Three-point Bending Research Articles

Experimental and meshless numerical simulation on the crack propagation processes of marble SCB specimens

In order to correctly understand the rock multi-fissure interactions and crack propagation laws, three-point bending fracture tests of the marble semi-circular bend samples (SCB samples) are carried out, and the crack propagation processes are simulated by the Smoothed Particle Hydrodynamics (SPH) method. Results show that: Cracks initiate from the guide fissure tip and propagate vertically in the SCB sample with no obstacle fissures; The overlap positions of crack1 and the obstacle fissure are biased towards the lower left end of the obstacle fissure with the increase of the inclination angle α; With the increase of the eccentric distance d, the overlap positions of crack1 and the obstacle fissure are biased towards the upper right end of the obstacle fissure; The peak load of the samples decreases with the increase of inclination angle α, while increases with the increase of eccentric distance d. The “failure coefficient” η is introduced into the conventional SPH momentum equations, which can simulate the multi-fissure propagations of the SCB samples. The simulation results are consistent with the experimental results, and the mechanisms of the crack propagation morphologies between the guide fissure and the obstacle fissure are discussed. The research results can provide some references for correctly understanding the crack propagation mechanisms of multi-fissure rock masses and the applications of the SPH method into simulating rock multi-fissure interactions.

Bending performance and failure mechanisms of composite sandwich structures with 3D printed hybrid triply periodic minimal surface cores

In this paper, a novel hybrid triply periodic minimal surface (TPMS) core with a nonlinear transition region was designed by combining two types of TPMS (Diamond and Schwarz P) structures using the sigmoid function. The width of the transition region was precisely regulated by adjusting the gradient control parameter r in the sigmoid function. Composite sandwich structures (CSS) were fabricated by bonding two carbon fiber reinforced polymer (CFRP) face sheets to a 3D printed polylactic acid (PLA) core. The bending performance and failure mechanisms of the CSSs with the hybrid TPMS cores were analyzed through three-point bending tests and finite element analysis (FEA). The results indicate that as r increases, the transition region of the hybrid TPMS cores becomes narrower, leading to a gradual decrease in bending strength, bending stiffness, and core shear stress. The failure process of the CSSs in the experiment aligns well with the FEA results. Through comparative analysis of the stiffness-to-weight and strength-to-weight ratios of the CSSs with the native TPMS cores, the hybrid TPMS cores with a wider transition region enhance the structural efficiency of the CSSs, while those with a narrower transition region negatively impact the performance of the CSSs.

Effect of Austempering Go-Kart Rear Axle on Toughness Properties and Microstructure Morphology

A Go-Kart is a four-wheeled vehicle that exhibits characteristics similar to a motorcycle. Additionally, since Go-Kartslack shock absorbers, it is crucial to use an engine that minimizes vibrations. The shaft, a typically circular rotating part, is oftenattached to elements like gears and endures continuous loads, which can lead to breakage. Shaft failures are common and often result from incidents caused by the need to use lightweight materials for faster performance. This study aims to examine the strength characteristics of the Go- Kart rear wheel shaft made from ASTM A414 Grade A steel after undergoing bending tests, impact tests, and microstructure analysis. Specifically, it investigates the effects of temperature on the toughness and curvature of the Go-Kart rear wheel shaft post-normalizing and tempering processes. Methods employed include heat treatment, three-point bending tests, Charpy impact tests, and ASTM E3-11 microstructure analysis. The highest impact value, 0.644joules/mm2, was observed in specimen B, which underwent a normalizing process at 850°C and tempering at 300°C. The lowest impact value, 0.190 joules/mm2, was found in specimen A, which underwent a normalizing process at 800°C and tempering at 250°C. The highest three-point bending strength, 2520.1 N/mm2, was also recorded in specimen B, while the lowest, 2255.4 N/mm2, was in specimen C, which underwent normalizing at 900°C and tempering at 350°C. Microstructure analysis revealed that higher temperatures during the normalizing and tempering processes result in the formation of more pearlite crystals and a denser microstructure.

