Static Compression Research Articles

Study on static performance and dynamic characteristics of a spoke cable-truss suspen-dome system

The proposed spoke cable-truss suspen-dome structure is a new structure system based on the traditional chord-supported dome structure. In this structure, the upper lattice shell is modified to a radial cable-truss structure. The lower part of the structure is a cable network structure composed of radial cables, ring cables and radial cables. There are few research results on the mechanical properties of the new structure, so a 1:10 scale model is established, multi-condition static loading test, local cable force failure test and natural vibration characteristic test are carried out, and the measured results are compared with the finite element results. The changes of axial force and joint displacement under different loads, the changes of static properties under cable damage and the dynamic characteristics of the structure are obtained. The results show that the loading method adopted meets the test accuracy requirements. Under the action of uniform load, the upper chord, the lower chord end and the inner ring truss of the main truss are in a pure compression state. The middle bar of the lower chord span and the outer ring truss change from the compression state to the tension state with the increase of load. The structure is still in the elastic stage when part of the cable fails, and the coordinated deformation ability is strong. The base frequency of the measured structure is 7.97 Hz, and the stiffness distribution is uniform.

Bismuth Ordering and Optical Anisotropy in GaAsBi Alloys

Reflectance anisotropy spectroscopy (RAS) is applied to investigate GaAsBi samples grown by molecular beam epitaxy on (001)‐oriented GaAs substrates with GaAs or InGaAs buffer layers, resulting in nearly lattice‐matched or compressive strain conditions, with Bi concentration in the alloy in the range 2–5%. These new samples allow to bridge the gap in the Bi concentration values of previous RAS experiments (C. Goletti et al., Appl. Phys. Lett. 2022, 120, 031902), confirming the [110]‐polarized Bi‐related anisotropy in optical spectra below 3 eV and the linear dependence of its amplitude on Bi concentration. The characterization of the grown GaAsBi samples by X‐Ray diffraction and transmission electron microscopy clearly demonstrates the presence of CuPt‐like ordering in the bulk. CuPt structure is the primary origin of the optical anisotropy measured by RAS and by polarized photoluminescence, due to the anisotropic strain produced in the bulk crystal lattice. The lineshape of the RAS spectra above 3 eV, with its overall and characteristic positive convexity, confirms this conclusion.

Dynamic mechanical behavior of titanium matrix composites reinforced with graphene nanoplatelets

In this investigation, graphene nanoplatelets reinforced pure titanium matrix (GNPs/TA1) composites were synthesized via short-term ball milling followed by spark plasma sintering. The mechanical properties and microstructure evolution of these composites were examined under both quasi-static and dynamic compression conditions. The results indicate that as the strain rate increases from 10−3 to 3000 s−1, the yield strength rises from 436.9 MPa to 1209.6 MPa, consistent with the positive strain rate effect. The superior yield strength of GNPs/TA1 composites arises from the dynamic Hall-Petch effect, dislocation strengthening and load transfer strengthening, with the contribution from load transfer strengthening being the most significant due to the reinforcement's (TiC-GNPs-TiC) facilitation of load transfer. As the strain rate increases, interfacial debonding gradually extends along the reinforcement and grain boundaries, but no macroscopic fracture occurred in this study. At a strain rate of 3000 s−1 during compression, {112‾2}, {101‾2}, and {11 2‾ 1} twins were generated. However, at a strain rate of 10 s−1, only {112‾2} and {101‾2} twins were produced, while {11 2‾ 1} twin was inhibited. Under high strain rate loading, the plastic flow behavior of GNPs/TA1 composites was predicted using the Johnson-Cook constitutive model, modified to account for adiabatic temperature rise, and the predictions showed good agreement with experimental results.

