Dominant Failure Mode Research Articles

Bond properties of GFRP rebars in UHPC under different types of test

Bond properties of Glass Fiber-Reinforced Composite (GFRP) rebars in Ultra-High-Performance Concrete (UHPC) are the key to designing the FRP-reinforced UHPC structures. In this paper, bond properties between sand-coated/deformed GFRP rebars and UHPC within various embedment lengths and covers were estimated using three types of tests, namely the pullout test, modified pullout test and beam test. It was revealed that the dominant failure mode was the pulling-out of GFRP bars, evidenced by interlaminar shearing devastation, showing the shearing of the ribs and a significant reduction of the rebar diameter. Two classes of bond stress-slip relationships were summarized depending on the embedment length. The micro-slip, slip, decline and oscillation parts were captured, with the oscillation characteristic being more related to the ribs of GFRP rebars. Bond strengths of GFRP rebars under the beam test increased by 4.2 %− 10.0 % to the pullout test, and those obtained from the modified pullout test and pullout test remained little difference within 3.3 %. Both increasing the embedment length and lowering the cover could cause a linear decrease in the bond strength. Specifically, regarding beam tests, the bond strength demonstrated reductions of 11.4 % and 29.5 %, respectively, when the embedment length increased from 2.5d to 5d and 5d to 10d. Moreover, the bond strengths under three types of tests were compared with the ones predicted by existing methods, and the design recommendation was presented.

Optimizing the Microstructure and Properties of Fe–Ni–Cu–Mo–C Sintered Steel by TiB2

The Fe–Ni–Cu–Mo–C powder metallurgy sintered steels with TiB2 reinforced were prepared by the conventional powder metallurgy techniques. This study explored the influence of incremental TiB2 additions, ranging from 0.1 to 0.6 wt.%, on the microstructure and properties of these steels. The results reveal that the microstructures primarily consist of martensite, Ni-rich austenite, Cu-rich pearlite, TiB2, and Ti–O rich nanoparticles. The latter form via a reaction between TiB2 and free oxygen. Notably, both the density and impact strength of the steels showed enhancement with increasing TiB2 content. The optimal values, 7.25 g/cm3 for density and 17.23 J/cm2 for impact strength, were observed at a TiB2 concentration of 0.5%. The hardness and ultimate tensile strength also increased steadily, reaching maxima of 38.7 and 1083.7 MPa at 0.6% TiB2, respectively. However, excessive TiB2 led to the formation of a net-like B-containing eutectic network, adversely affecting the steel properties. Steels with 0.5% TiB2 exhibited excellent wear resistance. At 200 rpm, the dominant failure mode was abrasive wear, which shifted to adhesive wear with oxidation at 400 rpm, followed by abrasive wear.

Safety assessment of interaction behavior of high cycle and very high cycle fatigue with creep at high temperature

Interaction of fatigue and creep behavior is the dominant failure mode for high cycle or very high cycle fatigue under high mean stress at high temperature. As for large rotating component working as high-speed at high temperature, such interaction drives the need to update strength assessment and design method. In this work, a constant life diagram incorporating dual-criterion for evaluating the interaction behavior between high cycle/very high cycle fatigue and creep at high temperature was proposed, and then verified using six types of materials data. This dual-criterion method was proved to be more precise for assessing the serious fatigue-creep interaction behavior in long-life regime, that was promising for design and safety assessment of high-temperature rotating components.