Small data reliability analysis in concrete three-point bending tests: A Weibull mixture model approach based on Weibull fracture theory

Due to the high costs and time-consuming nature of experiments, data from concrete three-point bending tests are usually limited. Additionally, the performance of concrete is influenced by various factors such as mix composition and sample preparation methods, leading to significant variability in test results. This poses a major challenge for the reliability analysis of small data from repeated tests. In reliability analysis, statistical models are particularly important as they allow for the prediction of performance and failure probabilities based on existing data. However, traditional statistical methods require a large number of similar samples for data processing and may need specific adjustments due to the diversity of practical applications. To address these issues, this study proposes a mixture model that combines domain knowledge of concrete with Weibull fracture theory and uses the Clustering-Circular Block Bootstrap method for sample augmentation. By analyzing real data obtained from concrete three-point bending tests, we accurately estimated the failure probability of concrete. Additionally, the study uses Gaussian process regression with a spectral mixture kernel function to fit the threshold fracture strength of concrete and estimate failure probabilities. The results show that the proposed method can accurately fit small datasets, with a RMSE of 0.320 and a MAPE of 0.100. The nominal bending strength range at a 5% failure probability is 2.0 MPa to 6.5 MPa, depending on the sample height and pre-crack length. Statistical learning demonstrates that the proposed method excels in fitting small datasets, providing a solid framework for predicting concrete strength and reliability.

Failure analysis of titanium honeycomb sandwich structures subjected to three-point bending in high-temperature condition

In this study, the failure process and failure mechanism of Ti65 titanium sandwich structure subjected to three-point bending under high temperature are explored by the combination method of experimental analysis and numerical prediction. Test results show that the failure modes change and a 50% decrease in the peak compressive load occurs under high temperature. A self-developed parametric finite element model is deployed to recreate the structural details of sandwich honeycomb structures and exhibit the failure process of the titanium sandwich structure under three-point bending. The predicted failure process and critical parameters have excellent consistency with test results.

Flexural Strength of Different Yttrium Oxide Containing Monochrome and Multilayer Partially Stabilized Zirconia upon Various Sintering Rates.

Purpose: Sintering procedures influence the properties of zirconia. This study evaluated the effect of varying sintering rates on flexural strength (σ) of 3, 4, and 5 mol% yttria (Y) containing monochrome (Mo) and multilayer (Mu) zirconia. Materials and Methods: 270 specimens (width×length×thickness = 11.2×20×1.5 mm) were prepared from Mo and Mu of 3Y, 4Y, and 5Y zirconia and randomly sintered at regular (RS: 10 °C/min), fast (FS: 35 °C/min), and speed (SS: 70 °C/min) sintering (n = 15/group). Three-point bending test was determined for σ. ANOVA and Bonferroni test were analyzed for significant differences of σ (a=0.05). The microstructure and crystalline [monoclinic (m), tetragonal (t), and cubic (c)] phases were evaluated by SEM and XRD.Results: σ of zirconia was affected by zirconia type, shade pattern, and sintering rate. Significant higher σ for 3Y>4Y>5Y (p<0.05). Significant greater σ for Mu>Mo (p<0.05). Significant reduction of σ upon SS than RS and FS (p<0.05). However, no significant effect on σ upon varying sintering rates within each type of zirconia (p>0.05). SEM indicated greater grain size in 5Y than in 4Y and 3Y. XRD indicated higher t phase in 3Y, whereas higher c phase in 5Y. Mo indicated a higher c phase than Mu.Conclusions: σ was influenced by Y content (3Y>4Y>5Y), shade pattern (Mu>Mo), and sintering rate (RS@FS>SS). Nonetheless, no influence of varying sintering rates on σ for each type of zirconia, suggesting sintering zirconia with RS and FS for expecting higher σ and at SS for acceptable σ for chair-side cost-effective restoration.

Bending behaviors of carbon fiber composite honeycomb cores with various in-plane stiffness

Designing curved surfaces with a traditional straight-walled honeycomb is challenging due to its excessive in-plane stiffness, making it prone to fracturing during bending. The research motivation is overcoming the flexibility limitation of conventional straight-wall honeycombs with the new curved-wall design. Moreover, the three-dimensional failure mechanism map based on the theoretical models is expected to contribute to the design of a carbon fiber composite curved-wall honeycomb. This paper outlines the fabrication process using a modified co-curing method. It also includes theoretical models developed to examine the effect of the center angle of curved walls on the honeycomb’s in-plane stiffness and bending behavior. In-plane tensile and three-point bending tests were conducted to verify the theoretical modes. Finite element model was created to study the stress distribution and damage degree. The study is also aimed at examining the load-bearing capacity of sandwich beams with curved-wall honeycomb cores. A three-dimensional failure mechanism map shows how the failure modes of sandwich structures are affected by the center angle of the curved walls. The study offers a new approach to designing carbon fiber composite honeycombs with flexible bending deformation and high load-bearing capacity. These honeycombs could potentially be used in lightweight launch-vehicle shell structures.