Design of hybrid multi-crosslinked hydrogel with a combination of high stiffness, elastic applied in high temperature and high salinity reservoirs

The mechanical strength of conventional hydrogels is inadequate for preventing leakage in high-temperature and high-salinity reservoirs, primarily due to the increased mobility of polymer chains and the degradation of crosslinked networks. Herein, we employed the strategy of ’network nesting and layer reinforcement’ to design a hybrid multi-site crosslinked hydrogel. This approach enhances the interconnections between polymer chains and fortifies the crosslinked network. The shear rheological behavior and temperature sensitive characteristics of the profile control working fluids were evaluated based on rheological dynamics. In the high temperature (140 ℃) and high salinity (21.81 × 104 mg/L) preparation environment, the effects of different components to the mechanical strength of the hydrogel were investigated under dynamic shear and uniaxial compression conditions. The incorporation of N-(hydroxymethyl)acrylamide (NMA) in the copolymerization with acrylamide (AM) resulted in an increase in the covalent cross-linking density, leading to a rise in the shear elastic modulus from 105 Pa to 238 Pa. The use of pre-gelatinized cassava starch (PGCM) as the grafting framework enhanced the bonding between the polymer chains, as evidenced by the increase in uniaxial compressive strength from 0.018 MPa to 0.081 MPa and the rise in peak strain from 55.0 % to 72.9 %. Furthermore, the synergistic effect of fumed silica (AEROSIL), which exploits mechanical coupling between inorganic nano-fillers and organic polymers, increased the compressive strength from 0.081 MPa to 0.418 MPa and raised the peak strain from 72.9 % to 81.8 %. It provides an effective approach to enhance the plugging performance of hydrogels in high temperature and high salinity reservoirs.

Effect of aspect ratio and geometric defects on the stability performance of U-rib stiffened plates

As an important component of steel-box beams, the stability of stiffened plates is a key factor that affects the safety of bridge structures. The geometric dimensions, such as the width-to-thickness ratio of the motherboard, stiffening rib thickness, and ratio of stiffening rib area to motherboard area, of stiffened plates have been considered in existing studies. However, the impact of the aspect ratio has not been reported in the literature. This study systematically investigated the effect of the aspect ratio on the stability performance of U-rib stiffened plates. Five sets of stiffened plate specimens with different aspect ratios were designed and manufactured. After testing the initial geometric defects of the specimens, axial compressive stability tests were conducted. Rotational hinge supports were placed at both ends of the specimens in order to simulate simply supported boundary conditions. The influence of geometric defects and aspect ratio on the stability of stiffened plates was discussed through numerical simulation. The results reveal that as the width of the stiffened plate increases, the initial geometric defects are distributed in a half-wave form along both the longitudinal and transverse directions, exhibiting an overall hemispherical distribution. The instability mode of a single-rib stiffened plate is characterized by local instability, whereas multi-rib stiffened plates exhibit global instability. The buckling mode is significantly influenced by the distribution of initial geometric defects. As the aspect ratio of the specimen decreases, the average stress at instability decreases and the stiffened plate gradually undergoes a biased compression state during the compression process. Failure of the specimen typically results in pure bending deformation when the aspect ratio is relatively large, whereas when the aspect ratio is relatively small, failure may result in bending and twisting deformation. Finally, a reasonable aspect ratio recommendation value was given.

Microscopic interface deterioration mechanism and damage behavior of high-toughness recycled aggregate concrete based on 4D in-situ CT experiments

High-toughness recycled aggregate concrete (HTRAC), as an innovative green building material, showcases outstanding performance and environmental attributes. To investigate its microscopic structural characteristics and the mechanisms of damage evolution under loading, a series of 4D in-situ X-ray computed tomography (CT) experiments were conducted under uniaxial compression conditions. During the experimental process, detailed scans were performed on six key loading points (0 %, 30 %, 60 %, and 100 % of the peak load, 70 % and 40 % of the post-peak load of the specimen). Advanced three-dimensional image processing techniques were utilized to conduct a comprehensive analysis of internal features within the specimen, including pores, steel fibers, and cracks. The evolution of damage in HTRAC was characterized by both qualitative 2D crack slice analysis and quantitative 3D reconstruction analysis of cracks. Changes in the average grayscale values of CT cross-sectional images were also examined. The deterioration mechanism of recycled aggregate concrete interface cracks was elucidated by the combination of CT images and modeled HTRAC. Furthermore, a statistics model illustrating the interaction mechanism between damage, cracks, and strain was proposed. This study provides technical and theoretical support for the further promotion and application of high-toughness recycled aggregate concrete.

