Compressive Fracture Behavior Research Articles

Evaluation of retrofitting effect of concrete filling in hollow RC columns using XFEM

Hollow RC columns are widely utilized in the construction of high piers in mountainous regions. Recently, precast hollow RC columns have been increasingly used to enhance transportability and ease of handling, aiding Accelerated Bridge Construction. This paper evaluated the effectiveness of concrete-filling retrofitting measures for hollow RC columns using eXtended Finite Element Method (X-FEM). Our focus was particularly on instances where original hollow sections and post-filled concrete sections don't behave as unified structures. The proposed X-FEM model's reliability was validated through simulations replicating compressive strength tests on molded concrete specimens and previous static loading tests on hollow RC columns conducted to evaluate the efficacy of concrete-filling retrofitting for hollow RC columns. The proposed X-FEM model successfully represents the compressive softening and fracture behavior of concrete under uniaxial compression. It also successfully replicated the lateral load capacity and the crack patterns of hollow RC columns observed in the previous experiments. When comparing the component ratios of bending and shear deformation of the columns, the shear deformation component of the hollow RC column retrofitted with the concrete filling was about 1.5 times larger than that of the solid RC column at each displacement. This result indicates that concrete-filling retrofitting might not enhance the shear capacity of hollow RC columns to the anticipated level in scenarios where the pre-existing hollow portion and the post-filled concrete portion fail to function as unified structures. Based on these findings, this study investigated the efficacy of anchor reinforcement in hollow RC columns filled with concrete to enhance the structural unity of existing and filled portions. The results indicate that anchor reinforcement improved the shear resistance properties by enhancing the structural unity between the pre-existing hollow portion and the post-filled concrete portion.

Filled-hole Compressive Strength and Fracture Behavior of CFRP Laminates

Filled-hole Compressive Strength and Fracture Behavior of CFRP Laminates

Quasi-static compressive fracture behavior of three-period minimum surface Al2O3 / Al composites fabricated by stereolithography

Extensive research has been conducted on the structures and preparation methods of ceramic/metal composites to achieve materials with superior strength and toughness. Among these, the triply periodic minimal surface (TPMS) structure stands out due to its remarkable advantages. In this study, we employed SLA additive manufacturing to fabricate a Gyroid-structured ceramic skeleton, and utilized metal infiltration to prepare interpenetrating Al2O3/Al composites. A comparison was made between the compressive properties of Al2O3/Al interpenetrating composites with Gyroid curved surface structure and those with honeycomb structure. The experimental outcomes indicate that compressive failure in both structural composites primarily occurs at the bond interface between the ceramic framework and the metal. These composites exhibit brittle fracture and experience shear failure. Furthermore, the compressive failure mechanism involves a mixed fracture composed of cleavage and micropore polymerization fractures. Gyroid curved structural composites exhibit lower local stress concentration due to their smooth and regular topology, rendering them with higher strength and ductility compared to honeycomb structural composites. The ultimate compressive strength of the Gyroid curved composite is 264 MPa, representing a 3.8-fold increase over the honeycomb structure.

Compressive Fracture Behavior of Zirconia/Resin Composites Prepared by Fused Deposition Modeling Combined with Vacuum Infiltration.

Although bioceramic materials exhibit good biocompatibilities and bone conductivities, their high brittleness and low toughness properties limit their applications. Zirconia (ZrO2)/resin composites with idealized structures and properties were prepared by fused deposition modeling (FDM) combined with a vacuum infiltration process. The porous structure was prepared using the FDM three-dimensional printing technology, with granular zirconia as the raw material, and the relationship between the pore shape, pore size, and deformation was discussed. The results showed that square pores were more suitable than honeycomb pores for printing small pore sizes, and the resolution was high. Scanning electron microscopy observations showed that the superposition of multiple printing paths promoted the emergence of hole defects. The effects of the resin and the pore shape on the compressive strengths of the composites were studied. It was found that the compressive strengths of the honeycomb pore ZrO2/resin composites and porous ceramics were superior to those of the square pore samples. The introduction of the resin had a significant effect on the compressive strengths of the composites. The compressive strength increased in the direction perpendicular to the pores, while it decreased in the direction parallel to the pores.

