Constant Loading Rate Research Articles

A new nanoindentation approach for determining both indentation size effect and continuous apparent activation volume during loading of nanocrystalline Ni and Ni-20 wt.% Fe alloy

A new nanoindentation approach is developed in this study to determine both indentation size effect (ISE) and continuous apparent activation volume () during loading of nanocrystalline nickel (NC Ni) and nanocrystalline nickel-20 wt.% iron alloy (NC Ni-Fe alloy). This approach involves conducting nanoindentation tests under loading modes controlled by both constant strain rate (CSR) and constant loading rate (CLR). Firstly, a new empirical expression for the parameter in the modified Nix-Gao model is established to study the strain rate dependence of the ISEs created in the CSR and CLR tests. Then, continuous data of each individual sample (indentation) during loading are obtained in the CLR test through the alternative use of continuous stiffness measurement technique. The stress dependence of is analyzed based on Duhamel et al.’s model, which considers the role of vacancies generated during inhomogeneous dislocation nucleation. Finally, based on the above experimental and theoretical work as well as transmission electron microscopy observation, the influences of loading mode, loading rate, and material properties (stacking fault energy) on resulting intrinsic hardness of NC Ni and NC Ni-Fe alloy are analyzed. The nanoindentation approach developed in this study provides profound insights into the mechanical behaviors during loading and underlying mechanisms of materials.

Microbial Selection for the Densification of Activated Sludge Treating Variable and High-Strength Industrial Wastewater

This study investigates the densification/granulation of activated sludge with poor settleability, treating real industrial wastewater from a tank truck cleaning company. The wastewater is low in nutrients, acidic in nature, and high and variable in chemical oxygen demand (COD, ranging from 2770 mg·L−1 to 14,050 mg·L−1). A microbial selection strategy was applied to promote slow-growing glycogen-accumulating microorganisms (GAO) by the implementation of an anaerobic feast/aerobic famine strategy in a sequencing batch reactor (SBR). After 60 to 70 days, the uptake of carbon during the anaerobic phase exceeded 80%, the sludge morphology improved, and the sludge volume index (SVI) dropped below 50 mL·g−1. 16S rRNA gene sequencing showed the enrichment of the GAOs Defluviicoccus and Candidatus Competibacter. Stable sludge densification was maintained when using a constant organic loading rate (OLR) of 0.85 ± 0.05 gCOD·(L·d)−1, but the sludge quality deteriorated when switching to a variable OLR. In view of the integration of densified/granular sludge in a membrane bioreactor configuration, the filtration properties of the densified SBR sludge were compared to the seed sludge from the full-scale plant. The densified sludge showed a significantly lower resistance due to pore blockage and a significantly higher sustainable flux (45 vs. 15 L·(m2·h)−1).

Damage Evolution and Fractal Characteristics of Granite under the Influence of Temperature and Loading

To study the damage characteristics and evolution law of granite under the influence of temperature and loading rate, uniaxial compression tests at different loading rates were performed for granite samples at 30 °C, 40 °C, 60 °C, and 80 °C. The damage characteristics and evolution law of granite were studied in conjunction with acoustic emission ringing, acoustic emission b values, acoustic emission signaling constellations, and fractal dimensions. The results showed the following: (1) At a low loading rate (0.005 mm/s), the peak stress of the granite increases gradually as the temperature increases. At high loading rates (0.01 mm/s and 0.02 mm/s), the peak stress of the granite first decreases, then increases as the temperature increases. The elastic modulus at different loading rates decreases first, then increases as the temperature increases. The elastic modulus of the granite is the lowest at 40 °C; (2) At the same temperature, specimens subjected to higher loading rates exhibit accelerated internal damage progression, with a precipitous decrease in the b-value occurring earlier. At a loading rate of 0.005 mm/s, the total number of acoustic emission ring-down events is at least 1.7 times greater than that at other loading rates, indicating a more complex development of internal cracks in the granite specimens. Moreover, as the temperature increases under a constant loading rate, the concentration of acoustic emission ring-downs intensifies during the unstable crack development and failure phases, accompanied by progressively larger fluctuations in the b-value; (3) Under the same temperature conditions, the acoustic emission signals in the specimens loaded at 0.005 mm/s and 0.01 mm/s propagate from one end to the other. At 0.02 mm/s, emissions appear simultaneously at both ends of the specimen and converge toward the center. The proportion of damage and energy associated with compression differs with temperature; at 30 °C and 40 °C, damage and energy are concentrated in the early phase of compression, whereas at 60 °C and 80 °C, they are more significant during the later stages; and (4) The fractal dimension of the granite specimens generally decreases, then undergoes a phase of fluctuating growth, followed by a decline. With increasing loading rates at a constant temperature, the compaction of the granite specimens decreases; the orderliness of the crack patterns gradually increases. As the temperature increases, the distribution of cracks during the compaction and failure phases becomes more orderly. During the crack initiation and development phases, the dispersion of cracks and the formation of crack networks are more pronounced. These findings provide a theoretical reference for understanding the microscale damage and failure mechanisms of granite under varying loading rates and temperatures.

