Dynamic Loading Rates Research Articles

Influence of therapeutic grip exercises induced loading rates in distal radius fracture healing with volar locking plate fixation

Background and objectiveTherapeutic exercises could potentially enhance the healing of distal radius fractures (DRFs) treated with volar locking plate (VLP). However, the healing outcomes are highly dependant on the patient-specific fracture geometries (e.g., gap size) and the loading conditions at the fracture site (e.g., loading frequency) resulted from different types of therapeutic exercises. The purpose of this study is to investigate the effects of different loading frequencies induced by therapeutic exercises on the biomechanical microenvironment of the fracture site and the transport of cells and growth factors within the fracture callus, ultimately the healing outcomes. This is achieved through numerical modelling and mechanical testing. MethodsFive radius sawbones specimens (Pacific Research Laboratories, Vashon, USA) fixed with VLP (VRP2.0+, Austofix) were mechanically tested using dynamic test instrument (INSTRON E3000, Norwood, MA). The loading protocol used in mechanical testing involved a series of cyclic axial compression tests representing hand and finger therapeutic exercises. The relationship between the dynamic loading rate (i.e., loading frequency) and dynamic stiffness of the construct was established and used as inputs to a developed numerical model for studying the dynamic loading induced cells and growth factors in fracture site and biomechanical stimuli required for healing. ResultsThere is a strong positive linear relationship between the loading rate and axial stiffness of the construct fixed with VLP. The loading rates induced by the moderate frequencies (i.e., 1–2 Hz) could promote endochondral ossification, whereas relatively high loading frequencies (i.e., over 3 Hz) may hinder the healing outcomes or lead to non-union. In addition, a dynamic loading frequency of 2 Hz in combination of a fracture gap size of 3 mm could produce a better healing outcome by enhancing the transport of cells and growth factors at the fracture site in comparison to free diffusion (i.e. without loading), and thereby produces a biomechanical microenvironment which is favourable for healing. ConclusionThe experimentally validated numerical model presented in this study could potentially contribute to the design of effective patient-specific therapeutic exercises for better healing outcomes. Importantly, the model results demonstrate that therapeutic grip exercises induced dynamic loading could produce a better biomechanical microenvironment for healing without compromising the mechanical stability of the overall volar locking plate fixation construct.

Analysis of the Quasi-Static and Dynamic Fracture of the Silica Refractory Using the Mesoscale Discrete Element Modelling.

Computer modelling is a key tool in the optimisation and development of ceramic refractories utilised as insulation in high-temperature industrial furnaces and reactors. The paper is devoted to the mesoscale computer modelling of silica refractories using the method of homogeneously deformable discrete elements. Approaches to determine the local mechanical properties of the constituents from the global experimental failure parameters and respective crack trajectories are considered. Simulations of the uniaxial compressive and tensile failure in a wide range of quasi-static and dynamic loading rates (102 s−1) are performed. The upper limit of the dynamic loading rates corresponds to the most severe loading rates during the scrap loading on the refractory lining. The dependence of the strength, fracture energy, and brittleness at failure on the loading rate is analysed. The model illustrates that an increase in the loading rate is accompanied by a significant change in the mechanical response of the refractory, including a decrease in the brittleness at failure, a more dispersed failure process, and a higher fraction of the large grain failure. The variation of the grain–matrix interface’s strength has a higher impact on the static compressive than on the static tensile properties of the material, while the material’s dynamic tensile properties are more sensitive to the interface strength than the dynamic compressive properties.

