Cracking Behavior Research Articles

Uncertainty quantification for conical hole expansion test of DP800 sheet metal

The hole expansion ratio (HER) observed in a standardized hole expansion test (HET) is commonly used to determine the edge fracture of steel sheets. A large variation of the measured HER restricts the practical application of the method. This study presents a systematic investigation on uncertainties in the HER of DP800 sheet material, including the hole-edge quality, pre-strain due to the hole-punching process, the friction coefficient, and the determination of fracture. An artificial neural network was trained to develop a surrogate model using a database gained from a thousand finite element simulations of the HET. Monte-Carlo simulations were performed using the trained surrogate model to characterize the distribution of the HER. Sensitivity analysis via Sobol’s indices is calculated to determine the influence of the input variables on the output. It is found that the pre-strain and pre-damage generated during the hole punching process in the shear-affected zone dominate the variation of the HER. Discussions on reducing the output’s variation are detailed. In general, these findings provide valuable insights for the determination of HER as well as the edge crack behavior of the investigated DP800 steel sheet.

In-situ experimental investigation of the small fatigue crack behavior in CP-Ti: The influence of loading parameters and directions

This study quantitatively investigates the influence of loading parameters and directions on the behavior of small fatigue cracks (SFC) in commercially pure titanium (CP-Ti). It is observed that reductions in peak stress and increases in stress ratio correlate with a decrease in SFC growth rate and an intensification of growth rate fluctuations. Notably, crack growth along the transverse direction (TD) generally exhibits lower rates compared to that along the rolling direction (RD), with more pronounced fluctuations. Through metallographic analysis of crack paths, roughness-induced crack closure (RICC) is identified as a significant factor contributing to the observed variations in SFC growth behavior under different loading conditions. Furthermore, electron backscatter diffraction (EBSD) characterization reveals that crack propagation along the RD is primarily governed by prismatic slip, while TD samples exhibit more engagement of non-prismatic slip systems with higher activation stress. This results in a more tortuous crack path and pronounced crack arrest phenomena. Finally, a modified multi-scale rate prediction model based on the reference stress ratio method is proposed. Comparative analysis demonstrates that the modified model outperforms existing models by offering enhanced predictive capability across diverse loading conditions, thereby reinforcing its robustness in predicting SFC behavior of CP-Ti.

Local FRP Cracking and Global Structural Behavior of Stub Concrete-Filled FRP Tubes under Concentric and Eccentric Compression

Local FRP Cracking and Global Structural Behavior of Stub Concrete-Filled FRP Tubes under Concentric and Eccentric Compression

Atomic insights into the ductile–brittle competition of cracks under dissolution

Environmental effects can determine the ductile–brittle behavior of cracks at the atomic scale, but the underlying processes remain poorly understood and contentious. Here, we report the competition between ductile and brittle behaviors at crack tips induced by the prevalent environmental effect of dissolution. Our findings reveal that this competition is driven by two fundamental deformation mechanisms related to dissolution: crack blunting and defect accumulation. Through separate evaluations of dissolution-induced cleavage and dissolution-induced plasticity, we demonstrate that these deformation mechanisms not only dominate brittle fracture toughness but also lead to dislocation slip. We have developed a theoretical model to predict the ductile and brittle behavior of cracks under dissolution, and the theory aligns well with the simulation results and remains consistent with existing experimental trends. This work will broaden the microscopic understanding of ductile and brittle fracture of cracks in complex environments.

Hydrogen-induced crack behavior of a precipitation-strengthened Ni50Cr20Co15Al10V5 high entropy alloy

The hydrogen-induced cracking behavior and mechanism of an L12-strengthened Ni50Cr20Co15Al10V5 high entropy alloy was evaluated using the tensile test after hydrogen charging. The microstructures and hydrogen-induced cracks were characterized by electron backscatter diffraction and electron channeling contrast imaging methods. The results revealed that hydrogen decreased the strain hardening rate and induced pronounced cracks, leading to significant degradation in elongation. After deformation, the local strain was concentrated in the precipitate-matrix interfaces. The precipitate-matrix boundary and the interior of precipitates were prone to hydrogen embrittlement, where hydrogen-induced cracks tended to propagate, attributing to the hydrogen-enhanced decohesion mechanism.

