Smooth Fracture Surface Research Articles

The effect of stress concentration on the bending behavior of a ZrCuNiAl bulk metallic glass

The bending behaviors of a Zr55Cu30Ni5Al10 bulk metallic glass (BMG) samples with different notch radii are studied. The artificial notch will introduce stress concentration within the BMG sample during bending. That means, smaller notch radius leads to greater stress concentration around the notch area, and thus results in earlier failure and smoother fracture surface. Then, the sample with smaller notch radius possesses smaller fracture toughness. The relationship between the stress concentration and deformation feature has been discussed in terms of grease model.

Histological Characteristics, Cell Wall Hydrolytic Enzymes Activity and Candidate Genes Expression Associated with Seed Shattering of Elymus sibiricus Accessions.

Elymus sibiricus (siberian wildrye) is a perennial, cool-season, self-pollinating, and allotetraploid grass. As an economically important species, it has been widely grown and used for pasture and hay in northern China. Because of serious seed shattering (SS), however, E. sibiricus is difficult to grow for commercial seed production. To better understand the underlying mechanism of SS, we investigated the differences in SS of cultivars and wild accessions in relation to morphological and genetic diversity, histological characteristics, lignin staining, cell wall hydrolytic enzymes activity and candidate genes expressions. We found high level of morphological and genetic diversity among E. sibiricus accessions. In general, cultivars had higher average pedicel breaking tensile strength (BTS) value than wild accessions, of which PI655199 had the highest average BTS value (144.51 gf) and LQ04 had the lowest average BTS value (47.17 gf) during seed development. SS showed a significant correlation with seed length, awn length and 1000-seed weight. SS was caused by degradation of abscission layers that formed at early heading stage, and degradation of abscission layers occurred at 14 days after heading. Histological analysis of abscission zone (AZ) showed a smooth fracture surface on the rachilla in high SS genotype, suggesting higher degradation degree of abscission layers. This may resulted from the increased cellulase and polygalacturonase activity found in AZ at seed physiological maturity. Staining of pedicels of two contrasting genotypes suggested more lignin deposition in low SS genotype may play a role in resistance of SS. Furthermore, candidate genes that involved in cell wall-degrading enzyme and lignin biosynthesis were differentially expressed in AZ, indicating the involvement and role in SS. This study provided novel insights into the mechanism of SS in E. sibiricus.

An Examination of the Transition of Fracture Characteristics in Long Bones from Fresh to Dry in Central Florida: Evaluating the Timing of Injury.

It is important to conduct timing of injury research analyzing fracture characteristics at known postmortem intervals (PMI) because bone can retain fresh characteristics throughout the PMI. Defleshed pig (Sus scrofa) long bones were fractured weekly in two environments (full sun and shade) over 14 weeks in Central Florida and fracture characteristics were categorized (N = 136) for analysis. Results of analysis of variance (ANOVA) using time in weeks (PMI) as a dependent variable indicate significant relationships between PMI and Fracture Angle (p < 0.001), Fracture Surface (p < 0.001), and Fracture Outline (p < 0.001). Fracture characteristics associated with perimortem trauma (smooth Fracture Surfaces and curved or V-shaped Fracture Outlines) were commonly observed. Analysis of fracture characteristics for each environment demonstrated similar patterns. Overall, the loss of only fresh fracture characteristics for each bone was noted earlier in the PMI for the Central Florida region than previously reported.

Synthesis of 1,2,3-triazole functionalized hyperbranched poly(ethyleneimine) and its use as multifunctional anionic macroinitiator for diglycidyl ether of bisphenol A curing

Hyperbranched poly(ethyleneimine) (PEI) has been modified by the addition of propargyl acrylate following a Michael addition reaction. On this polymer (PEI-yne) a copper (I)-catalyzed azide alkyne cycloaddition (CuAAC) has been performed to obtain a multifunctional triazole initiator (PEI-TA). After structural and thermal characterization, this polymer has been used in different proportions as anionic multifunctional macroinitiator in diglycidyl ether of bisphenol A (DGEBA) homopolymerization. The curing process has been studied by calorimetry and the thermosets obtained have been thermally characterized and compared with thermosets prepared by using 1-methylimidazole (1-MI) as standard initiator. The electron microscopy inspection of the fracture surfaces of the new materials prepared shows the formation of submicrometer particles that should enhance toughness characteristics, changing smooth fracture surfaces in 1-MI initiated materials to multi-planar surface with tortuous and thicker cracks.