A study of dynamic recovery and recrystallisation mechanisms in aluminium alloy AA7050 at different thermomechanical processing conditions

The effects of hot deformation strain rates and temperatures on aluminium alloys' dynamic recovery and recrystallisation mechanisms have been widely discussed in the literature. However, their influence remains controversial due to a need for comprehensive and detailed thermomechanical testing and characterisation data across a wide range of hot deformation conditions. In this study, hot compression tests of AA7050 were conducted at strain rates of 0.0005–5 s−1 and temperatures of 380–460 °C. The geometrically necessary dislocation (GND), low-angle grain boundary (LAGB) and high-angle grain boundary (HAGB) were acquired by the latest high angular resolution, high-speed EBSD detector (OI Symmetry 2), and their underlying mechanisms were analysed in relation to Zener-Hollomon parameter (Z). It was found that within the tested range of the hot compression condition (ln (Z) between 20.23 and 29.45), continuous dynamic recrystallisation (CDRX) predominates at lower ln (Z) values with its activity being initially increased and then decreased as ln (Z) rises, while discontinuous dynamic recrystallisation (DDRX) becomes dominant at higher ln (Z) levels. This transition of the dominant mechanism is intriguingly reflected in the evolution of HAGB length, which increases, then decreases and finally increases again. The LAGB length shows a relatively linear relationship with ln (Z), and the average GND density exhibits a near-linear correlation until reaching a plateau. Based on the obtained results, the transformation of the dominant microstructural evolution mechanisms with increasing ln (Z) was clarified: from grain growth, to recovery, to CDRX, and then to DDRX, along with the quantitative trend of HAGB length per unit area. This transformation mechanism is believed to encompass the full range of material processing window, providing a basis for justifying the previous controversial proposition in literature and a guide for defining and fabricating microstructures in manufacturing applications.

Comparative fatigue performance of as-built vs etched Ti64 in TPMS-gyroid and stochastic structures fabricated via PBF-LB for biomedical applications

PurposeThis study compares the fatigue performance and biocompatibility of as-built and chemically etched Ti-6Al-4V alloys in TPMS-gyroid and stochastic structures fabricated via Powder Bed Fusion Laser Beam (PBF-LB). This study aims to understand how complex lattice structures and post-manufacturing treatment, particularly chemical etching, affect the mechanical properties, surface morphology, fatigue resistance and biocompatibility of these metamaterials for biomedical applications.Design/methodology/approachSelective Laser Melting (SLM) technology was used to fabricate TPMS-gyroid and Voronoi stochastic designs with three different relative densities (0.2, 0.3 and 0.4) in Ti-6Al-4V ELI alloy. The as-built samples underwent a chemical etching process to enhance surface quality. Mechanical characterization included static compression and dynamic fatigue testing, complemented by scanning electron microscopy (SEM) for surface and failure analysis. The biocompatibility of the samples was assessed through in-vitro cell viability assays using the Alamar Blue assay and cell proliferation studies.FindingsChemical etching significantly improves the surface morphology, mechanical properties and fatigue resistance of both TPMS-gyroid and stochastic structures. Gyroid structures demonstrated superior mechanical performance and fatigue resistance compared to stochastic structures, with etching providing more pronounced benefits in these aspects. In-vitro biocompatibility tests showed high cytocompatibility for both as-built and etched samples, with etched samples exhibiting notably improved cell viability. The study also highlights the importance of design and post-processing in optimizing the performance of Ti64 components for biomedical applications.Originality/valueThe comparative analysis between as-built and etched conditions, alongside considering different lattice designs, provides valuable information for developing advanced biomedical implants. The demonstration of enhanced fatigue resistance and biocompatibility through etching adds significant value to the field of additive manufacturing, suggesting new avenues for designing and post-processing implantable devices.

