Observation Of Crack Propagation Research Articles

Reactive sintering of TiB2 composites with Ti3SiC2 and B4C

Achieving densification in sintering of titanium diboride (TiB2) is challenging due to its high covalent bonding and low self-diffusion coefficient, necessitating the use of external pressure and high temperature. To enhance densification, a combination of reaction sintering and liquid phase sintering was employed in this study. Different ratios of sintering aids were tested via vacuum sintering. B4C and Ti3SiC2 were chosen as sintering aids, reacting to produce TiB2, TiC, and SiC. Co, known for their good wettability with TiB2, were used as metal sintering aids, along with Mo, which contributes to grain refinement in TiB2-based ceramic composites. A core-rim structure was observed after first holding at 1100–1150 °C, where B4C reacted with Ti3SiC2, and subsequently sintering at 1900 °C and 1950 °C facilitated densification. Mo diffused into TiC, surrounding the original TiB2 grains along with trace amounts of Co, thereby inhibiting TiB2 growth. The recipe of 90 wt% TiB2+10 wt% (B4C + Ti3SiC2+Co + Mo) achieved the highest relative density at 94.37 % and a hardness of 28.56 GPa. The observed crack propagation exhibited transgranular cracking, crack bridging, and branching, absorbing higher energy and enhancing fracture toughness.

Exploring anisotropic mechanical properties of lobster claw exoskeleton through fractal models

The outstanding mechanical properties of lobster claw exoskeletons are intricately tied to their internal microstructure. Investigating this relationship can offer vital insights for designing high-performance additive manufacturing structures. Fractal theory, with its fractional dimensional perspective, suits the complexity of real-world phenomena. Our study examines fully hydrated lobster claw exoskeletons using a multifaceted approach: four-point bending tests, scanning electron microscopy observations, and fractal models. Test results reveal superior mechanical properties in longitudinal specimens. Scanning electron microscopy shows non-uniform fiber helical structures and porous elements in the exoskeleton. Fracture mechanisms involve both breaking fiber fragments perpendicular to the cross-section and tearing between these fragments. The observed crack propagation paths exhibit statistical self-similarity. Consequently, we develop fractal models for the crack propagation paths in longitudinal and transverse specimens, calculating crack extension forces. Using the box-counting method and its improved variant, we determine the fractal dimensions of specimen sections. The fractal dimension of longitudinal models exceeds that of transverse models, and calculated crack extension forces are higher in longitudinal models. These findings align well with experimental data, demonstrating fractal theory's efficacy in analyzing the lobster claw exoskeleton's anisotropic mechanical properties.

Experimental and numerical analysis on shear capacity of steel-reinforced geopolymer concrete beams with different shear span ratios

PurposeThe purpose of this study is to use the corrected stress field theory to derive the shear capacity of geopolymer concrete beams (GPC) and consider the shear-span ratio as a major factor affecting the shear capacity. This research aims to provide guidance for studying the shear capacity of GPC and to observe how the failure modes of beams change with the variation of the shear-span ratio, thereby discovering underlying patterns.Design/methodology/approachThree test beams with shear span ratios of 1.5, 2.0 and 2.5 are investigated in this paper. For GPC beams with shear-span ratios of 1.5, 2.0 and 2.5, ultimate capacities are 337kN, 235kN and 195kN, respectively. Transitioning from 1.5 to 2.0 results in a 30% decrease in capacity, a reduction of 102kN. Moving from 2.0 to 2.5 sees a 17% decrease, with a loss of 40KN in capacity. A shear capacity formula, derived from modified compression field theory and considering concrete shear strength, stirrups and aggregate interlocking force, was validated through finite element modeling. Additionally, models with shear ratios of 1 and 3 were created to observe crack propagation patterns.FindingsFor GPC beams with shear-span ratios of 1.5, 2.0 and 2.5, ultimate capacities of 337KN, 235KN and 195KN are achieved, respectively. A reduction in capacity of 102KN occurs when transitioning from 1.5 to 2.0 and a decrease of 40KN is observed when moving from 2.0 to 2.5. The average test-to-theory ratio, at 1.015 with a variance of 0.001, demonstrates strong agreement. ABAQUS models beams with ratios ranging from 1.0 to 3.0, revealing crack trends indicative of reduced crack angles with higher ratios. The failure mode observed in the models aligns with experimental results.Originality/valueThis article provides a reference for the shear bearing capacity formula of geopolymer reinforced concrete (GRC) beams, addressing the limited research in this area. Additionally, an exponential model incorporating the shear-span ratio as a variable was employed to calculate the shear capacity, based on previous studies. Moreover, the analysis of shear capacity results integrated literature from prior research. By fitting previous experimental data to the proposed formula, the accuracy of this study's derived formula was further validated, with theoretical values aligning well with experimental results. Additionally, guidance is offered for utilizing ABAQUS in simulating the failure process of GRC beams.

