Compression Fracture Surface Research Articles

Compression Strength and Porosity of Single-Antibiotic Cement Vacuum-Mixed With Vancomycin

We evaluated the ultimate compression strength (UCS), porosity, and fracture surface roughness of 2 commercially available single-antibiotic bone cements vacuum-mixed with additional amounts of vancomycin (2, 4, 6, and 8 g). At least 8 g could be added to Palacos R + 0.5 g gentamicin (UCS = 75.04 ± 6.64 MPa) and no more than 6 g to Simplex P + 1 g tobramycin (UCS = 78.93 ± 4.98 MPa) to maintain a UCS above the International Organization for Standardization minimum standard (70 MPa). Increasing vancomycin concentration correlated with a decrease in porosity but showed a trend towards greater fracture surface roughness.

Microstructure and mechanical behavior of die casting AZ91D-Fly ash cenosphere composites

The feasibility of incorporating fly ash cenospheres in die cast magnesium alloy has been demonstrated. The effects of fly ash cenosphere additions on the microstructure and some of the salient physical and mechanical properties of magnesium alloy (AZ91D) metal matrix composites were investigated. The control AZ91D alloy and associated composites, containing 5, 10, and 15 wt.% of fly ash cenospheres (added), were synthesized using a die casting technique. A microstructural comparison showed that microstructural refinement – occurred due to the fly ash additions and became more pronounced with an increase in the percentage of the fly ash added. The metal matrix areas nearer to the fly ash particles exhibited a greater degree of refinement than was observed in the areas further away from these particles. Both filled and unfilled fly ash cenospheres, and porosity were observed in the composite microstructures. The composite specimen densities decreased and the coefficient of thermal expansion did not change significantly as the volume percent of fly ash was increased within the range investigated. The hardness values of the composite specimens exhibited an increase in proportion to the increase in percentage of added fly ash. The tensile strength of the composites also increased as the concentration of fly ash cenospheres was increased. In contrast, the Young’s modulus of these composite samples, as measured by non-destructive pulse-echo method, decreased as the percentage of fly ash in the composite was increased. SEM micrographs of the tensile fracture surfaces showed broken cenospheres on the fracture surface and evidence of ‘pull outs’, where fly ash particles were previously embedded in the matrix. Compression testing results showed that the presence of 5 wt.% cenospheres decreased the compressive strength and compressive yield strength of the composite relative to that of the AZ91D matrix alloy. Surprisingly, a significant change in compression strength was not observed for the composites with 10 and 15 wt.% cenospheres in comparison to the AZ91D matrix alloy. In contrast to the tensile tests, no cenosphere remnants were observed on the compressive test fracture surface of the composites. This observation suggests that the fracture of the composite was initiated within the AZ91D matrix by normal void nucleation and growth, followed by crack propagation through the matrix, avoiding any of the cenospheres, leading to composite fracture of the matrix.

Nanoscale ripples on the compressive fracture surface of a bulk metallic glass with microscale crystals

Some periodic and straight strips with about 60 nm spacing were observed on the compressive fracture surface of Ni42Cu5Ti20Zr21.5Al8Si3.5 bulk metallic glass (BMG) rods containing minor microscale crystals. The characteristic difference between amorphous matrix and microscale crystals also reveal why periodic corrugations could not be observed on the fracture surface of metal crystals. The dynamic crack instability may be explained by the interaction of the propagating crack and the internal micro-cracks. This kind of periodic morphologies showed in-plane feature, which may be attributed to the non-intense interaction between dynamic crack and micro-crack.

SAMPLE-SIZE EFFECTS ON THE COMPRESSION BEHAVIOR OF ANi-BASED AMORPHOUS ALLOY

Ni42Cu5Ti20Zr21.5Al8Si3.5bulk metallic glasses rods with diameters of 1 mm and 3 mm, were prepared by arc melting of composing elements in a Ti -gettered argon atmosphere. The compressive deformation and fracture behavior of the amorphous alloy samples with different size were investigated by testing machine and scanning electron microscope. The compressive stress-strain curves of 1 mm and 3 mm samples exhibited 4.5% and 0% plastic strain, while the compressive fracture strength for 1 mm and 3 mm rod is 4691 MPa and 2631 MPa, respectively. The compressive fracture surface of different size sample consisted of shear zone and non-shear one. Typical vein patterns with some melting drops can be seen on the shear region of 1 mm rod, while fish-bone shape patterns can be observed on 3 mm specimen surface. Some interesting different spacing periodic ripples existed on the non-shear zone of 1 and 3 mm rods. On the side surface of 1 mm sample, high density of shear bands was observed. The skip of shear bands can be seen on 1 mm sample surface. The mechanisms of the effect of sample size on fracture strength and plasticity of the Ni -based amorphous alloy are discussed.

