Compression Fracture Surface Research Articles

Improving biological and mechanical properties of bioprinted PCL-alginate-chondrocyte scaffolds for patellofemoral cartilage tissue regeneration

In this study, polycaprolactone (PCL) scaffolds have been employed as structural framework scaffolds for patellofemoral cartilage tissue regeneration. The biomechanical and biological properties of different scaffolds were investigated by varying alginate concentrations and the number of scaffold layers. Patellofemoral cartilage defects result in knee pain and reduced mobility, and they are usually treated with conventional methods, often with limited success. Generally, tissue-engineered PCL-alginate scaffolds fabricated by bioprinting technology show promise for enhanced cartilage regeneration due to the biocompatibility and mechanical stability of PCL. In addition, alginate is known for its cell encapsulation capabilities and for promoting cell viability. Biological and morphological assessments, utilizing water contact angle, cell adhesion tests, MTT assays, and scanning electron microscopy (SEM), informed the selection of the optimized scaffold. Comparative analyses between the initial optimal scaffolds with the same chemical composition also included flexural and compression tests and fracture surface observations using SEM. The controlled integration of PCL and alginate offers a hybrid approach, that assembles the mechanical strength of PCL and the bioactive properties of alginate for tissue reconstruction potential. This study aims to identify the most effective scaffold composition for patellofemoral articular cartilage tissue engineering, emphasizing cell viability, structural morphology, and mechanical integrity. The results showed that the optimum biomechanical and biological properties of scaffolds were obtained with a 10% alginate concentration in the monolayer of PCL structure. The findings contribute to regenerative medicine by advancing the understanding of functional tissue constructs, bringing us closer to addressing articular cartilage defects and related clinical challenges.

Mechanism of Low‐Temperature Brittle–Ductile Transition of Polypropylene/Low‐Density Polyethylene Blend Foam under Compressive Stress Caused by Cell Stretching

To enhance the low‐temperature toughness of polypropylene/low density polyethylene (PP/LDPE) blend, which is a crucial blend for polyolefin material with wide applications in frigid regions, the PP/LDPE blend foam with stretched cells is fabricated via a facile injection foaming together with open‐mold stretching process. During the open‐mold stretching, the relatively miscible PP and LDPE chains are debonded, and then the stretched and oriented cells structure with lots of tiny interphase cavities between the PP and LDPE phases and the fine lamellae are formed in the foam system. Such interphase cavities provide an adequate movement space for the frozen PP and LDPE chains and lamellae, and effectively relaxed and transferred stress, which greatly promote the uniform compressive behavior accompanied by the completely compacted cells at −25 °C. Moreover, the compressive fracture surface changes from relatively flat and smooth for the stretched PP foam to obvious yield folds and deformation for the stretched blend foam, and the compressive strain of stretched PP/LDPE blend foam is highly enhanced by a roughly 31%, 53%, and 44% increase than that of PP, PP/LDPE, and stretched PP foam samples, respectively, achieving the low‐temperature brittle–ductile transition for PP.

Inconel 718-CoCrMo bimetallic structures through directed energy deposition-based additive manufacturing

Bimetallic structures and coatings through additive manufacturing (AM) have demonstrated a high degree of freedom for tailoring properties depending on the application. In this study, Inconel 718 and CoCrMo were used as both are common alloys and exhibit unique properties, such as high-temperature oxidation, wear, and fatigue resistance. Using directed energy deposition-based metal AM, bimetallic structures containing these two alloys were manufactured, and the resulting structures exhibited no intermetallic phase formation, cracking, or porosity. Scanning electron microscopy and energy dispersive spectroscopy revealed a smooth elemental transition between the two compositions. Hardness testing showed a linear transition in the interfacial zone, validating no brittle intermetallic phase formation. Compression testing and fracture surface analysis revealed that the failures were not dependent on the interface properties. High-temperature oxidation showed no distinct effect on the interface, a firmly attached chromium oxide layer on the Inconel 718 side and a loosely attached chromium oxide layer on the CoCrMo side. There was also evidence of pit formation on the Inconel 718 surface, but not on the CoCrMo. These findings confirm a stable bimetallic system in which one of the two alloys can be used on the other material to improve the structure’s high-temperature oxidation or wear/corrosion resistance.