Simulation and analysis of rust expansion cracking of reinforced concrete

Reinforced concrete is used in complex environment, and the damage of concrete protective layer caused by steel corrosion will seriously reduce the durability of the structure. In order to deal with the different corrosion morphology of steel bars in engineering, three different function expressions are proposed to describe the uniform and non-uniform corrosion of steel bars. Based on PF_CZM phase field model and adaptive refinement mesh technology, the cracking of concrete protective layer caused by different corrosion types of steel bars is simulated. The simulation results are close to the experimental or actual observed crack propagation. The research shows that the non-uniform corrosion coefficient (α) of steel bars affects the crack propagation form of protective layer. When α=1,2, the thinnest part of the protective layer will be penetrated by the main crack, and two secondary cracks will be produced on both sides. The characteristic displacement in the process of crack propagation is similar, and the maximum expansion displacement of steel bar is less than 125 μm when there is obvious crack in the protective layer. When α=4,8, the protective layer will produce two main cracks. The corrosion characteristic displacement is also similar, and the maximum expansion displacement of steel bars exceeds 180 μm when there are obvious cracks in the protective layer. However, with the increase of non-uniform corrosion coefficient, the amount of steel corrosion required for obvious damage and cracks gradually decreases, and the structure is more likely to be damaged. When non-uniform corrosion occurs in both longitudinal and transverse directions of steel bars, cracks will originate from the most serious corrosion of steel bars and spread to both sides. Compared with the two-dimensional simulation results, the simulated crack propagation morphology and the predicted structural durability results are more accurate. The coarse mesh is used to verify the adaptability of the method to the project, which provides reference for the engineering design and durability research of concrete structures.

Adaptive coupling of non-ordinary state-based peridynamics and classical continuum mechanics for fracture analysis

In this study, we proposed a coupled model between non-ordinary state-based peridynamics (NOSPDs) and classical continuum mechanics (CCMs) using the Morphing strategy for both quasi-static and dynamic fractures. We leveraged a novel strategy to approximate the deformation energy of the NOSPD model, which can unify the existing BPD and OSPD cases. We established the unified governing equations for NOSPDs and CCMs and applied the generalized strength criteria in the coupling model to activate the NOSPDs only when necessary. The critical stretch is recalibrated for the NOSPD model, and generalized strength-based bond failure criteria are proposed to determine bond failure. The model was numerically implemented using the finite element method (FEM) supplemented with discrete elements in the NOSPD subdomain. Parallel in-house code is written on graphics processing units (GPU) using the Compute Unified Device Architecture (CUDA). The 1-, 2- and 3-dimensional (D) numerical results demonstrated the accuracy and efficiency of the proposed method. Notably, the relative errors due to coupling during wave propagation in a 1D bar and uniform deformation in a 2D plate were less than 0.0375% and 0.14%, respectively. Further, the observed crack propagation speed aligned with the reference value.

Formation of Thick Immersion Coatings and Residual Stress Evaluation in the System ZrB2-ZrO2: Experimental and Numerical Investigation.