A stepped vibrating screening device with a crushing function based on the difference in tuber-soil aggregate breakage behaviour

To increase the difference in the particle size distribution of root tuber and soil aggregates and further promote the segregation effect of the binary mixture under external force. The present study investigates the bulbs of Fritillaria thunbergii (BFT) as the research subject. Initially, static compression and dynamic impact tests were conducted on BFT and soil aggregates. Subsequently, a breakage model of BFT and soil aggregates was established based on the Tavares UFRJ Breakage Model, and the accuracy of the breakage model and mechanical parameters was verified. Lastly, the optimal structural and operating parameters of the screening device with a crushing function were determined through single-factor testing and multi-objective optimization. The results indicate that the breakage resistance of BFT was significantly higher than that of soil aggregates, as evident from the differences in fracture energy and damage parameters. Furthermore, the optimal operating parameters of the new vibrating screen were determined by maximizing the soil aggregate breakage rate and minimizing the BFT breakage rate.

Experimental and numerical study on behavior of demountable shear connectors in sustainable reinforced concrete beam-slab

Developed herein is a novel fully demountable shear connector, P-DBSCs (Demountable Bolted Shear Connectors with End Plate), aimed at enhancing the economic and environmental advantages of traditional buildings undergoing disassembly and reconstruction. This work numerically and experimentally assessed the shear performance of P-DBSCs via seven push-out tests and finite element simulations. Results revealed a uniform failure mode across seven specimens characterized by bolt fractures, absent of significant beam or slab cracking, evidencing remarkable post-failure demountability. According to the assessments of the specimens' force state, encompassing Digital Image Correlation (DIC) and anti-lifting capacity analyses, established that specimens fitted with larger bolts maintained better integrity and the concrete beam is under compression state, with lifting displacements remaining below 1.2 mm. Further, a verified finite element model's parameter study explored the influences of factors such as slab concrete strength, channel spacing, steel box thickness, channel thickness, steel box strength, and the diameter and strength of bolts on the shear performance of these connectors, finding these attributes to significantly affect shear performance within specific ranges, except for the slab concrete strength, to which shear performance displayed lesser sensitivity. Regression analysis facilitated the proposition of a mechanical constitutive model and stiffness degradation model for this connector type, validated through correlation with experimental results. These models provide a solid theoretical foundation for implementing demountable reinforced concrete (RC) beam-slab systems.

Rock damage and fracture characteristics considering the interaction between holes and joints

The work studied the damage and fracture characteristics of granite samples with circular holes and parallel fractures of different lengths under uniaxial compression conditions. Acoustic emission (AE) monitoring and digital image correlation (DIC) were used to analyze the dynamic changes of AE parameters, the evolution characteristics of the deformation field on the sample surface, and the correlation between the fractal dimension and the fracture geometry parameters. A computational model was proposed for evaluating the intensity factor of the fracture tip in a double-fracture structure with holes. The interaction between the fractures was considered to reveal the complex law of the intensity factor and the fracturing angle with the fracture geometry. The changes in AE parameters and fractal dimension indicated the influence of fracture extension on the damage mode of samples. Besides, the fracture length affected the micro-fracture behavior. The surface displacement and strain characteristics of samples revealed the modulation effect of the fracture length on the failure mode. The inclination angle, length, holes, and size of the fractures’ friction coefficient significantly affected the evolution of the intensity factor, which in turn regulated the changes in the fracture angle. The work offers a novel quantitative analytical approach and a theoretical framework for comprehending the damage and failure mechanisms of porous and fractured rocks through extensive experimentation and theoretical analysis. It holds significant practical relevance in geological engineering, mining, and tunnel construction.

Load–displacement behavior of helical pile using Frustum Confining vessel (FCV) and full-scale testing in Babolsar sand

Nowadays, the use of deep foundations in various civil engineering projects, especially in marine and coastal structures, has been increasing. One type of deep foundations are helical pile foundations, which have gained significant attention in recent decades. This research investigates the load–displacement behavior of different helical pile configurations regarding geometry, i.e., helix diameter and spacing ratio (S/D) in two different soil densities under pullout and compressive loading conditions via the FCV-AUT device. Babolsar sand from the southern coast of the Caspian Sea was utilized for advancing this study. Additionally, four full-scale pile tests were conducted on the Caspian Sea coast under both grouted and non-grouted conditions for pullout and compressive loading. The results indicate that increasing the helix diameter, soil density, and S/D ratio enhances the compressive load-bearing capacity. However, in tensile loading, the ultimate load decreases with an increase in the spacing ratio. Furthermore, the grouting process in the three-helix pile exhibits better performance compared to the two-helix pile, potentially increasing the pile capacity up to 30%. In conclusion, the results obtained from the FCV device, utilizing scale theory, have been generalized to the large-scale pile test results in the field, are representative of in agreement and compatible.