Synthetical improvement of dynamic mechanical property and toughness for precast concrete element based on optimization design of composition and curing regime

The brittleness and toughening measures of steam-cured concrete are currently less researched aspects. This study focuses on exploring the improvement in the toughness of steam-cured concrete and evaluating its influence on dynamic mechanical properties through a series of macroscopic performance tests. These tests include four-point bending tests, three-point bending fracture tests, uniaxial compression tests, and drop hammer impact tests, all conducted from the perspective of optimizing composition materials and steam curing regimes. The experimental results indicate that, under a relatively short heating time and a prolonged constant temperature curing period, the pure cement steam-cured concrete (S1 group), compared to the S2 group which used 20 % FA and 10 % GGBS to replace cement while also increasing the aggregate content with a modified steam curing regime, exhibited higher strength and elastic modulus but also showed greater brittleness. For example, the damping ratio increased to 0.6–0.7, the flexural-to-compressive strength ratio exceeded 6, and the number of specimens damaged by drop hammer impact significantly decreased, and the notch specimen exhibits lower peak load and displacement during fracture, with generally lower fracture parameter values. The fracture energy of the S2 group is 100–130 N·m-1 higher than that of the S1 group, reaching approximately 670 N·m-1, and the ductility index increased by 0.3–0.4. This research can provide technical support for the high-quality preparation of precast components using steam-cured concrete and offer a theoretical basis for reducing the brittleness of steam-cured concrete.

Crystal plasticity finite element simulations on extruded Mg-10Gd rod with texture gradient

The mechanical properties of an extruded Mg-10Gd sample, specifically designed for vascular stents, are crucial for predicting its behavior under service conditions. Achieving homogeneous stresses in the hoop direction, essential for characterizing vascular stents, poses challenges in experimental testing based on standard specimens featuring a reduced cross section. This study utilizes an elasto-visco-plastic self-consistent polycrystal model (ΔEVPSC) with the predominant twinning reorientation (PTR) scheme as a numerical tool, offering an alternative to mechanical testing. For verification, various mechanical experiments, such as uniaxial tension, compression, notched-bar tension, three-point bending, and C-ring compression tests, were conducted. The resulting force vs. displacement curves and textures were then compared with those based on the ΔEVPSC model. The computational model's significance is highlighted by simulation results demonstrating that the differential hardening along with a weak strength differential effect observed in the Mg-10Gd sample is a result of the interplay between micromechanical deformation mechanisms and deformation-induced texture evolution. Furthermore, the study highlights that incorporating the axisymmetric texture from the as-received material incorporating the measured texture gradient significantly improves predictive accuracy on the strength in the hoop direction. Ultimately, the findings suggest that the ΔEVPSC model can effectively predict the mechanical behavior resulting from loading scenarios that are impossible to realize experimentally, emphasizing its valuable contribution as a digital twin.

Numerical Analysis on Fatigue Behavior of Plain Concrete and Alkali-activated Concrete

Abstract Alkali-activated concrete (AAC) has recently gained a lot of potential to become one of the most recommended sustainable replacements for Ordinary Portland cement concrete (OPCC). In the present investigation, an attempt has been made to study the static and fatigue flexural behavior of AAC compared to that of OPCC by using numerical modeling FEA software, ABAQUS. The nonlinear behavior of the stress-strain curve of the concrete has been studied using the concrete damage plasticity (CDP) model. A 2D notched beam was modelled using plane stress condition and three-point bending tests were performed under monotonic loading to obtain the static behavior of concrete. The result obtained has been utilized to fix the loading range for cyclic loads in fatigue analysis and at different loading frequencies. The load-CMOD curves and load-deflection curves were obtained for both static and fatigue loading, and the number of cycles to failure during fatigue. From the results, it has been observed that the Ordinary Portland cement concrete specimens sustain more load than that of Alkali-activated concrete under monotonic loading. However, AAC has shown more resistance to fatigue than that of the OPCC and the frequency of loading significantly influences the fatigue performance.

