Brittle Failure Mode Research Articles

Cyclic shear testing of artificially corroded reinforced concrete short circular piers

Chloride-induced deterioration of reinforced concrete (RC) structures is an increasingly vital topic among asset management and structural maintenance fields, as many RC bridges and other structures are reaching the end of their initial design lives. Deterioration of the transverse reinforcement in RC piers leads to the direct loss of shear and confinement-related mechanical properties as degradation advances with time. This research investigates the seismic response of fourteen short RC circular piers subjected to artificial chloride-induced corrosion. Each pier is designed to trigger a shear-dominated failure and artificially corroded at two current densities. A maximum average mass loss of 10.5% and 43.0% was measured in the longitudinal and spiral reinforcement, respectively. The influence of confinement effectiveness, spiral diameter, and aspect ratio on the rate of shear capacity degradation are included as test parameters in this study. Results indicate that shear deformation begins to govern performance at moderate to severe deterioration, which precedes the onset of brittle shear-dominated failure modes. Ultimate deflection is more adversely affected by increasing corrosion than all other measured properties, with a maximum observed reduction of 70.9% compared to a maximum 37.5% reduction observed in peak shear capacity. Several existing theoretical models are introduced and evaluated on their ability to predict the shear capacity of the experimental tests. Based on the results, those models directly evaluating the circular section without needing an equivalent section transformation offer the most accurate and reliable predictions.

Versatile coupling of MPM and FEM: A case study of the stability of vegetated slope

Evaluating root reinforcement in the root–soil composite is challenging due to the complex interactions among its components and the variable configurations of the roots. A proposed FEM-MPM coupled model is dedicated to examining the influence of roots on slope stability. The FEM component employed the Truss structural element type to model the dynamics and physics of the root, coupled with a damaged constitutive model, which sheds light on the effects of orientation, cohesion, and friction on the brittle or progressive failure modes of the root. The MPM counterpart provided the capability for large deformation simulation in the post-failure phase of the slope. The framework’s integration was achieved through a penalty method, correcting the dynamics of its members (translation and orientation) and linking the decay of the root with the plastic behavior of the soil through updated geometrical and mechanical properties. Several geotechnical tests and examples, such as pull-out tests, direct shear tests, and vegetated slope collapse simulations, were conducted to validate and verify the robustness of the proposed approach. The results demonstrate the methodology’s capability to capture the mechanism of root reinforcement in vegetated slope stability.

Study on impact properties of carbon/kevlar fiber hybrid composites

AbstractIn this article, carbon/kevlar hybrid composites were prepared using Vacuum Assisted Resin Infusion (VARI). The sandwich structure with plain carbon weave fabric as the core layer and plain kevlar weave fabric as the surface layer was selected as reinforcement and the solution of epoxy resin and curing agent was selected as matrix. The low velocity impact experiment and compression after impact (CAI) experiment were carried out on the samples at different hybrid ratio and different temperatures, and the mechanical response on the impact loads were analyzed respectively. The results show that the specimen can limit the delamination defect expansion of the surface kevlar fiber as the carbon fiber used as the core layer, which reduce the delamination defect area and improve the impact resistance of the sample. The toughness of the sample improves the brittle failure mode, that is, the sample still has a certain bearing capacity after the load exceeds the maximum strength, the sandwiched composites presents a positive hybrid effect. With the increase of temperature, the matrix was obviously softened, the macromolecular movement in the system was intensified, the three‐dimensional network macromolecular structure of the matrix and the fiber/matrix interface properties were damaged, and the mechanical properties showed an obvious downward trend. As far as the influences of hybrid ratio and temperature on impact behavior of composite are concerned, it lay a theoretical foundation for the industrial application of carbon/kevlar hybrid composites.Highlights The sandwiched structure was used to design the composites, which greatly improves the impact properties of the specimens. The impact properties and compression after impact properties at different hybrid ratios and different temperatures were studied. Based on the hybrid effect and temperature effect, the impact failure mechanism of the sample was analyzed.