Uniaxial Compression Fractal Damage Constitutive Model of Rock Subjected to Freezing and Thawing

Mechanical properties of the rock in the cold regions are often affected by freeze-thaw cycles and loads. It is of great theoretical significance and engineering value to establish a uniaxial compression damage constitutive model of the rock under freeze-thaw cycles that can reflect the relationship between macroscopic and mesoscopic structural damage. In this paper, macroscopic and mesoscopic methods are combined with statistical methods to quantitatively analyze the damage degree of rock under freeze-thaw cycles and loads. Combined with the fractal features of the macroscopic image of the section, a fractal damage constitutive model considering the residual strength of rock is established. In addition, the model is subsequently verified by the experiment. The experiment shows that the mechanical properties of rocks subjected to freeze-thaw cycles and loads are determined by freeze-thaw damage variables, load damage variables, and their coupling effects. As the number of freeze-thaw cycles increases, the uniaxial compressive strength and elastic modulus of rocks decrease, and peak strain increases. By using the fractal dimension of the compression fracture surface as a bridge considering the residual strength of the rock, the constitutive model can better reflect the compaction stage, elastic deformation stage and plastic deformation stage of the uniaxial compression process of the freeze-thaw rocks.

Microstructure and Mechanical Behavior of CrFeNi2V0.5Wx (x = 0, 0.25) High-Entropy Alloys

CrFeNi2V0.5Wx (x = 0, 0.25) alloys based on these parameters of mixing enthalpy (ΔHmix), mixing entropy (ΔSmix), atomic radius difference (δ), valance electron concentration, and electronegativity difference(Δχ) were designed and prepared. The microstructure and room-temperature mechanical behavior of both alloys were investigated. Compressive test results showed that the CrFeNi2V0.5W0.25 alloy had higher yield strength than that of the W-free CrFeNi2V0.5 alloy, although they all exhibited quite larger compressive plasticity (ε > 70%). Compression fracture surface of CrFeNi2V0.5W0.25 alloy revealed a ductile fracture in the face-centered cubic (FCC) phase and a brittle-like fracture in the σ phase. Moreover, tensile test results indicated that the CrFeNi2V0.5W0.25 alloy exhibited excellent mechanical property with an ultimate tensile strength of 640 MPa and a high tensile elongation of 15.7%. The tensile deformation mode of the FCC phase in the CrFeNi2V0.5W0.25 alloy is dominated by planar glide, relating to dislocation configurations, high-density dislocations, and dislocation wall. Therefore, dislocation slip plays a significant role in tensile deformation of CrFeNi2V0.5W0.25 high-entropy alloy. The higher strength of CrFeNi2V0.5W0.25 alloy is predominantly due to the solid solution strengthening of W element and σ phase precipitation strengthening. Combination of the higher tensile strength and plasticity suggests that the CrFeNi2V0.5W0.25 alloy can be a promising aerospace material.

Crystallization kinetics and mechanical properties of Zr56Cu24Al9Ni7-xTi4Agx (x = 0, 1, 3, 5, and 7) metallic glasses

The effect of the replacement of Ni with Ag on the crystallization kinetics and mechanical properties of Zr56Cu24Al9Ni7-xTi4Agx (x = 0, 1, 3, 5, and 7 at.%) metallic glasses were investigated by X-ray diffraction (XRD), differential scanning calorimetry (DSC), and microhardness/compressive testing. Proper Ag substitution significantly improved of the glass-forming ability, crystallization activation energy, and mechanical properties of these materials. The critical diameter increased to 6–8 mm for Ag contents of 1, 3, and 5 at.%. The Ag-containing glassy alloys displayed higher crystallization activation energies than their Ag-free counterparts, suggesting that proper substitution hindered crystallization. The specimens of 3 mm in diameter and a Ag content of 1 at.% showed the largest strain under compression (ca. 4.68 ± 0.03%) and fracture strength (up to 1826 ± 31 MPa). A combination of veins and droplets was observed on the compressive fracture surfaces of the alloys. Furthermore, the fracture mechanisms, which enhanced the plasticity of the alloys, were also discussed herein.

Porosity Effects on Mechanical Properties of 3D Random Fibrous Materials at Elevated Temperatures

In this study, we prepare the specimens of three-dimensional random fibrous (3D RF) material along its through-the-thickness (TTT) and in-plane (IP) directions. The experimental tests of tensile and compressive properties as well as fracture toughness of 3D RF material are performed at elevated temperatures. Then, the porosity (83%, 87% and 89%) and temperature dependence of the tensile and compressive strength, elastic modulus, fracture toughness and fracture surface energy of the 3D RF materials for both the TTT and IP directions are analyzed. From the results of the tensile strength and elastic modulus versus material porosities at various temperatures, we find that tensile strength and elastic modulus for the TTT direction are more sensitive to the porosity, but not for the IP direction. Fracture toughness increases firstly and then decreases at a certain critical temperature. Such critical temperature is found to be the lowest for the porosity of 83%. On the other hand, at below 1073 K, the temperature-dependent fracture surface energies with three porosities for the TTT direction show similar variation trends.