Electron beam powder bed fusion additive manufacturing of Ti6Al4V alloy lattice structures: orientation-dependent compressive strength and fracture behavior

High porosity level lattice structures made using electron beam powder bed fusion additive manufacturing (EBPBF) need to be sufficiently strong and the understanding of the mechanical anisotropy of the structures is important for the design of orthopedic implants. In this work, the combined effects of loading direction (LD), cell orientation, and strut irregularity associated with EBPBF of Ti6Al4V alloy lattices on the mechanical behavior of the lattices under compressive loading have been studied. Three groups of simple cubic unit cell lattices were EBPBF made, compressively tested, and examined. The three groups were [001]//LD lattices, [011]//LD lattices, and [111]//LD lattices. Simulation has also been conducted. Yield strength (σy-L) values of all lattices determined experimentally have been found to be comparable to the values predicted by simulation; thus, EBPBF surface defects do not affect σy-L. σy-L of [001]//LD lattices is 1.8–2.0 times higher than those of [011]//LD and [111]//LD lattices. The reason for this is shown to be due to the high stress concentrations in non-[001]//LD samples, causing yielding at low loading levels. Furthermore, plastic strain (εp) at ultimate compression strength of [001]//LD samples has been determined to be 4–6 times higher than the values of non-[001]//LD samples. Examining the tested samples has shown cracks more readily propagating from EBPBF micro-notches in non-[001]//LD samples, resulting in low εp.

Compressive Fracture Behavior and Acoustic Emission Characteristics of Sandstone under Constant Crack Water Pressure

Abstract Engineering rock containing flaws or defects under a large water source is frequently subject to the couple influence of constant crack water pressure and geostress. To investigate the fracture behavior of precracked rock under hydromechanical coupling with constant crack water pressure, compression tests were conducted on red sandstone specimens containing a single crack of different angles using a device to realize the constant crack water pressure during loading, and the failure process of rock specimens was monitored by acoustic emission (AE) technique. The results show that the presence of constant crack water pressure has a significant promotion effect on the development of shear wing cracks, and the promotion effect is influenced by the prefabricated crack angle and water pressure. As the constant crack water pressure increases, the failure mode of the 0° precrack specimen changes from “X”- shear failure to the single oblique shear failure along the shear wing crack direction, the main failure crack of the inclined precracked specimens (precrack angles of 15°, 45°, and 60°) changes from a small acute angle with the prefabricated crack to a direction along the shear wing crack, and irregular cracks occur at the chipped prefabricated crack in the 90° precracked specimen. With an increase in the constant crack water pressure, the average energy for a single hit, cumulative AE energy, and cumulative AE hits decrease, and the proportion of the tensile cracks increases and that of the shear cracks decreases.

3D mesoscale study on the effect of ITZ and aggregate properties on the fracture behaviors of concrete based on discrete element method

The discrete element method (DEM) was utilized to study the effect of the interface transition zone (ITZ) and coarse aggregate properties on the compressive fracture behaviors of concrete at a micromechanical level, in which the ITZ was represented by the contact bond and the coarse aggregate was crushable. The linear parallel bonded model was introduced to represent the constitutive model of concrete, and the meso-scale parameters were determined by laboratory mechanical tests. And then, a series of numerical tests were conducted under compressive loading, and the research objects contain ITZ strength, and aggregate properties (i.e., strength, content, size, and shape). The simulation results show that as the ITZ strength increases, the compressive strength shows a nonlinear increase trend. Moreover, as the aggregate strength and content increase, both compressive strength and strain to damage consequently increase, the aggregate shape is independent of the compressive strength. The increase in the aggregate size can reduce the total surface area of the aggregate, leading to a small compressive strength. The compressive strength appears to increase first and then decrease in trend as aggregate surface roughness increases. In addition, the increase in aggregate strength and content induces the failure pattern changes from local microcrack propagation to global failure. Overall, this work comprehensively evaluates the effect of ITZ and coarse aggregate properties on the damage of concrete at a micromechanical level.

The Cracking Behavior of Two Dental Composite Materials Validated through Multifractal Analyzes.

The aim of this in vitro study was to analyze, both experimentally and theoretically, the mechanical behavior of two types of composite materials used in restoring dental integrity. The samples of each composite resin, namely Filtek Supreme XT (3M ESPE, St. Paul, MN, USA) and Filtek Z250 (3M ESPE, St. Paul, MN, USA), were experimentally analyzed by determining their compressive strength and fracture behavior. The fractured fragments of the samples were subjected to surface evaluation by scanning electron microscopy. The compressive stress-compressive strain dependencies revealed stronger cracking of the Filtek Supreme XT composite than Filtek Z250 prior to fracture. Theoretically, the evaluation was made by means of holographic implementations of such types of composite materials. A Hooke-type equation in a differential form is presented, which links the proposed theoretical model with the experimentally obtained data.