Machining of Ni-based superalloys using CAPVD coated carbide tools

The ever-increasing demand for cost-effective machining of Ni (Nickel) based superalloys has made it necessary to explore nanocomposite coatings as a potential surface engineering solution. The present study aims to investigate the variation in machining performance of new-generation hard wear-resistant coatings in milling of IN 718 (Inconel 718), IN 625 (Inconel 625), and IN 617 (Inconel 617). TiAlSiN and CrAlSiN coatings were grown in-house over tungsten carbide (WC) milling inserts through the cathodic-arc PVD route. The TiAlSiN coating improved the tool life by 80 % and 60 % in the case of IN 718 and IN 625, respectively. However, in the case of IN 617, the TiAlSiN-coated tool could not even reach the uncoated tool life. The CrAlSiN coating, on the other hand, improved the tool life by more than 200 % in the milling of IN 617. Tool-chipping was the dominant failure mode among all observed, which included flank wear and workpiece adhesion. The repeated adhesion and removal of the workpiece layer from the tool surface was a major cause of tool failure. The coating layer delayed the initiation of the chipping and prolonged the flank-wear-dominated machining time, resulting in improved tool life. The wear resistance of coatings in machining different workpiece materials was greatly influenced by the relative affinity of constituting elements of workpieces for employed coatings. The machining chips exhibited shear bands and saw-tooth (serrated/segmented) morphology in almost all cases. The degree of segmentation showed a direct correlation with tool life. The present work helps identify the optimum coating and machining conditions for three different grades of Ni-based superalloys. Additionally, the underlying mechanisms were analyzed and discussed with scientific observations.

Behaviour of short and long columns made from bamboo scrimber subjected to uniaxial compression

Engineered bamboo has been getting recognition as a forerunner in terms of desirable mechanical properties and a sustainable construction material. One of the most widespread variants is bamboo scrimber, also known as Parallel Bamboo Strand Lumber (PBSL). This paper presents a holistic investigation into the uniaxial compressive capacity of short bamboo scrimber columns in terms of failure mode, size effect, aspect ratio and failure strain. The studies in focus have been collated from published articles in literature. Furthermore, intermediately slender to long columns have been investigated with respect to the most common international timber standards and, elastic and inelastic theories. It is shown that the dominant failure mode affects the ultimate strength, especially a failure mode called kinking/local buckling. A size effect was observed and discussed with respect to the failure modes. In addition, a tangent modulus theory was proposed from a constitutive model called the Full-range Ramberg Osgood model that could better predict the critical buckling stress of intermediate-long columns over the conventional theory. Moreover, a modified AS1720 design approach was proposed to accommodate the inherent column behaviour of bamboo scrimber. Finally, a modified Newlin-Gahagan approach was proposed which produced consistent predictions for the experimental buckling stress for columns with varying slenderness across four different studies.

Quasi-static axial crushing investigation of filament-wound eco-friendly energy-absorbing glass fiber and jute fiber composite structures

This study conducts a comparative analysis of glass fiber (GF) and jute fiber (JF) as energy-absorbing filament wound eco-friendly structures under quasi-static axial crushing with varying wall thickness, starting with a 2-layer configuration and progressing to 4 and 6 layers. Three primary failure modes, fiber-matrix fracturing, local buckling, and delamination were observed. Both JF and GF 2-layer configurations showed less progressive failure due to their lightweight nature, with crush force efficiency (CFE) of 0.44–0.46 and specific energy absorption (SEA) of 4.4–5.1 J/g, raising considerations for crash scenarios involving human safety. The 4-layer JF configuration demonstrated a significant increase in IPF to 3496 N, effectively restricting buckling and brittle fracture and leading to a higher SEA of 12.61 J/g. In comparison, the GF 4-layer configuration exhibits lower initial peak force (IPF) and SEA values but a higher CFE value of 0.64 at a lower weight of 58 g. The 6-layer JF configuration attains increased stability in load-bearing capacity with a CFE of 0.84 but at the cost of a high weight of 128 g. On the other hand, the 6-layer GF configuration showcases a higher SEA of 10.5 J/g with a moderate CFE of 0.75 and slightly lower weight, suggesting a delicate balance between performance and weight. Visual examination revealed dominant failure modes as local buckling in GF and brittle fracturing in JF configurations. Overall, the 4-layer configurations of JF and the 6-layer configuration of GF composite tubes demonstrate exceptional energy absorption efficiency, suggesting the potential for exploring hybrid configurations to achieve a balanced crashworthiness performance.