An assumed enhanced strain finite element framework for tensile fracturing processes with dual-mechanism failure in transversely isotropic rocks

We present an assumed enhanced strain finite element framework for the simulation of tensile fracturing processes in transversely isotropic rocks. Fractures along the weak bedding planes and through the anisotropic rock matrix are treated with distinct enrichment, and a recently proposed dual-mechanism tensile failure criterion for transversely isotropic rocks is adopted to determine crack initiation for the two failure modes. The cohesive crack model is adopted to characterize the response of embedded cracks. As for the numerical implementation of the proposed framework, both algorithms for the update of local history variables at Gauss points and of the global finite element system are derived. Four boundary-value problem simulations are carried out with the proposed framework, including uniaxial tension tests of Argillite, pre-notched square loaded in tension, three-point bending tests on Longmaxi shale, and simulations of tensile cracks induced by a strip load around a tunnel in transversely isotropic rocks. Simulation results reveal that the proposed framework can properly capture the tensile strength anisotropy and the anisotropic evolution of tensile cracks in transversely isotropic rocks.

Investigation into the stress‒strain compatibility and fracture behaviour of a TC18 titanium alloy with a multistage lamellar microstructure

Understanding the fracture mechanism is essential for optimizing the mechanical properties of titanium alloys. The relationship between fracture behaviour and the multistage lamellar microstructure of the TC18 (Ti–5Al–5Mo–5V–1Cr–1Fe) alloy was investigated via in situ tensile and three-point bending tests. The results indicate that the TC18 alloy, featuring a multistage lamellar microstructure (including a β matrix, primary lamellar α phase, bundles, and secondary lamellar α phase), exhibits an excellent combination of strength and ductility. The precipitation of the secondary lamellar α phase significantly enhances the alloy's strength but weakens the stress‒strain compatibility of the microstructure. This results in a smaller crack-tip plastic zone (CTPZ) and causes dislocations to concentrate more at the grain boundaries and, to a lesser extent, at the phase interfaces. Consequently, in the later stages of crack propagation, microvoids and microcracks tend to form at dislocation pile-ups. With increasing stress, these microvoids and microcracks rapidly coalesce, leading to a greater proportion of intergranular fracture and thus reducing the fracture toughness of the alloy.

Obtaining excellent mechanical properties with additively manufactured short fiber reinforced polyether-ether-ketone thermoplastics through simultaneous vacuum and infrared heating

Additive manufacturing of short fiber reinforced thermoplastic composite with high-performance engineering thermoplastics is important in various industrial sectors because of their ability to manufacture complex and lightweight products. Although extensive studies in the literature are aimed at enhancing the mechanical performance of additively manufactured short fiber reinforced thermoplastics through methods like refining printing parameters, enhancing fiber fractions, and optimizing printing parameters, their mechanical performance remains limited. In this study, the individual effects of vacuum-assisted printing and infrared pre-heater-assisted printing and their combined effects were investigated to substantially increase the mechanical properties, interlaminar performance, and crystallinity ratios. The polyether ether ketone (PEEK) samples were printed with vacuum-assisted, infrared-assisted, and a combination of vacuum and infrared-assisted environments were subjected to three-point bending tests to evaluate their mechanical properties. Synergistic vacuum and infrared-assisted printing significantly enhanced the mechanical properties as the flexural strength increased by 54.58 % compared to printing under vacuum alone. Moreover, the flexural strength and elasticity modulus of samples printed with vacuum-infrared-assisted manufacturing increased by 324.48 % and 239.77 %, respectively, when compared to printing under atmospheric pressure without additional heating. Thermal and structural characterizations of the printed parts revealed that this significant improvement was attributed to reduced porosity ratios and increased crystallinity.

Application of fractal analysis to characterise the fracture and mechanical properties of concrete.