Exploring the influence of pin geometry on metallurgical and mechanical characteristics of dissimilar aluminum TIG welds via friction stir processing

This study explored the effect of friction stir processing (FSP) on tungsten inert gas (TIG)-welded AA6061-T6 and AA7075-T6 joints by utilizing three different tool pin geometries, namely simple cylinder (SC), threaded cylinder with triflat faces (THF), and simple square (SS). The metallurgical aspects of unprocessed and processed weld regions were analyzed and correlated with the ultimate tensile strength, impact toughness, and microhardness properties. Results revealed that the post-FSP with a THF pin transformed the coarse dendritic structures (AGS of 34.55 µm) of the TIG weld into equiaxed fine structures (AGS of 3.51 µm) and increased the UTS, impact toughness, and microhardness by 71.51%, 95.40%, and 72.46%, respectively. The joint processed with the THF pin resulted in the highest ultimate tensile strength of 279 MPa, impact toughness of 15.02 J, and microhardness of 116.13 HV in the nugget region compared to the other two pin geometries. The highest joint properties of THF pin were attributed to the formation of fine grain structures in the nugget region, high effective strain and heat generation, improved material flow, and the decimation of intermetallic precipitates with their uniform dispersion in the nugget region. The tensile fractured surface of the TIG weldment had noticeable macro voids and coarse dimples with some rough cleavage facet in the fusion region, resulting in a brittle mode of failure. However, the tensile fractured surface of TIG + FSP weldments showed ductile failure due to the presence of fine and deep dimples with tear ridges without any void.

Experimental investigation to understand the effect of fracturing fluid on the geomechanical behavior of mowry shale

Hydraulic fracturing of shale reservoirs is one of the important technologies in the oil and gas industry. To ensure the safe operation of oil and gas recovery, it is important to study the shale-fluid interactions on the geomechanical behavior of shale. This study investigated the effect of fracturing fluid treatment on the mechanical and elastic properties of the Mowry Shale formation, Wyoming, USA. Cylindrical Mowry Shale specimens with a diameter of 12.5 mm collected from the United States Geological Survey (USGS) and School of Energy Resources (SER) of the University of Wyoming were treated with brine and brine + stimulation fluid for one month each at pressures of 9 and 11.7 MPa and temperatures of 96 and 66 °C, respectively. Triaxial compression experiments were conducted on the specimens. Results showed that all Mowry Shale specimens experienced an increase in maximum volumetric strain with the increase in effective confining pressure (Pd). Regardless of aging fluids, the maximum deviatoric stress (Δσd) of most Mowry Shale specimens increases with the increase in Pd. At a lower Pd, the USGS specimen aged with brine and stimulation fluid exhibits higher maximum Δσd than those aged with brine only. However, at a higher Pd, the USGS specimen aged with brine exhibits a higher maximum Δσd. SER specimens aged with brine and stimulation fluid exhibit higher maximum Δσd values than those aged with brine for all three Pd values. Regardless of the aging fluids, most USGS specimens experience a brittle failure mode, while SER specimens aged with brine and stimulation fluid experienced a more ductile behavior.

Discrete element simulation study on effects of grain preferred orientation on micro-cracking and macro-mechanical behavior of crystalline rocks

Abstract Grain-preferred orientation significantly influences the brittle fracture mechanism and failure mode of crystalline rocks. However, current grain-based models (GBMs) based on particle flow code (PFC) software are mostly proposed on the basis of the Voronoi tessellation method for grain boundary generation, which is difficult to simulate the heterogeneity of microstructure such as shape and orientation of rock minerals. To study the effect of grain-preferred orientation on macroscopic mechanical properties and microscopic characteristics of crystalline rocks, a novel grain-based microstructure transformation method (MTM) is proposed. Based on the MTM, a GBM with a target aspect ratio and crystal orientation is obtained by transforming the Voronoi crystal geometry through a planar coordinate mapping. Specifically, embedded FISH language is used to control random mineral seed size and distribution pattern to generate Tyson polygons. A polygon geometry that satisfies the rock texture is obtained as a grain boundary by spatially transforming the vertex of the Tyson polygon. The transformed complex geometry is taken as the crystal structure of the GBM, and the Lac du Bonnet granite models with different aspect ratios and crystal orientations were developed in PFC2D. Finally, a series of unconfined compressive strength tests are performed in PFC2D to verify the proposed modeling methods for the geometric variation of the crystals and to study the effects of the preferred orientation of the grains on the macroscopic mechanical properties and microscopic fracture mechanisms of the crystalline rocks from different perspectives.