Simulation and multi-dimensional damage evolution analysis of detailed micro-model representing ancient brick masonry compressive behavior

To further investigate the crack propagation and damage evolution mechanisms of ancient masonry under uniaxial compression, this study employs numerical simulation techniques alongside laboratory experiments to characterize and predict both the apparent and internal cracking behaviors of ancient masonry, utilizing a detailed micro-model constructed from the constitutive equations governing brick blocks and mortar. The findings indicate that this comprehensive micro-model effectively replicates the crack development process. The microscopic damage evolution is delineated by distinct stages: initiation, propagation, penetration, and ultimate failure. Furthermore, the mesoscopic fracture degree serves as a quantitative measure for assessing the mesoscopic evolution of ancient masonry during damage events. An internal damage assessment model has been developed to intricately describe the crack propagation process from within to outside. Additionally, recognizing the inherent randomness and complexity associated with crack development, we introduce a fractal dimension index which significantly enhances tracking accuracy throughout all phases of crack progression. Concurrently, in conjunction with a progressive damage model, multi-faceted predictions and evaluations regarding crack development are conducted to provide an effective framework for understanding the damage processes affecting ancient masonry.

Effects of moisture contents, fracture modes, and temperatures on fracture toughness and crack distribution of asphalt concrete at low-temperature

Low-temperature cracking of asphalt pavements is a major issue in highway construction. The deterioration of fracture resistance in asphalt pavements is accelerated by traffic loads when water infiltrates the cracks. However, previous studies have largely overlooked the effects of moisture content on the low-temperature cracking behaviour of asphalt concrete, particularly under different fracture modes. To address this gap, we investigated the fracture toughness and crack distribution of asphalt concrete using semicircular bending tests under five low-temperature conditions (-10 °C, -5 °C, 0 °C, 5 °C, and 10 °C), five moisture contents (0%, 25%, 50%, 75%, and 100%), three fracture modes (mode I, mode II, and mixed mode I&II), and two types of asphalt binders (base asphalt binder and styrene–butadiene–styrene modified asphalt binder).

Influences of the stress ratio and local micro mineral aggregates on small fatigue crack propagation in the shale containing bedding planes

Due to the existence of bedding planes in shale oil reservoirs, the complexity of crack networks created by conventional hydraulic fracturing (HF) technology is limited, resulting in low oil production. In this paper, a fatigue loading method was proposed to increase the complexity of the cracking network. The propagation behaviors of small cracks were investigated and compared under both monotonic and fatigue loading conditions by using SEM in-situ three-point bending tests. In addition, the influences of local micro mineral aggregates and stress ratios (R = 0.1, 0.3 and 0.5) on the propagation behavior of small fatigue cracks (SFCs) in shale were quantitatively evaluated. The SEM in-situ fatigue tests demonstrated the effectiveness of fatigue loading in enabling SFC to propagate through the bedding plane and increase crack network complexity from a micro perspective. A fitting exponential formula of the stress intensity factor range threshold ΔKth and stress ratio R was obtained. This study assists us in deeply understanding the influence of micro mineral aggregates and stress ratio on the SFC propagation mechanism and its implications for HF design in shale oil reservoirs.

Merging behaviour and fatigue life evaluation of multi-cracks in welds of OSDs

Experimental studies were conducted to investigate the merging behaviour of multiple fatigue cracks (MFCs) in rib-to-deck welds of orthotropic steel decks (OSDs). Numerical simulations were conducted to investigate the mechanism of the merging behaviour of MFCs on fatigue life. In addition, the sensitive parameter in the MFCs affecting the fatigue life were revealed. Finally, a comprehensively failure criterion for MFCs was proposed. Results show that the merging behaviour of MFCs can be effectively observed by the beach marks on the fracture surface of the rib-to-deck weld. The merging behaviour is a key factor driving cracks penetrating through the deck, which significantly increases the crack length and decreases the crack shape ratio. The fatigue life of MFCs with different crack sizes is mostly determined by the larger crack, while the shape ratio effect can be ignored. The crack number has the most significant effect on fatigue life, where the five-cracks case reducing the fatigue life by up to 39 % compared to a single crack. Due to the nonlinear effect of crack spacing on fatigue life, MFCs with the same fatigue life may have significantly different final crack length. Therefore, the proposed failure criterion for MFCs considers the effects of both crack depth and length.