Axial capacity of a novel cold-formed steel swaged section: Experimental tests and design

This paper reports a total of 101 experimental results on the axial behaviour of CFS columns having a swaged section at the end or in the middle of channels under a fixed-fixed boundary. For comparison, the equivalent CFS columns with plain sections were also tested; CFS columns with five different stud lengths and three different cross-sections were tested. It was found that compared to the plain sections, the average axial capacities of specimens having a swaged section are reduced by 5.5% for sections having the cross-section dimensions of 65 × 41.3 × 0.75 and 3.9% for sections of 100 × 50 × 0.95, respectively. For the columns with lengths of 1000 mm, 1200 mm, and 1400 mm, their primary failure mode was global buckling. However, for short columns (with lengths of 150 mm and 300 mm), the dominant failure mode was local buckling. A comparison between the experimental results and direct strength method (DSM) predictions from the AISI S100-16 and AS/NZS 4600:2018 was conducted, indicating that the DSM is un-conservative by approximately 1.4% on average while predicting the axial capacities of CFS columns having a swaged section.

Damage and fracture investigation of self-compacting concrete in the filling layer of CRTS-III using three-point bending tests

Literature about filling layer self-compacting concrete (FLSCC) has indicated that FLSCC plays a crucial role in its application to Chinese railway track system III (CRTS-III). It is apparent that the damage characteristics of FLSCC have not been clearly investigated, as the actual working conditions are not considered enough. There exists a remaining gap about the mechanical properties and fracture behaviors of FLSCC under bending loads. In order to fill this gap, in this study, three-point bending (TPB) tests on the FLSCC beams with precast notches were performed based on the real bending situation of FLSCC in CRTS-III. Acoustic emission (AE), strain gauges and a digital camera were utilized to monitor the fresh evolutionary laws of micro- and macro-cracks as well as the corresponding damage morphology. The study presents that the monitored load-crack mouth opening displacement (P-CMPD) curves, load-strain (P-ε) curves and AE activity curves all exhibited similar distributions, including four stages with increasing bending loads. In term of the AE activities, the first apparent crack in the interior and warning point of failure can be detected by analyzing the captured AE activities of the FLSCC beams. In addition, the dominant failure mode of the specimens was determined as tensile cracks according to the rising angle-average frequency (RA-AF) criterion for potential FLSCC application in terms of the limiting ratios. This failure mode indicates that under pure bending loads, the mid-span section is subjected to the maximum bending moment, and the specimen experiences tensile damage. Therefore, for future practical application, the structural health state of FLSCC in CRTS-III could be nondestructively real-time monitored by the AE technique. Meanwhile, the calculated fracture parameters of the FLSCC specimen can reflect the cracks stability of the specimen. This study can also present experimental and theoretical references for further studies on FLSCC in CRTS-Ⅲ under other types of loads.

Multiscale finite element analysis of layer interface effects on cracking in semi-flexible pavements at different temperatures

This paper presents comprehensive research work on the crack initiation behavior of Semi Flexible Pavements (SFP) with the help of a one-way coupled multiscale modelling approach. The study focuses on elucidating the influence of layer interface conditions on potential cracking patterns under different temperature conditions. By integrating material properties at both local (mixture) and global (pavement) scales using a local de-homogenization approach, the interlocking effect was addressed within the asphalt binder's mesoscale properties. CT-image based mesostructure was employed to reconstruct the Representative Volume Element (RVE). Cohesive Zone Model (CZM) was utilized to simulate cracking initiation within the RVEs, with simulation results validated against practical engineering inspections. Additionally, a potential macroscopic failure index was introduced for SFP. It was found that the typical macroscopic failure indexes utilized for AC pavement may not be suitable for SFP due to the higher degree of heterogeneity. Analysis showed that SFP layer's coarse aggregate and cement grout at the bottom may experience compressive stress, while asphalt binder beneath the tire load may face high tensile stresses. Regardless of the interface conditions, top-down cracking was found to be the dominating failure mode in SFP. Besides, the vulnerable area in bonded interface SFP shifts from under tire load to the adjacent area with the rise in pavement temperature, while bottom-up cracking may appear only in unbonded interface SFP under low temperature conditions. Subsequent analysis demonstrated that top-down cracking is prominent in bonded interface SFP, especially at higher temperatures, compared to unbonded interface SFP. It is expected that critical observations for SFP highlighted above will certainly help in understanding critical failure modes and, hence, designing and constructing durable SFP structures.

