Fracture Surface Features Research Articles

Fractography of Bone Using Reconstructed Computed Tomography (CT) Scans

Fractography has been shown to be applicable to forensic assessments of skeletal trauma by observing the presence and orientation of fracture surface features, which reveal information about the direction of crack propagation. Previous studies have examined dry or processed bone surfaces, often fractured under controlled experimental conditions. Here we assess a series of clinical computed tomography scans involving lower extremity injuries and find that a number of fracture surface features can be seen on three-dimensional computational models (surface and volumetric). These findings indicate that bone fractography can be used in skeletal trauma analyses without processing the remains and may also have clinical as well as forensic applications.

Experimental investigation on the mixed-mode fracture behavior of rock-like material with bedding plane

To investigate the combined effects of bedding plane angle and notch angle on the mixed-mode fracture behavior of rock-like material, three-point bending tests of semi-circular bend (SCB) rock-like specimens with two relative locations between bedding plane and notch were first conducted accompanied by acoustic emission (AE) tests. The fracture surface characteristics of SCB rock-like specimens were then scanned and analyzed. The experimental results revealed that both the bedding plane angle and notch angle showed strong influences on the fracture behavior of rock-like material. Under each bedding plane angle, most of the fracture load continuously increased with the increasing notch angle. Under each notch angle, the fracture load continuously decreased with the increasing bedding plane angle. The fracture load of SCB rock-like specimens when bedding plane pro-dip to the notch was larger than that when bedding plane anti-dip to the notch. With the increasing bedding plane angle, most of the values of mode I, mode II and effective fracture toughness continuously decreased. With the increasing bedding plane angle, the fracture modes of SCB rock-like specimens transformed to bedding plane dominant fracture. The fracture surface properties are closely related with the fracture mode of SCB rock-like specimens. When bedding plane anti-dip to the notch, joint roughness coefficient (JRC) values almost linearly decreased with the increasing bedding plane angle. With different bedding plane angles and notch angles, the relationships between fracture load and accumulated AE energy could be well described by the linear function.

A New Model for Predicting Flow in Fractured-Vuggy Carbonate Reservoirs under Pseudosteady State Condition

For constant rate production of a single well in a closed boundary fractured-vuggy carbonate reservoir, when the pressure wave propagates to the reservoir boundaries, boundary-dominated flow occurs, and the transient flow period ends, the reservoir will be in a state of pseudoequilibrium (i.e., pseudosteady state flow occurs, and the pressure at any point in the reservoir declines at the same constant rate over time). The characterization of fluid flow in the fractured-vuggy carbonate reservoir under pseudosteady state condition is of significance in describing the productivity index (PI) of the well. However, due to complex mechanisms (e.g., stress dependency of reservoir properties and crossflow between different systems of the reservoirs) during flow in fractured-vuggy carbonate reservoirs, researches on productivity prediction in fractured-vuggy carbonate reservoirs under pseudosteady state are very limited. The present work is aimed at developing a new analytical model for predicting flow in fractured-vuggy carbonate reservoirs under pseudosteady state condition. In the derived model, the crossflow between different systems (i.e., matrix, fracture, and vug) of the reservoirs was taken into account. In addition, based on Hooke’s law, a quantitative model was proposed to study stress-dependent permeability of the fracture system, which connects the reserve spaces. Moreover, the roughness morphology characteristics of fracture surface were taken into account with fractal theory. Finally, with our derived model, influences caused by various related factors on productivity were analyzed. The results show that well productivity during pseudosteady flow will be significantly affected by the morphology of fracture surface (e.g., fracture microstructure parameters) and effective stress. Specifically, due to effective stress, the fracture system in the fractured-vuggy reservoirs will be deformed, and the corresponding properties (e.g., permeability, porosity, and conductivity) will change, leading to the change of well productivity. In addition, there exists a negative relationship between the elastic storage capacity ratio of vugs and well productivity during pseudosteady flow. Moreover, a larger value of matrix-fracture interporosity flow coefficient or vug-fracture interporosity flow coefficient corresponds to a larger value of well productivity during the pseudosteady period. The new derived model is beneficial to improve the productivity prediction accuracy and reduce uncertainty. What is more, the findings of this study can help for providing theoretical reference for the design of efficient development of fractured-vuggy carbonate reservoirs.