Compressive fracture characteristics of Ni 42Cu 5Ti 19Zr 22.5Al 8Si 3.5 bulk metallic glass

The uniaxial compressive fracture behavior of Ni 42Cu 5Ti 19Zr 22.5Al 8Si 3.5 bulk metallic glass (BMG) was investigated. It was found that the 2 mm rod exhibited a high fracture strength of 2851 MPa and plastic strain of 0.5%, while the 3 mm sample showed a fracture strength of 2724 MPa and nearly zero plastic strain. The property difference in the two samples was explained due to different structure caused by different cooling rates in glass formation. The compressive fracture surfaces of the deformed samples consisted of a flat shear zone and a coarse zone. The compressive fracture angles between the stress axis and the fracture plane changed from <45 to 90° as the fracture proceeded, suggesting that the compression fracture mechanism of the alloy might be understood in terms of the ellipse criterion.

Characterization of strengthened rapidly quenched Zr-based alloys

The nominal composition components of alloy Zr66.4Nb6.4Ni8.7Cu10.5Al8 (Alloy A) were fabricated and characterized. The strengthening of in-situ alloys depends on the role of both the glassy matrix and the second phases. The glass transition and the crystallization kinetics were studied using DSC and X-ray diffraction as a function of element distribution. The amorphous and semi-crystalline structures were identified with the existence of nano crystals in the alloy nominal compositions. The Elastic compression modulus were found to increase with transition to crystallite phase. Where as, the microhardness decreases dramatically with the change from crystalline to amorphous phase. The compression fracture surface shows classic veins behavior. In mode of continuous heating and adiabatic annealing the glass transition, T g , and the crystalline peak, T p , temperatures display a strong dependency on heating rate. The activation energy for glass transition and crystallization were determined as E g = 226 KJ/mol based on Kissinger method, but during the isothermal process E g = 121 KJ/mol.

Quasi-static and dynamic compressive fracture behavior of carbon/carbon composites

To understand the dynamic compressive fracture behavior of carbon/carbon composites, their compressive behavior was investigated at a strain rate of 500/s using a modified split Hopkinson pressure bar. Quasi-static compressive tests were conducted on a universal test machine and compared with those at high strain rate. Scanning electron microscopy was used to observe the compressive fracture surfaces. The results show that the compressive strength and stiffness are increased at high strain rate. Fiber failure under quasi-static compressive loading is characterized by fiber bundle debonding, breakage and pull-out, while the fiber failure under dynamic compressive loading is characterized by multiple splitting without extensive debonding.

Microstructure evolution and mechanical properties of Cu 46Zr 47Al 7 bulk metallic glass composite containing CuZr crystallizing phases

Cu 46Zr 47Al 7 ternary bulk metallic glass (BMG) and its composite containing CuZr crystallizing phases were obtained through water-cooled copper mold casting. There is an obvious microstructure transition of CuZr crystallizing phase due to the decrease in the cooling rate: disperse small dendrites–regular radial dendrites–martensite phase. Under compression, the CuZr crystallizing phases particularly for martensite phase yield first and stimulate the formation of multiple shear bands in the matrix, which enhanced the ductility of the composite. The quasi-static compression fracture surface of the BMG its composites display a mixture of three distinct patterns: vein-like, smooth regions and river-like patterns. The river-like pattern was related with the secondary shear bands or tertiary shear bands and its area fraction on the fracture surface was dependent on the plasticity.

Mechanical properties and microstructure of commercial amorphous golf club heads made of Zr–Ti–Cu–Ni–Be bulk metallic glass

