Fracture Surface Morphology Research Articles

Effect of confining pressure on shear fracture behavior and surface morphology of granite by the short core in compression test

The study on shear fracture behaviour at elevated confining pressure is very meaningful for a lot of practical activities in underground works. To understand the influence of confining pressure on shear fracture behavior, a series of confined rock fracture tests were performed on the short core in compression (SCC) specimens. Uniform confining pressure was applied on the entire surface of the rock specimen in the tests. The results show that the peak load, shear modulus, nominal shear strength and mode II fracture toughness of SCC specimens increase approximatively linearly with confining pressure. The shear fracture surfaces after confined SCC tests were measured by a three-dimensional (3D) optical scanner. Based on fractal and statistical theories, the effect of confining pressure on the morphological characteristics in shear fracture surfaces has been studied in depth. The results indicate the fracture surface roughness decreases slightly with the increase of confining pressure, which can be attributed to the restraining effect on fracture expansion and the friction effect on the two new shear fracture surfaces under large confining pressure. Generally, standard deviations and means for asperity height and standard deviations of slope angle decline with increasing confining pressure. Frequency distributions of aspect orientation become more evenly with confining pressure. Moreover, the feasibility of applying the Mohr-Coulomb criterion in the SCC approach was assessed. It is found that the cohesion and internal friction angle determined by the SCC method are very closed to the values calculated from uniaxial compression tests, indicating that the SCC method are feasible for estimating shear parameters of rock.

Novel approach to recycled carbon fiber suitability assessment for additive technologies

This article presents a new approach to suitability assessment of short reclaimed carbon fiber (rCF) for additive technologies via commonly used analytical methods. Acrylonitrile butadiene styrene (ABS) based plastics reinforced with virgin or recycled CF samples were received, their mechanical properties and morphology of tensile fractured surface were determined by SEM (Scanning Electron Microscopy) and tensile strength test. As long as operating characteristics of CFRP are affected by single fiber strength as well as adhesion (interfacial interaction) between matrix and CF, this research also includes investigation of fiber surface with Fourier-transform infrared spectroscopy (FTIR), Raman spectroscopy and X-ray diffraction (XRD). Correlation between suggested complex parameters of investigated CF and strength of plastics (CFRP) samples was shown. It was also established that contribution of each investigated parameter is additive.

Stress-controlled fatigue of HfNbTaTiZr high-entropy alloy and associated deformation and fracture mechanisms

The stress-controlled fatigue tests are carried out at a stress ratio of 0.1 and a frequency of 10 Hz, and span both low-cycle and high-cycle regimes by varying the applied stress amplitudes. The high-cycle fatigue regime gives a fatigue strength of 497 MPa and a fatigue ratio of 0.44. At equivalent conditions, the alloy's fatigue strength is greater than all other high-entropy alloys (HEAs) with reported high-cycle fatigue data, dilute body-centered cubic alloys, and many structural alloys such as steels, titanium alloys, and aluminum alloys. Through in-depth analyses of crack-propagation trajectories, fracture-surface morphologies and deformation plasticity by means of various microstructural analysis techniques and theoretical frameworks, the alloy's remarkable fatigue resistance is attributed to delayed crack initiation in the high-cycle regime, which is achieved by retarding the formation of localized persistent slip bands, and its good resistance to crack propagation in the low-cycle regime, which is accomplished by intrinsic toughening backed up by extrinsic toughening. Moreover, the stochastic nature of the fatigue data is neatly captured with a 2-parameter Weibull model.

Investigation of the Impact Resistance Behavior of Customized Hair Clipper Comb Fabricated by Fused Deposition Modeling

