Compressive Failure Modes Research Articles

Steel Fiber–Matrix Interfacial Bond in Ultra-High Performance Concrete: A Review

Ultra-high performance concrete (UHPC) is a relatively new cementitious concrete composite with significant application potential in infrastructure construction because of its excellent mechanical strength and durability. The steel fiber–matrix interfacial bond is the main factor that governs other mechanical properties of UHPC, including tensile, flexural, and compressive strengths and failure mode (fracture behavior). This paper presents a comprehensive review on the research progress of fiber–matrix bond behaviors of UHPC by discussing and comparing a range of fiber pullout testing methods and analytical models. The parameters of the fiber–matrix bond, including the geometry and orientation of fibers, surface treatment, and composition and strength of the matrix, are identified and discussed in detail. Lastly, recommendations for future research related to UHPC strengthening methods and testing details are provided based on recent progress.

Effects of Unit Cell Topology on the Mechanical Properties of Porous Tantalum Structures via Laser Powder Bed Fusion

Additive manufacturing (AM) of porous tantalum scaffolds receives extensive attention because the demands for tantalum implants grow rapidly. Understanding the effects of unit cell topology on the mechanical properties of porous tantalum scaffold structures is critical for durable implant design, but it is still lacking. Herein, porous tantalum structures with two types of unit cells (body‐centered cubic [BCC] and body‐centered cubic deformation [BCC‐D]) are additively manufactured with laser powder bed fusion (LPBF). The geometric characteristics and mechanical properties of the manufactured structures are comparatively studied. It is found that the mechanical properties of BCC porous tantalum in the building and horizontal directions are discovered to be nearly identical, with elastic modulus and yield strength of nearly 1.9 GPa and 56 MPa, respectively. Unit cell topology dominates the mechanical anisotropy and compressive failure mode of porous tantalum. The mechanical properties of the BCC‐D topology are anisotropic, and the fracture morphology indicates that it is a cleavage fracture and a minor ductile fracture. The capacity to finely control the mechanical properties of porous tantalum structure through unit cell topology is prominent for optimizing implant structure for personalized medical care.

Failure Mechanisms and Constitutive Model of Composite Rock under Dynamic Loading

Abstract In order to investigate the dynamic response characteristics of composite rock with different joint angles, static compression test and dynamic impact test are carried out using WDW-300E servo pressure-testing machine and split Hopkinson pressure bar (SHPB) test system. The dynamic compressive strength, energy dissipation, and failure modes are compared between rock coal (R-C) and coal rock (C-R). Furthermore, a 3D SHPB simulation system is constructed using coupling finite difference method and discrete element method (FDM-DEM) to reproduce the energy evolution and failure modes of composite rock with different joint angles, and the fabric tensor is obtained based on secondary development. Finally, a constitutive model of composite rock is established considering joint angles. The results of experiment, simulation, and theoretical analysis show that for the case of uniaxial compression test, with the increase of joint angle, the peak stress of composite rock shows obvious U-shaped change, and the elastic modulus increases gradually while the peak strain decreases gradually. For the case of dynamic impact test, the peak stress, strain, and energy dissipation values of composite rock decrease first and then increase with the increase of angle, and the elastic modulus of composite rock increases monotonically after a slight fluctuation of 30°. The stress, energy dissipation and elastic modulus of composite rock R-C are larger than that of composite rock C-R. However, the strain value of composite rock R-C is generally less than of composite rock C-R. The failure mode of composite rock with small and large angle is mainly splitting under dynamic impact, and the fracture fragmentation is relatively small with high energy absorption rate, while the fracture fragmentation is mainly shear and splitting mixed failure with low energy absorption rate. The energy accumulation and transformation process inside the composite rock are analyzed by 3D simulation system, and the damage of the composite rock under impact is mainly concentrated on the coal side, and peak values of contact number and contact force with different joint angles are calculated by using fabric tensor. Based on Weibull distribution, a constitutive model of composite rock is constructed considering initial damage and dynamic failure effect, which is in good agreement with experimental and simulation results, verifying the correctness of the constructed model.