Modelling the effect of concrete cement composition on its strength and failure behavior

Typical concrete is a mixture of Portland cement, water, and aggregates. While aggregates have a substantial effect on the concrete strength and fracture behavior, the focus of the present study is on the hardened cement paste which can be further divided into the unreacted core, inner and outer products. In high strength concrete, water-to-cement ratio is low, and thus the distance between cement particles is small. Also, the amount of unreacted (high strength) core is higher, and the porosity is low. When water-to-cement ratio is higher, both the distance between cement particles and the porosity due to capillary pores increases. In the present study, we develop a numerical model based on the embedded discontinuity finite elements to predict the effect of the water-to-cement ratio on the compressive fracture behavior of concrete. Representative 2D plane strain simulations demonstrate that the present method captures the major features of concrete fracture and, particularly, qualitatively predicts the known effects of the water-to-cement ratio on concrete compressive strength.

Estimation of Concrete Mechanical Properties by Acoustic Emission with Random Forest Algorithm

The concrete structures are damaged by environmental factors and external loads. To maintain such ages structures, it is necessary to properly determine the mechanical properties and accumulated damage level suffered by concrete using core tests. In this study, relationship between the stress level of damaged concrete under uniaxial compression test and acoustic emission (AE) parameters was investigated using clustering and regression analysis with random forests to identify the most important AE parameters. For clusters 1 and 3, R2 is higher, and RMSE and MAE are lower than for non-clustered cases. Therefore, cluster analysis can be expected to improve the accuracy of AE testing. Thus, the most important parameter is determined to be rise time, the secondly is detected the centroid frequency. These two parameters can be used to clarify compressive fracture behavior of damaged concrete.

Compression and shear fracture behavior of single rice paddy under effect of husking operation

Husking is an important process to determine rice quality. Husking ratio and fracture behavior are key points during paddy husking, which are affected by rubber roller line speed, rice moisture content and drying temperature. Based on husking process, the intrinsic property and mechanical-structural damage behavior of three kinds typical rice paddy were tested under different working condition and analyzed by texture analyzer with in-situ observation, optical and electron microscope. Results showed that three kinds rice paddy have different fracture forms and show obvious plastic deformation at the rice grain center under compression, with similar fracture energy and fracture strength. Shear force exerted by PU led to a change in the fracture form of rice grains, showing crack and fracture in the short axis direction. Degree of shear fracture was greater for rice paddy at high speed. In addition, with the increase of soaking time, the moisture content of rice grains increased along with the internal generation of hygroscopic cracks, which led to the decrease of fracture strength and fracture energy. During the drying process, the glassy transformation of the rice grains will reduce their quality, and as the temperature rises, the hardness increases and cavities are created inside.

Formability, surface quality and compressive fracture behavior of AlMgScZr alloy lattice structure fabricated by selective laser melting

Due to the comprehensive advantages of lightweight and integration of structure and function, aluminum alloy lattice structures are widely applied in aerospace, automotive industry and biomedical fields. Selective laser melting (SLM) additive manufacturing technology can significantly improve the overall performance of the structure, reduce the production cycle and manufacturing cost by integrated manufacturing. In this paper, five lattice structures (BCC, BCCZ, FCC, FCCZ, Cubic) of AlMgScZr alloy were fabricated by SLM, and the formability, surface quality and compressive properties were systematically studied. It shows that printing defects are easily formed at high power and fast scanning speed. Comparatively, the lattice structures fabricated at low power and slow scanning speed (100 W-250 mm/s) have better overall forming performance at the same energy density. The Cubic type structure has the highest compressive strength of the five lattice structures, which has a compressive strength of 95.2 MPa under the 200 W-500 mm/s condition.