The combination of various oxide ceramics in layered and functionally graded composites allows for the development of novel materials, including for high-temperature applications. This study demonstrates the possibility of obtaining a thick ZrO2-based coating on a ZrB2-SiC ceramic substrate by the immersion method. For better wettability, the porous ZrB2-SiC substrate is treated with cold plasma without changing the structure and phase composition of the surface. Immersion of the substrate in a ZrO2-based slurry results in the formation of a gradient transition layer due to ZrO2 particle penetration into the pore volume. The interfacial residual microstresses are evaluated experimentally. The residual macrostresses in the samples are calculated by finite element simulation. It is shown that the thermal residual stresses in the ZrB2-SiC substrate are compressive and do not exceed 43 MPa. In the ZrO2 coating and transition layers of the composite, the residual stresses are tensile. Their values increase as they get closer to the outer layer of the ZrO2 coating and reach 1525 MPa. This confirms the conclusions about the presence of tensile residual stresses made in the experimental part of the work when observing crack propagation in the surface layers during indentation.

Quasi-in-situ observations of crack propagation and microstructure evolution of high manganese austenitic steel at −196 °C

The crack propagation behaviors and microstructure characteristics in the high manganese austenitic steel were comprehensively investigated by quasi-in-situ observations at −196 °C. The steel exhibits a superior fracture toughness at −196 °C than at room temperature. It is found that a severe plastic deformation is necessary for a crack initiation. Although the main crack propagates along the {111} planes due to the plastic strain localization caused by an extensive planar slip, the steel still possesses a superior crack propagation resistance, which is attributed to the activations of multiple twinning and slipping systems, which provide two positive effects on blocking a crack propagation: (1) the plastic deformation further enhanced by multiple twinning and slipping systems as well as (2) a tortuous crack propagation path caused by numerous twin boundaries. Besides, the pronounced deflections at grain boundaries also have a large contribution to block a crack propagation.

Landfill gas emission through compacted clay considering effects of crack pathway and intensity

Compacted clay barrier plays an important role in reducing landfill gas transport due to its low gas permeability. There is limited understanding of desiccation cracks and to what extent they can cause preferential pathways of landfill gas through compacted clay barriers. This study investigated the intensity and pathway of desiccation cracks as well as its effects on gas emission through compacted clay. The compacted clay with and without scratched compaction interface was subjected to drying to simulate desiccation cracks. The clay was then extruded from large containers into one dimensional columns to allow observation of crack propagation using an X-ray computerized tomography scanner. After that, gas emission rate was measured from each column under different gas pressures (i.e., 1, 5, 10 and 20 kPa). Furthermore, a simplified method is proposed to predict gas emission rate with consideration of intensity and characteristics of cracks. Test results demonstrated that desiccation cracks were initiated mainly at the center of each container (i.e., within 40% of container dimension). Gas emission rate can be increased at least 10 times with the presence of desiccation cracks (i.e., at gas pressure of 5 kPa). As compared to the depth and continuous pathway of cracks which significantly increased gas emission rate, the discontinuous crack pathway can reduce the gas emission rate by up to 3 times. The findings towards crack characteristics and gas emission observed in this study are crucial for safety design and long-term operation of compacted clay barriers in landfill covers.

Two-layer laser clad coating as a replacement for chrome electroplating on forged steel

Chrome plating is one of many surface engineering techniques used for corrosion resistance, as well as a protective coating against surface damage in load bearing applications, with surface hardness in the region of 1000 Hv. Laser cladding is an alternative hardfacing technique often chosen for corrosion resistance and for increasing the surface hardness of components, through thick clad coatings. The application of chrome plating and other similar surface engineering techniques for thick coatings can be inefficient and costly with practical process limitations. The objective of this case study was to investigate the feasibility of replacing the chrome plated layer of a rod mill pinion, made of forged steel, with a Nickel-based Tungsten-Carbide (Ni-WC) composite layer and an intermediate layer of Inconel 625. Mechanical properties were obtained using microhardness and nanoindentation techniques. Three-point bend tests were performed on test specimens from a pinion sample, in order to observe crack propagation resistance, a challenging task due to the curved geometry of the pinion sample and the difference in thickness between the existing and proposed coating layers. Crack development was captured, and plastic deformation was quantified with the use of Digital Image Correlation (DIC). In bending it was found that the bond between the composite coating, Inconel 625 and the steel substrate provided improved resistance to axial crack propagation, where the composite coating could withstand more than twice the bending tool displacement than the chrome electroplating.