Assessing Impact Direction in 3-point Bending of Human Femora: Incomplete Butterfly Fractures and Fracture Surfaces,.

Current literature associates bending failure with butterfly fracture, in which fracture initiates transversely at the tensile surface of a bent bone and branches as it propagates toward the impact surface. The orientation of the resulting wedge fragment is often considered diagnostic of impact direction. However, experimental studies indicate bending does not always produce complete butterfly fractures or produces wedge fragments variably in tension or compression, precluding their use in interpreting directionality. This study reports results of experimental 3-point bending tests on thirteen unembalmed human femora. Complete fracture patterns varied following bending failure, but incomplete fractures and fracture surface characteristics were observed in all impacted specimens. A flat, billowy fracture surface was observed in tension, while jagged, angular peaks were observed in compression. Impact direction was accurately reconstructed using incomplete tension wedge butterfly fractures and tension and compression fracture surface criteria in all thirteen specimens.

Compressive mechanical properties of HTPB propellant at low temperatures and high strain rates

To study the compressive mechanical properties of the hydroxyl-terminated polybutadiene (HTPB) propellant at high strain rates (700–1900/s) and low temperatures (−50 °C to 25 °C), we conducted a dynamic mechanical experiment using cylindrical specimens on a split Hopkinson pressure bar (SHPB). In addition, scanning electron microscopy was employed to observe the compressive fracture surfaces. The experimental results indicate the effectiveness of the proposed SHPB testing for the HTPB propellant. The effects of the strain rate and low temperature remarkably influenced the variations in stress. The lower temperatures and higher the strain rate generated an obvious increase in the modulus and compressive strength. Even at −50 °C and 1900/s, the propellant still maintained its viscoelastic characteristics. On the basis of the time–temperature equivalence principle, we obtained the master curves of the mechanical parameters. The propellant mainly exhibited transgranular fracture damage, increased porosity, and matrix tearing after impact.

Microstructure and Mechanical Behavior of Hot Pressed Cu-Sn Powder Alloys

Cu-Sn based alloy powders with additives of elemental Pb or C were densified by hot pressing technique. The influence of densifying on the properties of the hot pressed materials was investigated. The properties, such as the hardness, compressive strength, and wear resistance of these materials, were determined. The hot pressed Cu-Sn specimens included intermetallic/phases, which were homogeneously distributed. The presence of graphite improved the wear resistance of Cu-Sn alloys three times. Similarly, the presence of lead improved the densification parameter of Cu-Sn alloys three times. There was no significant difference in the mechanical behavior associated with the addition of Pb to the Cu-Sn alloys, although Cu-Pb alloys showed considerably higher ultimate strength and higher elongation. The Cu-Sn-C alloys had lower strength compared with those of Cu-Sn alloys. Evidence of severe melting spots was noticed in the higher magnifications of the compression fracture surface of 85% Cu-10% Sn-5% C and 80% Cu-10% Sn-10% Pb alloys. This was explained by the release of load at the final event of the fracture limited area.

Crack initiation and fracture features of Fe–Co–B–Si–Nb bulk metallic glass during compression

The aim of the paper was investigation crack initiation and fracture features developed during compression of Fe-based bulk metallic glass (BMG). These Fe-based BMG has received great attention as a new class of structural material due to an excellent properties (e.g. high strength and high elasticity) and low costs. However, the poor ductility and brittle fracture exhibited in BMGs limit their structural application. At room temperature, BMGs fails catastrophically without appreciable plastic deformation under tension and only very limited plastic deformation is observed under compression or bending. Hence a well understanding of the crack initiation and fracture morphology of Fe-based BMGs after compression is of much importance for designing high performance BMGs. The raw materials used in this experiment for the production of BMGs were pure Fe, Co, Nb metals and nonmetallic elements: Si, B. The Fe–Co–B–Si–Nb alloy was cast as rods with three different diameters. The structure of the investigated BMGs rod is amorphous. The measurement of mechanical properties (Young modulus - E, compressive stress - ?c, elastic strain - ?, unitary elastic strain energy – Uu) were made in compression test. Compression test indicates the rods of Fe-based alloy to exhibit high mechanical strength. The development of crack initiation and fracture morphology after compression of Fe-based BMG were examined with scanning electron microscope (SEM). Fracture morphology of rods has been different on the cross section. Two characteristic features of the compressive fracture morphologies of BMGs were observed. One is the smooth region. Another typical feature of the compressive fracture morphology of BMGs is the vein pattern. The veins on the compressive fracture surface have an obvious direction as result of initial displace of sample along shear bands. This direction follows the direction of the displacement of a material. The formation of veins on the compressive fracture surface is closely related to the shear fracture mechanism. The results of these studies may improve the understanding on the fracture features and mechanisms of BMGs and may provide instructions on future design for ductile BMGs with high resistance for fracture.