3D meso-scale modelling of tensile and compressive fracture behaviour of steel fibre reinforced concrete

This paper presents a novel meso-scale modelling framework to investigate the fracture process in steel fibre reinforced concrete (SFRC) under uniaxial tension and compression considering its 3D mesostructural characteristics, including different types of fibres, realistic shaped aggregates, mortar, interfacial transition zone and voids. Based on a hybrid damage model consisting of cohesive element method and damage plasticity method, a cost-effective finite element approach was proposed to simulate the fracture behaviour of SFRC in terms of stress–strain response, energy dissipation and crack morphology. The results indicated that under given conditions, the straight and hooked-end fibres improved the compressive damage tolerances of concrete over 11.5% while the spiral fibres had a negligible effect of 2.6%. The tensile macro-damage level index introduced was reduced over 15% by all fibres. Compared to straight fibres, the higher anchoring capacity of spiral fibres reduced the reinforcement performance while hooked-end fibres did not exhibit a significant influence.

Effects of sample diameter, aspect ratio, and strain rate on compressive deformation and fracture behavior of Zr50Cu34Al8Ag8 metallic glass

In this paper, Zr50Cu34Al8Ag8 metallic glass bars with diameters of 2, 3, and 4 mm were prepared by copper mold suction casting. The compressive mechanical properties of metallic glass samples having different diameters, aspect ratios, and strain rates were tested by a universal testing machine. The microstructure of metallic glass samples was analyzed by X-ray diffractometer, scanning electron microscope, and transmission electron microscope. The experimental results show that the mechanical properties of Zr50Cu34Al8Ag8 metallic glass improve with decreasing sample diameter, aspect ratio, and strain rate. The maximum compressive strength, ultimate strain, and plastic strain of 1991.2 MPa, 7.95%, and 4.99% were respectively achieved for the metallic glass sample of φ = 2 mm. The main reason for the metallic glass's superior mechanical properties is its higher free volume content. For the metallic glass samples with the same diameter and different aspect ratios, the compressive strength and ultimate strain of the metallic glass with φ = 3 mm and aspect ratio = 1 is the largest, which are 2052.8 MPa and 15.2%, respectively, and the plastic strain is 11.09%. The improvement of mechanical properties of metallic glass samples is primarily attributed to the change of stress state. When the strain rate is 3 × 10−4 s, the compressive strength and ultimate strain of the sample are 1851.2 MPa and 4.09% respectively. This study will help to improve our understanding of the compression deformation and fracture behavior of metallic glasses, as well as promote their application.

Advanced Estimation of Compressive Strength and Fracture Behavior in Ceramic Honeycombs by Polarimetry Measurements of Similar Epoxy Resin Honeycombs.

Finding a non-destructive characterization method for cellular ceramics’ compressive strength and fracture behavior has been a challenge for material scientists for years. However, for transparent materials, internal stresses can be determined by the non-destructive photoelastic measurements. We propose a novel approach to correlate the photoelastic stresses of polymer (epoxy resin) prototypes with the mechanical properties of ceramics (alumina). Regular and inverse epoxy honeycombs were 3D-printed via stereolithography with varying structure angles from −35° to 35°, with negative angles forming an auxetic and positive hexagonal lattice. Photoelastic measurements under mechanical loading revealed regions of excess stress, which directly corresponded to the initial fracture points of the ceramic honeycombs. These honeycombs were made by a combination of 3D printing and transfer molding from alumina. The photoelastic stress distribution was much more homogeneous for angles of a smaller magnitude, which led to highly increased compressive strengths of up to 446 ± 156 MPa at 0°. By adapting the geometric structural model from Gibson and Ashby, we showed that we could use a non-destructive technique to determine the compressive strength of alumina honeycombs from the median photoelastic stress measured on similar epoxy honeycomb structures.

Failure-mode dependence of the strengthening effect in Ti3AlC2/10 vol.% Al2O3 composite

Abstract The high-temperature mechanical properties of both Ti3AlC2 and Ti3AlC2/10 vol.%Al2O3 composite, including compressive strength, bending strength, and fracture behavior, were investigated. The strengthening effect caused by Al2O3 strongly depended on the mode of failure: significant enhancement in strength was only observed under the brittle mode of failure; whereas under the ductile mode of failure the strengthening effect was impaired due to Ti3AlC2 matrix softening and stress relaxation.