Compressive behaviors of thermo-oxidative aged three-dimensional angle-interlock woven composites under different strain rates

The mechanical behaviors of three-dimensional angle-interlock woven composites (3DAWCs) after thermo-oxidative aging under different strain rates are imperative to retain safety in high-temperature conditions. This work presents the thermo-oxidative aging effects on strain rate sensitivity and compression failure mechanism of 3DAWCs based on the digital image correlation technique and finite element analysis. The results revealed that the compressive modulus and maximum stress of the 3DAWCs are strain rate sensitive, while the thermo-oxidative aging would reduce the strain rate sensitivity. The strain rate coefficient of the resin and composite decreased by approximately 9% and 25% after thermo-oxidative aging, respectively. The compressive damage failure modes of the 3DAWCs mainly include resin cracks, interfacial debonding, and yarn fracture. The strain rate has effects on damage initiation and brittle-ductile fracture behavior. The aging effect changes the crack propagation path, but does not affect the inclined 45° shear mode. In addition, the strain rate effects on strain localization were found and will be enhanced after thermo-oxidative aging.

Experimental Investigation on Uniaxial Compressive Strength of Thin Building Sandstone

Thin sandstone is a widely used building material; however, its compressive behavior is not well understood. Four groups of cylinders were manufactured in a factory to investigate the uniaxial compressive behavior of red sandstone. Uniaxial compression tests were performed to determine the compressive behavior and failure mode of the specimens. The geometry of the stress–strain diagram varied among the four groups. The critical strain generally increased with a decrease in the height of the cylinder, whereas the compressive strength exhibited an inverse trend. The experimental diagrams were normalized with the peak stress and corresponding critical strain to represent the stress–strain diagram of each group of cylinders. A formula consisting of two parabolas was employed for regression to obtain a representative mathematical expression of the diagram. The correlations between porosity, compressive strength, and elastic modulus were evaluated based on empirical expressions. Normalized strength was employed to evaluate the size effect on the diameter and length–diameter ratio (L/D) of the cylinder; the latter provided a better prediction of the experimental results than the former. A new expression in terms of L/D was proposed based on the regression analysis of the experimental results. This study is beneficial for the engineering application of sandstone as a construction material.

Experimental Study on Compressive Behavior of Concrete Cylinders Confined by a Novel Hybrid Fiber-Reinforced Polymer Spiral.

Modern fiber-reinforced polymer (FRP)-reinforced concrete structures are excepted to achieve superior mechanical performances and long service lives, even in harsh service environments. Hybrid FRP material could potentially meet this goal with its relatively high strength-to-cost ratio. This paper presents an experimental study on the compressive behavior of concrete cylinders confined by a novel hybrid fiber-reinforced polymer (HFRP) spiral. Nine types, forming a total of 27 confined or non-confined concrete cylinders, were subjected to an axial compressive-loading test. Concrete cylinders confined either with different spiral types or different spiral spacings were comparatively studied in the experiment. The results showed that the compressive failure modes and the stress-strain relationships of the HFRP-spiral-confined cylinders were similar to those of basalt-fiber-reinforced polymer (BFRP)-spiral-confined cylinders. The actual fracture strain of the HFRP spiral (tested as a single rod) was larger than that of the corresponding carbon-fiber-reinforced polymer (CFRP) bar, indicating the advantageous composite effect of the HFRP spiral. The maximum strain of the HFRP spiral reached over 70% of its ultimate strain in the cylinders compared to the BFRP spiral, which only reached 50%. Most of the existing models overestimated the ultimate stress and strain of the HFRP-spiral-confined cylinders. Wu's model was proved to be the most accurate model, yet proper modification was required for predicting the peak strain of the HFRP-confined cylinders.

Experimental investigation on eccentric compression behavior of FRP-confined concrete-encased cross-shaped steel columns

FRP-confined concrete-encased cross-shaped steel column (FCCSC), composed of an outer square glass-fiber-reinforced plastic (GFRP) tube, the internal cross-shaped steel, and the filled concrete, is a novel type of composite column. Eleven square FCCSCs were tested subject to eccentric axial compression load. The influence of eccentricity and slenderness ratio was evaluated and investigated. The test results showed that both the axial load-bearing capacity and lateral confinement efficiency of FRP tube reduced with the increase of eccentricity and slenderness ratio. The maximum reduction in axial load-bearing capacity was up to 50.7 % and 71.1 %, with the eccentricity varying from 0 mm to 50 mm and 100 mm, while the maximum reduction was about 18.1 % and 27.5 % when slenderness ratios increased from 10.44 to 20.87 and 34.79, respectively. The ductility of eccentric compressed FCCSCs can be evaluated by combined strain. It is indicated that short columns exhibited the best ductility, and the ductility increased with the increase of eccentricity. However, the ductility of slender columns reduced with the increase of eccentricity. Based on the test results, the experimental axial force (N)-moment (M) interaction curve of FCCSCs was obtained, and the balanced failure between compression and tension failure mode was recommended.