Mechanical properties and microstructures of Zr 41.2Ti 13.8Cu 12.5Ni 10Be 22.5 (numbers indicate at.%) bulk metallic glass taken from commercial golf club heads were investigated at room temperature and 573 K. Transmission electron microscopy (TEM) and differential scanning calorimetry (DSC) indicate that the thin central section of the golf club head is amorphous and the outer rim of the head is crystallized. X-ray diffraction (XRD) analyses revealed the presence of Zr 2Cu, ZrBe 2, Cu 2Ni and BeNi in the rim of the iron head. In the crystallized region, crystalline particles with the size of ∼1 μm were observed. At room temperature, amorphous sample (∼2100 MPa) revealed higher fracture stress than crystallized sample (∼1700 MPa). Crystallized sample fractured in the elastic region whereas the amorphous sample displayed some plasticity corresponding serrated flow before the fracture. The serrated flow region with some plasticity in the amorphous alloy results from strain hardening and repetitive shear band initiation and propagation. The crystallized alloy extracted from the thick part of the club fractured in the elastic region, at a much lower stress level than the amorphous, suggesting that relatively coarse crystal particles formed during cooling cause the brittle fracture. Scanning electron microscope observations revealed that the compressive fracture surface of the samples from the central thin section mainly consisted of vein-like structure, but the samples from the outer rim of the head showed mixture of vein-like structure and featureless brittle fracture morphology. At 573 K, both samples exhibited the decrease of strength and fractured in the elastic region. In this study, the effect of crystallization on the reliability and safety of golf club heads was also examined.

Fracture surface morphology of compressed bulk metallic glass-matrix-composites and bulk metallic glass

The fracture morphology of Zr-based bulk metallic glass-matrix-composites (BMGCs) and Cu-based bulk metallic glass (BMG) after compression testing has been studied. The quasi-static compression fracture surface displays a mixture of three different distinct patterns: vein-like, smooth featureless and river-like features. The last one corresponds to the morphology known from tensile tests of BMGs. Moreover, randomly distributed transversal steps on the fracture plane are also present. This is in contrast to previous studies where a characteristic vein-like pattern is considered a unique feature of the fracture of BMGs under quasi-static uniaxial compression. The presence of different fracture features indicates that the development of the fracture plane occurs in a stepwise mode.

Effects of deformation behavior on fatigue fracture surface morphology in a nickel-base superalloy

Fatigue crack propagation fracture surface morphologies in nickel-base superalloys vary substantially with changes in loading parameters such as temperature, Δ K, load ratio, frequency, and additionally microstructure. Quantitative fracture surface roughness can vary from sub-micron levels to a maximum value of approximately half the grain size. Atomic Force Microscope studies of surface slip traces in compression specimens revealed a clear relationship between slip homogeneity in compression testing and fracture surface roughness under similar fatigue loading conditions. It has been shown in this study that changes in Δ K, strain level, temperature, grain size, and load ratio can all affect slip heterogeneity, which in turn controls the fracture surface roughness. Finally, a model is developed that quantitatively predicts fracture surface roughness and roughness-induced crack closure stress intensity values from measurements of slip line spacing in a compression specimen.

Compressive fracture of Zr55Al10Ni5Cu30 bulk amorphous alloy at high temperatures

The fracture behavior of the Zr55Al10Ni5Cu30 bulk amorphous alloy under uniaxial compression at high temperatures has been investigated. At room temperature, the fracture occurred along the maximum shear plane which declined by 45° to the direction of the applied load, and a crack with serrated edge appeared on the ridge of the veins at the fracture surface for the Zr55Al10Ni5Cu30 bulk amorphous alloy. At high temperatures, the compressive fracture surface of the Zr55Al10Ni5Cu30 bulk amorphous alloy became much rougher than that at room temperature and steps appeared on the fracture surface. With increasing temperature, a different pattern from the vein-like morphology appeared on the fracture surface, which is very similar to the lava-flow. This type of fracture pattern is most likely due to the adiabatic heating created by plastic flow.

Difference in compressive and tensile fracture mechanisms of Zr 59Cu 20Al 10Ni 8Ti 3 bulk metallic glass

The compressive and tensile deformation, as well as the fracture behavior of a Zr 59Cu 20Al 10Ni 8Ti 3 bulk metallic glass were investigated. It was found that under compressive loading, the metallic glass displays some plasticity before fracture. The fracture is mainly localized on one major shear band and the compressive fracture angle, θ C, between the stress axis and the fracture plane is 43°. Under tensile loading, the material always displays brittle fracture without yielding. The tensile fracture stress, σ F T, is about 1.58 GPa, which is lower than the compressive fracture stress, σ F C(=1.69 GPa). The tensile fracture angle, θ T, between the stress axis and the fracture plane is equal to 54°. Therefore, both θ C and θ T deviate from the maximum shear stress plane (45°), indicating that the fracture behavior of the metallic glass under compressive and tensile load does not follow the von Mises criterion. Scanning electron microscope observations reveal that the compressive fracture surfaces of the metallic glass mainly consist of a vein-like structure. A combined feature of veins and some radiate cores was observed on the tensile fracture surfaces. Based on these results, the fracture mechanisms of metallic glass are discussed by taking the effect of normal stress on the fracture process into account. It is proposed that tensile fracture first originates from the radiate cores induced by the normal stress, then propagates mainly driven by shear stress, leading to the formation of the combined fracture feature. In contrast, the compressive fracture of metallic glass is mainly controlled by the shear stress. It is suggested that the deviation of θ C and θ T from 45° can be attributed to a combined effect of the normal and shear stresses on the fracture plane.

