Static Compression Research Articles

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.

Phase transition behavior of benzene under dynamic compression: A stable precocious phase

The phase transitions of benzene under static and dynamic compression were measured by Raman spectroscopy. Under a static compression of up to 23.90 GPa, benzene underwent two phase transitions at approximately 0.71 GPa and 2.73 GPa, and one chemical transformation above 21.95 GPa. Under dynamic compression, liquid benzene was solidified by rapid compression from approximately 0.36 GPa to 3.81 GPa, 6.68 GPa, 9.96 GPa and 16.68 GPa, step by step within 5 ms. It was discovered that liquid benzene changed from the liquid phase into the coexistence phase of I&II at 3.81 GPa and 6.68 GPa, but then changed into two precocious phases at 9.96 GPa and 16.68 GPa. According to the alteration and evolution of the ν1 ring breathing mode (992 cm−1), rapid compression might hasten the mixed-phase’s structural transformation and make it easier to generate benzene pure phase. Decompression measurements on benzene suggest the precocious pure phase II produced by rapid compression can maintain its stable structure rather than undergo a phase change as the pressure decreases to 2.76 GPa. These phase behaviors may be attributed to the dynamic lattice instability brought on by the faster compression rate as well as the deviation from equilibrium state brought on by the dynamic pressure-induced temperature rise.

Some Unfamiliar Structural Stability Aspects of Unsymmetric Laminated Composite Plates.

It is widely recognized that certain structures, when subjected to static compression, may exhibit a bifurcation point, leading to the potential occurrence of a secondary equilibrium path. Also, there is a tendency of deflection increment without a bifurcation point to occur for imperfect structures. In this paper, some relatively unknown phenomena are investigated. First, it is demonstrated that in some conditions, the linear buckling mode shape may differ from the result of geometrically nonlinear analysis. Second, a mode jumping phenomenon is described as a transition from a secondary equilibrium path to an obscure one as a tertiary equilibrium path or a second bifurcation point. In this regard, some non-square plates with unsymmetric layer arrangements (in the presence of extension-bending coupling) are subjected to a uniaxial in-plane compression. By considering the geometrically linear and nonlinear problems, the bucking modes and post-buckling behaviors, e.g., the out-of-plane displacement of the plate versus the load, are obtained by ANSYS 2023 R1 software. Through a parametric analysis, the possibility of these phenomena is investigated in detail.

Role of gravity magnitude on flowability and powder spreading in the powder bed fusion additive manufacturing process: Towards additive manufacturing in space

Understanding powder spreading under low gravity conditions is essential for optimizing final products using additive manufacturing in space. In this study, we investigated the role of gravity on flowability and spreading mechanisms through combined experimental and discrete element method (DEM) studies. Three powders with different theoretical densities were used to reenact low compressive conditions resembling those in a low-gravity environment. The influence of low compressive conditions on flowability and spreading behavior was examined using the Hall flowmeter, rotating drum, and spreading experiments. In the experimental result, the static flowability was primarily affected by the presence of elongated particles rather than the compressive conditions. The dynamic AoR of TD_4 powder increased compared to that of TD_8 powder, despite the presence of spherical particles with a smooth surface finish. A DEM simulation study was conducted using TD_8 powder to investigate the impact of different gravity levels on dynamic flowability. The DEM studies revealed that the dynamic flowability under rotation was decreased under low gravity owing to the promoted cohesive interactions. The powder spreading experiment was performed using the three powders with different theoretical densities. The in-situ observation with particle image velocimetry analysis revealed that kinetic energy dissipation in the spreading process was accelerated in the TD_8 powder pile, despite its high interparticle friction and cohesive force. The powder spreading simulation was conducted using TD_8 powder to clarify the effect of low gravity on the powder spreading process. In TD_8 powder under 1 G, particle supply was facilitated by a synergistic effect of free-falling and deposited particles. However, increased cohesive interactions under 0.5 G and 0.16 G restricted particle supply via free-falling, consequently reducing the powder bed density by about 2 % and 6.2 %, respectively. These findings prove that the cohesive force predominantly controls dynamic flowability and powder bed quality in the spreading process under low gravity conditions.

Centrifuge modelling of dry granular run-out processes under deflective Coriolis condition

Coriolis effects, encompassing the dilative, compressive, and deflective manifestations, constitute pivotal considerations in the centrifugal modelling of high-speed granular run-out processes. Notably, under the deflective Coriolis condition, the velocity component parallel to the rotational axis exerts no influence on the magnitude of Coriolis acceleration. This circumstance implies a potential mitigation of the Coriolis force's deflective impact. Regrettably, extant investigations predominantly emphasize the dilative and compressive Coriolis effects, largely neglecting the pragmatic import of the deflective Coriolis condition. In pursuit of this gap, a series of discrete element method (DEM) simulations have been conducted to scrutinize the feasibility of centrifugal modelling for dry granular run-out processes under deflective Coriolis conditions. The findings concerning the deflective Coriolis effect reveal a consistent rise in the run-out distance by 2%–16%, a modest increase in bulk flow velocity of under 4%, and a slight elevation in average flow depth by no more than 25%. These alterations display smaller dependence on the specific testing conditions due to the granular flow undergoing dual deflections in opposing directions. This underscores the significance and utility of the deflective Coriolis condition. Notably, the anticipated reduction in error in predicting the final run-out distance is substantial, potentially reaching a 150% improvement compared to predictions made under the dilative and compressive Coriolis conditions. Therefore, the deflective Coriolis condition is advised when the final run-out distance of the granular flow is the main concern. To mitigate the impact of Coriolis acceleration, a greater initial height of the granular column is recommended, with a height/width ratio exceeding 1, as the basal friction of the granular material plays a crucial role in mitigating the deflective Coriolis effect. For more transverse-uniform flow properties, the width of the granular column should be as large as possible.