Characteristic analysis of acoustic emission monitoring parameters for crack propagation in UHPC-NC composite beam under bending test

Ultra high performance concrete (UHPC) has more outstanding mechanical properties and durability than normal concrete (NC) materials. Currently, analysis methods for the mechanical properties of UHPC structures and UHPC composite structures, such as measuring structural deflection, strain, and observing crack propagation, are relatively single. Acoustic emission (AE) technique is a non-destructive testing method that evaluates the damage state of structures effectively. The variation characteristics of AE parameters can be used to analyze the damage process and the failure precursor information of the structures. On this basis, AE technique was used to monitor the crack propagation of the UHPC-NC composite beam under four-point bending test in this study. Results showed that the U-shape UHPC layer gave full play to its high strength and ductility characteristics under bending, which was mainly manifested in reducing the number and width of cracks of the UHPC-NC composite beam, reducing the mid-span deflection and increasing the cracking load (Pcr) and ultimate load (Pu). AE ringing counts, energy, and b-value showed different and easily distinguishable variation characteristics at each failure stage of UHPC-NC composite beam and can be considered the optimal AE monitoring parameters. RA-AF association analysis can be used to further analyze the failure mode of UHPC-NC composite beam. AE monitoring method can be considered an alternative to traditional monitoring methods for the real-time monitoring of crack propagation in UHPC-NC composite beams.

Mechanical characteristics of metal nanoparticle thin film on flexible substrate exposed to saline solution

The robust and reliable mechanical characteristics of metal nanoparticle (NP) thin films on flexible substrates are important because they operate under tensile, bending, and twisting loads. Furthermore, in wearable printed electronics applications, salty solutions such as sweat and seawater can affect the mechanical reliabilities of devices. In this paper, we investigated the effect of sodium chloride (NaCl) solutions on silver (Ag) NP thin films on flexible polymer substrate. After exposure to NaCl solution of Ag NP thin film, we observed the aggregation behavior between Ag NPs and formation of larger pores in the film due to the removal of organic capping layer from the surface of Ag NPs. The average porosity and 5% deviation strains of Ag NP thin films on the polyimide substrate were dramatically increased and decreased from 2.99% to 9.64% and from 3.94% to 0.87%, respectively, after exposure to NaCl solution for 1 h. Also, we verified a drastic deterioration of the surface adhesion of the Ag NP thin film to the substrate by exposure to NaCl solution. We could observe crack propagation and delamination by in-situ scanning electron microscope imaging. In addition, passivation effect by a parylene layer for preventing the permeation of the saline solution was investigated.

The influence of strain hardening of copper on the crack path in Cu/Al2O3/Cu direct bonded copper substrates

In automotive applications, Cu/Al2O3/Cu compounds are widely used as substrates in electronic power devices due to their high thermal and electrical conductivity.The significance of this research are Vickers hardness measurements that reveal the hardening of Cu in Cu/Al2O3/Cu compounds under thermal cycling for the first time. A key finding was that the Cu hardening dictates the characteristics of the observed crack propagation path. Using a kinematic and isotropic Cu hardening model in finite element simulations and a fracture mechanical modeling methodology, we were able to predict the crack path in very good agreement with experimental observations.

