry (DEXA) scans, but changes in bone quantity (bone mass) and quality (trabecular structure, material properties, and tissue composition) are not distinguished. Yet, osteoporosis is known to cause a deterioration of the trabecular network, which might be related to changes at the tissue scale—the material properties. The goal of the current study was to use a previously established test method to perform a thorough characterization of the material properties of individual human trabeculae from femoral heads in cyclic tensile tests in a close to physiologic, wet environment. A previously developed rheological model was used to extract elastic, viscous, and plastic aspects of material behavior. Bone morphometry and tissue mineralization were determined with a density calibrated micro‐computed tomography (μCT) set‐up. Osteoporotic trabeculae neither showed a significantly changed material or mechanical behavior nor changes in tissue mineralization, compared with age‐matched healthy controls. However, donors with osteopenia indicated significantly reduced apparent yield strain and elastic work with respect to osteoporosis, suggesting possible initial differences at disease onset. Bone morphometry indicated a lower bone volume to total volume for osteoporotic donors, caused by a smaller trabecular number and a larger trabecular separation. A correlation of age with tissue properties and bone morphometry revealed a similar behavior as in osteoporotic bone. In the range studied, age does affect morphometry but not material properties, except for moderately increased tissue strength in healthy donors and moderately increased hardening exponent in osteoporotic donors. Taken together, the distinct changes of trabecular bone quality in the femoral head caused by osteoporosis and aging could not be linked to suspected relevant changes in material properties or tissue mineralization. © 2021 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

Room temperature ferromagnetic behavior of nickel-doped zinc oxide dilute magnetic semiconductor for spintronics applications

Abstract The multifunctional zinc oxide (ZnO) nanoparticles were economically grown through a simple co-precipitation technique. Ni-doped (1, 3, and 5 wt%) ZnO nanoparticles were also grown to comprehend their influence on the ferromagnetic property of the ZnO, especially at room temperature. The structural and surface morphological features of the prepared nanoparticles were studied through X-ray diffraction (XRD) and Scanning electron microscopy (SEM) techniques, respectively. Diffused reflectance, Photoluminescence, and Fourier transform infrared spectroscopic analyses were also carried out to understand the consequence of Ni doping on the ZnO nanostructure. The secondary phase formations such as NiO and NiO2 elucidate the solid solubility limit of three percent of nickel in the ZnO matrix. Size-strain analysis was performed to evaluate the crystallite size and apparent strain values. An increase in the agglomeration of particles is evidenced by SEM micrographs with an increase in the Ni doping percentage. The bandgap measurements showed a redshift from 3.25 to 3.18 eV for the Ni-doped nanoparticles. Photoluminescence study reveals the existence of lattice defects including interstitials and vacancies in the synthesized nanostructures. The vibrating sample magnetometer studies divulge that 3% Ni-doped ZnO nanoparticles show an intense ferromagnetic property at room temperature. These experimental observations manifested that the Ni-doped ZnO nanoparticles are potential candidates for spintronics device applications.

Damage monitoring in rock specimens with pre-existing flaws by non-linear ultrasonic waves and digital image correlation

Pre-existing discontinuities act as the primary source of damage initiation processes in rock masses, and consequently govern their overall deformational behavior. As laboratory tests are critical for establishing constitutive behavior of rocks, in this study, the impact of a pre-existing flaw on rock damage behavior has been analyzed through laboratory-scale experiments. For this purpose, prismatic Barre granite specimens with an existing flaw were progressively damaged under uniaxial loading condition. A state-of-the-art non-linear ultrasonic testing (NLUT) method – the Scaling Subtraction Method (SSM) – was implemented in tandem with the two-dimensional (2D) digital image correlation (2D-DIC) technique for monitoring the impact of the flaw on the rock damage processes. NLUT-SSM allowed for experimental tracking of damage progression by analyzing the elasto-dynamic non-linear response of the rock volume originating at dynamic levels of strain. The non-linear response was characterized through the frequency-domain based evaluation of the non-linear indicator in the ultrasonic imaging areas (UIA). The 2D-DIC full-field strain profiles enabled a strain-based quantitative assessment of the magnitude of tensile and shear damage visible on the rock surface through the estimation of non-elastic apparent tensile and shear strains. The stress-induced changes in the magnitude of the non-linear indicator in the UIA regions showed that the NLUT-SSM technique is sensitive to capture the signatures of rock damage initiation and progression, with the pre-flawed region showing a higher degree of variation in the magnitude of the non-linear indicator. The results also quantitatively demonstrate that damage initially nucleates at the flaw tips, with the flaw tips having a relatively higher magnitude of tensile and shear damage in comparison to other areas of the specimen. The correlation between the non-linear indicator and damage showed that non-linear indicator has a near-linear direct correlation with tensile damage. In contrast, the magnitude of the non-linear indicator increased in an inconsistent non-linear manner with continued accumulation of shear damage. These findings are significant, in the sense that very few prior studies quantitatively analyzed the influence of a pre-existing flaw on rock damage behavior and examined the primary rock damage mechanism (tensile or shear) influencing changes in non-linear ultrasonic characteristics.