The axial tensile performance of DSCW-RC joints with lap-spliced bars

Joints formed between double-skin concrete shear walls (DSCWs) and reinforced concrete (RC) foundations commonly utilize lap-spliced bars to transfer forces. However, the behavior and design of these critical connections have not been thoroughly investigated. This study experimentally analyzes a steel-reinforced DSCW-to-RC foundation anchorage joint under monotonic uniaxial tension loading. Seven 1:3 scale specimens were tested to examine the effects of varying lap-spliced bar diameter, steel plate thickness, and stud bolt spacing. Crack propagation, load-displacement response, and reinforcement strain were measured. The results characterize two potential failure modes: ductile steel yielding and brittle stud shearing. Steel strains developed linearly up to yielding, demonstrating uniform transmission of tensile loads. Increased plate thickness and decreased stud spacing enhanced capacity. To mitigate sudden shear failures, the number and strength of studs must exceed the expected tensile demand. New design recommendations are proposed, including minimum stud bolt shear strength and the use of confining tie bars. This study provides an improved understanding of the behavior of DSCW-to-RC foundation lap-spliced connections, enabling resistance to axial demands while avoiding brittle failure modes. The experimental data will inform future analytical models and design provisions for these critical structural joints.

Utilizing ensemble learning in the classifications of ductile and brittle failure modes of UHPC strengthened RC members

This study aims to achieve the swift and precise classification of ductile and brittle failure modes in flexural reinforced concrete (RC) members, specifically those with tension sides strengthened by ultrahigh performance concrete (UHPC). Employing six ensemble learning techniques—Bagging, Random Forest, AdaBoost, Gradient Boosting, XGBoost, and LightGBM—the authors utilize a comprehensive dataset comprising 14 features, which include manually labeled failure modes obtain from load–deflection curves. The model training spans four scenarios, varying in the inclusion or exclusion of features describing the cross-sectional area of RC members and moment resistance. XGBoost emerges as the most effective classifier, achieving an impressive 84% accuracy with high confidence. Additionally, the study employs the Shapley Additive Explanation (SHAP) technique on the best-performing model to illuminate the significance and impacts of various features in UHPC-strengthened flexural members’ failure modes. Notably, moment resistance and UHPC tensile strength surface as the most influential factors in predicting failure modes. Increased rebar yield strength, UHPC compressive strength, UHPC reinforcement ratio, and steel fiber volume in UHPC contribute to enhanced ductility in flexural members, while heightened moment resistance and UHPC layer thickness, along with a robust RC-UHPC interface, tend to induce brittleness. The introduction of such an effective failure modes classification model, coupled with the model’s explainability, instills trust in its predictions and facilitates seamless integration into real-world applications, particularly in seismic areas. The model’s ability to operate without the need for pre-experimental tests marks a significant advancement in the field.

Mechanical behavior of sheathing-to-framing connections in laminated bamboo lumber shear walls

The capacity and stiffness of laminated bamboo lumber (LBL) shear wall sheathed by oriented strand boards (OSBs) is significantly influenced by the structural performance of the nailed connections. Single-connector sheathing-to-framing connections were experimentally tested under monotonic and cyclic loading. The parameters investigated were the nail diameter, the loading direction, the edge distances of nails in the OSB and the LBL. The minimum edge distance for nails in both the LBL stud and the OSB panel was found to be 15 mm. Nails with a smaller edge distance within the members are at higher risk of failing prematurely under lower loads, demonstrating a brittle failure mode. The specimens subjected to cyclic and monotonic loading showed quite different damage. Fatigue fracture due to repeated reverse bending was the typical failure mode for nails in the cyclic experiments. The maximum load of the specimens increased with a larger nail diameter and the load-carrying capacity of parallel-to-grain specimens was greater than that of perpendicular-to-grain specimens. The energy-dissipation capacity of the connections increased with an increase in nail diameter and an increase in the edge distance of the nail in both the LBL and the OSB.