Experimental investigation of out-of-plane behaviour of unreinforced masonry panels strengthened with TRM

This study addresses the out-of-plane collapse mechanism occurring in medium-sized masonry panels frequently encountered during earthquakes. First of all, a total of nineteen masonry panels with dimensions of 100 mm × 410 mm x 1200 mm were produced. In the production of the masonry panels, solid brick unit with dimensions of 50 mm × 100 mm x 200 mm, and high strength repair mortar were used. Eighteen specimens were strengthened with textile-reinforced mortar (TRM), and one was selected as an unstrengthened reference specimen. Type of textile material (basalt, glass, and carbon), number of strips (1, 2, and full wrap), and anchorage effect were selected as variables. The specimens were subjected to a statically bending three-point test at a constant loading rate. Load and displacement measurements were taken at the instant of the experiment. Employing these data, ultimate load-carrying capacity, displacement at the ultimate load, and stiffness values were obtained accordingly. Additionally, the energy dissipation capacity values of the specimens were also calculated. From the main findings of this study, it has been revealed that strengthening masonry panels with textile-reinforced mortar is efficacious against the out-of-plane collapse mechanism.

Impact of strain rate on the Indentation Size Effect: Evidence of an intimate link between Size effect, Strain Rate and Ductility in Soda-lime Silica glass

Many glasses exhibit the so-called indentation size effect (ISE), where the indentation hardness decreases with the maximum applied force. Here, we seek to uncover the connection between the ISE and strain rate in soda-lime silica (SLS) glass using micro-indentation. Two different loading protocols: constant loading rate (CLR), resulting in a nonlinear strain rate through the depth of indent, and a non-linear loading rate that gives a constant strain rate (CSR) with depth, are used to determine Hardness for six different strain rates and seven peak forces. A modified Bernhardt size effect law is then used to determine the extent of the ISE and load-independent hardness. We show that a small increase in micro-ductility, which can be achieved by either switching from a CLR to CSR protocol or by increasing the applied rates, can greatly reduce the extent of the ISE and slightly reduce the load-independent hardness.

Application of Mechano-Luminescence-Optoelectronic Composites for Delamination Detection in Fiber Reinforced Polymer Composites

Abstract Fiber reinforced polymer (FRP) composites have attracted significant attention from the aerospace industry in recent years. FRP composites have the advantage of being light weight, high strength and resistant to corrosion making them an attractive option for various applications in the aerospace industry. However, FRP composites are prone to delamination which can eventually compromise structural integrity leading to sudden failure. An effective damage detection methodology is therefore necessary to monitor delamination in structures. In this study, mechano-luminescence-optoelectronic (MLO) composites were integrated with FRP composites to create MLO-FRP test coupons for delamination detection. The MLO composites were prepared by coupling a Poly(3-hexylthiophene) (P3HT)-based sensor with a copper dopped zinc sulfide (ZnS:Cu) composite. MLO composites were attached to the surface of FRP composites to create MLO-FRP test coupons. The MLO-FRP test coupon was mounted on a 3-point bending load frame and subjected to cyclic loading and unloadings at various displacements with the first displacement starting from zero to 5 mm. The second displacement starting from zero to 6 mm and so on. A direct current (DC) voltage was recorded from the MLO composites at a constant loading rate to validate its DC-based strain sensing capability. Other parameters such as applied load, strain energy release rate and strain were also obtained with the aim of tracking delamination propagation in FRP composites. Results showed MLO composites were sensitive to delamination propagation highlighting their potential to be used in structures for health monitoring.