Study on the Expansion and Compression Resistance of 3D-Textile-Reinforced Self-Stressing Concrete.

Textile-reinforced concrete (TRC), as a kind of high-crack-resistance and high-corrosion-resistance material, has been widely studied. The current research has begun the exploration of the change of textile form, such as 3D-textile-reinforced concrete (3D TRC), and its superior bending performance has been verified. In order to pursue better mechanical properties, combined with the characteristics of self-stressing concrete and 3D textiles, three-dimensional-textile-reinforced self-stressing concrete (3D-TRSSC) specimens were designed in this research. The expansive and compressive properties of specimens with two types of textiles were tested by self-stress and compressibility tests, and the results showed the compressive property and failure mode of 3D-TRSSC were improved compared with 2D-TRSSC and SSC: the increase in compressive strength was 16.3% and 35.1%, respectively. In order to explain the improvement of the compressive strength of the 3D-TRSSC specimens, the triaxial self-stress state analysis of the compressive specimen was carried out, and then a set of calculation methods based on deformation analysis was designed to explain the upward displacement of the necking position of the TRSSC compressive specimen. The theoretical results and experimental data were 27.2 mm and 28–30 mm, respectively. In addition, the improvement of the compressive strength of the 3D-TRSSC specimens relative to that of the 2D-TRSSC specimen was predicted. The calculation results were highly consistent with the predicted values.

Damage evolution and failure mechanism of asymmetric composite laminates under low-velocity impact and compression after impact

The damage mechanisms of the balanced symmetrical laminates under low-velocity impact (LVI) and compression after impact (CAI) loading conditions are not fully applicable to composite stiffened panels. However, studies on LVI and CAI damage evolution and failure mechanism for asymmetric composite laminates are very rare, which poses challenges to the theoretical study, strength prediction, and application of composite structures, and increases the risk of sudden failure under load. In this study, the damage evolution and failure mechanisms of asymmetric composite laminates under LVI and CAI loading conditions were studied experimentally and numerically. Ultrasonic phased array C-scan technique was used to analyze damage state, damage size, and delamination damage induced by LVI under different impact energies in impact tests. Moreover, a three-dimensional digital image correlation (3D-DIC) technique was employed to monitor the evolution of full-field displacement and strain in the asymmetric composite laminates during the CAI tests. A three-dimensional damage model considering the interaction among the interlaminar delamination damage, intralaminar matrix damage, and intralaminar fiber damage was proposed, and an interface-based cohesive behavior embedded framework in ABAQUS/Explicit was used to define and capture the interlaminar damage. The damage initiation, evolution, and propagation behaviors of different damage modes were simulated to study the complex damage and failure mechanisms of the asymmetric laminates in the LVI and CAI processes. The relationships among the different impact energies and the impact damage modes, delamination morphologies, and compression damage propagation and failure modes were discussed.

Compressive properties and microscopic analysis of engineered cementitious composites after salt freezing

In order to study the compressive properties of Engineered Cementitious Composites (ECC) after salt freezing, the failure, compressive strength, and deformation capacity of cubic concrete specimens subjected to single-side freezing–thawing cycles considering the number of cycles, aggregate type Maowusu or Tengger Desert sands (MDS and TDS, respectively) and river sand (RS), and salt medium (NaCl or NaCl + Na2SO4). The results showed, In the presence of salt, the compression failure modes of all samples involved the formation of vertical cracks in the stress direction, but MDSECC and TDSECC showed better integrity than C30 concrete. With increasing freeze–thaw cycles, the strengths, slopes of the stress–strain curves, peak stress, and curve area of the desert sand specimens decreased, but the residual stress and ductility increased. Through regression analysis of the strength loss rate, the ECC lifetime was predicted, and using X-ray diffractometry and scanning electron microscopy, the effects of salt freezing on the mechanical properties of ECC were revealed.