This study consists of the development of a hair clipper comb finite element (FE) model, impact test analysis on the FE model, fabrication of the product using commercially available materials, followed by physical impact testing of the comb. Moreover, microscopic examination of the combs was performed to analyze the quality of the product and correlate the defects with the failure mechanism. The 3D model of comb for a Philips hair clipper was developed using ONSHAPE software, followed by a design study to understand the impact resistance of the product. The design study was performed using finite element analysis (FEA) explicit dynamic module, where two hair clipper comb designs, one with a solid body and the other with a shell were subjected to drop test simulation in two orientations: leg and head drop. Two readily available 3D printable plastic materials, Acrylonitrile Butadiene Styrene (ABS) and Polylactic acid (PLA) were selected for the FEA simulation while the comb was subjected to free fall from a height of 5 ft (1.67 m). The comb was dropped in two orientations: the head drop configuration and the leg drop configuration. For all combinations, the maximum stresses generated as a result of impact were noted and experiments performed to validate the simulation results. The four models were fabricated using fused deposition modeling (FDM) technique and were manually dropped from the same height. In line with the simulated results, models prepared from PLA material failed upon the impact while ABS samples having a comparatively better impact resistance sustained the impact without failure. Finally, fracture surface morphologies of the failed PLA component and the surface of ABS in as-printed condition were analyzed using Scanning Electron Microscopy (SEM). Based on the obtained results, the shell model made of ABS material turns out to be the most suitable choice out of all the designs considered.

Research on dynamic mechanical properties and plastic constitutive relation of Ti3Al intermetallic compounds under mechanical-thermal coupling

Ti3Al intermetallic compounds is a lightweight, high-temperature resistant rare aerospace materials, whose dynamic mechanical properties concern the accuracy of simulation analysis and further development in material manufacturing. To obtain the plastic constitutive relation of Ti3Al under the action of mechanical-thermal coupling, material rheological behavior was investigated by using the separation Hopkinson pressure bar (SHPB) system with a high-temperature synchronous assembly. Meanwhile, the Johnson-Cook plastic constitutive model was calculated and modified by introducing strain compensation and adiabatic temperature rise at the range of strain rate of 0.001–6500 s−1 and deformation temperature of 293–1173 K. Furthermore, the microstructure evolution of Ti3Al fracture surface morphology was discussed. Experimental results showed that the flow stress had a weak positive strain rate enhancement effect, significant negative temperature thermal softening effect and strain rate plasticizing effect. Adiabatic temperature rise was accompanied by the high strain rate, and its value increased exponentially with the strain rate. The adiabatic deformed shear band (ADSB) appeared at an edge of 45° along the loading direction at the strain rate 4500 s−1 and the deformation temperature 273 K, respectively. ADSB tended to expand internally along with the strain rate and evolved into an adiabatic transformed shear band (ATSB) when the temperature rose to 973 K. The maximum relative errors in the modified J-C model at the high strain rate and the room temperature, the high strain rate and the high temperature were 3.11% and 14.91%, respectively. Consequently, the modified J-C model described in dynamic mechanical properties of Ti3Al was more accurate than the conventional J-C model.

Use of DIC and AE for investigating fracture behaviors of cold recycled asphalt emulsion mixtures with 100% RAP

Cracking damage have great influence on the service life of cold recycled asphalt emulsion mixtures (CRAEM). As non-destructive methods, digital image correlation (DIC) and acoustic emission (AE) techniques can diagnose and visualize various distresses efficiently. The objective of this research was to explore and characterize the fracture behaviors of CRAEM with DIC and AE. Firstly, the semi-circular bending (SCB) tests, accompanied with DIC and AE monitoring were conducted on CRAEM with different cement contents. Secondly, the fracture energy examined by DIC as well as the tracked cracking path were analyzed to correlate with the fracture characteristics of CRAEM. Then, the variation of AE parameters (i.e., AE energy, AE amplitude) were investigated to identify the damage stages of SCB specimens. Finally, the box-counting dimension and the AE b-value were established based on cumulative AE energy and AE amplitude separately to quantitatively assess the transition of damage state. The results indicate that the cement content would significantly affect the cracking resistance performance of CRAEM, and CRAEM with a moderate content could have the benefits of more alternative energy release paths in the process of crack initiation and propagation. The fracture failure process of CRAEM could be divided into four stages through the simultaneous mutations of cumulative AE energy and AE amplitude. The difference of fracture surface morphologies of CRAEM with different cement contents obtained by the digital microscope could provide a reliable explanation for the fracture behaviors of the whole damage evolution process of CRAEM. The transition of the value of box-counting dimension from the maximum to the minimum could reflect the formation of macrocracks of CRAEM. The inflection point of the AE b-value curve arriving at the minimum value could be regarded as a precursor information to predict the complete fracture of CRAEM.