Incorporation of Disposed Face Mask to Cement Mortar Material: An Insight into the Dynamic Mechanical Properties

Incorporating masks into building materials offers a potential solution to the environmental threat of disposable masks with promising material performance. However, research on their dynamic properties is lacking to further determine the application range of the new composite. This study addresses this gap by shredding face masks into strips and incorporating them into mortars at varying volume ratios. The integrity and compactness of the mortar was measured and characterized by P-wave velocity, while dynamic compression properties were explored using a split Hopkinson pressure bar (SHPB) system. Subsequently, sieve analysis was conducted on the fractured specimens. The results indicate that incorporating masks generally improves the mortar integrity and the fragmentation after impacting. The dynamic uniaxial compression strength (DUCS) decreased for all mixing designs compared to plain ones under a constant loading rate. Meanwhile, the dissipated energy density showed a similar trend to the P-wave velocity, exhibiting less pronounced enhancement at higher loading rates. According to the dynamic characteristics, a dynamic constitutive model based on the Lemaitre principle and Weibull distribution of damage is developed and validated. The test results are further understood through the perspective of the mechanism of mask inclusion.

Theoretical study of the nonlinear force-loading control in single-molecule stretching experiments

Force spectrum measurements with constant loading rates are widely used in single-molecule manipulation experiments to study the mechanical stability and force response of biomolecules. Force-dependent transition rates can be obtained from the transition force distribution, but it is limited to the force range with non-zero force distribution. Although constant loading rate control can be realized with magnetic tweezers, the loading rate range is limited due to the slow movement of permanent magnets. Non-linear exponential and exponential squared force loading functions are more feasible in magnetic tweezers, while there is no theoretical result available for these two kinds of non-linear force loading functions. In this study, we solved the unfolding process of a protein following Bell’s model under nonlinear exponential and exponential squared force loading functions, which offer a broader range of unfolding force distribution compared to the traditional constant loading rate experiments. Furthermore, we derived two force loading functions, which can produce uniform unfolding force distribution. This research contributes fundamental equations for the analysis of experimental data obtained through single-molecule manipulation under nonlinear force loading controls, paving the way for the use of nonlinear force control in magnetic tweezer experiments.

Importance of Water‐Clay Interactions for Fault Slip in Clay‐Rich Rocks

AbstractClay‐rich rocks are integral to subduction zone dynamics and of practical importance, for example, as barriers in nuclear waste and CO2 repositories. While the effects of swelling strain on the self‐sealing capabilities of these rocks are relatively well‐established, the implications of polar fluids interacting with charged clay particles on the frictional behavior, and the role of swelling stress in initiating slip in critically stressed faults, remain ambiguous. To address these uncertainties, we conducted triaxial friction experiments using saw‐cut samples, with the upper half composed of Opalinus claystone (OPA) and the lower half of Berea sandstone (BER). The frictional strength of the non‐wetted OPA‐BER interface was estimated based on experiments at confining pressures of 4–25 MPa and constant axial loading rate (0.1 mm/min). Fluid injection friction experiments were performed using decane (non‐polar fluid) or deionized water (polar fluid) at 10 and 25 MPa confining pressures and constant piston displacement control. Macroscopic mechanical data were complemented by distributed strain sensing on the sample surface. Compared to decane, the frictional strength of the OPA‐BER interface tended to decrease when injecting water, which is attributed to phyllosilicate lubrication and the transition of the OPA from a solid rock to an incohesive mud near the saw‐cut surface. When injecting water, slip was initiated during initial hydration of the OPA‐BER interface, although the apparent stress state was below the yield stress. To explain this behavior, we propose that the swelling stress is a crucial factor that should be integrated into the effective stress model.

Investigating the high-impact deformation behavior of induced-nano precipitation hardened in718 alloy

Superalloys are the preferred materials for modern high-rotational complex components due to their exceptional ability to maintain critical properties such as strength, oxidation/corrosion resistance, even under extreme temperatures and dynamic impacts. This study investigates the dynamic impact response of nanoprecipitation-hardened 718 alloy (NPH-718 alloy) under various loading conditions. The wrought nickel-based NPH-718 alloy was transformed into a nanostructured state through a precise heat treatment process involving controlled cooling rates (28℃∙s‒1 to 30℃∙s‒1). A mechanical compression test, leading to failure, was employed to assess the alloy's ability to withstand dynamic impacts. The compressive dynamic behavior of the alloy at high strain rates (4000 s‒1 to 7500 s‒1) and temperatures ranging from ‒180℃ to 750℃ was evaluated using a custom-built direct impact Hopkinson pressure bar apparatus. The flow data obtained for NPH-718 alloy exhibited sensitivity to thermally activated processes. Consequently, as the temperature increased at a constant high loading rate, both flow stress and adiabatic effect increased. Conversely, at a constant deformation temperature, the flow characteristics exhibited an increase as the loading rate decreased. This study establishes key trends in the flow stress, adiabatic effect, temperature, and the strain rate sensitivities of NPH-718 alloy, offering valuable insights for design and performance evaluation purposes. It underscores the significant influence of temperature and strain rate on the flow behavior of NPH-718 alloy, further solidifying its reliability in demanding applications.