Deformation failure and acoustic emission characteristics of continuous graded waste rock cemented backfill under uniaxial compression.

In order to study the effect of backfill aggregate particle size on the compressive strength and failure mode of cemented backfill, uniaxial compression tests were carried out on seven kinds of cemented backfills with different particle size gradations. By analyzing the AE characteristics during the failure process of the backfill, the damage evolution mechanism of the cemented backfill with different particle size gradations was discussed. The test results show that with the increase of the Talbot gradation index n, the compressive strength of the backfill specimens first increases and then decreases, and the failure mode gradually changes from shear failure to tensile failure. With the increase of particle size gradation, the particle size of aggregate increases, the interface between aggregate and cement matrix is more likely to be fractured, and the characteristic parameters of acoustic emission are more active. During the failure process of backfill, the AE energy rate increases rapidly in the plastic development stage, and reaches maximum value before and after the peak stress, which can be used as the precursor to judge the failure of waste rock cemented backfill. According to the test results, the damage model and constitutive equations of waste rock cemented backfill with different Talbot particle size gradations are established, which can provide engineering guidance for filling mined-out areas with waste rock to ensure safe production of mines.

Microstructure-guided computational model for predicting effective thermal conductivity of cementitious composites filled with phase change particles

Functional composite phase change materials (CPCMs) are particularly emphasized by integrating PCM particles in building materials for energy-saving applications, due to PCM's excellent temperature adjustment capacity. However, the inherent drawback of low thermal conductivity of PCM decreases its phase-changing efficiency. Finding highly-efficient heat transfer technique becomes quite necessary. This work utilizes small hollow steel balls (HSBs) to encapsulate paraffin to provide a simple and practical solution, not only ensuring sufficient protection to PCM core in alkaline environment but also enhancing heat transfer into PCM. Then the PCM-HSBs aggregates mix with cementitious matrix to fabricate CPCM. The composite thermal conductivity (CTC) is respectively determined by experiment, theory and computational microstructure model precisely representing random morphology of PCM-HSBs in matrix, and a good agreement is observed between them. Then the dependence of CTC on microstructure features is illustrated to identify their roles. Finally, the composite compressive strength (CCS) and failure mode is discussed briefly to establish comprehensive understanding of composite properties. The results show that CTC has a significant increase of 25.84%, while CCS decreases 12.7%, when 15.28% PCM-HSBs are used. The degradation of CCS is mainly attributed to the smooth surface of HSB, which can be roughened by abrasive blasting.

Effect of thermal and hydrothermal aging on the crashworthiness of carbon fiber reinforced plastic composite tubes

Thin-walled structures constructed of fiber reinforced composites are increasingly being employed in engineering practice. However, there is limited investigation into their residual properties after high temperature and hygrothermal aging. The aim of this experimental investigation is to study how moisture absorption and high temperatures affect the mechanical characteristics of fiber reinforced plastic (FRP) composite tubes. A set of accelerated thermal and hygrothermal aging experiments are designed to imitate the service conditions of carbon fiber reinforced plastic (CFRP) structure in harsh environment. Based on the glass transition temperature obtained by dynamic mechanical analysis (DMA), the specimens are divided into two groups for various temperatures (25°C, 70°C, 100°C, 160°C) and hydrothermal aging (25°C, 70°C). The specimens of hydrothermal aging group are immersed for about 700 h to monitor the water absorption of the specimens in hygrothermal environments with different aging time. Aged composite tubes subjected to quasi-static axial compression are tested to identify compressive strength, failure modes and structural degradation process. The scanning electron microscope (SEM) is used to explore the microscopic failure mechanism of CFRP tubes. As temperature and moisture absorption rate increase, the crashworthiness characteristics decrease drastically; and the failure modes differ substantially with three different failure types identified. The crashworthiness of CFRP has a nonlinear relationship with temperature, but it is related to the glass transition temperature of the matrix. Furthermore, moisture absorption can be divided into two stages and temperature affects the moisture absorption of CFRP. Microscopically, the morphology and bonding conditions between fiber and resin is found to change significantly on the microscale as a result of various temperatures and hydrothermal aging.