Tessellated dimple geometry of high entropy alloy

This article focuses on the characterization and analysis of dimple geometry on the published tensile fracture surfaces of a HfNbTaTiZr refractory high entropy alloy of different matrix microstructures, generated through cold deformation and systematic annealing treatments. Changes in different microstructural states which led to different tessellated fracture complexions have been quantified, compared and correlated with the corresponding tensile responses of the alloy. This interpretation allows the use of fracture surface morphology and image texture in a quantitative way.

Processability and Physical Properties of Compatibilized Recycled HDPE/Rice Husk Biocomposites

The circular economy promotes plastic recycling, waste minimization, and sustainable materials. Hence, the use of agricultural waste and recycled plastics is an eco-friendly and economic outlook for developing eco-designed products. Moreover, new alternatives to reinforce recycled polyolefins and add value to agroindustrial byproducts are emerging to develop processable materials with reliable performance for industrial applications. In this study, post-consumer recycled high-density polyethylene (rHDPE) and ground rice husk (RH) of 20% w/w were blended in a torque rheometer with or without the following coupling agents: (i) maleic anhydride grafted polymer (MAEO) 5% w/w, (ii) neoalkoxy titanate (NAT) 1.5% w/w, and (iii) ethylene–glycidyl methacrylate copolymer (EGMA) 5% w/w. In terms of processability, the addition of RH decreased the specific energy consumption in the torque experiments with or without additives compared to neat rHDPE. Furthermore, the time to reach thermal stability in the extrusion process was improved with EGMA and MAEO compatibilizers. Tensile and impact test results showed that using coupling agents enhanced the properties of the RH composites. On the other hand, thermal properties analyzed through differential scanning calorimetry and thermogravimetric analysis showed no significant variation for all composites. The morphology of the tensile fracture surfaces was observed via scanning electron microscopy. The results show that these recycled composites are feasible for manufacturing products when an appropriate compatibilizer is used.

Fracture micrographic analysis of a carbon FML under three-point bending load

The core of the present work concerns the analysis of the failure mode and the fracture process induced by the flexural load in Fibre Metal Laminates (FMLs). The influence of the connection layer placed between the composite ones and the metal sheets on the fracture mode was analysed. The considered FML was made of aluminium sheets interposed with carbon fibre reinforced polymer (CFRP) layers, joined with two different types of interface: by using a structural adhesive, or by relying on the bonding capacity of the prepreg resin. Then, the mechanical performances of the produced laminates were determined through the three-point bending test procedure, and the support span was varied to investigate different loading conditions. Finally, the fracture surface morphology was analysed by using both optical and scanning electron microscopes. The type of interface was found to influence the strength of the studied FML, and different fracture modes were observed, depending on the loading condition.

Damage characteristics of sandstone with different crack angles subjected to true triaxial cyclic loading and unloading

Cracks in the rock are among crucial defects affecting its deformation and strength characteristics. Particularly in underground or mining engineering, the initiation and development of cracks due to cyclic unloading are critically affected by the fracture of the rock mass. In order to scrutinize the mechanical behavior of rocks with different crack angles, a true triaxial cyclic loading and an unloading test are carried out on sandstone samples with prefabricated cracks of various angles. The cracked sandstone samples do not considerably expand under action of triaxial stresses, commonly exhibit non-ideal elastic characteristics, and mainly undergo shear failure. As the crack angle grows, the tensile properties become pronounced, and the fracture surface morphology of the cracked samples presents a huge difference. The change rules of the irreversible axial and lateral strains are apparently different, and the rate of change of the irreversible lateral strain in terms of the applied stress is more sensitive than that of the axial irreversible strain. The energy evolution law of the hysteresis loop formed in the sample cyclic load test has no evident influence on the crack angle of the sample; however, the larger the crack angle of the sample, the more energy consumption during failure. Based on the equivalent irreversible strain and the hysteretic loop energy dissipation indicators, the damage law of sandstone samples can be described. It is also revealed that the damage rule determined according to the equivalent irreversible strain index is more conducive to characterizing the initial characteristics of damaged samples. Additionally, the damage rule determined based on the hysteretic loop energy dissipation index would better describe the damage rule associated with the understudy samples. There are obvious discrepancies in the morphological characteristics of the fracture surface in the scanning electron microscope images of the typical fracture surface of the samples with various crack angles, indicating that the damage and destruction of the sample acted upon by the shear and tensile shear are wholly dissimilar.