Effect of Flax By-Products on the Mechanical and Cracking Behaviors of Expansive Soil.

Expansive soils, prone to significant volume changes with moisture fluctuations, challenge engineering infrastructure due to their swelling and shrinking. Traditional stabilization methods, including mechanical and chemical treatments, often have high material and environmental costs. This study explores fibrous by-products of flax processing, a sustainable alternative, for reinforcing expansive clay soil. Derived from the Linum usitatissimum plant, flax fibers offer favorable mechanical properties and environmental benefits. The research evaluates the impact of flax tow (FT) reinforcement on enhancing soil strength and reducing cracking. The results reveal that incorporating up to 0.6% randomly distributed FTs, consisting of technical flax fibers and shives, significantly improves soil properties. The unconfined compressive strength (UCS) increased by 29%, with 0.6% FT content, reaching 525 kPa, compared to unreinforced soil and further flax tow additions, which led to a decrease in UCS. This reduction is attributed to diminished soil-fiber interactions and increased fiber clustering. Additionally, flax tows effectively reduce soil cracking. The crack length density (CLD) decreased by 6% with 0.4% FTs, and higher concentrations led to increased cracking. The crack index factor (CIF) decreased by 71% with 0.4% flax tows but increased with higher FT concentrations. Flax tows enhance soil strength and reduce cracking while maintaining economic and environmental efficiency, offering a viable solution for stabilizing expansive clays in geotechnical applications.

Interaction mechanism of radial collinear cracks on a high-speed train brake disc

This article focuses on the problem of multiple crack damage in brake discs. Using the extended finite element analysis method, the interaction mechanism between radially collinear multiple cracks in brake discs is analyzed, and the influence of crack spacing and length ratio on the propagation behavior of multiple cracks is further investigated. The results indicate that the interaction mechanism between multiple radial collinear cracks on the brake disc is complex, not only influenced by the crack spacing and crack length ratio but also related to the location of the cracks on the brake disc. The interaction of radial collinear cracks on the brake disc is mainly concentrated in the stress field at the vicinity of the adjacent tips between the cracks and has little effect on the crack opening displacement field. When the distance between cracks is less than half the length of the crack of interest, the two collinear radial cracks have a significant mutual influence and tend to merge into a longer crack. The length ratio between cracks has a significant impact on the stress transmission path around the cracks, and increasing the length ratio accelerates the crack-to-crack coalescence.

Role of Loading Rate on Cracking Behavior in Granite Disks With Laboratory Experiments and Grain‐Based Modeling

ABSTRACTThe investigation of the tensile properties of rock materials is essential for understanding the failure mechanism of engineering rock masses. In this study, we conducted a series of Brazilian splitting tests on granite specimens under three different loading rates, concurrently monitored using acoustic emission (AE) and digital image correlation (DIC) techniques. The results show that the mechanical parameters of granite disks are positively correlated with the loading rate. The AE waveforms are found to be associated with the lower frequency band, suggesting that this frequency range primarily dominates the failure mechanism in granite disks. Furthermore, the onset of micro‐tensile fractures precedes the development of micro‐shear ones. The elevation distribution of the fractured surfaces of the granite disks follows a Gaussian function. The fractal dimension increases progressively with the loading rate, whereas the complexity and irregularity of the fractured surface decrease. Moreover, the cracking mechanism of granite disks at the microscale was revealed using grain‐based modeling (GBM). The intergranular tensile cracks predominantly form along the radial direction, and the proportion of intergranular shear cracks is the smallest.

The influence of bi-directional material gradation on a mode-III crack in functionally graded material via strain gradient elasticity theory

In contrast to classical mechanics, which primarily relies on continuum assumptions and neglects micro-structural effects, the strain gradient elasticity (SGE) theory represents a paradigm shift in understanding the mechanical behavior of materials at small length scales. In this article, the influence of the bi-directional material gradation on a mode-III crack in functionally graded material via SGE theory is studied. The SGE theory uses two material characteristic lengths, ℓ and ℓ′, to account for volumetric and surface strain-gradient factors, respectively. Our investigation is centered on a material gradation model assumed to vary exponentially, with the shear modulus represented as G(x,y)=G0eβx+γy, where β and γ are material gradation constants. To address the crack boundary value problem under consideration, we employ a methodology combining Fourier transforms and an innovative hyper-singular integro-differential equation approach. Using this approach, we systematically formulate a system of equations, which can be solved by selecting suitable collocation points. The closed-form analytical expressions are derived for the standard fracture parameters such as crack surface displacement (CSD), stress intensity factor (SIF), and energy release rate (ERR). Numerical studies are illustrated for the derived standard fractures, and the influence of these parameters β, γ, ℓ, ℓ′, and applied shear load is graphically presented. Through comprehensive analysis, our aim is to provide insights into the complex interplay between material parameters, loading conditions, and crack behavior in functionally graded materials.