Mechanical Behavior Assessment of Ti-6Al-4V ELI Alloy Produced by Laser Powder Bed Fusion

The present work correlates the quasi-static, tensile mechanical properties of additively manufactured Ti-6Al-4V extra low interstitial (ELI, Grade 23) alloy to the phase constituents, microstructure, and fracture surface characteristics that changed with post-heat treatment of stress relief (670 °C for 5 h) and hot isostatic pressing (HIP with 100 MPa at 920 °C for 2 h under an Ar atmosphere). Ti-6Al-4V ELI alloy tensile specimens in both the horizontal (i.e., X and Y) and vertical (Z) directions were produced by the laser powder bed fusion (LPBF) technique. Higher yield strength (1141 MPa), higher tensile strength (1190 MPa), but lower elongation at fracture (6.9%), along with mechanical anisotropy were observed for as-stress-relieved (ASR) samples. However, after HIP, consistent and isotropic mechanical behaviors were observed with a slight reduction in yield strength (928 MPa) and tensile strength (1003 MPa), but with a significant improvement in elongation at fracture (16.1%). Phase constituents of acicular α′ phase in ASR and lamellar α + β phases in HIP samples were observed and quantified to corroborate the reduction in strength and increase in ductility. The anisotropic variation in elongation at fracture observed for the ASR samples, particularly built in the build (Z) direction, was related to the presence of “keyhole” porosity.

Surface characteristics analysis of fractures induced by supercritical CO2 and water through three-dimensional scanning and scanning electron micrography

Morphology of hydraulic fracture surface has significant effects on oil and gas flow, proppant migration and fracture closure, which plays an important role in oil and gas fracturing stimulation. In this paper, we analyzed the fracture surface characteristics induced by supercritical carbon dioxide (SC-CO 2 ) and water in open-hole and perforation completion conditions under triaxial stresses. A simple calculation method was proposed to quantitatively analyze the fracture surface area and roughness in macro-level based on three-dimensional (3D) scanning data. In micro-level, scanning electron micrograph (SEM) was used to analyze the features of fracture surface. The results showed that the surface area of the induced fracture increases with perforation angle for both SC-CO 2 and water fracturing, and the surface area of SC-CO 2 -induced fracture is 6.49%–58.57% larger than that of water-induced fracture. The fractal dimension and surface roughness of water-induced fractures increase with the increase in perforation angle, while those of SC-CO 2 -induced fractures decrease with the increasing perforation angle. A considerable number of microcracks and particle peeling pits can be observed on SC-CO 2 -induced fracture surface while there are more flat particle surfaces in water-induced fracture surface through SEM images, indicating that fractures tend to propagate along the boundary of the particle for SC-CO 2 fracturing while water-induced fractures prefer to cut through particles. These findings are of great significance for analyzing fracture mechanism and evaluating fracturing stimulation performance.

Correction to: Estimation of Low-Cycle Fatigue Lifetime in Aluminum-Silicon-Magnesium Alloy of Cylinder Heads based on Striation Marks as Failure Features of Fracture Surfaces and Paris Crack Growth Law

Correction to: Estimation of Low-Cycle Fatigue Lifetime in Aluminum-Silicon-Magnesium Alloy of Cylinder Heads based on Striation Marks as Failure Features of Fracture Surfaces and Paris Crack Growth Law

Durability of a novel effective microfine cementitious grouting material in corrosion environments