Mechanism of matrix influencing the cryogenic mechanical property of carbon fibre reinforced epoxy resin composite

This study focuses on the cryogenic mechanical property of carbon fibre reinforced epoxy resin composite (CFRP) unidirectional laminate, and the cryogenic evolution mechanism is discussed from the microstructural perspective of resin free volume and intermolecular forces. The primary transition temperature (147 °C) and the secondary transition temperature (−25 °C) is identified through dynamic mechanical analysis. As the cryogenic condition (−196 °C) is significantly lower than the temperature of main-chain segmental and micro-structure unit motion, the resin molecular segments are frozen, free volume fraction and resin toughness are reduced, thus the brittleness increases. These effects reduce the cryogenic failure strain of CFRP at break by 43.7% compared to room temperature, resulting in a smoother fracture surface morphology. Resin molecules under cryogenic condition have higher packing density, stronger intermolecular forces, which increase the strength and modulus of both resin and CFRP.

Creep rupture behavior of 2.25Cr1Mo0.25V steel and weld for hydrogenation reactors under different stress levels

Abstract In the present research work, the 2.25Cr1Mo0.25V steel plates with a thickness of 112 mm were welded using the multi-pass submerged automatic arc welding process. The creep specimens were prepared from the base metal (BM) and weld metal (WM) in the welded joint after heat treatment process. The uniaxial creep tests were performed to investigate the creep deformation and rupture behaviors at 550°C under different applied stress levels. The microstructure and fracture surface morphology of crept BM and WM samples were also characterized using the scanning electron microscope with energy-dispersive X-ray spectroscopy. The results showed that typical three-stage creep deformation curves are observed in both BM and WM specimens, and the BM exhibits a faster deformation rate than the WM. Both the creep rupture time and uniaxial creep ductility are found to be increased with a decrease in applied stress. Furthermore, the relationship between the minimum creep rate and time to rupture of both BM and WM samples was obtained, and it can be described using a unified Monkman–Grant equation. In addition, it is found that the creep fractures of the BM and WM are a transgranular ductile failure. The creep damages of both materials are mainly associated with the microstructural degradations, that is, the initiation and coalescence of creep cavities at second phase particles such as carbide and inclusion particles along the loading direction.

Effects of hydrostatic pressure on hydraulic fracturing properties of shale using X-ray computed tomography and acoustic emission

The study of the hydraulic fracturing characteristics in shale reservoirs is crucial for improving the permeability of shale gas reservoirs. In this study, hydraulic fracturing tests are conducted on full-diameter shale cores, and the hydraulic fracturing characteristics of shale with different bedding angles under high hydrostatic pressure are studied. The results show that under a hydrostatic pressure of 59 MPa, the shale sample will rupture twice in the breakdown stage during hydraulic fracturing. When the bedding inclination increases from 0° to 90°, the shale fracture breakdown pressure first decreases and then increases, showing an overall downward trend. Under high hydrostatic pressure, shale specimen surface fracture morphology and X-ray computed tomography reveal that a bedding angle close to 45° is more conducive to forming a complex hydraulic fracture network, which makes the fractal dimension of the fracture network larger. The bedding plane of shale is the direct cause of the diverse propagation patterns of hydraulic fractures. The b-value is a parameter that characterizes the magnitude–frequency relationship of an earthquake, and it is closely related to the rock rupture process. The b-value varies with different trends with the expansion of hydraulic fractures, but they all reach the lowest point before the failure of the shale sample. The higher the hydraulic fracture network complexity, the lower the peak b-value is. This work provides a qualitative understanding and scientific explanation of the hydraulic fracturing characteristics of anisotropic shale under hydrostatic pressure.

Numerical and Analytical Study of Fluid Flow and Thermal Transfer in a Rough Fracture

The surface morphology of rough fractures significantly affects the fluid flow and heat transfer characteristics in the fractures. A thermal-flow coupling model with specific geometric fractures was established to investigate the influence of surface morphology on the heat transfer characteristics of a single fracture. The effect of temperature on the physical properties of rocks and fluids was included in the study to reflect the actual situation more realistically. The research results show that the temperature of the fluid in the rough fracture is nonlinearly distributed along the flow direction and the higher the flow velocity, the higher the heat transfer efficiency. The fracture surface morphology has a significant impact on the heat transfer characteristics, and the surface fluctuation will greatly affect the flow velocity, causing the fluid temperature to change abruptly at the fracture surface. Under the same flow rate, with the increase of the fluctuation degree of the fracture surface and the fluctuation frequency, the larger the heat exchange area of the fracture surface, the stronger the heat exchange performance. The heat transfer efficiency of the fracture is directly related to the heat transfer area of the fracture, so even with the same permeability, the heat transfer performance of fractures with different surface topography is different.