On the strain rate-dependent mechanical behavior of PE separator for lithium-ion batteries

The separator is a critical component for ensuring electrochemical cycling performance and preventing internal short circuits in lithium-ion batteries. For the collision safety of lithium-ion batteries, understanding the rate-dependent mechanical behavior of the separator is essential for battery impact modeling and safety prediction. This study conducts a comprehensive experimental investigation into the strain rate–dependent tensile/compressive behavior and failure mechanism of the polyethylene (PE) separator under quasi-static and dynamic conditions. The combination of deformation images recorded by cameras and post-mortem characterization using SEM was employed to clarify the rate-dependent deformation and fracture mechanism of the separator under both tensile and compressive loading. The experimental results demonstrate a significant strain rate effect on the tensile/compressive mechanical properties and damage/failure behavior of the separator. Furthermore, the effect of the strain rate on the mechanical properties, including the tensile strength, tensile fracture strain, tensile elastic modulus, compressive modulus, yield stress and yield strain of separator, was analyzed and discussed. A significant strain rate-dependent tensile damage and fracture behavior of the separator was observed, where the fracture site exhibited an obvious phase transition and skeletal lamella fracture under extremely high strain rate tensile loading. The separator underwent severe damage under dynamic compressive conditions. The results of this study provide an important basis for the establishment of rate-dependent safety criterion and short circuit prediction of lithium-ion batteries under impact loading, and shed light on understanding separator failure-induced short circuit issues in battery collision safety scenarios.

Comparative analysis of mechanical properties and fracture characteristics between sodium silicate modified polyurethane and polyurethane materials

Sodium silicate modified polyurethane (SS/PU) and polyurethane (PU) have become the most widely used grouting materials at present, but their differences in mechanical properties and fracture characteristics remain unclear. In this study, uniaxial compression, digital image correlation (DIC), split Hopkinson pressure bar (SHPB), and scanning electron microscopy were used to compare the dynamic and static mechanical properties and fracture characteristics of the two materials at different aging times. In terms of static mechanics, the stress-strain curve evolution, compression strength characteristics, and crack evolution fracture of SS/PU and PU were compared and analyzed. In dynamic mechanics, the impact compression stress-strain curve, peak strength, strength evolution characteristics, and micro-damage fracture characteristics of the materials were explored. Based on static compression measurements, both materials belong to viscoelastic bodies, with SS/PU being more rigid and PU being more elastic. SS/PU exhibits higher early strength (6 h, 36.9 MPa), while PU shows higher later strength (36 h, 48.9 MPa). Cracks appear instantaneously before or after the peak strength in both materials, with vertical cleavage fracture predominating. Under dynamic impact compression, both materials exhibit an increase with increasing impact velocity, showing a significant strain rate strengthening effect. At different aging times (6 h, 12 h, 24 h, 36 h), the dynamic compression strength of PU is greater than that of SS/PU. The fracture of SS/PU mainly involved continuous fracture, while the fracture of PU mainly involved polymer tearing. In general, when grouting reinforcement projects require materials with higher early strength and better rigidity, SS/PU is more suitable. If the area to be reinforced is in a dynamic impact environment and requires higher final strength, PU is preferable.

An Experimental Study on the Thermomechanical Coupling Effects of Carbon-Fiber-Reinforced Polyetheretherketone under Dynamic Impact.