Sagittal plane moment responses of the THOR-05F anthropomorphic test device

Objective Anthropomorphic test devices (ATD) are used in crashworthiness studies to advance safety in automotive, military, aviation, and other environments. The Test Device for Human Occupant Restraint (THOR) is an advancement over the widely used Hybrid III ATD. The female version THOR-05F is different from the male as it is not a scaled-down version of the male, and it is based on the recognition that the cervical spines (necks) of females have a different response than males. The objective of this study is to evaluate its response at dynamic rates of loading and compare it with previous postmortem human surrogate (PMHS) responses under sagittal plane bending. Methods The head/neck assembly was separated from the thorax, and a lower neck plate was attached to the head/neck assembly to mount the preparation to the frame of an electro-hydraulic testing device. A custom upper neck interface plate was attached to a novel angular displacement test device that converted the linear motion of the vertical electrohydraulic piston to moment loading at the occipital condyle joint. The neck was preconditioned by applying a sinusoidal 10-degree flexion-extension cycle for 90 s and then three repeat dynamic tests at a target rate of 90 Nm/s. Flexion and extension tests were performed with and without the front and rear neck cables of the THOR-05F neck. Targets were fixed to the upper neck adapter plate, occipital condyle joint, mid-spine aluminum puck, and lower neck adapter plate. The targets’ three-dimensional positions were measured using a seven-camera optical motion capture system. Upper neck load cell and occipital condyle potentiometer data were sampled at 20 kHz, and loading rates were determined by calculating the sagittal moment slope between 15% and 85% of the signal. Results The mean occipital condyle angle versus sagittal moment response from the 12 tests (three tests each with and without cables and under flexion and extension) are given in the body of the manuscript. With and without cables, the loading rates for flexion tests were 89.3 ± 0.5 Nm/s and 86.3 ± 0.4 Nm/s, and for extension tests they were 90.8 ± 1.2 Nm/s and 88.0 ± 1.5 Nm/s. The average peak sagittal moments were 34.2 ± 0.3 Nm and 30.3 ± 0.2 Nm for flexion and 50.6 ± 0.3 Nm and 47.0 ± 0.3 Nm for extension tests. The mean peak occipital condyle angles were 23.5 ± 0.2 deg and 25.3 ± 0.1 deg for flexion and 22.7 ± 0.2 deg and 25.8 ± 0.1 deg for extension. Conclusion Using the angular motion as a basis and comparing it with the previously conducted PMHS tests, the THOR-05F neck has approximately twice the stiffness of the human under sagittal plane bending.

Influence of adhesive spew geometry and load eccentricity angle on metal-composite bonded joints tested at quasi-static and dynamic loading rates

Joining techniques for multi-material structures are critical for increased use of lightweight materials in the automotive industry. This paper investigates the combined effect of spew geometry and load eccentricity angle on the mechanical performance of bonded single-lap joints (SLJ), employing carbon-fibre thermoplastic composite and aluminium adherends. Spew geometries – half-rounded and flat, and eccentricity angles – 0.48°, 0.62°, 0.78°, and 0.91°, considered here, are relevant to typical joints in thin-walled automotive structures. Of the geometries investigated, in the first the excess adhesive was allowed to take its “natural” half-rounded shape, while the second involved a simple additional step, suitable for high-volume production. Moreover, considering the use of dissimilar adherends and crash-durable epoxy adhesives, and limited accessibility to both adherend free ends in practical joints, the flat-spew geometry was formed at the free end of the composite adherend, resulting in SLJs with asymmetrical spew geometries. The SLJs were tested at dynamic crash loading rates (0.5 m/s and 3 m/s) as well as in-service quasi-static loading rates. The load eccentricity was found to significantly affect the half-rounded spew joint performance, particularly at the dynamic loading rates. The asymmetric spew shape significantly minimised the detrimental eccentricity effects, at all loading rates. The SLJs with flat-spew shows 92%−120% higher energy absorption under dynamic loading, relative to half-rounded spew joints. The joint deformation mechanisms and post-failure surfaces are examined. Further, finite element analysis was performed to understand the influence of the investigated spew geometries on the adhesive stress distribution. The proposed flat spew geometry achieved the lowest peel stresses and the highest shear to peel stress ratio, in addition to having low sensitivity to changes in geometry.