Experimental study on the shear behaviour of high-strength lightweight concrete beams incorporating graphene oxide

Graphene oxide (GO) has achieved significant progress in the material behaviour of cement-based materials. However, research on its structural behaviour in high-strength lightweight concrete (HSLWC) structures is limited, which restricts its engineering applications. This study focused on investigating the effects of low contents of GO on the shear behaviour of HSLWC beams. A total of four HSLWC beams with GO contents of 0, 0.01, 0.03 and 0.05% (by weight of cement) were designed to observe failure modes, load‒deformation curves, shear capacities, crack behaviour and load‒strain curves under four-point loading by a 300 kN servo loading device. The results revealed that all the beams exhibited shear compression failure. GO improved the shear capacity of the HSLWC beams, and this strengthening effect increased with increase in GO content. When the content of GO was 0.05%, the ultimate load of the beam reached a maximum, which was 39.2% greater than that of the control beam. GO can endow the HSLWC beams with a certain degree of ductility. In addition, a modified JGJ 12-2006 model was proposed to predict the shear capacity of HSLWC beams containing different GO contents on the basis of a comparison of typical models. This study can provide exploratory engineering practice for evaluating and designing GO-reinforced HSLWC structures.

Flexural post-cracking performance of macro synthetic fiber reinforced super workable concrete influenced by shrinkage-reducing admixture

Most literature has focused on the effect of shrinkage-reducing admixture (SRA) in shrinkage mitigation resistance of concrete. This study aims to examine the impact of SRA on the efficiency of macro synthetic fibers (MSF) in enhancing the flexural post-cracking behavior of fiber-reinforced super workable concrete (FR-SWC). A comparative analysis of the influence of fiber combinations on the flexural post-cracking behavior of beams is also included. Results showed that a higher dosage of SRA, particularly at 5 % by mass of binder, had a noticeable negative impact on flexural post-cracking performance of beams while exhibiting positive effect on workability and shrinkage reduction. However, incorporating low dosages of SRA (1.25 % by mass of binder) did not have a significant impact on the ability of MSF. This was attributed to the reduction of the MSF-matrix bond strength caused by a significant delay in cement hydration. The characteristics of selected MSF type, including length and surface roughness had a positive effect on the post-cracking performance of FR-SWC, regardless of SRA dosage. The notched beams made with 100 % MSFA outperformed those made with fiber combination of 25 % MSFA and 75 % MSFB. Beams made with 100 % MSFA showed 55 % higher residual flexural tensile strength, 49 % higher equivalent flexural tensile strength, 50 % higher fracture energy, and 35 % higher equivalent flexural strength ratio compared to beams made with fiber combination of 25 % MSFA and 75 % MSFB. Therefore, the negative effect of SRA on the flexural-post cracking behavior can be partial compensated by adjusting MSF content and combinations.

Investigation on the Influence Mechanism of Mg Contents on the Hot Cracking Behavior of Al–Cu–Mg Alloys

Investigation on the Influence Mechanism of Mg Contents on the Hot Cracking Behavior of Al–Cu–Mg Alloys

Short Crack Behavior of an Additively Manufactured Ti–6Al–4V Alloy Under Ultrasonic High Cycle Fatigue Testing

ABSTRACTThe high cycle fatigue (HCF) behaviors of an additively manufactured (AM) Ti–6Al–4V alloy with fully lamellar microstructures processed electron beam powder bed fusion (EB‐PBF) and wire‐fed electron beam directed energy deposition (Sciaky) routes were compared. Ultrasonic fatigue (USF) testing at the stress ratio of R = −1 was applied to monitor the growth of small cracks initiated at surface micronotches. Crack growth rates lower than 10−8 (m/cycle) at ΔK = 6 MPa·m1/2 were measured in samples processed by both methods. The finer α lath thickness (~1 μm) of the Sciaky samples resulted in a slower fatigue crack growth rate than the EB‐PBF samples with coarser laths. The interaction of cracks with the lamellar microstructures was characterized by electron backscatter diffraction. Crack propagation largely followed the lath interfaces in the Sciaky samples, whereas cracks cut across colonies in the EB‐PBF samples. Different fatigue fracture surface characteristics were observed for the EB‐PBF and Sciaky samples.