Fabrication and characterization of Sn-57 wt% Bi film by pulse DC current co-electrodeposition and reflow

The electrodeposited Sn-Bi eutectic alloys can satisfy the need for micro-bumps with low melting point in 3D packaging. We deposited Sn-Bi film by pulse DC current in electroplating solutions based on methane sulfonic acid (MSA). The effects of MSA concentrations and pulse frequencies on morphology and composition of deposits were investigated. As the MSA concentration increased from 120 ml/L to 160 ml/L, the hydrogen evolution reaction weakened resulting in smoother deposited surfaces, and the Bi content decreased. In the use of pulses allowing deposits to become more uniform and denser, the Sn-56.73 wt% Bi film with smooth surfaces were fabricated at a pulse frequency of 4 Hz and an MSA concentration of 120 ml/L, of which melting point was 134.35 °C. By using transmission electron microscopy (TEM) and electron backscattered diffraction (EBSD), the structures were characterized more microscopically, which are essential for diffusion and electromigration of micro-bumps. The near-eutectic deposits, both before and after reflowing, consisted of uniformly distributed tetragonal β-Sn phases and hexagonal Bi phases, and the most preferred orientations after reflowing were the same as before reflowing, that were (220)//ND for β-Sn and (1̅012)//ND for Bi. The average grain sizes of Sn and Bi in the deposits after reflowing were 1.44 µm and 0.64 µm, respectively, which were much smaller than those of Sn58Bi alloy obtained by rapid solidification. Dislocations were observed in Sn grains and misorientation values in β-Sn phases were larger, which illustrated that the β-Sn phase carried larger strains. As evaluated by constant loading rate (CLR) nanoindentation tests, the hardness and modulus were significantly improved after reflowing, and creep stress indices of the deposits before and after reflowing were 51.74 and 7.07, respectively.

Uniaxial Compressive Damage Characteristics of Rock-like Materials with Prefabricated Conjugate Cracks

Joined fractures are an important factor affecting natural rock masses’ mechanical and deformation properties. In this paper, indoor uniaxial compression experiments reproduce prefabricated cracks’ generation, extension, and coalescence in rock-like specimens. For the fractured specimens, a single crack with an inclination of α = 45° was placed on the left and right sides, and a third crack with an angle of β = 30°, 45°, 60°, and 90° to the single crack on the right side was placed in groups III–VI, respectively. All cracks extended in the thickness direction. Vertical pressure was applied at a constant loading rate of v = 0.1 mm/min until the stress dropped dramatically. In addition, numerical calculations were performed on the rock specimens using PFC2D, a sub-module of the Discrete Element Method (DEM). The experimental results agree with the numerical simulations in that the strength of the specimens containing a conjugate crack is significantly reduced, and the mechanical and deformation properties of the specimens are related to the internal angle of the conjugate crack, with the lowest peak strength and lowest percentage energy dissipation at β = 45°.

Exploring strain rate variation in the adhesive layer during constant speed mode I fracture tests: Loading speed and test temperature effects

The existing literature primarily explores fracture energy concerning test rate. However, for numerical simulations and bonded joint design, understanding the fracture energy strain rate sensitivity is key, not test speed. Even at a constant speed in fracture tests, adhesive strain rate varies during crack propagation, complicating strain rate sensitivity analysis. The current study aims to comprehend the strain rate sensitivity of the fracture energy, as opposed to the loading rate sensitivity of two different polyurethane adhesives subjected to mode I loading conditions. The study experimentally examines strain rate variations under constant loading rates and investigates how test speed affects the strain rate in mode I fracture tests. The impact of testing temperature on the strain rate is also explored by performing tests at −30 °C and 23 °C. Digital image correlation (DIC) and tracking methods are employed to improve the understanding of strain rate characteristics in these tests. To analyse the effect of loading rate on strain rate, the tests were conducted at different speeds as well. The influence of adhesive thickness on the strain rate was also explored. It was experimentally found that the strain rate at the crack tip varies even at a constant loading rate. The variation in strain rate is mainly evident in tests performed at higher loading rates, where the strain rate range increases. The tests performed at low temperature revealed less variation of strain rate than the ones tested under the same loading rate condition at 23 °C. For the same adhesive, thicker bondlines are less likely to cause a substantial error in fracture energy results than thinner bondlines.