Development of a 3-D Dynamic Fracture Process Analysis code to Simulate Intermediate Loading Rate

For the stimulation solutions for oil and gas wells, the creation of multiple fractures that extend deep into surrounding rock formation is important to improve productivity or injectivity. For this purpose, the application of “not too slow but not too fast dynamic loading rate (hereafter intermediate dynamic loading rate)” has been proposed in the literature, which utilizes solid propellants. While previous researchers have experimentally demonstrated their applicability, our understanding of the detailed mechanism of rock fracturing for such an intermediate dynamic loading rate has not been mature enough. We have self-developed a state-of-the-art 3D combined finite-discrete element simulator that can model the complex dynamic fracture process of rocks. This paper applied the developed code to investigate its applicability to this class of problem characterized by the intermediate dynamic loading rate. NRC (new rock cracker) based on the water vaporized pressure due to the thermit reaction of the non-explosive ingredients was used. Based on the measured pressure as an input to the developed code, the 3D dynamic fracture process analysis (DFPA) was conducted. The involving dynamic fracture process and resultant fracture pattern were discussed. In addition, the required future tasks for more reasonable numerical simulation were also pointed out.

Mechanical Properties of Roof Rocks under Superimposed Static and Dynamic Loads with Medium Strain Rates in Coal Mines

Roof rocks in coal mines are subjected to the combination of in situ stresses and dynamic stresses induced by mining activities. Understanding the mechanical properties of roof rocks under static and dynamic loads at medium strain rates is of great significance to revealing the mechanism of rock bursts. In this study, we employ the digital image correlation (DIC) technique to investigate the energy concentration and dissipation behaviors, failure mode, and deformation characteristics of roof rocks under combined static and dynamic loads. Our results show that both the static pre-stress and dynamic loading rate have significant effects on the uniaxial compressive strength of rock specimens. From the energy principle, when the static pre-stress is the same, both elastic strain energy density and dissipated energy density increase with increasing dynamic loading rate. The hazard of rock bursts increases with decreasing static pre-stress and increasing dynamic loading rate. At higher dynamic loading rates, more cracks are generated, and the failure becomes more violent. The crack initiation, propagation and coalescence processes are identified, and the failure mode is closely related to the evolution of the global principal strain field of the rock specimens.

Influence of Adhesion Properties on the Crash Behavior of Steel/Polymer/Steel Sandwich Crashboxes: An Experimental Study

The energy absorption behavior of crashboxes made of steel/polymer/steel (SPS) sandwich sheets can be influenced by numerous parameters, such as the materials used, their thicknesses and stacking, and the adhesion properties between their layers. Therefore, in the present study, the impact of steel/polymer adhesion quality on the occurring failure modes of the crashboxes and the resulting energy absorptions are experimentally analyzed. For this purpose, axial crushing and three-point bending tests on double-hat and top-hat crash boxes were performed, respectively. Three levels of adhesion quality are investigated: none, weak, and strong adhesion strengths. Additionally, the structural crash properties, such as energy absorption and maximal intrusion, are determined and analyzed at both of the quasi-static and highly dynamic loading rates. The results of these investigations show that the adhesion strengths chosen here significantly influence both the failure modes and the energy absorption values. In particular, the structural parameters, in the case of no adhesion, are at most half of those in the case of strong adhesion. However, it is also shown that, in the case of weak adhesion, the structural characteristics are slightly reduced. Based on these results, the possibility to adjust the adhesion strength—globally and/or locally—could be used in future activities to purposefully tailor the failure behavior of hybrid crashboxes.