Carbon-fiber-reinforced polyetheretherketone (CF/PEEK) composites are widely utilized in aerospace, medical devices, and automotive industries, renowned for their superior mechanical properties and high-temperature resistance. Despite these advantages, the thermomechanical coupling behavior of CF/PEEK under dynamic loading conditions is not well understood. This study aims to explore the thermomechanical coupling effects of CF/PEEK at elevated strain rates, employing Hopkinson bar impact tests and scanning electron microscopy (SEM) for detailed characterization. Our findings indicate that an increase in temperature led to significant reductions in the yield strength, peak stress, and specific energy absorption of CF/PEEK, while fracture strain had no significant effect. For instance, at 200 °C, the yield strength, peak stress, and specific energy absorption decreased by 39%, 37%, and 38%, respectively, compared to their values at 20 °C. Furthermore, as the strain rate increased, the yield strength, peak stress, specific energy absorption, and fracture strain all exhibited strain-hardening effects. However, as the strain rate further increased, above 4000 s-1, the enhancing effect of the strain rate on the yield strength and peak stress gradually diminished. The interaction of the temperature and strain rate significantly affected the mechanical performance of CF/PEEK under high-speed impact conditions. While the strain rate generally enhanced these properties, the strain-hardening effect on the yield strength weakened as the temperature increased, and both the temperature and strain rate contributed to the increase in specific energy absorption. Microdamage mechanism analysis revealed that interface debonding and sliding between the fibers and the matrix were more pronounced under static compression than under dynamic compression, thereby diminishing the efficiency of stress transfer. Additionally, higher temperatures caused the PEEK matrix to soften and exhibit increased viscoelastic behavior, which in turn affected the material's toughness and the mechanisms of stress transfer. These insights hold substantial engineering significance, particularly for the optimization of CF/PEEK composite design and applications in extreme environments.

Quantitative calculation of rock strain concentration and corresponding damage evolution analysis

Understanding the critical strain and damage evolution process of sandstone can help engineers more accurately predict the failure modes and critical states of sandstone in actual engineering structures. Therefore, this article quantitatively analyzes the strain field data obtained through digital image correlation (DIC), and for the first time establishes a strain concentration calculation model (SCCM) to analyze the critical strain, compaction, and damage evolution process of sandstone under uniaxial compression conditions. The experimental results show that both elastic and plastic strain zones exist on the specimen surface. The proportion curve of strain concentration calculated by SCCM indicates that the strain field ε1 generally undergoes two stages: the elastic strain fluctuation stage and the plastic strain development stage. In contrast, the strain field ε2 exhibits roughly three stages: a rapid change phase, a slow change phase, and a stability phase. Microscopic strain analysis reveals an overlap between the compaction and damage processes of the specimen, and the critical strain value εmd for micro-damage in the specimen is significantly smaller than values obtained by traditional discrimination methods. Specifically, when the defect width of the specimen is 15 mm and 40 mm, the mean εmd vaules are approximately 0.006016 and 0.00539, respectively. In contrast, the mean critical strain values determined by traditional discrimination methods are 0.0180 and 0.0178, respectively. The above research results provide a new method for analyzing the strain field data of geotechnical materials, serving the optimization of engineering structure design.

First-principles study on thermal transport properties of GaN under different cross-plane strain

With the development of power devices towards high integration and power, the electrical and thermal stresses per unit area become more concentrated and intensified. The impact of cross-plane strain resulting from inverse piezoelectric effect and thermal expansion on power devices cannot be ignored. Cross-plane strain has a substantial influence on the thermal properties of GaN. However, the research on the influence of cross-plane strain on the thermal conductivity of GaN has not been reported in the literature. Based on the first-principles calculation method and the phonon Boltzmann transport equation, the influence of cross-plane strain on the thermal conductivity and phonon characteristics of the GaN lattice is systematically studied in this study. The thermal conductivity of GaN has anisotropy and increases significantly with the decrease in temperature. The thermal conductivity of GaN at room temperature under the free state is calculated to be 257 and 275 W/(m·K) for in-plane (k⊥) and cross-plane (k∥) directions, respectively. Compared with previous theoretical reports, our calculation results are more consistent with the existing experiment values. Under the state of cross-plane strain, the lattice thermal conductivity changes remarkably. In detail, the average thermal conductivity at room temperature decreased by 35 % under a 5 % cross-plane tensile strain state, while it increased by 11.5 % under a 5 % cross-plane compressive strain state. According to the calculation results, the influence of cross-plane on lattice thermal conductivity is mainly due to the change in phonon lifetime. The analysis of two mechanisms of phonon lifetime suppression indicates that the cross-plane strain will significantly change the frequency of the high-frequency optical acoustic branch. This result leads to a change in the phonon scattering process and thus affects the phonon lifetime. Besides, the anisotropy of thermal conductivity changes under different strain values, which may be due to the weakened piezoelectric polarization effect induced by strain.