Abstract Concrete structures consist of cracks even under service loads. The presence of micro-cracks and other flaws such as pores and voids act as potential sources for crack propagation leading to fracture under external loadings. Irregularities produced during the fracturing process in concrete are manifested on the fracture surface, characterizing it as fractal. Therefore, the investigation and quantification of the fractal pattern exhibited by fracture surfaces have become a focal point of research in recent years. In this work, beam specimens made with four different concrete mixes underwent a three-point bending test in order to determine a correlation between the fracture energy and mechanical characteristics of concrete. Concrete’s mechanical characteristics and fracture energy are discovered to be positively correlated. The fractal analysis is done using an LVDT instrument. Using a program written in MATLAB code, the fractured surface is regenerated with measured undulations. Concrete’s flexural strength and fracture energy are then connected with the fractal dimension value that was found. In conclusion, it was observed that a strong correlation exists between the fractal dimension value and fracture energy.

Numerical Study on Static and Fatigue Behavior of Alkali-Activated Fly Ash Concrete Modelled using Concrete Damage Plasticity (CDP) Model

Abstract Alkali-activated concretes (AAC) are considered as an alternative to Portland cement concretes because of their much lower carbon emissions. To study its characteristics is of utmost importance. In the present research, an attempt is made to create a numerical model to analyze the static and fatigue flexural behavior of alkali-activated fly ash concrete (FC) and compare them with ordinary Portland cement concrete (PCC). Three-point bending tests are simulated for the monotonic load to obtain the static behavior of a 2D notched rectangular beam. A 2D beam specimen of size 262.5 mm x 75 mm, with a notch of size 15 mm x 3 mm was provided at the bottom middle. Fly ash-based alkali-activated concrete (FC) and corresponding PCC of similar strength are modeled in ABAQUS CAE using the concrete damage plasticity (CDP) model. The ultimate loads, maximum deflection, and CMOD for each of them were obtained from the history output manager. The results of monotonic tests are utilized for creating a sinusoidal load cycle for fatigue tests with various loading frequencies and stress ratios. Different structural responses are examined under the fatigue test. The results showed that FC performs better than PCC under static and fatigue tests. Fatigue performance of both FC and PCC is influenced by the frequency of loading and fatigue life increases at higher frequencies. It is also found that stress reversal negatively impacts the fatigue life of both FC and PCC.

A Comparative Study for the Mesoscale Models of Concrete

Abstract This paper provides an overview of mesoscale models used to simulate concrete behavior. A comparative analysis was carried out using mesoscale models with two dimensions. The impact of material type on three tests: the indirect tensile splitting test, the three-point bending test, and the direct tensile test was examined in the study. Additionally, a comparison is made between the findings obtained with and without the application of ITZ and the analysis results obtained from the direct tensile test. The results showed that the fixed crack model had higher stiffness than isotropic damage model in both direct tensile test, and three-point bending test. In indirect tensile splitting test, only fixed crack model gave meaningful results. The models with ITZ had most of the cracks in ITZ rather than in the mortar.

Microstructure, mechanical, and cutting performance properties of B4C and SiC reinforced sandwich composite segments

This study aims to extend the work-life of diamond-cutting segments and to economize the operating cost of diamond-cutting tools. In order to achieve this object, bronze matrix sandwich segments reinforced with SiC and B4C were produced utilizing the hot pressing technique. In the term of the cutting segments, it is favorable that the outer layers are wear-resistant and the middle layer is tough. SEM and XRD analysis were used to determine the microstructural properties. Mechanical properties were evaluated by conducting hardness, wear, cutting performance, and three-point bending tests. The cutting performance of the segments was determined by turning andesite marble. SEM examinations showed that SiC and B4C grains were homogeneously distributed in the bronze matrix. The highest hardness value was 113.9 HB in the B4C reinforced sandwich segment. The reciprocating wear test findings indicated that the matrix exhibited the lowest wear rate in the B4C reinforced sandwich composite segment, followed by the hybrid sandwich composite segment. The lowest amount of cutting loss after turning andesite stone was achieved in the SiC, and B4C reinforced hybrid sandwich composite segment. The cutting performance of the hybrid sandwich composite segment increased by 46.15 % compared to the conventional segment without additives. The highest value of the transverse rupture strength of the specimens was 380 MPa for the B4C reinforced sandwich composite segment and 352 MPa for the hybrid sandwich composite segment. Considering all the tests and analyses, the hybrid sandwich composite segment sample may be the most suitable for diamond-cutting tools.