Stochastically homogenized peridynamic model for dynamic fracture analysis of concrete

Dynamic compact tension tests in concrete are investigated using an intermediately-homogenized peridynamic (IH-PD) model, and the results are compared with a fully-homogenized peridynamic (FH-PD) model as well as with experimental data from the literature. In the IH-PD model, concrete is considered as a two-phase material composed of aggregate and mortar, partially homogenized via a stochastic procedure. Both the FH and IH-PD models capture well the experimentally measured reaction-force time-evolution and crack paths for a wide range of dynamic loading rates, without the need for an explicit representation of microstructure geometry of the concrete material or of rate-dependent parameters. The IH-PD model is more accurate than the FH-PD in reproducing the peak loads and produces crack path tortuosity and randomness, similar to what is observed experimentally. These benefits come from the preservation of some micro-scale heterogeneity, stochastically generated to match the concrete’s aggregate volume fraction. We also find that it matters where one measures the reaction force when trying to connect it to fracture and damage progression in the sample: only when measured on the dynamically loaded side of the pre-notch are features in the reaction-force profile matching critical moments like crack initiation, crack branching, and sample final failure. These results provide guidance for future experiments seeking best placement of damage detection sensors and using elastic wave signal analysis in structural health-monitoring of concrete structures.

Effect of strain rate on strength and deformation behavior of an Fe-Mn-Al-Ni shape memory alloy

The strength and deformation behavior of an Fe-Mn-Al-Ni shape memory alloy at different strain rates was studied. Furthermore, the effect of grain size was investigated. To this end, a batch with bamboo-like grain arrangement and a batch with smaller, nevertheless coarse, grains were analyzed. Tensile tests at quasi-static, intermediate, and dynamic loading rates were performed. Digital image correlation and microstructural analysis revealed the localized deformation and phase transformation in favorable oriented grains. At higher strain rates, a increased number of orientations was activated for the phase transformation. A higher strain rate resulted in an increased strength for the coarse-grained material while the bamboo-like material did not show this effect. The analysis of fracture surfaces revealed ductile fracture and cleavage fracture for all strain rates.

Dynamic Compression–Shear Response and Failure Criterion of Rocks with Hydrostatic Confining Pressure: An Experimental Investigation

Rocks in the deep underground are likely subjected to both hydrostatic confining pressure and dynamic compression–shear load. Thus, accurately characterizing the dynamic properties and failure mechanism of hydrostatically confined rocks under combined compression–shear impacting is crucial for the stability assessment of deep underground rock structures. In this study, on the basis of an improved split Hopkinson pressure bar (SHPB) apparatus, the combined dynamic compression–shear tests are performed on inclined cylindrical sandstone specimens with hydrostatic confining pressures. During the test, the dynamic force balance of rock specimens can be well satisfied using the pulse shaping technique. Our results show that the hydrostatic confining pressure and dynamic loading rate help strengthen the load-carrying capacity of rocks. In contrast, the shear component in the dynamic load limits the dynamic peak stress of rocks. As hydrostatic confining pressure increases, the failure surface based on the Drucker–Prager criterion gradually expands outward. Under dynamic loading, the compressive deformation modulus of rocks decreases with increasing shear component in the dynamic load, contrary to its response to hydrostatic confining pressure. Fragmentation analysis indicates that the hydrostatic confining pressure and the shear component of dynamic loading restrict the fracture behavior of rocks. Besides, as the specimen inclination angle and the hydrostatic confining pressure increase, the failure pattern of rock specimens changes from the tensile-dominated failure with a truncated conical surface to the shear-dominated failure with a single shear plane along its short diagonal.

Field-scale anaerobic baffled reactor for domestic wastewater treatment: effect of dynamic operating conditions

Abstract A 45 m3/d field-scale anaerobic baffled reactor (ABR) was studied for its performance to remove carbonaceous organic content and suspended solids under a dynamic hydraulic loading rate (HLR) and organic loading rate (OLR). Sludge granulation effect was also assessed with and without sand as a bio-carrier aided with poly aluminium chloride. ABR was subjected to a significant variation in HLR (0.26 to 7.72 m3/m2.d) and OLR (0.03 to 8 kg COD/m3.d). Tracer study showed flow-through time was 50% of theoretical hydraulic retention time. The initial compartments of ABR were more effective for the removal of organic carbon. An overall CODTotal removal of 60 to 90% was possible for OLR in the range 1 to 8 kg COD/m3.d irrespective of low/high HLR. OLR dominated the performance of ABR compared to HLR. The compartmentalized nature of ABR was visualized through a two-phase system of anaerobic digestion as alkalinity increased while VFA decreased from the first to last compartment even under dynamic conditions. Sludge granulation with sand and PAC increased the size of granule from 629 to 1,471 μm, decreased sludge depth by 20% and enhanced CODTotal removal within a month. ABR is sturdy to sustain low/high HLR with low/high OLR conditions without impairing CODTotal removal efficiency significantly.