Intrinsic healable and recyclable thermoset epoxy based on shape memory effect and transesterification reaction

A shape memory and healable epoxy was prepared based on esterification between diglycidyl ether of bisphenol A and tricarballylic acid. The healing was achieved through transesterification at the fracture surface between two epoxy blocks in a confined space assisted by shape recovery force. The shape recovery of the compression programmed epoxy at elevated temperature tightly closed the gap between the two epoxy blocks, whose fracture surfaces are saw-cut and not perfectly matched during healing, which is the worst case scenario for the healing test. A healing efficiency of ∼60% was achieved. This suggests that, for naturally cracked surfaces, which have smoother fracture surfaces and better surface alignments during healing, higher healing efficiencies could be expected. We believe that the combination of shape memory and intrinsic healing capability within one network will broaden the applications of thermosets and enable recycling.

A New Flexible Soy-Based Adhesive Enhanced with Neopentyl Glycol Diglycidyl Ether: Properties and Application.

Soy-based adhesives inherently possess low water resistance and brittleness, which limit their application on plywood fabrication. This investigation involves using a long chain cross-linker, neopentyl glycol diglycidyl ether (NGDE), to produce an intrinsic toughening effect to reduce the brittleness and improve the water resistance of a soybean meal–based adhesive. The solids content, viscosity, functional groups, fracture surface micrographs, and thermal stability of the adhesives were measured. Three-layer plywood was fabricated using the resultant adhesive, and the tensile shear strength of the plywood was measured. All adhesive properties were compared with a soybean meal/polyamidoamine-epichlorohydrin (PAE) adhesive and commercial melamine urea formaldehyde resin. The results showed that adding 6 g NGDE improved the water resistance of the soybean meal-based adhesive by 12.5%. This improvement is attributed to the following reasons: (1) a dense cross-linked network is formed by the chemical reaction between NGDE and protein molecules; (2) the toughness of the adhesive increases and a smooth and homogeneous fracture surface is created, which effectively prevents moisture intrusion; (3) the addition of NGDE increases the thermostability of the cured adhesive. The tensile shear strength of the plywood bonded with the soybean meal-based adhesive with 6 g NGDE was 286.2% higher than that without NGDE and attained 1.12 MPa, which was attributed to the reduction in the adhesive’s viscosity, and the improvement in the water resistance and toughness of the adhesive. The tensile shear strength of the plywood bonded with 6 g NGDE was 19.1% higher than that with 6 g PAE and was similar to the MUF resin, which validated the novel adhesive being suitable for use as an industrial plywood adhesive.

Effect of Fracture Roughness, Shear Displacement, Fluid Type, and Proppant on the Conductivity of a Single Fracture: A Visual and Quantitative Analysis

Summary Proppants are one of the essential parameters in fracturing design. They not only provide fracture conductivity but also prevent “healing” of fractures. Hence, the quantification of proppant-transport characteristics is highly critical in a sustainable production from hydraulically fractured wells. Previous attempts in this regard were limited to smooth (parallel) fracture surfaces to a great extent, but the roughness of fractures may control the conductivity of hydraulic fractures in the presence of proppants. This paper focuses on experimental measurements to visually and quantitatively investigate the hydraulic characteristics of rough fractures in the presence of proppants. Transparent models of the fractures of different origin rocks (granite, marble, and limestone) were prepared. Water and polymeric solutions representing typical rheological properties of hydraulic-fracturing fluids were injected through the models (joint and sheared fractures) with and without propping agents. The conductivity changes caused by proppant distribution caused by the roughness of fracture surfaces were quantified and correlated to different fractal characteristics of surface roughness. Qualitative and quantitative analyses were supported by images collected through the experiments. Proppant behaviors in joint- and shear-type fractures were observed to be different. In both cases, fracture-closure areas existed, which controlled the proppant transportation and fracture conductivity. The qualitative and quantitative data provided on the degree of conductivity change in a single fracture (in the presence and absence of propping agents) are expected to be useful in accurate performance estimation of oil/gas production from fractured systems.