High durability requirements of grouting materials have been proposed gradually in corrosion environments. To evaluate and improve durability of grouting material, ordinary Portland cement (OPC), microfine Portland cement (MC), microfine sulphoaluminate cement (MSAC), and newly developed effective microfine cement-based grout (EMCG) were selected. Early impermeability, flexural strength (FS), unconfined compressive strength (UCS), corrosion resistance coefficient (KFS and KUCS), volumetric and mass variations, characteristics of fracture surface, corrosion mineral, microstructure and pore size distribution are studied synergistically. The water-binder ratios (W/Bs) of OPC and microfine grouts are 1.0 and 1.0–1.5. The concentrations of sodium sulfate and sodium chloride corrosion solutions are 0.3%, 5% and 10%. Corrosion ages are 3d, 7d, 28d, 91d, 181d and 360d. The 3d or 7d impermeable pressure of EMCG exceeds 1.0 MPa. The anti-corrosion strength and durability of EMCG under the W/B of 1.5 are acceptable. KFS and KUCS of MC and OPC are low. Although KFS and KUCS of MSAC are over 1.0, its strength needs to be enhanced further. The KFS, KUCS and actual strength of EMCG are satisfied. The corrosion expansion rate of EMCG is the lowest (no more than 0.058%), and its effectiveness of hydration and anti-corrosion is the optimal. The EMCG’s interconnection degrees among gels are the highest, its number of holes is the minimum and its pore structure is satisfactory. The EMCG satisfies demands of high durability in corrosion environments in underground, hydraulic, civil and ocean engineering.

Tensile Strength of Artificially Cemented Sandstone Generated via Microbially Induced Carbonate Precipitation.

Artificially bio-cemented sands treated with microbially induced calcite precipitation are weakly cemented rocks representing intermediate materials between locked and carbonate sands. Variations in cementation significantly affect the strength of sample, particularly tensile stregth. The modes of fracture and the surface characteristics resulting from the indirect tensile strength tests (Brazilian tests) are strongly correlated with the specimen strength and consequently the degree of cementation. This study examines the tensile strength of bio-cemented fine and coarse sands (average particle diameter 0.18 and 1.82 mm, respectively) and investigates failure modes by recording fracture evolution at both sides of specimen and surface characteristics of the reconstructed surfaces. The dimensionless slope parameter provided the best fit with respect to tensile strength while the power spectral density was a good indicator of surface anisotropy. Finally, wavelet decomposition allowed for comparison of fracture surface characteristics of the two sands ignoring the grain size effects.

Study on Geometry, Dimensional Accuracy and Structure of Parts Produced by Multi Jet Fusion.

Multi Jet Fusion (MJF) is one of the newest additive manufacturing technologies for polymer powders, introduced in recent years. This fully industrial technology is gaining big interest as it allows fast, layer-by-layer, printing process, short production cycle, and very high printing resolution. In this paper, twelve thin-walled, spherical PA12 prints were studied in terms of geometry, dimensional accuracy, and fracture surface characteristics. The various characteristic features for MJF prints were observed here for parts produced according to four various print orientations and having different thicknesses, i.e., 1, 2 or 3 mm. The study showed that MJF technology can print such difficult shapes. However, the set of parameters allowing producing parts with highest geometrical and dimensional accuracy causes at the same time some microstructural issues, like great interlayer porosity or high number of non-processed powder particles embedded in the print structure.

Permeability Evolution of Fractures in Shale in the Presence of Supercritical CO2

AbstractWe experimentally examined the impact of supercritical carbon dioxide (scCO2) on fracture permeability and fracture surface characteristics in shales of various compositions. We measured permeability and fracture normal displacement at different effective stresses using both argon and scCO2 as pore fluids. Both natural fractures and saw cuts in intact samples were used in our study. The permeability and fracture normal displacement decrease after multiple loading/unloading cycles, apparently as the result of inelastic compaction. In samples with high carbonate content, we observe an increase in permeability and fracture surface degradation after more than 3.5 days of exposure to scCO2, apparently due to carbonate dissolution. We demonstrate that the sensitivity of permeability to effective normal stress correlates well with the fracture normal displacement. The dependence of permeability on effective normal stress increases after exposure to scCO2 as the fracture surface became more compliant.