Gradient ceramic structures via multi-material direct ink writing

Dense boron carbide-silicon carbide specimens with composition tailored at the mesoscale were produced by direct ink write additive manufacturing in three configurations: I, 2 % and II, 10 % compositional layer-to-layer steps, and III, homogeneous composition throughout. Flexural strength, indicative of tensile failure, is the highest for the Type-II design (366 MPa) due to its compressive residual stress state in the surface layers. Analysis of thermally-induced residual stresses predicts the ranking of the flexural strengths obtained for Type-II (highest), Type-I (intermediate), and Type-III (lowest) specimens. Compressive strength is load-orientation independent, highly strain-rate dependent, and reduced for specimens with thermal residual stress. Mechanical tests were performed in cube and dumbbell geometries. Dumbbell geometry compression specimens have a compressive strength that is 68 % (quasistatic) and 86 % (dynamic) higher than that of cube geometry and show a greater strain rate dependence. The rate dependency is attributed to the competition between crack propagation and loading velocities. Type-I dumbbells show the highest mean compressive strength of 3.96 GPa (quasi-static) and 5.11 GPa (dynamic). The failure mode evolves from mixed intergranular/transgranular at low strain rates to transgranular at high strain rates. High-speed video analysis indicates that dumbbell geometry specimens fail in compression due to microcrack growth and coalescence, while cubes fail due to the axial macrocracks that develop at the specimen/load platen interface and propagate into the specimen parallel to the loading direction (end splitting). This work demonstrates the impact of compositional variation, tailored by additive manufacturing, on the mechanical performance of ceramic composites.

Study on the mesoscopic mechanical behavior and damage constitutive model of micro-steel fiber reinforced recycled aggregate concrete

This study employs in-situ 4D CT experimental techniques to investigate the mesostructured changes and mechanical behavior of micro steel fiber-reinforced recycled aggregate concrete (MSF-RAC) under uniaxial compression and cyclic loading conditions. The research aims to address the scientific problem of limited understanding of how micro steel fibers affect the mesoscopic mechanical behavior and structural damage characteristics of recycled aggregate concrete. High-resolution CT scanning technology was utilized for real-time observation of crack initiation and propagation, revealing the micro-mechanisms by which micro steel fibers enhance RAC. The study found that incorporating micro-steel fibers significantly improves the density of the interfacial transition zone (ITZ), inhibits crack development, and enhances the mechanical properties of the concrete. Based on these observations, an improved stiffness degradation damage constitutive model was proposed, which comprehensively considers the distribution orientation of micro steel fibers and ITZ characteristics. The model effectively predicts the stress-strain relationship of MSF-RAC under various conditions, demonstrating high accuracy and practicality. These findings provide important theoretical support and experimental evidence for the optimal design of RAC, showcasing significant engineering application value by promoting the sustainable use of recycled materials in construction.

A Dynamic Damage Constitutive Model of Rock-like Materials Based on Elastic Tensile Strain

To accurately characterize the damage of rock-like materials under simultaneous or alternating tensile and compressive loading, a dynamic damage constitutive model for rock-like materials based on elastic tensile strain is developed by integrating the classical compressive plastic damage model and the tensile elastic damage model. The model is based on the Holmquist–Johnson–Cook (HJC) and Kuszmaul (KUS) models, categorizing the element stress state into tensile and compressive states through positive and negative elastic volumetric strain. It utilizes elastic tensile strain to enhance the calculation method for tensile cracks, determining the tensile strength of the principal direction based on the contribution rate of tensile principal stress for uniaxial/multiaxial loading. Additionally, it establishes a maximum elastic tensile strain rate function to rectify the model’s effect on the tensile strain rate. Through the LS-DYNA subroutine development, the model proficiently delineates the distribution of ring-shaped cracks on the frontal side and strip-shaped cracks on the rear side of the reinforced concrete slab subjected to impact loading. Numerical simulations demonstrate that the model provides more accurate damage prediction results for stress conditions involving simultaneous or alternating compression and tension, offering valuable insights for damage analysis in engineering blasting or impact penetration.