Preparation of tannin–formaldehyde–furfural resin with pretreatment of depolymerization of condensed tannin and ring opening of furfural

As renewable and economical bio-based resources, tannin can polymerize with aldehyde to form resin, furfural can partially substitute formaldehyde for the preparation of resin with phenols. Aiming to enhance the reaction efficiency between tannin and furfural by weakening the steric hindrance, a pretreatment was applied to depolymerize the macromolecule of tannin into small one and open the furan ring structure of furfural before the preparation of tannin–formaldehyde–furfural (TFFu) resin. Modified furfural was used to partially substitute formaldehyde by the ratios of 10, 20, and 30%. Chemical structure characteristics, thermal behaviors, dynamic viscosity, and fracture surface micrograph of the TF and TFFu resins were analyzed by Fourier transform infrared spectroscopy, differential scanning calorimetry and thermogravimetric analysis, rheological measurement, and scanning electron microscopy, respectively. The result indicated that co-polycondensation with modified furfural decreased the free formaldehyde content of TFFu resin, and increased the thermal stability. Moreover, when the formaldehyde was substituted by modified furfural in 10%, the TFFu resin had the most smooth and compact fracture surface.

A comparative study of Cn/Sn/Cu and Ni/Sn/Ni solder joints for low temperature stable transient liquid phase bonding

Two sandwich structured solder systems (Cu/Sn/Cu and Ni/Sn/Ni) were investigated in terms of interfacial reaction and mechanical reliability for low temperature wafer bonding. The relationship between chemical reaction and mechanical reliability of the solder joints was investigated by varying thickness ratio of Cu/Sn (Ni/Sn). The Cu/Sn/Cu joint was proved to be stronger, revealing very smooth fractured surface through Cu6Sn5 grains (intragranular fracture). Meanwhile, the Ni/Sn/Ni joint showed rough fractured surface through Ni3Sn4 grain boundaries and Ni3Sn4/Ni3Sn2 interphase boundaries (intergranular fracture).

Evaluationof fracture toughness ofalpha-Nb5Si3 by micro-sized cantilever beam testing

ABSTRACTA micro-sized fracture testing method has been applied to investigate fracture toughness of alpha-Nb5Si3. Chevron-notched single crystal specimens with a size of 3 x 3 x 15 μm3 were prepared in a grain of polycrystalline alpha-Nb5Si3 by focused ion beam, FIB, technique. Fracture tests were conducted using a nanoindenter at room temperature and linear load-displacement curves and smooth fracture surfaces were obtained. This fracture behavior was presumed to be brittle fracture similar to bulk alpha-Nb5Si3. The average of fracture toughness KQ is 3.45 ± 0.29 MPa√m under a small-scale yielding condition.

Fractures in a trachyandesitic lava at Öræfajökull, Iceland, used to infer subglacial emplacement in 1727–8 eruption

We present detailed field observations of cooling fractures in a small-volume trachyandesitic lava, informally named the Slaga lava, on the south west flank of Öræfajökull volcano, south east Iceland. Columnar joints, pseudopillow fracture systems, and curved platy jointing occur in the lava, whose exposed section is approximately 600m in length and generally 2–3m in thickness. Columnar jointing may occur at the base of flow lobes, whereas pseudopillow fracture systems occur throughout the lava in an outer, glassy, fractured carapace, and curved platy fractures occur in the centres of larger flow lobes. Pseudopillow fracture systems, composed of a single master fracture and multiple subsidiary fractures formed normal to the master fracture, are of two types: G-type pseudopillow fracture systems have very narrow striae (chisel marks) on their master fractures, indicative of rapid cooling and brittle fracture; SR-type pseudopillow fracture systems display alternating smooth and rough master fracture surface textures, evidence of alternating brittle and ductile fracture propagation mechanisms. Subsidiary fractures in both types show curved striae on their fracture surfaces, which enable the determination of fracture propagation directions. Pseudopillow fracture systems are thought only to form in the presence of water, including water caused by the melting of ice and snow. The curved platy fractures display prominent river lines and may have resulted from cooling contraction, post-emplacement degassing, flow deflation or shearing in the flow against the outer solid crust of the flow during inflation. Due to recent advances in the understanding of the formation mechanisms of pseudopillow fracture systems they, and the other fractures present in the flow, can be used to reconstruct the cooling environment. The lava is inferred to have been emplaced within subglacial drainage channels incised into or beneath a thin alpine-type glacier, with coolant infiltrating the lava radially from all sides and ponding or draining of water at or along the lava base. We link this flow to the 1727–8 eruption of Öræfajökull volcano on the basis of historical records, which describe lava effusion in this approximate location and striking chemical compositional similarity between 1727 tephra and the Slaga lava.