Simultaneous Improvement of the Strength and Plasticity for Ti‐Reinforced Fine‐Grained Magnesium Matrix Composites Prepared by Powder Metallurgy

Ti‐reinforced AZ61 magnesium matrix composites, demonstrating enhanced strength and plasticity, are synthesized via powder metallurgy method, including mechanical milling and spark plasma sintering. This study investigates the evolution of microstructure and compressive mechanical properties of Ti/AZ61 composites across various Ti weight percentages: 0%, 5%, 10%, 15%, and 20%. The composites at 5, 10, 15, and 20 wt% Ti concentrations are effectively compacted, achieving relative densities of 99.1%, 99.4%, 98.7%, and 98.6%, respectively. The integration of Ti particles facilitates a refinement of the Mg grain size. The average Mg grain size in the AZ61 alloy is refined from 8.7 ± 3.6 to 7.2 ± 4.5 μm and 4.4 ± 2.2 μm upon the addition of 5 and 10 wt% Ti particles. Conversely, incremental Ti concentrations of 15 and 20 wt% result in minor increases in the average Mg grain size to 5.3 ± 2.6 and 5.7 ± 3.2 μm, respectively. Interfacial compounds, notably Al3Ti, are identified. Compressive mechanical properties, including compressive yield stress (CYS), ultimate compressive stress (UCS), and compressive failure strain (CFS), are synergistically enhanced with Ti particle incorporation. Optimal mechanical properties, specifically CYS at 250 MPa, UCS at 502 MPa, and CFS at 13%, are observed in the 10 wt% Ti/AZ61 composite. The enhanced compressive behavior is attributed to strong interfacial bonding between deformable Ti and Mg, effective load transfer, and grain refinement. Additional contributing factors include variations in the elastic modulus and thermal expansion coefficients between Ti and Mg. The fracture mechanisms observed in the Ti/AZ61 composites involve both ductile and brittle modes of failure.

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.

Brittle Failure Modes and Mechanisms in Foliated Rock Under Uniaxial Compression: Laboratory Testing and Particle Flow Modeling

Brittle Failure Modes and Mechanisms in Foliated Rock Under Uniaxial Compression: Laboratory Testing and Particle Flow Modeling

Fracture behavior of concrete made with sintered fly ash lightweight coarse aggregate in comparison to normal weight concrete

Sintered fly ash lightweight aggregate based concrete has been reported to give mechanical and durability properties similar to conventional concrete. But concrete made up of lightweight aggregate possesses lower stiffness and shear strength resulting into a brittle mode of failure due to crack propagating directly inside aggregate which is weak in nature. The study presents findings from the experimental investigation of fracture behavior of concrete made with sintered fly ash lightweight coarse aggregate in comparison to normal weight concrete (NWC) at w/b ratio of 0.5, 0.4 and 0.3. The mixes have been tested for compressive and split tensile strength for both concrete types. On notched beams of size 100x 100 x 500 mm, a three-point bend test has been carried out for both lightweight and normal weight concrete to evaluate fracture parameters. The results of split tensile strength test indicated that the split tensile to compressive strength ratio lies in the range of 5-8% for lightweight concrete and this ratio lies between 5-10% for normal weight concrete. The study indicates comparable fracture behavior for both lightweight and normal weight concrete. The non-linear ascending and descending branches in load vs deflection curve of concrete with sintered fly ash lightweight coarse aggregate can be linked with the non-linearity in tensile type stress-strain behavior and formation of the fracture zone in front of the initial notch. The modulus of elasticity of lightweight concrete is significantly lower than normal concrete. The modulus of elasticity, area under the load deflection curve, tensile strength, fracture behavior etc. needs to be considered appropriately in the non-linear analysis of lightweight concrete.