Calculating changes in fractal dimension of surface cracks to quantify how the dynamic loading rate affects rock failure in deep mining

The split-Hopkinson pressure bar (SHPB) and digital image correlation (DIC) techniques are combined to analyze the dynamic compressive failure process of coal samples, and the box fractal dimension is used to quantitatively analyze the dynamic changes in the coal sample cracks under impact load conditions with different loading rates. The experimental results show that the fractal dimension can quantitatively describe the evolution process of coal fractures under dynamic load. During the dynamic compression process, the evolution of the coal sample cracks presents distinct stages. In the crack propagation stage, the fractal dimension increases rapidly with the progress of loading, and in the crack widening stage, the fractal dimension increases slowly with the progress of loading. The initiation of the crack propagation phase of the coal samples gradually occurs more quickly with increasing loading rate; the initial cracks appear earlier. At the same loading time point, when the loading rate is greater, the fractal dimension of the cracks observed in the coal sample is greater.

The transient intrusion effect of high energy fluid on the rock failure around the wellbore during the dynamic stimulation process

Dynamic wellbore stimulation technologies, such as high-energy gas fracturing, electrical pulse fracturing, hydraulic pulsation fracturing, are generally designed to multi-fracture the near-wellbore region through generating high energy pulse with intermediate or high loading rate. During the stimulating process, the dynamic strength and failure mode of saturated rocks around the wellbore can be largely affected by the transient intrusion of high energy fluid. Accordingly, an experimental method was developed to provide a method to apply the tailored pulse loading in the central borehole of the cylindrical rock samples. Three groups (Saturated + Center hole exposed (S-CHE), Saturated + Center hole wall isolated (S-CHI), Dry + Center hole wall isolated (D-CHI)) tests were carried out. The borehole fluid pressure-time curves and the failure modes of rock samples were tracked, analyzed and compared for all of the experiments. Experimental results demonstrate that: The relationship between rock dynamic strength and loading rate is monotonic direct proportionality. The dynamic strength of saturated rock shows a much stronger strain rate dependence than that of the dry rock. At the same loading rate, fluid penetration can largely weaken the dynamic strength of rock samples. The stress pulse generates a complex crushed zone around the wellbore, while the fluid penetration tends to produce radial multi-fractures. These phenomenons were explained using the micromechanics-based macroscopic damage theory, which is capable of obtaining the relationship between the fluid intrusion and the fracture deformation in the rock dynamic failure process.

Experimental study on dynamic mechanical responses of coal specimens under the combined dynamic-static loading

Dynamic mechanical responses of the coal and rock mass under the combined dynamic-static loading are critical issues for exploring the disaster-causing mechanism of rock burst in coal mining. In this paper, the acoustic emission (AE) technique and high-speed camera imaging were employed, and the burst proneness of the coal specimen, the variation of AE parameters, the specimen failure mode, and the particle distribution of the fractured specimens were investigated by the combined dynamic-static loading experiments. The results indicate that the burst proneness of the coal specimen increases non-linearly as the dynamic loading rate increases. Both the energy input rate, the ringdown counts, and the hits undergo the slow increase, fast increase, and abrupt increase stages. The failure mode of the specimen is changed from shear failure to axial splitting and the final bursting failure. The relationships between the fractal dimension of the specimen fragmentation mass and the dynamic loading rate can be described by a quadratic function. When the specimen reaches the maximum damage degree, an extreme value of the dynamic loading rate (2.8 × 10−3 s−1) is obtained in experiments. The disaster-causing mechanism of rock burst induced by the combined dynamic-static load is discussed from the aspects of the burst proneness of coal specimens, dynamic variation of AE parameters, the change of failure modes of specimens, and the propagation and coalescence of microcracks.