The effect of surface roughness and mixed-mode loading on the stiffness ratio κx/κz for fractures

The characterization of fractures using elastic waves requires a parameter that captures the physical properties of a fracture. Many theoretical and numerical approaches for wave propagation in fractured media use normal and shear fracture specific stiffness to represent the complexity of fracture topology as it deforms under stress. Most effective medium approaches assume that the normal and shear fracture specific stiffness are equal, yielding a shear-to-normal specific stiffness ratio of one. Yet several experimental studies show that this ratio can vary from zero to three. We conducted a series of experiments to determine the stiffness ratio for fractures with different surface roughness subjected to mixed-mode loading conditions. Specimens containing a single fracture were subjected to either normal loading or combined normal and shear loading during ultrasonic measurements of transmitted and reflected P- and S-waves. Theoretical analysis based on the displacement discontinuity theory shows, for P- and S-waves with the same wavelength, that the theoretical stiffness ratio is not equal to one, but depends on the ratio of S- to P-wave velocities. The conventional stiffness ratio limit of unity is determined to be appropriate for very smooth fracture surfaces even under mixed-mode loading conditions. However, rough fracture surfaces result in stiffness ratios that are greater than the theoretical limit and the magnitude of the ratio depended on the relative ratio of shear-to-normal stress. The results from the experiments suggest that the conventional practice of assuming a constant stiffness ratio equal to 1.0 may not be appropriate. Therefore, the ratio of shear-to-normal fracture specific stiffness depends on the roughness of the fracture surface and the loading conditions.

Hybrid Poly(aryl ether sulfone amide)s for Advanced Thermoplastic Composites

An organocatalytic approach to the depolymerization of poly(ethylene terephthalate) (PET) with selected nucleophiles generates high‐value terephthalate‐based monomers. These monomers are subjected to nucleophilic aromatic substitution (SNAr) polymerizations in order to circumvent many of the traditional drawbacks of unmodified materials such as poly(aryl ether sulfone)s (PESs). The synthesis and molecular characterization of novel poly(aryl ether sulfone‐amide)s (PAESAs) containing 10–30 wt% amide functionality are described. PAESAs containing 30 wt% amide are fabricated via extrusion and solvent casting for mechanical characterization. The mechanical behavior of the extruded PAESA is studied through dynamic mechanical analysis (DMA) and tension tests. The DMA studies are performed at a frequency of 1 Hz, in the temperature range of 22–275 °C, indicating a storage modulus of 2.77 ± 0.58 MPa at 30 °C. The glass transition temperature (Tg) of the material, as the temperature corresponding to tanδ peak, is measured to be 217.1 ± 1.7 °C, consistent with DSC measurements. The tension tests on extruded samples reveal a ductile fracture, evidenced with neck formation and propagation on the macroscale, and a rough fracture surface on the microscale. The yield strength of the sample is found to be 52.8 ± 9.2 MPa, with a ductility ranging from 6% to 11%. In contrast to extruded samples, the solvent‐cast PAESA samples fail in a brittle fashion, with relatively smooth fracture surface and no sign of necking. image

Effect of different amounts of modified talc on the mechanical, thermal, and crystallization properties of poly(butylene succinate)