Effect of microwave on mechanical properties of laser-sintered carbon nanotube polymer composites

ABSTRACT In this work, carbon nanotubes (CNT)/polyethersulfone (PES) polymer composites were prepared by selective laser sintering, and the effects of microwave treatment on mechanical properties and tensile fracture surfaces of the composites were investigated. The experimental results indicated that tensile strength and bending strength of the composites upon microwave treatment for 5–25 s were improved by 4–20.4% and by 4.5–47.7%, respectively. The tensile fracture surface morphology of the composites depended on the time length of microwave treatment. Upon microwave treatment, the fracture surface showed fewer pores and better interfacial bonding between adjacent polymer particles. The fracture mechanisms for the microwave-treated carbon nanotube/polymer composites prepared by selective laser sintering were discussed.

Experimental assessment on the fatigue mechanical properties and fracturing mechanism of sandstone exposed to freeze-thaw treatment and cyclic uniaxial compression

The coupling problem of freeze-thaw (F-T) treatment and cyclic loading is extremely prominent for rock engineering in Tibetan Plateau, which has triggered many serious geotechnical engineering disasters. It is thus essential to systematically characterize the fatigue mechanism of rocks exposed to F-T treatment and cyclic loading. In this study, a series of cyclic uniaxial compression tests are conducted on sandstone subjected to 0, 10, 20, 30, 40 and 50 artificial F-T cycles to investigate the influence of F-T treatment on the fatigue mechanical properties of sandstone, regarding the fatigue deformation characteristics, energy evolution and coupled F-T-fatigue damage. Our testing results indicate that sandstone specimens exposed to higher F-T cycles are featured by larger irreversible strain and faster damage accumulation, leading to higher fatigue damage variable and lower fatigue life. By virtue of the digital image correlation (DIC) technique and scanning electron microscope (SEM), the progressive fatigue fracture process and the microscopic morphologies of fracture surfaces of the F-T treated sandstone specimens are revealed. During the cyclic loading process, the strain field in specimens uniformly distributes initially, and then it localizes continually with increasing cyclic number, triggering the eventual fatigue fracture. With increasing F-T cycles, the fatigue fracture of sandstone is more ductile and progressive. Moreover, the hidden linkage between microscopic fracture mechanism and macroscopic mechanical properties is further analyzed based on the test results. In addition, the microscopic fracture mechanism of F-T treated sandstone under cyclic loading and monotonic loading is also compared and discussed: the primary micro-mechanism causing the fatigue fracture of sandstone is the inter-granular (IG) fracture, while the micro-mechanism triggering the monotonic failure is the trans-granular (TG) fracture.

Bonding strength enhancement of low temperature sintered SiC power module by femtosecond laser induced micro/nanostructures

In this work, a low-temperature and low-pressure method was proposed for the bonding strength enhancement of SiC chips and substrates using micro/nanostructures fabricated by femtosecond laser. It is demonstrated that a reliable bond was achieved at 180 °C without assistant pressure. When the sintering temperature reached 250 °C and the assistant pressure was 10 MPa, the average shear strength reached 45 MPa, which was more than 3 times that of the flat substrate. The fracture surface morphology and the cross-section of the sample were characterized by SEM to analyze the enhancement mechanism of shear strength. The shear strength under different sintering conditions was also discussed. The thermomechanical coupled finite element simulation results demonstrate that the power module possessed excellent thermal capability and reliable lifetime under a temperature shock environment (−50 °C–250 °C). It is proved that the measured temperature distribution of the joint is in agreement with the simulation results. This method has great application prospects in microelectronic packaging, especially for wide-bandgap power semiconductors.