Characterization of fatigue crack growth behavior in welded tubular T-joint

This paper focuses on investigating the fatigue crack growth (FCG) characteristics and residual fatigue life of tubular T-joints which are prone to suffer fatigue damage at the brace and chord intersections under multi-axial stress. Static and fatigue loading tests are performed to investigate the FCG behaviors of tubular T-joints, combining beach marking technique. The evolution of FCG characteristics is studied during the crack growth, convergence and wall penetration through an efficient co-simulation system that established using the multi-scale modeling technique. Fracture morphology analysis is conducted to gain insight into the FCG behaviors combining the scanning electron microscope (SEM) observation. Results indicate that multiple cracks initiate at the crown regions and subsequently evolve circumferentially around the weldments in a doubly-curved shape towards wall-thickness. Interaction effects between adjacent cracks extend the fatigue life along the outer surface, attributed to the premature exposure of converged crack front and the induced variation of stress intensify factor (SIF) distribution along the crack front. The dominant failure mode of tubular T-joints is characterized by an opening mode crack, with the contribution of anti-plane shear mode crack gradually increasing as structural symmetry diminishes. The established co-simulation system shows advantage in capturing the FCG behavior, predicting the fatigue life and characterizing the FCG characteristics with a good balancing of simulation efficiency and calculation accuracy.

Platelet critical length for Prepreg Platelet Molded Composites

This work presents a comprehensive evaluation of platelet critical length in Prepreg Platelet Molded Composites (PPMCs), addressing the complex failure mechanisms in these material systems. An array of overlaid platelets is loaded under uniaxial tension while evaluating the failure mechanism as a function of platelet length. The research identifies two primary failure mechanisms: interface failure and platelet failure, which are distinctly dependent on platelet length. The transition between the dominant failure modes occurs at a critical platelet length, marking a critical juncture in the PPMC performance. This study offers insights into the stress transfer mechanisms within an array of platelets leading to failure. To evaluate the critical length, a continuum-based damage model for the platelets and a cohesive zone-based damage model for the platelet interfaces was implemented in a Finite Element Analysis (FEA) framework. The cohesive based interface allows for mode-I and mode-II failure types, with the approach being validated through benchmark studies of Double Cantilever Beam (DCB) and End-Noted Flexure (ENF) simulations. The central idea of the paper posits that the length of platelets impacts the mechanical properties and performance of PPMCs. It details the complex stress transfer mechanisms in PPMCs and their relation to the dominant failure mechanisms.

Failure analysis of underground concrete silo under near-field soil explosion

The underground concrete silo is commonly constructed severing as vertical transport passages in mining and emergency exits for buried structures like tunnels, which, however, is possible to encounter accidental or intentional soil explosions (e.g., blasting excavation). The purpose of this study is to reveal the failure mode and mechanism of an underground concrete silo (46 m in height) subjected to a near-field soil explosion. The Coupled Lagrangian-Eulerian (CEL) method, along with two well-developed material models respectively for soil and concrete, is employed to handle the violent interactions between the exploded soil and the concrete silo. The numerical framework is first validated by simulations of a soil explosion beneath a concrete slab, where the predicted crack patterns of the concrete slab accord well with the experimental results. Subsequently, comprehensive numerical simulations are conducted to investigate the failure of the concrete silo under various soil explosion scenarios. The results indicate that the concrete silo experiences successively or simultaneously tensile spalling failure, local compression-induced tensile failure, and bending-induced tensile failure, with one or two predominating. The prevailing failure mode of the concrete silo is highly dependent on the intensity of the shock wave and the loading area. Further investigations expose that with the scaled distance increasing from 0.12 to 0.4 m/kg1/3, the dominant failure mode of the concrete silo transforms from local compression-induced tensile failure to overall bending-induced tensile failure. The critical scaled distance is 0.2 m/kg1/3. Regardless of the dominant failure mode, three-dimensional fracture planes that split the silo structure are generated. Besides, the tensile spalling failure, arising from the reflected tensile stress wave, is severe on the internal surface of the silo structure, consequently, fragments with velocities up to 12 m/s are produced, posing potential risks to humans and facilities inside the silo if any. This is the first time, to the authors’ knowledge, the failure of the prototype of a large-scale underground concrete silo arising from a large-yield and near-field soil explosion has been investigated. The finding can benefit the research community and provide a reference for the protection of the underground concrete silo as well as the facilities inside it to withstand soil explosions.