Failure mechanism of 6252-armor steel under hypervelocity impact by 93W alloy projectile

In this study, we analyzed the fracture mechanism of the 6252-armor steel target exposed to the impact of a kinetic energy projectile made of 93W alloy. By examining the impact pressure, crater morphology, and fracture mechanism at various impact velocities, we established the relationship among these factors. As the impact velocity increased, the ratio of penetration depth to crater diameter initially increased, then stabilized, and ultimately approached 0.7 when impact pressures exceeded 49.78 GPa. For impact pressures below 70.71 GPa, macroscopic cracks were predominantly observed on the side of the crater, with no macroscopic cracks found at the bottom. However, if the pressure exceeded 70.71 GPa, the majority of macroscopic cracks occurred at the bottom of the crater. We also found a decrease in spacing between cracks or shear bands and the recrystallized grain size at the interface when the impact velocity increased. Notably, the fracture patterns demonstrated a mixture of brittle and ductile failure modes simultaneously.

High-Velocity Impact Penetration Behavior of Recycled Aluminum Alloy 6061: A Brief Look

Aluminum demand is projected to increase in the future. To help meet the demand, recycling aluminum has been employed for quite some time. Conventional recycling of aluminum leads to CO2 and greenhouse gas emissions. Therefore, direct recycling techniques such as hot press forging are being used and researched to provide an alternate recycling route that leads to even lower emissions, material losses, and energy consumption. The recycled aluminum 6061 alloy obtained from hot press forging is relatively new. Hence, not much is known about its capabilities and properties, including its impact penetration behavior. In this study, recycled 6061 aluminum alloy plates of 5 mm obtained through hot press forging are used in high-velocity impact tests using a single-stage gas gun to test the material’s penetration behavior. Two tests are carried out at velocities ranging from 141 to 308 m/s, all resulting in full penetration. The material was observed to have decent energy absorption capabilities, ranging from 70% to 81%. The penetration behavior, however erratic, shows signs of both ductile and brittle failure modes.

Mechanism of enhanced room temperature ductility of cold–rolled tungsten under micro-bending test

The enhanced ductility of cold-rolled (CR) tungsten at room temperature is considered to be related to the activities of dislocations and the associated microstructures. However, the specific mechanism and the exact roles that dislocation activity and microstructure effects play in enhancing ductility in CR tungsten are still subjects of conjecture. In this context, three-dimensional electron backscatter diffraction reveals that a CR tungsten micro-cantilever fractures in a semi-brittle manner within the L-T fracture system. The ductile, blunted region shows high dislocation mobility away from the cracking tip, and its emission pathway is strongly correlated with low-angle grain boundaries. Meanwhile, strain and dislocations blocked at high-angle grain boundaries induces stress cracking and results in brittle intergranular fracture. These ductile and brittle failure modes trigger the crack bridging effect, ultimately leading to controlled crack propagation. This work would provide valuable idea for future investigations into the ductility enhancement of ultra-fine grain W.

Experimental and FEA Analysis of Bonded Connection in Glass Fiber-reinforced Polymer Short Column

Glass Fibre Reinforced Polymer (GFRP) is a synthetically manufactured material that is derived by compressing multiple layers of glass fiber in a resin matrix. GFRPs can be used as compressive members and hold good compressive strength. These materials display a brittle mode of failure at maximum loading and this aspect is the major disadvantage of these materials. This study intends to tackle this disadvantage by designing and analyzing a connection method called non-bearing spliced connection by Eurocode 3 based on BS EN 1990 and BS EN 1991 guidelines. The connections are established using only bonding as the type of connection. There are two types of bonds established in this study based on the thickness of the epoxy used to establish the bonded connection. A 2 mm thick bond and a 5 mm thick bond are used to create 5 samples of each bond thickness samples. A detailed study of their behavior is established in this study by testing them manually and by using Finite Element Analysis (FEA). The required properties such as failure load, maximum displacement, stiffness, compressive strength, failure modes, and load versus displacement graph behavior are compared and explained in detail in this study.