Effect of Rolling Process Parameters on Transverse Cracks on the Surface of Q345 Steel

This article examines the evolutionary behavior of transverse surface cracks in Q345 steel during the hot‐rolling process under various rolling conditions. “V”‐shaped cracks are prefabricated on the billet surface for laboratory hot‐rolling tests, and a corresponding rolling model is developed to validate its accuracy. The slab rolling model is established based on actual onsite rolling process parameters. The aim is to analyze the effects of different rolling conditions on the surface crack morphology and aspect ratio. The results indicate that variations in roll diameter (1400, 1300, and 1200 mm) influence crack propagation, with cracks unfolding earlier when the roll diameter is 1400 mm. At varying initial rolling temperatures (1300, 1200, and 1100 °C), cracks begin to unfold earlier at the highest temperature of 1300 °C. When examining different friction coefficients (0.4, 0.5, and 0.6), cracks unfold earlier at the highest coefficient of 0.6. Similarly, at different rolling speeds (3, 4, and 5 m s−1), cracks unfolded earlier at the highest speed of 5 m s−1. Analysis of changes in crack depth and aspect ratio during rolling shows that the initial few passes have a greater influence on crack depth and unfolding. In the later stages of rolling, cracks continue to unfold, though the depth shows minimal variation, and the aspect ratio tends to approach zero.

Cracking of silty mudstone subjected to wetting-drying cycles

Cracking affected by wetting-drying cycles is a major cause of shallow failure of soft rock slopes. Knowledge of rock tensile properties and cracking behaviors helps better assess the stability of soft rock slopes. This study aims to examine the cracking behaviors and tensile strength of silty mudstone under wetting-drying cycles. The wetting-drying cycles and Brazilian splitting tests were performed on silty mudstone considering various cycle number and amplitude. The cracking behaviors of wetting-drying cycles were analyzed by digital image correlation, three-dimensional (3D) scanning technology, and scanning electron microscopy. The results reveal a spiral-like pattern of crack ratio escalation in silty mudstone, with a higher crack ratio observed during drying than wetting. Tensile strength and fracture energy correlate negatively with cycle number or amplitude, with cycle number exerting a more pronounced effect. The variance of the maximum principal strain reflects stages of initial deformation, linear deformation, strain localization, and stable deformation. The formation of strain localization zones reveals the physical process of crack propagation. Crack tip opening displacement progresses through stages of slow growth, exponential growth, and linear growth, delineating the process from crack initiation to stable extension. Failure modes of silty mudstone primarily involve tensile and tensile-shear failure, influenced by the geometric parameters of cracks induced by wetting-drying cycles. Fracture surface roughness and fractal dimension increase with cycle number due to mineral dissolution, physical erosion, and nondirectional crack propagation. Hydration-swelling and dehydration-shrinkage of clay minerals, along with absorption-drying cracking, initiate and merge cracks, leading to degradation of the rock mechanical properties. The findings could provide insights for mitigating shallow cracking of soft rock slopes under wetting-drying cycles.

Multiscale cracking behavior in the Full Stress-Strain process of recycled concrete with real aggregate morphology

The significant amount of waste concrete generated during wars, earthquakes, building demolitions, and urban renewal projects can be processed into recycled aggregates, thus aiding environmental protection and promoting the sustainability of the construction industry. However, the complex mechanical properties of recycled concrete, such as its cracking behavior, considerably limits its application in structural engineering. In this study, a numerical theoretical model of real recycled aggregate concrete (RAC) was established to investigate its mechanical behavior and cracking mechanisms. The model accurately captured the internal crack evolution and stress–strain relationship variation in RAC under uniaxial compressive loading, accounting for the effects of the recycled aggregates, old mortar, interfacial transition zone, type of natural aggregates, and microporosity. The findings of this study can serve as a basis for elucidating RAC failure mechanisms and highlight the impact of recycled aggregates on structural concrete design.