Effect of Loading Rate on Dynamic Fracture Morphology of a Zr-Based Bulk Metallic Glass

Low-velocity plate impact experiments using a single-stage gas-gun are performed on Zr58.5Cu15.6Ni12.8Al10.3Nb2.8. Compressive fracture surfaces of the samples subjected to varying impact velocities and stress amplitudes are evaluated in order to study their loading rate dependence. Samples impacted at increasing loading rates, from increasing velocities of impact, show a larger extent of localized melting while those subjected to increasing stress show a transition from ductile to brittle fracture. These observations suggest that the mechanisms and morphology of fracture are strain-rate dependent. [doi:10.2320/matertrans.M2014467]

Compressive behavior of C/SiC composite sandwich structure with stitched lattice core

C/SiC composite sandwich structure with stitched lattice core was fabricated by a technique that involved polymer impregnation and interweaving. The mechanical behaviors of C/SiC composite sandwich structure were investigated at room temperature. The out-of-plane compressive strength was 20.97MPa while modulus was 1473.55MPa. The microstructural evolution on compression fracture surfaces of the stitching yarns was investigated by scanning electron microscopy, and the damage pattern of fibers on compression fracture surface was presented and discussed. Under an in-plane compression loading, the C/SiC composite sandwich structure displayed a linear-elastic behavior until failure. The peak strength and average modulus are 165.61MPa and 19.74GPa, respectively. The failure of the specimen was dominated by the fracture of the facesheet.

Longitudinal direct compression test of a single carbon fiber in a scanning electron microscope

Longitudinal direct compression testing of a single polyacrylonitrile-based carbon fiber (T800S) is performed with a piezo-actuated testing machine installed in a scanning electron microscope, and the longitudinal compressive behavior of a carbon fiber is observed during loading. The compressive stress–compressive strain relation is linear in the early phase, and then becomes non-linear. The longitudinal tangent modulus in the compression decreases with increasing compressive strain. The failure strain seen in compression is much higher than that in tension. The variability of the compressive strength is evaluated via Weibull analysis, and is found to be smaller than the tensile strength variability. The compressive fracture surface is irregular and possesses a serrated morphology that is different from the tensile fracture surface. The representative strength ratio of the compressive to tensile strengths of the carbon fiber is ≈0.5, which almost matches the compressive to tensile strengths ratio of the unidirectional carbon fiber reinforced plastic.

Compressive Fracture of Brittle Geomaterial: Fractal Features of Compression-Induced Fracture Surfaces and Failure Mechanism

Compressive fracture is one of the most common failure patterns in geotechnical engineering. For better understanding of the local failure mechanism of compressive fractures of brittle geomaterials, three compressive fracture tests were conducted on sandstone. Edge cracked semicircular bend specimens were used and, consequently, fresh and unfilled compressive fracture surfaces were obtained. A laser profilometer was employed to measure the topography of each rough fracture surface, followed by fractal analysis of the irregularities of the obtained compression-induced fracture surfaces using the cubic cover method. To carry out a contrastive analysis with the results of compressive fracture tests, three tension mode fracture tests were also conducted and the fractal features of the obtained fracture surfaces were determined. The obtained average result of the fractal dimensions of the compression-induced surfaces was 2.070, whereas the average result was 2.067 for the tension-induced fracture surfaces. No remarkable differences between the fractal dimensions of the compression-induced and tension-induced fracture surfaces may indicate that compressive fracture may occur, at least on the investigative scale of this work, in a similar manner to tension fracture.

Influences of Y and Y-Rich Mischmetal Additions on Microstructure and Compressive Properties of As-Cast Al-Mg-Mn Alloy

The influences of Y and Y-rich mischmetal (Ym) additions on microstructural and compressive properties of as-cast Al-13Mg-0.8Mn alloy prepared by vacuum suction casting were investigated in this study. The average secondary dendrite arm spacing (SDAS) was decreased when adding Y and Ym additions. Moreover, the Al2Y and Al2Ym phases formed during the solidification were mainly distributed along the grain boundary. The mechanical results reveal that both Y and Ym additions are effective in increasing the compressive strength and hardness. The values of yield compressive strength, ultimate compressive strength, and Brinell hardness of the as-cast Al-13Mg-0.8Mn-0.8Y alloy are 357 MPa, 510 MPa, and 138, respectively. The improved mechanical properties are mainly attributed to fine SDAS and precipitation strengthening. A typical cleavage fracture mode is observed on the compressive fracture surfaces of the alloys.