Prediction of Crack Propagation Rate and Stress Intensity Factor of Fatigue and Welded Specimen with a Two-Dimensional Finite Element Method

This paper presents the fundamental investigation on crack propagation rate (CPR) and Stress Intensity Factor (SIF) for a typical fatigue and welded specimens which are Compact Tension (CT) and Single Edge Notch Tension (SENT) as well as Butt and longitudinal T-joint. The material data of austenitic stainless steel SS316L was used to observe crack propagation rate with different initial crack length and different tensile load was used for the fracture mechanics investigation. The geometry of the specimens was modelled by using open source software CASCA while Franc 2D was used for post processing based on Paris Erdogan Law with different crack increment steps. The analysis of crack propagation using fracture mechanics technique requires an accurate calculation of the stress intensity factor SIF and comparison of the critical strength of the material (KIC) was used to determine the critical crack length of the specimens. it can be concluded that open source finite element method software can be used for predicting of fatigue life on simplified geometry.

Higher Toughness of Metal-nanoparticle-implanted Sodalime Silicate Glass with Increased Ductility

In this report, we propose a novel framework for toughening brittle oxide glass originated from enhanced ductility by implanting a secondary material comprising different mechanical properties. To do so, copper-metal nanoparticles are implanted into the subsurface layer of commercial soda-lime silica glass by using the electrofloat method. The crack initiation load of the implanted glass is found to be comparable to the glass chemically strengthened in ordinary tempering conditions. By observing crack propagation and stress distribution from cross-section, it is found that the crack propagation stops within the metal nanoparticle implanted layer, due to the stress dissipation or relaxation. The copper-implanted glass shows improved toughness with decreased hardness. The toughening mechanism of the composite glass is theoretically studied using molecular dynamics calculations on an amorphous silica model with copper nanoparticles embedded, and Peridynamics fracture simulations for indentation on a glass sheet model whose surface was implicitly modeled as the copper-implanted oxide glass. The experimentally observed phenomena of intrinsic toughening were well explained by the series of the conducted simulations.

Real-time observation of crack propagation and stress analysis during laser cutting of glass

Laser cutting of glass using a continuous-wave laser is attracting considerable attention because of its high processing speed and minimized generation of microcracks. During laser cutting of glass, a crack develops because of thermal stress and divides the glass plate. In this study, we observed crack propagation during laser cutting of glass in real time and found the distance between the crack tip and the laser irradiation position was 150 μm. Furthermore, we investigated the influence of the distance between the crack tip and the laser irradiation position on stress distribution and the stress condition necessary for crack growth. The results show the maximum principal stress at the crack tip increased as the distance between the crack tip and the laser irradiation position increased. In addition, we found that the crack developed when the maximum tensile stress of the crack tip reached 99 MPa. These results can be expected to enable the control of crack propagation and the estimation of appropriate processing conditions during laser cutting of glass.

Combined static-cyclic multi-axial crack propagation in cruciform specimens

Two cracks, initiated from the opposite tips of a 45° inclined central notch, were considered in cruciform specimens made of Ti6246. A static load was applied along one arm of the specimen and a cyclic load (R = −1) was applied along the other arm. Crack propagation was carefully monitored by optical means for different ratios of static to cyclic load. The observed crack propagation was simulated using two numerical tools, involving two different mixed-mode crack propagation prediction methods. The experimental evidence shows that there is a switch in crack propagation direction from orthogonal to the cyclic load at low static load levels to orthogonal to the static load for high static load levels. Both numerical procedures were able to predict this switch, albeit at slightly different static to cyclic load ratios.

Crack Initiation, Propagation, and Coalescence Experiments in Sandstone Brazilian Disks Containing Pre‐Existing Flaws

This study aims to investigate the fracture behaviors of cracks and crack systems in Brazilian disk (BD) sandstone specimens under compressive line loading. We conduct a series of rock fracture experiments to investigate crack initiation, propagation, and coalescence in samples with one or more pre‐existing flaws under radial compressive stress. The displacements and failure loads of the tested specimens are measured. Experimental results show that there are two main types of cracks growing from the pre‐existing flaws: wing cracks and secondary cracks. Both initiate mostly from the tips of the pre‐existing flaws and propagate in a stable manner. The results reveal that wing cracks appear first and propagate toward the loading direction. Secondary cracks can form in some multiple pre‐cracked cases after wing cracks are already present. We also provide a characterization of the observed crack propagation paths and patterns and discuss the influence of pre‐existing crack or crack systems. The results help in investigating the failure mechanisms and mechanical properties of rock or rock‐like materials.