Experimental study on the quasi-static and dynamic tensile behaviour of thermally treated Barakar sandstone in Jharia coal mine fire region, India

In the present study, the effect of mild to high-temperature regimes on the quasi-static and dynamic tensile behaviours of Barakar sandstone from the Jharia coal mine fire region has been experimentally investigated. The experimental work has been performed on Brazilian disk specimens of Barakar sandstone, which are thermally treated up to 800 °C. The quasi-static and dynamic split tensile strength tests were carried out on a servo-controlled universal testing machine and Split Hopkinson Pressure Bar (SHPB), respectively. Microscopic and mineralogical changes were studied through a petrographic investigation. The experimental results suggest the prevalence of both, static and dynamic loading scenarios after 400 °C. Up to 400 °C, the quasi-static and dynamic tensile strengths increased due to the evaporation of water, which suggests a strengthening effect. However, beyond 400 °C, both strengths decreased significantly as newly formed thermal microcracks became prevalent. The dynamic tensile strength exhibits strain rate sensitivity up to 400 °C, although it shows a marginal decline in this sensitivity beyond this temperature threshold. The Dynamic Increase Factor (DIF) remained constant up to 400 °C and slightly increased after 400 °C. Furthermore, the characteristic strain rate at which the dynamic strength becomes twice the quasi-static strength remains consistent until reaching 400 °C but steadily decreases beyond this temperature. This experimental study represents the first attempt to validate the Kimberley model specifically for thermally treated rocks. Interestingly, the presence of water did not have a significant impact on the failure modes up to 400 °C, as the samples exhibited a dominant tensile failure mode, breaking into two halves with fewer fragments. However, as temperature increased, the failure behaviours became more complex due to the combined influence of thermally induced microcracks and the applied impact load. Cracks initially formed at the centre and subsequently, multiple shear cracks emerged and propagated in the loading direction, resulting in a high degree of fragmentation. This study also demonstrates that shear failure is not solely dependent on the loading rate but can also be influenced by temperature, further affecting the failure mode of the sandstone.

Tailoring adherend surfaces for enhanced bonding in CF/PEKK composites: Comparative analysis of atmospheric plasma activation and conventional treatments

Here, we propose the utilization of atmospheric plasma activation (APA), which outperforms peel-ply (PP) treatment and mechanical abrasion (MA) in achieving high-performance adhesively bonded carbon fiber/polyetherketoneketone (CF/PEKK) composites. This study covers several key aspects, including the chemical and morphological characterization of treated surfaces and mechanical performance assessments of single lap-joints (SLJs) under tensile and flexural loading conditions. In addition, in-situ acoustic emission (AE) monitoring is employed during tensile tests to determine dominant damage types and failure modes in the SLJs. Surface analysis shows that MA increases roughness, PP treatment decreases wettability, while APA enhances wettability by modifying the surface chemistry. Tensile and flexural tests reveal that APA-treated joints surpassed non-treated (NT) ones, with up to 5- and 7-times higher load-carrying performance, respectively, while fracture analysis suggests a shift from adhesive to cohesive failure. AE results show that increased AE events related to cohesive failure align with improved interface interactions.