Eccentric compression behaviour and assessment of CFET short columns offering spherical-cap gaps

This paper designs and tests a total of 14 specimens to explore the effect of load eccentricity and spherical-cap gap on the compressive strength, ductility, failure modes, and strain distribution of the concrete-filled elliptical steel tubular (CFET) short columns with spherical-cap gaps. A finite element (FE) model of the eccentrically-pressured CFET short column is established by taking the characteristics of spherical-cap gap and elliptical cross-section into consideration. Extensively parametric studies on the impact of various geometric and material variables are further developed via FE analytical models. Intensive mechanical responses, such as the contact pressure between concrete core and hollow steel section (HSS) and the compressive stress at the mid-height cross-section, are presented as well. Based on the comparison between the test results and the predicted data obtained from the design provisions in specifications EN 1994–1-1, AISC 360–16, and GB 50936–2014, proper design formulae for evaluating the eccentric compressive strength of the CFET-SG short columns are proposed. The research results show that the existence of the spherical-cap gap significantly weakened the interaction between the HSS and the concrete core, leading to a reduction in the eccentric compressive strength and ductility behaviour. The concrete around the gap region appeared brittle collapse due to the shrinking confining effect of the HSS, and the HSS exhibited inward and outward local buckling because of the lack of concrete supporting action. The observations of this paper may furnish a scientific reference for the performance evaluation and prevention measures of CFET short columns with spherical-cap gap defects.

Compressive strength characteristics of hybrid fiber-reinforced cemented soil

ABSTRACT Cemented soil commonly faces issues regarding strength, cracking resistance, and water stability when used in airstrip pavements. Three kinds of soil samples (low-liquid limit clay, high-liquid limit clay, and clayey sand), four kinds of fibers (basalt fiber, glass fiber, fine polypropylene fiber, and coarse polypropylene fiber), and one curing agent (cement) were analyzed in a systematic investigation of the compressive strength of fiber-reinforced cemented soil based on unconfined compressive strength (UCS), water stability, and failure mode. When 38 mm coarse polypropylene fiber at 0.3% content was mixed with 12 mm fine polypropylene fiber at 0.3% content, the hybrid fiber-reinforced cemented soil prepared after 7 d of saturated curing achieved UCS values of 4.18 (low-liquid limit clay), 4.36 (high-liquid limit clay), and 4.16 MPa (clayey sand), which satisfied airstrip requirements for the strength of base course. In this study, coarse polypropylene fiber was adopted and mixed with fine fiber to give full play to their respective advantages and effectively enhance the mechanical properties of cemented soil. The research results improved the understanding of the mechanical properties and reinforcement mechanism of coarse and fine fiber reinforced cemented soil in theory, and enriched the materials and methods of airstrip construction in engineering.

Compressive performance of H-shaped aluminium alloy members with web openings

In this study, experimental, numerical, and theoretical approaches are adopted to comprehensively investigate the compressive bearing capacity and failure modes of H-shaped aluminium alloy members with web openings. The influence of the opening parameters, section size, and slenderness ratio on the bearing capacity of such alloy members is analysed, and a calculation method is presented. Finite element models are established in Abaqus with the same configurations as the test specimens. The following conclusions are drawn from the analysis results: 1) The web openings weaken the practical section and destroy its continuity. Moreover, they affect the force flow transmission, thereby reducing the bearing capacity of the component and changing its failure mode. 2) Web openings have significantly larger impact on members with smaller slenderness ratios. The failure modes of members with different slenderness ratios are therefore different. 3) When the slenderness ratio is approximately 60, the weakening of the load displacement along the strong axis due to the web openings is significantly higher than that along the weak axis. 4) When the opening ratio exceeds 0.7, the openings greatly affect the stability of the components. In contrast, when the opening ratio is less than 0.3, the openings have negligible impact on the component stability. The numerical and theoretical analysis results are compared and verified by the experimental results.

Environmentally friendly bio‐inspired folded sandwich panels—Fabrication and mechanical behavior

AbstractA manufacturing method of folded and straight corrugated plate structure printed by environmentally‐friendly polylactic acid filled with environmentally‐friendly paraffin wax is proposed. Experimental investigations are conducted to characterize the out‐of‐plane compressive behaviors, including stress–strain curve, deformation processing, failure mode, strength, and energy absorption. By filling paraffin wax, the out‐of‐plane compression failure mode of sandwich materials from buckling (corresponding to empty corrugated sandwich panels) to wrinkling or crushing, which greatly improves the strength. Due to paraffin wax and its interaction with composite origami core, the energy absorption capacity is significantly enhanced. The research shows that the half‐filled folded corrugated sandwich structure not only has excellent specific energy absorption advantages, the paraffin wax has excellent heat absorption and release performance, and the unfilled part is just used as a heat flow channel to facilitate the flow of heat. This work has created a new method for rapid preparation of lightweight sandwich materials with not only high specific strength and high specific energy absorption, but also thermal channels.