Abstract Poly(butylene succinate) (PBS) with different ratios of modified talc was prepared by twin-screw extruding. The effect of different loading amounts of talc on the mechanical, thermal, and crystallization properties of PBS was investigated. The mechanical test results indicate that the stiffness of the composites was increased linearly with increasing talc content, and the tensile strength and elongation stayed at relatively high levels when the talc amount is &lt;15 phr. Thermal gravimetric analysis showed that the thermal stability of PBS composites was improved notably with a small amount (5–10 phr) of talc; however, high loading of talc did not help further improve the thermal stability. Differential scanning calorimetry data showed that the melting enthalpy (ΔHm), crystallization enthalpy (ΔHc), and crystallinity degree (Xc) decreased when the talc increased and crystallization temperature (Tc) was moving to relatively high values. The results of X-ray diffraction demonstrated that the incorporation of talc inhibited the PBS crystallization behavior significantly but did not change the crystal structure. Scanning electron microscopic studies indicated that the homogeneous dispersion and smoother fracture surfaces of the composite became inhomogeneous and coarse with higher talc loading.

Fracture toughness and cyclic fatigue resistance of resin composites with different filler size distributions

ObjectivesTo verify the influence of filler size distributions on fracture toughness (KIc), initial fracture strength (IFS) and cyclic fatigue resistance (CFR) of experimental resin composites. MethodsFour composites were prepared with same inorganic content (78wt%), in which 67wt% was constituted by glass particles with d50 of 0.5; 0.9; 1.2; 1.9μmKIc of the composites was determined by the single-edge notched beam (SENB) method. To evaluate the IFS and the CFR a biaxial bending test configuration was used. The CFR was determined under cyclic loading for 105 cycles using the ‘staircase’ approach. The fracture surfaces of IFS and CFR specimens were analyzed under scanning electron microscope (SEM). ResultsThere was a positive linear correlation between d50 vs. KIc and statistical difference was found only between C0.5 (1.24±0.10MPam0.5) and C1.9 (1.41±0.17MPam0.5). There were no statistical differences among IFS means, which ranged from 155.4±18.8MPa (C0.9) to 170.7±23.1MPa (C1.2). C0.5 (93.0±18.6aMPa) showed the highest and C0.9 the lowest CFR (82.5±8.0cMPa). There was no correlation between CFR with d50 values or with KIc means. SEM images showed the morphology with brittle fracture patterns for the surfaces of IFS specimens and a more smooth fracture surface for CFR specimens. SignificanceResin composites showed different failure mechanisms for quasi-static and fatigue loading. For KIc and IFS, composites with larger filler size distributions showed better results due to crack deflection; while under cyclic loading, viscous behavior was predominant and composites with smaller particles showed higher fatigue resistance.

Thermal performance of poly(ethylene disulfide)/expanded graphite nanocomposites

In this study, the influences of expanded graphite oxide (EG) nanosheets presence with and without surfactant on structural and thermal performance of poly(ethylene disulfide) (PEDS)-based nanocomposites are investigated. Sodium dodecylbenzenesulfonate (SDBS) is used as a surfactant for the preparation of modified-EG nanosheets. The structural, morphological, and thermal properties of prepared nanocomposites are studied using X-ray diffraction (XRD), scanning electron microscopy, and differential scanning calorimetry techniques, respectively. XRD patterns of nanocomposites reveal that a high degree of expanded graphite nanosheets dispersion is achieved with and without surface modification using in situ polymerization method. Moreover, the presence of immobilized polysulfide chains near the interface region of nanosheets is suggested as a possible reason for the observed increase in the number of semi-crystalline organic fractions in the structure of PEDS via EG nanosheets incorporation. In addition, the morphology of SDBS-modified-EG loaded nanocomposite shows a smoother fracture surface than unmodified-nanosheets reinforced nanocomposite. Therefore, more interactions between nanosheets and polysulfide chains are expected in the structure of unmodified-EG reinforced nanocomposite. Moreover, thermal resistance and degradation kinetics of prepared nanocomposites are studied using thermogravimetric analysis results and degradation activation energy calculations, respectively. The required activation energy for the degradation process of SDBS-EG loaded nanocomposite is about 140 kJ mol−1 lower than the required degradation activation energy of unmodified-nanosheets reinforced nanocomposite.