Compression deformation and fracture behavior of additively manufactured Ti–6Al–4V cellular structures

Corresponding research was carried out to assess if the porous structures with modified diamond-shaped lattice cells can provide better integrity of the constructions in the case of overloading. The aim of the study is designing the structures with high porosity for the biomedical applications (implants) having good load bearing capacity. Studied lattice structures are based on the modified tetrahedral beam-based cells with spherical reinforcements at the beam joints and variable beam diameter. Samples with a porosity of 50–80% were studied in present research. Structures were additively manufactured from a titanium alloy Ti–6Al–4V using SLM. Sample compression tests were carried out according to the ISO 13314 standard. Loading experiments were carried out and critical parameters extracted from the stress-strain curves. Finite element modeling was carried out for the analysis of the stress and assessment of the potential failure mechanisms. Corresponding hypothesis explaining the appearance of shear bands in porous structures under compression is formulated. Obtained results show that when the sample porosity rises from 50% to 80%, corresponding plateau stress decreases by 13 times, first maximum compressive strength decreases by 12 times, and compression offset stress decreases by 12 times, while the plateau end does not change significantly. The experiments revealed the barrel distortion of the samples geometry, which corresponds to the general knowledge how the friction between the solid compressing surfaces (anvils of the compression testing machine) and the lattice affects the sample deformation. Compression experiments also revealed the formation of shear bands during sample deformation. The stochastic nature of their development suggests that the main reason of shear bands appearing is the initial inhomogeneity of the boundary conditions of the experiment.Suggested modifications of the basic cells show a good potential for achieving regular beam-based lattice structures with high porosity and increased load bearing capacity. More experiments are needed for statistical analysis, and improvements of the loading experiments methodology for better failure mode analysis are planned for the future.

A poro-damage phase field model for hydrofracturing of glacier crevasses

Hydraulic fracture (or hydrofracture) can promote the propagation of meltwater-filled surface crevasses in glaciers and, in some cases, lead to full-depth penetration that can enhance basal sliding and iceberg calving. Here, we propose a novel poro-damage phase field model for hydrofracturing of glacier crevasses, wherein the crevasse is represented by a nonlocal damage zone and the effect of hydrostatic pressure due to surface meltwater is incorporated based on Biot’s poroelasticity theory. We find that the elastic strain energy decomposition scheme of Lo et al. (2019) with an appropriate fracture energy threshold can adequately represent the asymmetric tensile–compressive fracture behavior of glacier ice subjected to self-gravity loading. We assessed the performance of the model against analytical linear elastic fracture mechanics solutions by comparing their predictions of maximum crevasse penetration depth. The model simulates both surface crevasse propagation in the interior region of the glacier, as well as cliff failure in the terminus region. The excellent performance of the proposed model for air/water-filled surface crevasses in idealized land- and marine-terminating grounded glaciers illustrates its applicability to studying the dynamic response of glaciers to atmospheric warming.

Meso-scale modelling of compressive fracture in concrete with irregularly shaped aggregates

This paper presents a meso-scale modelling framework to investigate the fracture process in concrete subjected to uniaxial and biaxial compression accounting for its mesostructural characteristics. 3D mesostructure of concrete consisting of coarse aggregates, mortar and interfacial transition zone between them was developed using an in-house code based on the Voronoi tessellation and splining method, which enables to generate the realistic-look aggregates with controllable structural features such as content, location, size and shape. Based on the generated 3D mesostructure, the concrete damage plasticity approach was employed to simulate the compressive fracture behaviour of concrete in terms of crack morphology and stress-strain response against the shape parameters of aggregate. Results indicate that the shape of aggregate has a negligible effect on compressive strength of concrete, which is highly associated with the random location and size distribution of aggregate. The aggregate irregularity has a significant influence on crack initiation and growth of concrete.

Ozone and water immersion effects on compression strength and fracture behavior of carbon/epoxy laminates

Compression tests were assessed to evaluate the ageing effects on carbon fiber/epoxy resin laminates exposed to ozone and water immersion. Laminates with distinct fiber arrangements (unidirectional - UD and plain weave - PW) were tested under compression strength at room (22 °C) and high (82 °C) temperatures after conditioning. The results show that the composites were mainly affected by direct exposure to water and to the high temperature used in the tests. Ozone exposure was also harmful, but to a lesser extent due to ozone attack occurring on the outer surface of the composite. The UD laminate conditioned in water immersion showed that its compressive strength, tested at room temperature, decreased around 16%. This downward trend was accentuated in tests at higher temperatures. Regarding PW laminate, exposed to water immersion and tested at room temperature, a greater reduction was observed (~23%) in compressive strength. High temperature tests also show the influence of this agent on the degradation of the composités property, with a reduction of up to 25%. Fractographic analyses confirmed that the water immersion and the high temperature used in the mechanical tests promoted the degradation of matrix and fiber/matrix interface, with the presence of interface weakening, fiber splitting, delamination, and cracks.