Dynamic Mechanical Properties of TC11 Titanium Alloys Fabricated by Wire Arc Additive Manufacturing.

To study the compressive mechanical properties and failure modes of TC11 titanium alloy fabricated by wire arc additive manufacturing (WAAM) technology in a large strain rate range at room temperature, the quasi-static and dynamic compression tests were carried out. In addition, optical microscopy (OM) and scanning electron microscopy (SEM) were employed to observe the metallographic structure and fracture morphology, respectively. The stress–strain curves in the range of 0.001 s−1–4000 s−1, original and post-deformation microstructures, macroscopic damage patterns, and microscopic fracture morphology were obtained at two different loading directions, including the scanning and deposition directions, respectively. In uniaxial compression experiments, the material showed little difference in mechanical properties between the scanning and deposition directions, exhibiting a strain rate strengthening effect. However, the strain rate sensitivity of the material under quasi-static loading conditions is much less than that under dynamic loading conditions. In addition, combining the stress–strain curve with the fracture morphology analysis, the plasticity in the scanning direction is better than in the deposition direction. Based on the experimental results, a modified Johnson–Cook (JC) constitutive model considering strain rate sensitivity and the effect of strain rate on strain hardening was proposed, and the parameters were determined using a Multiple Population Genetic Algorithm (MPGA). The obtained constitutive model is in good agreement with the experimental data, which can provide a reference for the engineering numerical calculation of TC11 titanium alloy for WAAM. This study also provides a fundamental databank for the application and design of WAAM TC11 alloy in the manufacturing of large and complex structural parts.

Concrete-filled high strength steel tube stub columns after exposure to fire: Testing, numerical modelling and design

This paper reports experimental and numerical investigations into the structural behaviour and residual capacity of concrete-filled high strength steel tube (CFHST) stub columns after exposure to fire. The experimental investigation was conducted on twelve square CFHST stub column specimens after exposure to the ISO-834 standard fire for 15 min, 30 min and 45 min and four reference specimens at ambient temperature. The test results, including failure loads, load–end shortening curves, initial compressive stiffnesses and failure modes, were fully reported and discussed. A numerical investigation was subsequently conducted, where thermal and mechanical finite element models were developed and validated against the test results, and afterwards used to performed parametric studies to generate further numerical data over a wide range of cross-section dimensions. Owing to the absence of design codes for composite structures after exposure to fire, the relevant ambient temperature design rules, as set out in European code, American specification and Australian/New Zealand standard, were evaluated, using post-fire material properties, for their applicability to post-fire CFHST stub columns, based on the test and numerical data. The evaluation results revealed that all the three design codes generally yield accurate failure load predictions for CFHST stub columns after exposure to fire.

Flexural behavior and design of under-reinforced concrete beams with BFRP and steel bars

This study aims to investigate the flexural behavior of hybrid reinforced concrete beams and study the design methods. Seven concrete beams reinforced with basalt fiber-reinforced polymer (BFRP) bars and steel bars, including six under-reinforced concrete beams and one slightly over-reinforced concrete beam, were constructed and subject to four-point loading. The reinforcement ratio was the main test parameter. The experimental results showed a transition region between the tension and compression failure modes. The upper bound of the reinforcement ratio of this region was determined through a statistical analysis of available data. The under-reinforced concrete beams with BFRP and steel bars yielded large deflections and crack widths, and the deformability factors of these beams were significantly larger than those of over-reinforced concrete beams with hybrid bars reported previously. The American Concrete Institute (ACI) method and Xue’s equation were modified and employed to predict the flexural strength of under-reinforced concrete beams with hybrid bars. The experimental results were utilized to verify the accuracy of existing models to predict the pre-yielding and post-yielding deflections and assess the bond coefficients of the ribbed BFRP bars.