Estimation of Low-Cycle Fatigue Lifetime in Aluminum-Silicon-Magnesium Alloy of Cylinder Heads based on Striation Marks as Failure Features of Fracture Surfaces and Paris Crack Growth Law

Estimation of Low-Cycle Fatigue Lifetime in Aluminum-Silicon-Magnesium Alloy of Cylinder Heads based on Striation Marks as Failure Features of Fracture Surfaces and Paris Crack Growth Law

Alteration in micro-mechanical characteristics of wellbore cement fracture surfaces due to fluid exposure

The stiffness of wellbore cement fracture surfaces was measured after exposing to the advective flow of nitrogen, silicone oil, and medium sweet dead crude oil for different exposure periods. The test specimens were extracted from fractured cement cylinders, where the cement fracture surfaces were exposed to the different fluids up to 15 weeks. A nanoindenter with a Berkovich indenter tip was used to measure load-indentation depth data, which was used to extract the elastic modulus (E) and nano-hardness (H) of the cement fracture surfaces. A reduction in the elastic modulus compared with an unexposed specimen were observed in all the specimens. Both elastic modulus and nano-hardness for the specimens exposed to silicone oil were lower than specimens exposed to nitrogen gas and varied with the period of exposure. The elastic modulus and nano-hardness of the specimens exposed to crude oil were the lowest with a significant decrement with the exposure period. The frequency distribution of the nanoindentation measurements shows that the volume-fraction ratio of the two types of cement hydrated nanocomposites for both the unexposed and test specimens is about 70:30%. Phase transformation beneath the indenter is observed for all of the specimens, with more obvious plastic deformation in specimens exposed to crude oil. Analytical measurements (SEM, EDS, FT-IR, and XRD) on exposed cement fracture surfaces reveal different levels of physical and chemical alteration that are consistent with the reduction in stiffness measured by nanoindentation. The study suggests that cement stiffness will decrease due to crude oil exposure, and the fracture will be sensitive to stress and pore pressure with time.

Shear fracture in bulk metallic glass composites

Fracture behavior of bulk metallic glass matrix composites (BMGCs) with both transforming and non-transforming β-Ti dendrites under shear and opening modes was examined. Experimental results show that the fracture toughness of all three BMGCs is considerably lower in mode II than in mode I, due primarily to the shear dominant stress state in the former, which renders easy shear band initiation. However, stable crack growth in mode I is insignificant whereas it is considerable in mode II. The toughness of BMGCs reinforced with coarse but non-transforming dendrites in both the modes is higher than the respective values in BMGCs with transforming β-Ti inspite of their ability to strain harden and hence enhanced ductility. Fracture surface features and shear band patterns at notch tips of both mode I and mode II specimens indicate that despite the interactions of dendrites with the shear bands, the fracture criterion and mechanism of BMGCs is identical to that in BMGs. The differences in the fracture behaviour of these BMGCs is rationalized by considering the effect of relaxation enthalpy of the amorphous matrices in addition to the length scale and transforming tendency of the dendrites on the transformation of a shear band into a crack. Implications of these results in terms improving the fracture toughness of BMGCs with transforming dendrites is discussed.

Correlating interfacial fracture toughness to surface roughness in polymer-based interfaces

Statistical fractal characteristics are examined for polymer-based interfaces. Interfacial fracture behavior is modulated via exposure to varying levels of chemical contaminant concentration so as not to affect the initial interface roughness. The results of 1D height–height correlation analysis show a strong correlation between the interfacial fracture toughness and the resulting fracture surface roughness, and a toughness-independent roughness exponent; $$\beta \approx$$ 0.35 ± 0.04, which is the slope of the self-affine domain. The cut-off length scale of the self-affinity is found to scale with interface toughness, and equal the combined length scales of interfacial cohesive length and plastic zone size within the adhesive layer. The reported statistical characteristics of interfacial fracture surfaces is among the first to show the quantitative inter-correlation between interfacial adhesion and the resulting fracture surface roughness. With additional examination of other systems, the observed correlations have the potential to assess the interfacial fracture toughness for a wide range of polymer-based interfaces.

DETERMINATION OF MECHANICAL PROPERTIES OF COMPOSITE MATERIALS WITH DIFFERENT FILLERS POLYMER MATRIX

In this study, the preparation and characterization of carbon fiber reinforced epoxy composites are aimed at today's increasing use of composite materials. In this study, composite materials consisting of unidirectional carbon fiber-epoxy resin were prepared and the effects of fiber inclination angle on layered epoxy composite materials were investigated using various characterization techniques. Composite materials were prepared by autoclave method. At the stage of characterization of prepared composite materials Scanning electron microscopy (SEM) has been applied for tensile, compression tests and characterization of fracture surfaces to determine the mechanical properties. Keywords: Carbon fiber,epoxy resin,polymer composite,mechanical properties.