Quasi-static and dynamic response of GFRP and BFRP bars under compression

The application of fiber-reinforced polymers (FRP) bars in the building industry has grown intensively over the years, due to their numerous advantages such as corrosion resistance. However, current guidelines in design codes disregard the contribution of FRP bars in compression. The need of investigation of compressive mechanical properties of FRP bars is important, while there is a lack of experimental tests under varying dynamic and quasi-static loading rates. The present paper aims to evaluate the compressive strength and failure modes of glass and basalt fiber-reinforced polymer (GFRP and BFRP) bars. A series of quasi-static and dynamic tests were performed on different FRP bar sizes. Dynamic tests were conducted using the drop hammer procedure and different loading rates were achieved through varying the weight of mass and height of fall. Results showed that GFRP bars attained higher compressive strengths than BFRP bars for the same loading conditions. GFRP bars exhibited compressive strength in the range of 300 MPa to 600 MPa while the maximum compressive strength of BFRP bars was 470 MPa. The increase in the bar diameter resulted in an increase in the compressive strength of most FRP bars. However, Some FRP bars showed different variation in their compressive strengths at high loading rates. Finite element (FE) models were also developed to simulate the FRP bars under dynamic tests by considering the orthotopic material nature of the FRP composites. The FE models were verified with the experiments and successfully described qualitatively the trends observed during the full-scale drop-hammer tests.

Quasi-static and dynamic performance of novel interlocked hybrid metal-composite joints

This study presents a novel hybrid technique for joining composites to metal, employing an array of macro-scale interlocking features on the faying surfaces of adhesively bonded adherends. Single-lap, interlocking adhesive joints (IAJs) and baseline adhesive joints (BAJs), are tested at quasi-static and transient dynamic (0.5 m/s and 3 m/s) loading rates. The joint deformation mechanisms are examined and fractography analysis is performed at the macro and micro scales. Results indicate a 10% increase in lap-shear strength, and 75–120% increase in work to failure for the IAJs compared to the BAJs, at all loading rates. In addition, IAJs exhibit improved damage tolerance compared to adhesive joints, due to reduced joint rotation, more stable adhesive fracture growth, and the ability to sustain load even after cracks have propagated through the adhesive at the ends of the overlap region. The high energy absorption capacity (23–38 J) of IAJs indicates they could be used to significantly improve the crashworthiness performance of multi-material transportation structures.

Effect of liquid rubber modification on the bond behavior of externally bonded FRP laminate-concrete interface under dynamic loading

Interfacial debonding between fiber-reinforced polymer (FRP) laminate and concrete substrate is one of the critical issues in the externally bonded FRP strengthened concrete members. Existing studies have shown that the addition of liquid rubber into the bonding adhesives can increase debonding resistance of FRP laminate-concrete interface and consequently improve the comprehensive performance of FRP strengthened concrete members under quasi-static loading. The purpose of this study is to clarify the effect of liquid rubber modification on the bond behavior of FRP laminate-concrete interface under dynamic loading. Six groups of double-lap shear specimens with neat or rubber-modified epoxy were tested under static and two dynamic loading rates. The parameters of peak load, FRP strain distribution and interfacial bond stress-slip relationship are analyzed. Test results indicate that the liquid rubber modification can significantly improve the bond capacity of FRP laminate-concrete interface under dynamic loading. Further, the influence mechanism of liquid rubber modification on the dynamic bond behavior of FRP laminate-concrete interface is discussed. Finally, an empirical dynamic bond stress-slip model considering the effect of liquid rubber modification is proposed and validated.