Comparative Biomechanical Study of Fragment-Specific Plates and Headless Screws for Radial Styloid and Lunate Facet Fixation in Distal Radius Fracture Evaluated in a Synthetic Composite

To evaluate the compressive stiffness (ability to resist compression under an applied load) of fragment-specific plate and headless screw fixation for radial styloid and volar lunate facet fractures in a synthetic composite distal radius. A simulated radial styloid fracture (AO type B1.1) and simulated volar lunate facet fracture (AO type B3.3) were created in synthetic composite distal radii and fixed with a fragment-specific plate (FSP) using a radial styloid or lunate facet plate or with two- or three-headless screws (2HS, 3HS), creating 6 fixation models: B1.1/FSP, B1.1/2HS, B1.1/3HS, B3.3/FSP, B3.3/2HS, and B3.3/3HS. Compressive stiffness of fixation constructs under initial static load, cyclic load, and final static load was investigated. Nonaxial loadings, including shearing and rotation, were not evaluated. Regarding AO type B1.1, the mean stiffness of the B1.1/FSP construct was not significantly different from the intact radius, and the mean stiffness was greatest in the B1.1/3HS and lowest in the B1.1/2HS construct. For AO type B3.3, the mean stiffness of the B3.3/3HS construct was not significantly different from the intact radius, and the mean stiffness of the B3.3/FSP and B3.3/2HS construct was greatest and lowest, respectively. Minimal differences in stiffness between initial and final static loads confirmed that there was no evidence of failure implant under cyclic compressive loads. Fragment-specific plates and two- or three-headless screw fixation maintained mechanical stability through compressive cyclic loading for radial styloid and volar lunate facet fractures. The FSPs and three-headless screws fixations provided superior stiffness over the two-headless screws fixation. There was no articular fracture failure in all fixation constructs with initial static compression, cyclic loading, and final compression. Fragment-specific plates and headless screws can both be considered as adequate fixation for radial styloid and volar lunate facet fractures.

Prediction of axial compressive stresses in ultra-high-performance concrete blocks using non-destructive ultrasonic techniques

The application of ultra-high-performance concrete (UHPC) in civil engineering structures is growing rapidly. On the other hand, previous non-destructive testing (NDT) techniques mainly focused on determining the relationship between the acoustic characteristics and elastic modulus, Poisson's ratio, cracking resistance, and strength. This study presents an experimental approach utilizing ultrasonic techniques to predict the axial compressive stresses in UHPC structures. Both cubic and prismatic UHPC blocks were designed and tested under different compressive axial loading conditions, and their ultrasonic acoustic characteristics were evaluated in detail. Normal strength concrete (NSC) blocks were also included in the investigation for comparison purposes. A detailed account of the tests results is provided, including the relationships between the compressive stresses in UHPC blocks and the typical time- and frequency-domain acoustic parameters. Based on the experimental results, an analytical working stress evaluation method for UHPC components using the ultrasonic acoustic parameters is proposed. It is shown that there is close correlation and high prediction stability between the compressive stress in UHPC blocks and the ultrasonic velocity, which is suggested as the main acoustic parameter for stress detection. The correlation between the acoustic amplitude parameters and concrete compressive stress is also shown to be significant, yet is associated with relatively low prediction stability. Moreover, in comparison with conventional NSC blocks, greater correlation and regularity ratios are observed between the typical acoustic parameters and the axial compressive stress in UHPC specimens. Overall, the analytical models proposed in this study are shown to be in close agreement with the experimental results, and can be used, in conjunction with the ultrasonic NDT techniques, to provide a reliable prediction of the level of compressive stresses in UHPC members.

Controllable stress-adsorbed layers in Ti/TiN/TiAlN coatings: Mechanical performance and micropillar compression

Solid particle erosion often compromises the durability of turbine engine blades, particularly those used in offshore and desert environments. Surface protective coatings have emerged as a promising solution to significantly enhance the erosion resistance of compressor blades. In this study, TiAlN multilayer coatings were deposited onto Ti-6Al-4V substrates using a vacuum arc deposition technique. The article explored the strategic incorporation of TiN-Ti-TiN stress-adsorbed layers (SALs) within TiAlN-based coatings. It also investigated the microscale mechanisms leading to coating failure under conditions of micropillar compression. The findings revealed that the presence of metal/ceramic interfaces significantly improved the adhesion strength, crack resistance, erosion resistance and fracture toughness of the coatings. The multilayer deformation behavior of the coatings was primarily determined by the plastic flow of the softer metal layers. The SALs played a crucial role in reducing the elastic strain energy by generating nanotwins, coherent interfaces, and high-density dislocations during deformation, thereby improving the coatings' plastic deformation capability. Moreover, the implementation of dual-cycle SALs successfully reduced radial crack propagation, facilitating a transition from brittle fracture to a combined brittle-ductile fracture mechanism. This study highlights the critical role of metal/ceramic interfaces and SALs in improving the erosion resistance and co-deformability of TiAlN-based hard coatings.