Effects of various fillers on sintering, microstructures and properties of Ca-Ba-Al-B-Si-O glass/ceramic composites

Low-temperature sintering and properties of LTCC (low temperature co-fired ceramics) materials based on CaO-BaO-Al2O3-B2O3-SiO2 glass and various fillers such as Al2O3, silica glass, christobalite, AlN, ZrO2, MgO·SiO2, TiO2 were investigated. The results show that densification, crystallization, microstructures and dielectric properties of the composites are found to strongly depend on the type of filler. The densification process of glass/ceramic composites with various fillers is mainly from 600 °C to 925 °C, and the initial compacting temperature of samples is 600 °C. The initial rapid densification of samples starts at its glass softening temperature. LTCC compositions containing Al2O3, silica glass, AlN and MgO·SiO2 fillers start to have the crystallization peaks at 890, 903, 869 and 844 °C, respectively. The crystallization peaks are believed as correlated to the crystallization of CaAl2SiO8, β-SiO2, Ca2Al2SiO7 and β-SiO2. The composite ceramic with Al2O3, silica glass and TiO2 ceramic have a better dense structure and better smooth fracture surface. Sample for Al2O3 has the lowest dielectric loss tanδ value of 0.00091, whereas the sample for MgO·SiO2 has the highest dielectric loss tanδ value of 0.02576. The sample for TiO2 has the highest dielectric constant value of 14.46, whereas the sample for AlN has the lowest dielectric constant value of 4.61.

Casting effect on compressive brittleness of bulk metallic glass

An interesting phenomenon of cooling-rate induced brittleness in Zr52.5Cu17.9Ni14.6Al10Ti5 bulk metallic glass (BMG) was reported. It was found that the as-cast BMG specimens exhibited a brittle–ductile transition when the larger specimens were machined into smaller specimens through removing the cast-softening surface layer by layer. After compression tests, the as-machined small specimens, owing to the absence of the cast-softening surface, displayed highly dense and intersecting shear bands, and extensive plastic deformation. This is in contrast to the catastrophic failure and low deformability in the as-cast large specimens. More free volume was detected in the smaller as-fractured specimens, by differential scanning calorimetry, which may be attributed to the occurrence of strain softening and increased plasticity. Compared with the relatively smooth fracture surface in the smaller specimens, the larger specimens showed more diverse features on the fracture surface due to their graded structures.

Non-uniform dispersion of toughening agents and its influence on the mechanical properties of polypropylene

To achieve excellent properties of polymer blends and composites, good dispersion and uniform distribution of second component or filler in the matrix are often required. However, more and more evidences reveal that uniform distribution is not always the best. To further prove this idea, in this work, we purposely designed and prepared different samples of isotactic polypropylene (iPP)/elastomer or iPP/!-nucleating agent with uniform and non-uniform distribution of the modifiers via stacking the blending sheets in different sequence. It was found that for a given amount of toughening agent, the impact strength of polymer blends with non-uniform distribution of elastomer or !-nucleating agent could be much higher than its uniformly dispersed counterpart, while the tensile strength and tensile modulus remain relatively constant. The instrumented impact test confirmed that among the samples with different layered structures, the absorbed energy during crack initiation differs little from each other. Whereas absorbed energy during crack propagation process shows the same trend as final impact strength, making it the controlling parameter during the impact process. When cracks are initiated at higher toughening agents content side, the relatively smooth fracture surfaces near the crack edge area proved that they absorb small energy and the adjacent inner part showed obviously plastic deformation, corresponding to higher energy absorption. Our work demonstrates again that design and control of the hierarchical structure of polymer articles is vital for high performance properties and non-uniform distribution of filler could be much better than the uniform distribution.

Macroscopic scattering of cracks initiated at single impurity atoms

Brittle crystals, such as coloured gems, have long been known to cleave with atomically smooth fracture surfaces, despite being impurity laden, suggesting that isolated atomic impurities do not generally cause cracks to deflect. Whether cracks can ever deviate when hitting an atomic defect, and if so how they can go straight in real brittle crystals, which always contain many such defects, is still an open question. Here we carry out multiscale molecular dynamics simulations and high-resolution experiments on boron-doped silicon, revealing that cracks can be deflected by individual boron atoms. The process, however, requires a characteristic minimum time, which must be less than the time spent by the crack front at the impurity site. Deflection therefore occurs at low crack speeds, leading to surface ridges which intensify when the boron-dopage level is increased, whereas fast-moving cracks are dynamically steered away from being deflected, yielding smooth cleavage surfaces.