Breakage behavior of corn kernels subjected to repeated loadings

Studying the breakage behavior of corn kernels subjected to repeated compressive events, including at low frequency and low strain rate, are important for the development of breakage models for prediction of kernel breakage in handling and processing machines. The main purpose of this study was to identify the breakage behavior and mechanism of weakening of corn kernels under repeated loadings as affected by their moisture content and kernel thickness. Corn kernels at four moisture content levels (8.20%, 11.95%, 16.00%, 20.02%) and in four thickness ranges were subjected to repeated compressive loading between two parallel steel plates in quasi-static regime at a constant loading rate of 2 mm/min (strain rates from 4.7 × 10−3 to 1.0 × 10−2). Conducted experiments allow to observe the different grain breakage patterns, identify the crack initiation and its development, describe the weakening of kernels by changes in the total specific energy, plastic and elastic deformation energies, and the number of loading cycles to break (breakage probability) the kernels. The results indicate that the breakage models describing the damage and weakening of grains in terms of changes in the total and strain energy or changes in the stiffness can be used for understanding the effect of moisture content and thickness on breakage of corn kernels.

MODELING AND INVESTIGATION OF THE INFLUENCE OF LOADINGMODE ON THE DEFORMATION PROCESS OF ASPHALT CONCRETEMATERIALS

The article considers a problem of calculating the deformations of forward and reversed creep tension of rheonomic materials. The hereditary theory of creep by Yu.N. Rabotnov is used to describe the nonlinear deformation process. Proposed a method for determining the necessary material characteristics from forward and reversed creep data. During the experiments, there were tested two batches of asphalt concrete samples. Also, was shown behavior of asphalt concrete at cyclic increasing and constant loading modes. At a temperature T = 24 °C were tested 10 samples at cyclic increasing loading mode. Cyclic stresses were equal to 0.041; 0.074; 0.111; 0.148; 0.183 MPa and duration period between loading and relax period were chosen to be 570 seconds. At cyclic constant loading were investigated individual samples for the parameters of forward and reversed creep at stresses of 0.041; 0.117. Then, investigated the affect of reloading two reversed creep process of asphalt concrete samples. From first batch of samples were tested 9 samples before destruction with a period 65 seconds: forward creep of samples at for the following 5 seconds; reversed creep at for the following 60 seconds. From the second batch of samples were tested 11 samples of asphalt concrete before destruction with period 70 seconds: forward creep for the following 10 seconds and reversed creep at for the following 60 seconds. Test results showed that the level of return of second batch increased than the first batch of samples. In the work were tested 5 samples of asphalt concrete according to the direct tensile scheme until a complete failure. Test temperature was T=22-24 °C. For each level of loading with constant rate: 0,6519; 0,4678; 0,0580; 0,0489; 0,0055 MPas-1.Using experimental data, were found parameters of the deformation at different constant rate of loading. As a result, all samples fractured brittle at small deformations.

Material point method to simulate the evolution characteristics of loading damage in fractured sandstone

Cracks in rocks can lead to different load responses and mechanical properties. Primary and secondary cracks are altered during loading, with varying degrees of impact on the failure of underground engineering rock masses. However, the precise modeling of fracture initiation and propagation resulting in failure remains challenging, and the macroscopic evolution characteristics of cracks and stress fields have not been accurately described. In this study, a numerical simulation tool based on the material point method (MPM) and a strain softening model were used to establish a plane loading model with different cutting angles. A simulation of the damage evolution of fractured sandstone under constant-rate loading was conducted for different confining pressures and cutting angles. The results show the following. 1) A comparison of the simulation and experimental results indicates that the proposed numerical method accurately simulates the macroscopic crack generation and the complex physical processes of fractured sandstone during loading. 2) The stress concentration area originates from both ends of the crack and extends toward the edge in a diagonal direction until the crack has penetrated the rock. 3) The ranking of the cutting angle based on the sandstone strength is 0° > 90° > 60° > 30°. The cumulative dissipated energy exhibits an inflection point near the peak stress, and the increase after this point is primarily attributed to friction at the crack surface. The damage degree and dissipated energy of the rock in different stages correspond to the rock’s strength.