Numerical and experimental investigation on flexural properties of selective laser melting (SLM) manufactured strut lattices structures from Ti-6Al-4V and Inconel 625

Lattice structures hold a significant importance in the aerospace industry due to their ability to tailor the physical, thermal, and mechanical properties of complex components for optimal performance. This study is focused on evaluating the flexural properties of four lattice configurations - re-entrant, truncated octahedron, Kelvin, and octet cells - through static finite element analysis (FEA) and experimental three-point bending tests, as well as examining their microstructural features (as they affect the materials’ mechanical properties). High-performance alloys used for gas turbines components manufacturing, Ti-6Al-4 V and Inconel 625, were fabricated using selective laser melting (SLM) process. The necessity of this research resulted from the lack of information in the scientific literature regarding flexural properties of various additive manufactured cell types and metallic materials. The aim was to compile data that could be used to create a comprehensive database for various industrial applications. Findings from both simulations and experimental analyses indicated that the octet cell had the highest performance, with experimentally measured flexural strengths of 878 MPa for Ti-6Al-4V, respective 674 MPa for Inconel 625. Contrarily, the re-entrant cell exhibited the lowest performance, with flexural strengths of 125 MPa for Ti-6Al-4V and 116 MPa for Inconel 625. Failure in the re-entrant cells was attributed to the bending fracture of vertical rods at the connecting nodes or lattice struts, while other cell types experienced damage through a combination of bending and shear mechanisms. Dimensional deviations observed in all specimens were attributed to defects such as surface roughness, the stair-stepping effect, and internal stresses.

Experimental and numerical investigation of damage in multilayer sandwich panels with square and trapezoidal corrugated cores under quasi-static three-point bending

Multilayer composite sandwich panels with corrugated cores have the potential for structural applications requiring high stiffness and strength-to-weight ratios. This study aims to experimentally and numerically investigate the bending response of sandwich panels with novel square and trapezoidal corrugated core configurations fabricated from E-glass fiber-reinforced epoxy composites, both with and without polyurethane foam filling. Quasi-static three-point bending tests were conducted to evaluate and compare the flexural stiffness and maximum load capacity of the panel designs. The cores were manufactured using vacuum-assisted resin transfer molding. Key results showed that changing the core geometry from square to trapezoidal improved the bending stiffness by up to 26 %. Incorporating polyurethane foam further increased the bending stiffness by up to 41 % and maximum load by up to 47 % compared to solid cores. Failure initiation and progression were governed by matrix cracking in the face sheets and cores, followed by core cell wall buckling and delamination. Finite element modeling using ABAQUS captured the progressive damage behavior, exhibiting good agreement with experimental force-displacement responses. Failure modes included matrix cracks, fiber fractures, core buckling and delamination. This study provides valuable insights into the mechanical performance of innovative corrugated core sandwich panel designs under quasi-static bending loads. The validated FE approach also enables virtual testing and optimization of composite sandwich structures.

Customizable 3D-printed decoupled structural lithium-ion batteries with stable cyclability and mechanical robustness

Structural batteries are considered one of the promising strategies for improving the endurance of electric vehicles. However, the trade-off between load-bearing capability and electrochemical performance remains a significant challenge. This paper proposes an efficient 3D printing-assisted fabrication strategy for high-performance structural batteries with customizable geometric configurations. The composite structural battery sample shows a bending modulus of 24.5 GPa, which could withstand maximum tensile stress and three-point bending stress of 155 MPa (specific tensile strength of 88340 N m kg−1) and 123 MPa (specific bending strength of 61553 N m kg−1). Meanwhile, it can achieve a high energy density of 120 Wh kg−1 and 210 Wh L−1 (3.5 mA cm−2) and superior capacity retention of up to 92 % after 500 cycles (10.5 mA cm−2). More importantly, the in-situ mechanical-electrochemical test demonstrates exceptional performance, retaining an ultra-high capacity of 98.7 % under a tensile stress of 80 MPa, and maintaining a capacity retention rate of 97 % with an average capacity decay per cycle of only 0.18 % under a bending stress of 96.3 MPa. In addition, finite element analysis is also used to verify the failure mechanism of the battery under bending load. Meanwhile, the fabricated structural battery can be applied to autonomous mobile robots, showing the multifunction energy storage and load-bearing. As a result, this work showcases the great potential of incorporating high-performance structural batteries into engineering applications such as small-scale warehousing, logistics equipment, and intelligent robotics.