Effect of high strain rate and low temperature on mode II fracture toughness of ductile adhesive

Adhesive joints have a great potential use in different industrial applications which may encounter low temperature and high strain rate conditions, the fracture behavior of adhesive needs to be reliably predicted under such conditions. This paper experimentally studies the mode II fracture toughness of a polyurethane (PU) adhesive at room temperature (RT) under quasi-static condition with J-integral method and at low temperatures under high strain rate conditions with compliance-based beam method (CBBM), which does not need the observation of crack propagation. Typical R-curves of the PU ductile adhesive under the loading rate of 2 m/s, 3 m/s and at RT, −20°C, −40°C respectively are obtained. From the experimental results, low temperature and high strain rate has great effect on mode II fracture toughness of adhesive. The mode II fracture toughness of this PU adhesive decreases by at least one order of magnitude when conditions vary from quasi-static to high rate. Under the high strain rate conditions, the mode II fracture toughness of adhesive increases with the decrease of the temperature. At −40°C under the loading rate of 3 m/s, mode II fracture toughness of adhesive increases by 130% compared with the data at RT under the loading speed of 2 m/s. Through the experiment, the relationship between the mode II fracture toughness of adhesive, the nominal shear strain rate and the temperature is obtained. It is concluded that the mode II fracture toughness of adhesive at RT under quasi-static condition cannot be used to design and analyze adhesive joints at low temperatures under high strain rate conditions.

Rapid Solder Interconnect Fatigue Life Test Methodology for Predicting Thermomechanical Reliability

A rapid reliability test methodology was devised for simulating mechanical stresses induced from thermal expansion induced shear in temperature cycling of flip-chip devices in order to de-convolute shear stress from thermal effects in typical environmental tests. Using controlled force application according to spring deflection, a test stand was created to mechanically apply shear stress to solder interconnects in flip chip devices at isothermal conditions. The shear stress was applied cyclically using a tribometer to simulate the mechanical stresses induced in the interconnects of a device during a thermal cycle while in operation or accelerated testing. In the mechanical application of shear, the control of loading and cyclic rate can be precisely controlled while monitoring key factors for observing crack propagation and damage. In doing so, this novel approach introduces the ability to directly correlate shear stress and plastic work accumulation (damage) to fatigue life in a generic device, utilizing help from finite element models alongside data acquisition. Using the obtained correlations, lifetime predictions through early stage design analysis are possible, paving the way for a-priori optimized design for thermomechanical reliability in flip-chip devices. The methodology presented herein creates the opportunity to eliminate costly lifetime testing on multiple electronic device designs/configurations, while also expediting any data collection needed for new materials or process related impacts to reliability.

Paraglacial Rock Slope Adjustment Beneath a High Mountain Infrastructure—The Pilatte Hut Case Study (Écrins Mountain Range, France)

Landslides triggered by shrinking glaciers are an expected outcome of global climate change and they pose a significant threat to inhabitants and infrastructure in mountain valleys. In this study we document the rock slope movement that has affected the Pilatte hut (2572 m a.s.l.) in the Ecrins range (French alps) since the 1980s. We reconstructed the geometry of the unstable rock mass using Terrestrial Laser Scanning and quantified the unstable volume (~ 400,000 m3). Field observations and annual crack surveys have been used to identify the dynamics of past movements. These movements initiated in the late 1980s and have accelerated since 2000. The current trend seems to be towards a relative stabilization. Reconstruction of the glacier surface using past images taken since 1960 and ‘Structure from Motion’ photogrammetry showed that the glacier probably applied stresses to the rock slope during its short-lived advance during the 1980s, followed by debuttressing caused by rapid surface lowering until the present day. The relationship between observed crack propagation and glacier surface change suggests that the rock slope instability is a paraglacial response to glacier surface changes, and highlights that such responses can occur within a decade of glacier change.