Fabrication and structural characterisation of hybrid timber-cardboard sandwich beams

This paper develops a novel class of timber-cardboard sandwich (TCS) panels, consisting of low-cost timber facings and a block-laminated corrugated cardboard core. Experimental and analytical studies are conducted to characterise the flexural performance of TCS beams made from recycled or waste materials. TCS beams made from scrap cardboard cores have the exceptional characteristic of being made mostly from waste, up to 91% by volume or 76% by weight, and are demonstrated to have equivalent performance to beams made with recycled cores. TCS beam flexural behaviour is found to be primarily governed by timber face sheets, with very strong composite action and no observed core shear or debonding failure. The strength, stiffness, and dominant failure mode of TCS beams are thus shown to be accurately predicted using composite sandwich beam theory and cross-sectional analysis. TCS beam bending strength is also found to be significantly higher than conventional foam-core structurally-insulated panels with comparable densities, making them highly viable as a bio-based structural alternative. These research findings enhance the capacity and confidence by which cardboard can be used as a construction feedstock, supporting societal progression toward a greener and more circular economy.

Micromechanical modelling of transverse fracture behaviour of lamellar bone using a phase-field damage model: The role of non-collagenous proteins and mineralised collagen fibrils

At the tissue-scale and above, there are now well-established structure-property relationships that provide good approximations of the biomechanical performance of bone through, for example, power-law relationships that relate tissue mineral density to elastic properties. However, below the tissue-level, the individual role of the constituents becomes prominent and these simple relationships tend to break down, with more detailed theoretical and computational models are required to describe the mechanical response. In this study, a two-dimensional micromechanics damage-based representative volume element (RVE) of lamellar bone was developed, which included a novel implementation of a phase-field damage model to describe the behaviour of non-collagenous proteins at mineral-mineral and mineral-fibril interface regions. It was found that, while the stiffness of the tissue was governed by the relative proportion of extra-fibrillar mineral and mineralised collagen fibrils, the strength and toughness of the tissue in transverse direction relied on the interactions occurring at mineral-mineral and mineral-fibril interfaces, highlighting the prominence of non-collagenous proteins in determine fracture-based processes at this scale. While fractures tended to initiate in mineral rich areas of the extra-fibrillar mineral matrix, it was found that the presence of mineralised collagen fibrils at low density did not provide a substantial contribution to crack propagation behaviour under transverse loading. However, at physiological volume fraction (VfMCF=50%), different scenarios could arise depending on the relative strength value of the interphase around the MCFs (σfInterphaseMCF) to the interphase between individual minerals (σfInterphaseHA): (i) When γ=σfInterphaseMCFσfInterphaseHA<1, MCFs appear to facilitate crack propagation with MCF-mineral debonding being the dominant failure mode; (ii) once γ>1, the MCFs hinder the microcracks, leading to inhibition of crack propagation, which can be regarded as an energy dissipation mechanism. The effective fracture properties of the tissue also experience a sudden increase in fracture work density (J-integral) once the crack is arrested by MCFs or severely deflected. Collectively, the predicted behaviour of the model compared well to those reported through experimental and computational methods, highlighting its potential to provide further understanding into the mechanistic response of bone ultrastructure alterations related to the structural and compositional changes resulting from disease and aging.

Enhancing the fiber-based modeling approach for flexure-shear behavior in seismic evaluation of long-span railway masonry arch bridges

Masonry arch bridges are considered a significant part of the rail and road transportation infrastructures in many countries, and seismic assessment of these structures is of great importance for increasing their resilience. Despite some shortcomings in comparison to more complicated modeling techniques, i.e. continuous and discrete techniques, one-dimensional continuous modeling approaches such as the fiber beam approach are more practical for engineering purposes. Although the fiber models can acceptably predict the axial and flexural behavior of structural members, shear or flexure-shear failure behavior, which could be one of the dominant failure modes in masonry structures, cannot be predicted appropriately in this approach. The purpose of this article is to enhance fiber-based modeling approach to consider these brittle failure modes for the seismic assessments of long-span masonry arch bridges. Using the existing analytical-empirical prediction equations reported on the results of stone masonry walls, an iterative approach is proposed to enhance fiber-based model to include flexure-shear interaction. the proposed method is verified with a series of arch samples with different geometric properties with results from discontinuous models of the sample arches. Following that, different models of a span of a case-study masonry arch bridge is created, verified with health monitoring field observation, and analyzed to compare from different aspects and validate the application of the fiber beam method along with its enhancements. The results of the proposed method for fiber models show promising conformity with the results of more precise numerical models, and it can be used for the seismic evaluation of long-span stone masonry bridges.