Roughness and Scaling Properties of Oxide Glass Surfaces at the Nanoscale.

Using atomistic computer simulations we determine the roughness and topographical features of melt-formed (MS) and fracture surfaces (FS) of oxide glasses. We find that the topography of the MS is described well by the frozen capillary wave theory. The FS are significant rougher than the MS and depend strongly on glass composition. The height-height correlation function for the FS shows an unexpected logarithmic dependence on distance, in contrast to the power law found in experiments. We unravel the crucial role of spatial resolution on surface measurements and conclude that on length scales less than 10nm FS are not self-affine fractals.

Effects of overload mode-mixity on fatigue damage behavior and governing micromechanisms in AA7075 under biaxial fatigue loading

An investigation into the effects of overload mode-mixity on crack growth behavior and governing micromechanisms of AA7075 T6 has been conducted. Cruciform AA7075 T6 specimens were subjected to constant amplitude planar biaxial fatigue with single overloads, and key fatigue damage behavior, including fatigue life, crack growth rate, and recovery distance, were investigated and correlated to overload parameters. Additionally, SEM fractography was conducted to identify and relate fracture surface features to governing fatigue damage micromechanisms. An increase in fatigue life was observed for all cases of mode-mixity, with the minimum increase occurring at 45°. The mix-mode overloads also caused crack retardation in all cases. In the shear dominant overloads, however, initial post-overload crack acceleration occurred and was immediately followed by crack retardation. Microscale analysis showed distinct fracture features in the pre-overload, transient, and post-overload regions for both tensile and shear dominant overloads.

Characterization of 3D printed ABS specimens under static and cyclic torsional loadings

In this work, the high cycle fatigue response of fused filament fabrication acrylonitrile butadiene styrene solid cylinder specimens under static and cyclic torsional loadings is studied. A first experimental phase was conducted varying the number of external walls between one, two and three contours and with two different infill patterns – concentric and zigzag. Monotonic torsion tests were performed with this first set of specimens to find the best configuration. The best parameter configuration was chosen for a second experimental phase where specimens were subjected to fully reversed load-controlled loading conditions (R=-1) at room temperature. Seven different stress levels were defined to construct the S-N curve of this 3D printed configuration. The microscopic images of the fractured surfaces were also depicted after monotonic and fatigue tests, aiming to study crack initiation, propagation and to characterize the features of fracture surface.

Reassembly method of cultural relic fragments based on the neighborhood characteristics of fracture surface

Reassembly method of cultural relic fragments based on the neighborhood characteristics of fracture surface

Dynamic Compression Properties of the Resistance Spot Welding of High Strength Steels under Varying Temperature Conditions

In this paper, we have studied the dynamic compression performance of the RSW of QP980 steel and TRIP800 steel by using a split Hopkinson pressure bar (SHPB), and we have also examined the fracture mode of the two research objects. It is found that the spot welding zone is primarily composed of the martensite structure, and there is a sparse defect of crystal structure adjacent to the center of nugget. In addition, there are evident gaps between the plates on both sides of the spot welding zone. Through the measurement of the microhardness of the two grade steel, it is found that the average hardness of the RSW of QP980 steel is higher than that of TRIP800 steel. There is a softening region in the interface of the heat affected zone and the substrate zone. The dynamic compression experiments are carried out on the RSW of QP980 steel and TRIP800 steel under 200°C and 300°C conditions, and it is found that the strain rate would increase with the rising temperature, but the compressive strength would experience declines. Furthermore, the sparse defects of crystal structure adjacent to the center of nugget would lead to stress rebound when the specimen is compressed. Moreover, through the observation of the fracture surface of the recovered specimens, it is found that the fracture of the nugget is brittle, whereas the fracture mode of the sample is more complicated. In addition, the fracture surface features a number of “river pattern” cleavage facets, and there are very few dimples of ductile tearing. This study is expected to have huge implications to the safety of vehicle body under high‐speed impact.