INFLUENCE OF WATER ON MECHANICAL PROPERTIES AND FRACTURE MECHANISM OF CFRP/ARAMID HONEYCOMB CORE SANDWICH BEAM

Carbon fiber reinforced facing/aramid honeycomb core sandwich composite materials were studied through three point bending test. In order to clarify the influences of water on the stiffness and strength, the dry and wet specimens were used. At the same time, the fractured specimens were inspected by a scanning electron microscope (SEM) and a scanning acoustic microscope (SAM) to observe the superficial and interior fractures of the specimens, respectively, and the fracture mechanism was analyzed. The experimental results showed the following.(1) Sandwich material increased the bending stiffness a little after its absorption of 6wt.% water, but decreased the shearing stiffness by about 10%.(2) Water absorption affected the core shearing strength more than the facing strength.(3) The strength of interface between the facing layer and core of sandwich materials was larger than that of the matrix resin.(4) The buckling axis was observed on the compressive fracture surface of the wet specimens more than that of the dry specimens, which shows that most fibers in the wet specimens are fractured by compressive stress.(5) In case of short span beams whose length was shorter than 200mm, the wet specimens flexed more than the dry specimens. It is thought to be caused by the degradation of cell wall of the core.

The deformation and fracture of a dual-phase intermetallic alloy

Ordered intermetallic alloys possess many attractive properties, yet their use as a structural material has been severely limited by a general lack of low temperature ductility. The beta/gamma-prime dual-phase Ni50Fe30A120 (atomic percent) intermetallic alloy has shown remarkable ductility, exhibiting fracture strains in excess of 20% in both tension and compression. This behavior is yet unexplained, thus an investigation was conducted to study the deformation and fracture behavior of this alloy.The material studied was a Ni50Fe30A120 (nominal composition) directionally solidified alloy. TEM specimens were made from the as cast material in an unstrained condition and with a 1% strain in compression. The foils were hand ground to a thickness of about 75 um and electrothinned in a Tenupol twin jet polisher with a methanol-based solution containing 2% perchloric acid and 35% butyl cellosolve at -20C. A JEOL 2000 FX AEM was used to examine the strained and unstrained foils. STEM microanalysis was performed on the unstrained foil with a Phillips CM-12 AEM to determine the composition of the two phases. Finally, the compression fracture surface was studied using a Hitachi S520 SEM.

Fatigue of graphite fibre-reinforced epoxy in compression

Abstract Direct observation of compressive fatigue of pre-notched unidirectional graphite fibre composites reveals that fatigue cracking extends transverse to the fibre direction, via micro-buckling. An elasto-plastic-strain hardening model of the material behaviour, based on experimental measurements of material properties, is used, together with a finite element computation, to obtain the stress and strain distribution near the notch tip. The calculated radius (Rp) of the plastic zone at the notch tip is shown to correlate with the observed fatigue crack propagation rates (dc/dN) via: dc dN = 10 5 R p 6 ( in/cycle ) Fatigue cracking is seen to decelerate with crack extension, indicating a residual bearing strength of newly-generated compressive fracture surfaces of approximately 104 psi. The implications of compressive fatigue in composites design are discussed. It is pointed out that prevention of axial cracking in the composite is a key element in preventing compressive fatigue

Fatigue of Prenotched Graphite Fiber Composites in Compression

Direct observation of compressive fatigue of prenotched unidirectional graphite fiber composites reveals that fatigue cracking extends transverse to the fiber direction, via microbuckling. An elasto-plastic-strain hardening model of the material behavior, based upon experimental measurements of material properties, is used together with a finite element computation to obtain the stress and strain distribution near the notch tip. The calculated radius Rp of the plastic zone at the notch tip is shown to correlate with the observed fatigue crack propagation rates via Fatigue cracking is seen to decelerate with crack extension, indicating a residual bearing strength of newly generated compressive fracture surfaces of approximately 10 4 Ib/in.2 The implications of compressive fatigue in composites design are discussed. It is pointed out that prevention of axial cracking in the composite is a key element in preventing compressive fatigue.