Evaluating the axial compression behaviour of hollow concrete block masonry walls with small-size openings: Various opening positions and their influence on experimental results

Openings such as windows or channels for ventilation and heating systems are commonly encountered in masonry buildings to meet with functional needs. Although these openings are known to reduce the strength and stiffness of masonry walls, however, the relationship between the position of openings and load bearing capacity of masonry walls is not well understood. Therefore, the primary aim of this study is to investigate the effect of double opening positions on the axial compressive behaviour of masonry walls constructed with hollow concrete block units. Seven one-half scale walls with different double opening positions were constructed using hollow concrete block units and subjected to a uniformly distributed axial load. The compressive performance such as the strength, stiffness, load-deformation behaviour, stress-strain response, cracking pattern and failure behaviour of the walls have been reported. The results indicate that the 50% reduction in sectional area ratio caused by introducing two small openings in the walls reduced the load bearing capacity by 36 to 50%. Measured ultimate strain values ranges between 5.5 to 38.8% reduction in walls with openings compared with the wall without opening. Vertical cracking, face spalling, and block rupture were the dominant failure modes for walls with double openings, in contrast to mainly vertical cracks observed in the solid wall. This research provides valuable insights into how the positions of double openings influence the performance and overall structural response of hollow concrete block masonry walls under compression load.

Moisture-induced stresses and damage in adhesively bonded timber-concrete composite connection

An experimental program was conducted to clarify the wood swelling effect on the shear strength and failure modes of adhesively bonded timber-concrete composite (TCC) joints. A total of 150 TCC joints were fabricated and cured in the condition of 20 °C & 55% relative humidity (RH) for one month, then the joints were divided into three groups (50 each group) and treated at 20 °C and 55%, 75%, and 95%RH, respectively. After about 30-, 100-, 200-, 300-, and 390-day treatment, ten samples from each group were tested to determine their shear strength and failure modes. It was found that an increase in moisture content (e.g., by 10.8%) caused a reduction of shear bond strength (e.g., by 25%). Concrete failure was found to be the dominant failure mode for all tested joints. Finite element (FE) analyses were performed to facilitate understanding of the underlying mechanisms of wood swelling effects. When the moisture content of wood increased by 10.8%, the FE analyses showed that the wood swelling resulted in significant internal stresses and concrete tensile damage at the wood/concrete bonding interface, which was the main reason for the reduction of the shear bond strength. In addition, the effects of essential factors, such as material properties of adherents, orientation of wood components relative to the bonding surface, and bonding width perpendicular to the grain direction of wood, on the moisture-induced stresses were studied. Concrete grades hardly had influence. For the bonding process of TCC structure in practice, a smaller orientation angle (i.e., the angle between the radial direction and the bonding surface) is recommended to avoid moisture-induced damage in wood and concrete at their interface. In other words, the surface of a Glulam or CLT product designed for bonding should be as close as possible to R-L planes of the constituent wood blocks and avoid T-L planes. Furthermore, a larger bonding width resulted in higher moisture-induced stresses.

Low-Velocity Impact and Post-Impact Residual Flexural Properties of Kevlar/EP Three-Dimensional Angle-Interlock Composites.

In this study, five three-dimensional angle-interlock fabrics with different warp and weft densities were fabricated using 1000D Kevlar filaments. The Kevlar/EP composites were prepared by vacuum-assisted molding techniques. The low-velocity impact property of the composite was tested, focusing on the effects of the warp and weft densities, impact energy, impactor shape, and impactor diameter. The damage area, dent depth, and crack lengths in the warp and weft direction were used to evaluate the impact performance, and the specimens were compared with plain-weave composites with similar areal densities. The dominant failure mode of the conical impactor was fiber fracture, while the dominant failure mode of the hemispherical impactor was fiber-resin debonding. The cylindrical impactor showed only minor resin fragmentation. The residual flexural strength of the composite after impact was tested to provide insights into its mechanical properties. The study findings will provide a theoretical basis for the optimization of the design of impact-resistant structures using such materials and facilitate their engineering applications.