Experimental evaluation of the thermal effect on dynamic behavior of travertine rock

When an engineering structure regarding a rock is affected by dynamic loads (due to the occurrence of natural hazards, such as earthquakes and landslides, or man-made hazards, such as explosions or impacts), correct prediction of changes in the strength behavior and deformability of the rock relative to its static state is necessary for reducing the damages and costs. On the other hand, rocks are always influenced by environmental conditions, such as temperature changes due to fire and weather during their lifetime, which should be considered when using them. In these cases, the mechanical behavior of the rock can usually be determined under different loading and environmental conditions using stress–strain curves. This study investigates rocks’ dynamic strength and deformability behavior at different loading rates and temperatures. For this purpose, 30 travertine rock samples from the Torshab mine, located in the Markazi province of Iran, were first heated up to 100°C, 200°C, 400°C, 800°C, and 1000°C (six temperatures), and then subjected under the impact pressure with different loading rates from (five) 11 m/s to 15 m/s using the split Hopkinson pressure bar test. Comparing the obtained dynamic stress–strain curve shows that at a constant loading rate, increasing the temperature, especially at higher temperatures, reduces the dynamic strength and increases the rock’s deformability. Moreover, in all cases, at a constant temperature, increasing the loading rate, especially at higher rates, increases the rock’s dynamic strength and deformability.

Measurement of Creep Stress Exponent of TC17 Titanium Alloy by Nanoindentation Method at Room Temperature.

The creep stress exponent is commonly employed to characterize the deformation mechanism during the steady-state creep stage, serving as an indicator of creep behavior. The creep phenomenon of high melting point metallic materials is not obvious at room temperature. However, the nanoindentation method proves suitable for investigating the creep properties of metallic materials under such conditions. Consequently, this paper places emphasis on measuring the creep stress exponent of TC17 titanium alloy at room temperature using the load preservation stage of the nanoindentation method with a constant loading rate. In order to investigate the effects of loading rate and maximum load on the experimental results, different loading rates were applied to the diamond Berkovich indenter to reach different maximum loads. The indenter was held under the maximum load for a duration of 360 s, and the relationship between the indentation strain rate and indentation stress during the holding process was used to obtain the creep stress exponent of the material at room temperature. The findings indicate that within the loading rate range of 1.25 to 15 mN/s and maximum load range of 50 to 300 mN, the influence on the experimental results is insignificant. Ultimately, the distribution range of the creep stress exponent for TC17 titanium alloy at room temperature was measured to be 8.524-8.687.

Mechanoluminescence of (Eu, Ho)-doped oxynitride glass-ceramics from the BaO-SiO2-Si3N4 chemical system

Mechanoluminescence is observed in oxynitride glass-ceramics from the BaO-SiO2-Si3N4 chemical system, doped with Eu and Ho. Light emission was investigated by means of uniaxial compression experiments on disks and parallelepipedic bars with constant loading rates ranging from 0.3 to 300 MPa s−1 up to about 500 MPa. In agreement with previous reports on SrAl2O4-based materials [Dubernet et al., Appl. Phys. Lett. 107, 151906 (2015) and Dubernet et al., Sci. Rep. 10, 19495 (2020)], the mechanoluminescence intensity is found proportional to the mechanical power. Nevertheless, in contrast with SrAl2O4, no gain in the intensity is observed at the onset of the unloading stage, but a drop of the photoluminescence intensity during unloading. This stems from different electron trapping populations and associated energy levels for the Ba4Si6O16 phase (the dominant crystallized phase in the present glass-ceramics), which are discussed in light of density functional theory calculations.

Analysis on the turning point of dynamic in-plane compressive strength for a plain weave composite

Experimental investigations on dynamic in-plane compressive behavior of a plain weave composite were performed using the split Hopkinson pressure bar. A quantitative criterion for calculating the constant strain rate of composites was established. Then the upper limit of strain rate, restricted by stress equilibrium and constant loading rate, was rationally estimated and confirmed by tests. Within the achievable range of 0.001/s–895/s, it was found that the strength increased first and subsequently decreased as the strain rate increased. This feature was also reflected by the turning point (579/s) of the bilinear model for strength prediction. The transition in failure mechanism, from local opening damage to completely splitting destruction, was mainly responsible for such strain rate effects. And three major failure modes were summarized under microscopic observations: fiber fracture, inter-fiber fracture, and interface delamination. Finally, by introducing a nonlinear damage variable, a simplified ZWT model was developed to characterize the dynamic mechanical response. Excellent agreement was shown between the experimental and simulated results.