Covalent treatment of carbon fibre with functionalized MoS2 nanosheets using thiol-ene click chemistry: The improvement of interface in multiscale epoxy composites

The multiscaling method is contemplated as an effective approach for improving the interfacial adhesion in carbon fibre composites. Nonetheless, the lack of interactions between the nanomaterials and the other constitutes including fibre and matrix resulted in the deterioration of mechanical performance in composites. Herein, the combination of a scalable synthesis method based on ball milling and thiol-ene click chemistry has been utilized to graft the functionalized MoS 2 nanosheets with large lateral dimensions (∼537 nm) on the carbon fibres surface for the first time. The proposed method did not significantly affect the mechanical properties of the carbon fibre, leading to augmentation in the performance of composites by the virtue of higher surface energy and roughness of the fibre surface. In other words, the obtained results have demonstrated that the presence of activated MoS 2 nanosheets on the carbon fibre surface possesses the ability to promote interfacial adhesion and interlaminar shear strength by 74% and 36% respectively, compared to the pristine unsized carbon fibre. Additionally, the effectiveness and the efficacy of MoS 2 -CF reinforcements can be delineated by the enhancements of flexural strength and modulus of multiscale composites by 49.5% and 33.6%, respectively. The morphology of both fibres and fractured surfaces of composites indicated that the random distribution of nanosheets on the fibre surface facilitates the energy dissipation via breakage, pullout, and bridging mechanisms which subsequently improved the overall performance of the developed composites.

Performance comparison of carbon fiber reinforced polyaryletherketone and epoxy composites: Mechanical properties, failure modes, cryo‐thermal behavior, and finite element analysis

AbstractHigh‐performance thermoplastic composites are gaining attention as potential replacement for thermoset composites in high‐end structural applications owing to their superior fracture toughness and recyclability. In this study, polyaryletherketone (PAEK) and carbon fabric (CF) reinforced PAEK are compared with epoxy and epoxy‐CF composites. PAEK‐CF composites are prepared by film stacking method followed by compression molding while hand lay‐up technique was used for epoxy‐CF composites. PAEK and PAEK‐CF composites possess superior tensile properties, flexural strength and fracture toughness compared to those prepared from epoxy. The incorporation of CF improved the wear resistance in both PAEK and epoxy and PAEK‐CF exhibited the lowest wear rate. The investigation of interlaminar shear strength of the composites was conducted and the highest value observed for PAEK‐CF composite. Wear and fracture surface analysis suggested ductile failure for PAEK and PAEK‐CF composites and brittle failure in epoxy composites, as indicated by interfacial bonding/debonding and fiber pullout, at the fracture surface. Cryo‐thermal cycling effects on the tensile properties, fracture toughness and fracture surface morphology of the composites are studied. The failure behavior obtained from experimental studies was corroborated with finite element method‐based simulation models of fracture toughness response in single edge notch bend test using Abaqus/Explicit.

Effect of clamping pressure on interfacial fusion morphology and fracture mechanism of CFRTP/Ti6Al4V laser bonding joint featuring blind hole surface microtextures

Carbon fiber reinforced thermoplastic composites (CFRTP) and titanium (Ti) alloy are both important lightweight materials in aircraft and aerospace applications, whose heterogeneous hybrid structure manufactured by laser joining technology is propitious to leverage the performance advantages of each component. The clamping pressure during the laser joining procedure is one of the most critical process parameters affecting the joint performance. Laser joining of CFRTP to Ti alloy (Ti6Al4V) under various clamping pressure is carried out, aimed to investigate the effect of clamping pressure on interfacial fusion morphology, mechanical property and fracture mechanism of bonding joint featuring blind hole surface microtextures. The fusion morphology and element distribution at joining interface are observed by scanning electron microscope (SEM) and energy dispersive spectrometer (EDS). Moreover, the fracture morphology and fracture mechanism are analyzed after tensile-shear test. The results show that an appropriate increase of clamping pressure improves the filling effect of melted resin to microtextures on Ti alloy surface, while too high pressure is inclined to induce the generation of pores and cracks at the joining interface. The fracture load of the joints increases and then decreases as the pressure rises, and it reaches a peak value of 3821.4 N corresponding to the optimal interfacial fusion effect when the pressure is 0.8 MPa. Significant distinctions exist in the main fracture mechanisms under different clamping pressure conditions, which lead to different fracture surface morphologies and mechanical performance of laser bonding joints.