Discrete Element Analysis of Ice-Induced Vibrations of Offshore Wind Turbines in Level Ice

Self-excited vibrations of offshore structures interacting with sea ice, characterized by low frequency and high amplitudes, pose significant hazards to offshore wind turbines (OWTs) in cold seas. This study employs the discrete element method (DEM) with a parallel bonding model to investigate the interaction between sea ice and OWTs. Two bond-failure models are compared, with the results showing that the model considering stiffness softening and fracture energy provides better alignment with field data in the Bohai Sea. The DEM is employed to analyze the ice-induced vibration of OWTs under varying ice velocities, revealing that brittle failure of sea ice occurs at higher ice speeds, leading to random structure vibration. At slower ice speeds, both brittle and ductile sea ice failure modes result in self-excited vibrations. This suggests a strong connection between self-excited vibration and the brittle-ductile failure of sea ice, influenced by the relative speeds between ice and the structure. This study employs the DEM to elucidate the mechanism of self-excited vibrations in OWTs from the perspective of brittle-ductile sea ice failure. The results show that the DEM model accurately describes the brittle-ductile transition in sea ice failure, and that the structural motion aligns well with field measurements.

Closed-form expressions for partial safety factors used in the seismic assessment of existing RC buildings

A new set of partial safety factors is proposed for the seismic safety assessment of existing reinforced concrete buildings. These safety factors are derived using a framework that focuses on the determination of the uncertainty in the limit state capacities. Existing seismic safety assessment standards, such as EN1998-3 or ASCE 41-17, follow a component-based approach that consider limit-state acceptance criteria based on capacity-related parameters to verify the safety of ductile and brittle failure modes. Despite their similar limit-state philosophy, these standards consider different conceptual formats for introducing the effects of uncertainties: the current version of EN1998-3 adopts confidence factors (CF) that factorize the mean values of material strength, while ASCE 41-17 uses a knowledge factor (k) to reduce the capacity of the component. The CF-based approach of EN1998-3 has been seen to lead to unclear levels of safety that may not reflect the impact of all the uncertainties about the different parameters or the sensitivity of different capacity models to these parameters. To address these issues, the proposed framework establishes a set of partial safety factors derived using an approach similar to that of ASCE 41-17, and involves recent capacity models, their uncertainties and a clear uncertainty management strategy. Furthermore, these new partial safety factors can also be seen to be compatible with the safety format proposed by the upcoming second-generation EN1998-3.

Study of elastoplastic deformation and crack evolution mechanism of single-crystal ice during uniaxial compression using 3D digital image correlation

Single-crystal freshwater ice was subjected to uniaxial compression tests with different strain rates and crystal orientations, and the real-time full-field deformation and strain were measured by the three-dimensional digital image correlation (3D DIC) method. The mechanism of elastoplastic deformation and crack evolution of single-crystal ice is discussed based on the basal slip. The maximum compressive strength appeared when the crystal orientation (angle between the C-axis and loading direction) θ=0°/90°. When 45°<θ<90°, an inclined bearing layer appeared and caused the specimen to rotate simultaneously. When 0°<θ⩽45°, the vertical compressive stress was sequentially transmitted through the basal plane, two diagonal expansions to the sidewall appeared. The failure mode and compressive strength of ice exhibited a ductile–brittle transition. The strength was positively correlated with the strain rate below the ductile–brittle transition range. The stress concentration at the crack tip was released through basal slip, inhibiting crack propagation, which showed multi-crack ductile failure. When in the ductile–brittle transition range, the cracks could grow stably, leading to axial splitting failure. When the strain rate was higher, the crack tip could not grow stably, producing inclined cracks and resulting in spalling or axial splitting failure, and the ice exhibited a brittle failure mode.