The effect of loading direction on the fracture behaviors of cortical bone at a dynamic loading rate

In this study, the dynamic cracking processes in porcine cortical bone were visualized in real-time using the high-speed synchrotron X-ray phase-contrast imaging (PCI) technique in three osteon orientations: in-plane transverse, out-of-plane transverse and in-plane longitudinal. The dynamic flexural loading applied on the pre-notched bone specimens was introduced by a modified Kolsky compression bar. High-speed X-ray images of the entire loading events were documented with a high-speed camera. Three-dimensional X-ray micro-computed tomography was conducted to examine the intact microstructures and obtain the basic material properties of the bone material used for mechanical characterizations. The onset location, where crack initiated, and the subsequent direction, along which the incipient crack propagated, were measured quantitatively using the high-speed X-ray images and the latter was found dependent on the osteon direction significantly. The crack propagation velocities were dependent on crack extension over the entire crack path significantly for all the three directions while the initial velocity for in-plane longitudinal direction was lower than the other two directions. Straight-through crack paths were observed for in-plane longitudinal specimens while the cracks were deflected and twisted in the in-plane transverse direction. For out-of-plane transverse direction, the cracks follow paths with tortuosity fall in between the other two directions, showing a mixed mode of fractures of the former two extreme cases. The toughening mechanisms, visualized by the high-speed X-ray images, and the corresponding fracture toughness, evaluated in terms of fracture initiation toughness and crack growth resistance curve (R-curve), were also found significantly different among the three osteon directions, suggesting an overall transition from brittle to ductile-like fracture behaviors at the dynamic displacement rate (5.4 m/s) as the osteon orientation varies from in-plane longitudinal to out-of-plane transverse, and to in-plane transverse eventually.

Low temperature effects on the mechanical, fracture, and dynamic behavior of carbon and E-glass epoxy laminates

An experimental investigation through which the effects of low temperatures on the mechanical, fracture, impact, and dynamic properties of carbon- and E-glass-epoxy composite materials has been conducted. The objective of the study is to quantify the influence of temperatures from 20 °C down to −2 °C on the in-plane (tensile/compressive) and shear material properties, static and dynamic Mode-I fracture characteristics, impact/residual strength, and the storage and loss moduli for the materials considered. The low end of the temperature range considered in the study is associated with Arctic seawater as well as conditions found at extreme ocean depths (2 °C–4 °C). In the investigation, both carbon/epoxy and E-glass/epoxy laminates are evaluated as these materials are of keen interest to the marine and undersea vehicle community. The mechanical characterization of the laminates consists of controlled tension, compression, and short beam shear testing. The Mode-I fracture performance is quantified under both quasi-static and highly dynamic loading rates with additional flexure after impact strength characterization conducted through the use of a drop tower facility. Finally, dynamic mechanical analysis (DMA) testing has been completed on each material to measure the storage and loss moduli of the carbon fiber- and E-glass fiber reinforced composites. The findings of the study show that nearly all characteristics of the mechanical performance of the laminates are both material and temperature dependent.

Damage Evolution During Rock Pulverization Induced by Dynamic Compressive Loading

AbstractRock pulverization is a geological process in which fault zone rocks are shattered in situ, into fine grains much smaller than the original grain size, without significant shear strain. Investigations regarding the genesis of pulverized fault zone rock (PFZR) suggested that it is a coseismic phenomenon and may be closely associated with supershear earthquakes. The observation of dynamic damage evolution is thus significant for understanding the rock pulverization mechanism due to dynamic compressive load. In this study, the damage evolution of Laurentian granite under dynamic compression loading is studied by using the strain control technique in a split Hopkinson pressure bar system. Dynamic compression experiments are performed under different maximum strain levels and different loading rates. Tested specimens are recovered for postmortem examination with X‐ray micro‐computed tomography and microscopic observation. 3‐D microcrack networks due to different dynamic loading rates are examined, and the evolution of the crack volume and crack number at various loading rates are analyzed. The results reveal that the pulverization process during dynamic compression loading is categorized into three stages. Both a high loading rate and a sufficient strain are necessary for the rock pulverization to occur. The main features of fractures during rock pulverization are discussed, and the total dissipated energy for dynamic fracture and pulverization is quantified.