Prediction of Longitudinal Compression Strength for a 2.5D-C/SiC Composite Based on Laminate Theory

Based on the analysis of the woven structure, the compressive fracture process and strength of a 2.5D-C/SiC ceramic matrix composite were investigated by the classical laminate theory. The porous composite was regarded as a spatial layered structure, and the two classes of the warps and wefts in the 2.5D-C/SiC composite were treated as the corresponding layers. The strengths of the C/SiC bundle and C/SiC lamina were determined, and the compression strength for the composite was calculated by progressive fracture method of the layers and elastic degradation. The failure mechanisms and the angles of the compressive fracture surfaces coincided with the experimental result well. It was demonstrated that the strength predictive method of the classical laminate theory can be applied to the analysis of 2.5D-C/SiC composite.

Fuel Pellets from Wheat Straw: The Effect of Lignin Glass Transition and Surface Waxes on Pelletizing Properties

The utilization of wheat straw as a renewable energy resource is limited due to its low bulk density. Pelletizing wheat straw into fuel pellets of high density increases its handling properties but is more challenging compared to pelletizing woody biomass. Straw has a lower lignin content and a high concentration of hydrophobic waxes on its outer surface that may limit the pellet strength. The present work studies the impact of the lignin glass transition on the pelletizing properties of wheat straw. Furthermore, the effect of surface waxes on the pelletizing process and pellet strength are investigated by comparing wheat straw before and after organic solvent extraction. The lignin glass transition temperature for wheat straw and extracted wheat straw is determined by dynamic mechanical thermal analysis. At a moisture content of 8%, transitions are identified at 53°C and 63°C, respectively. Pellets are pressed from wheat straw and straw where the waxes have been extracted from. Two pelletizing temperatures were chosen—one below and one above the glass transition temperature of lignin. The pellets compression strength, density, and fracture surface were compared to each other. Pellets pressed at 30°C have a lower density and compression strength and a tendency to expand in length after the pelletizing process compared to pellets pressed at 100°C. At low temperatures, surface extractives have a lubricating effect and reduce the friction in the press channel of a pellet mill while no such effect is observed at elevated temperatures. Fuel pellets made from extracted wheat straw have a slightly higher compression strength which might be explained by a better interparticle adhesion in the absence of hydrophobic surface waxes.

Cyclic compression behavior of a Cu–Zr–Al–Ag bulk metallic glass

The cyclic compression behavior of a Cu 45Zr 45Al 5Ag 5BMG was investigated in order to elucidate the damage initiation and growth mechanisms. The present Cu 45Zr 45Al 5Ag 5 BMG was found to have a fatigue-endurance limit of 1418 MPa and fatigue ratio of 0.77. Fracture under cyclic compression occurred in a pure shear mode. The fracture surface forms an angle of 41° with respect to the loading axis. This angle was similar to the monotonic compressive fracture angle for the present BMG. The cyclic compression fracture surface displays a morphology nearly identical to the monotonic compression fracture surface. In addition to many shear bands and cracks, areas of “chipping” were commonly found on the outside surfaces of the fatigue specimens. An attempt was made to measure crack growth rates, and two types of crack growth behavior were found. With the first type, the growth rate decreased with cycles due to the decrease in the driving force for crack propagation. With the second type, the crack growth rate increased with cycles after chipped areas developed. The fatigue deformation process for BMGs under cyclic compression was carefully studied and rationalized.

The Effect of Purity of Zirconium Material on Mechanical Properties and Microstructure of Zr-Based Bulk Metallic Glass

Series of rod samples of Zr55Al10Ni5Cu30 alloy were prepared by magnetic suspend melting and copper mold suction casting method using 99.9wt% high purity zirconium and 99.4wt% low purity sponge zirconium respectively, the effect of purity of zirconium material on mechanical properties and microstructure of Zr-based bulk metallic glass were investigated. The result shows that high purity material alloy could enhance the thermal stability and glass forming ability of Zr-based bulk amorphous alloy, compression fracture surface analysis indicate that the vein patterns density increase with the material elements purity increase, the average compressive fracture strength is increased to 8.52% than that of low purity samples.