Compressive Fracture Behavior Research Articles

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.

Compressive deformation behaviors of tungsten fiber reinforced Zr-based metallic glass composites

Subjected to a wide range of strain rates, the compressive deformation and fracture behavior at different temperatures of tungsten fiber reinforced Zr-based metallic glass composites (BMGC) were investigated. Upon increasing temperature, the compressive strength decreases, accompanied with reduced elasticity and enhanced plasticity. In combination with fracture analysis, the effects of temperature, applied strain rate, and the reinforcement of tungsten fiber were explicitly described.

Effect of microstructures on the compressive deformation and fracture behaviors of Zr47Cu46Al7 bulk metallic glass composites

The compressive deformation and fracture behaviors of a Zr47Cu46Al7 bulk metallic glass (BMG) and its composites with different microstructures were investigated. For the fully amorphous alloy, due to the formation of coarse primary shear bands and multiple secondary shear bands, it exhibited a high plasticity up to 14.5% with a ‘work softening’ during compressive test. With the increase in the volume fraction of primary crystallizing phases, the BMG composites displayed low strength and poor plasticity even failing in a brittle mode. Furthermore, the effects of microstructures on the compressive deformation and fracture behaviors of the BMG composites were discussed.

Compressive fracture behavior of Cu-based bulk amorphous alloys

The mechanical properties of newly developed Cu 52.5 − x Ti 30Zr 11.5Ni 6Al x ( x = 0, 1, 1.5, 2 at.%) bulk amorphous alloys were investigated under compressive condition. They exhibit high fracture strength of 2212 MPa, 2165 MPa, 2209 MPa and 2286 MPa, respectively. Three distinct vein patterns corresponding to the different zones can be observed on the fracture surfaces of the samples. Fracture propagation along two different directions and formation of striated vein patterns may contribute to the higher compressive fracture strength of the tested Cu-based bulk amorphous alloys.

Compressive Properties and Fracture Behavior of Two‐and‐a‐Half‐Dimensional C/SiC Composites

Uniaxial compression tests for two‐and‐a‐half‐dimensional carbon fiber‐reinforced silicon carbide composites along the warp and weft directions were conducted at room temperature. The results show that the stress–strain behaviors for both loading directions exhibited great anisotropy. The compressive strength was greater in the weft direction than in the warp direction, which is attributed to good confinement of the weft yarns and resisting roles of the warp yarns in the former. Microscopic examinations reveal that the fracture surfaces had good correlation with the weave architecture, and the failure mechanism was characterized by transverse shear resulting from fiber microbuckling in the axial yarns.

Short-fibre reinforcement of calcium phosphate bone cement

Calcium phosphate cement (CPC) sets to form hydroxyapatite, a major component of mineral bone, and is gaining increasing interest in bone repair applications. However, concerns regarding its brittleness and tendency to fragment have limited its widespread use. In the present study, short-fibre reinforcement of an apatitic calcium phosphate has been investigated to improve the fracture behaviour. The fibres used were polypropylene (PP) fibres, 50 microm in diameter and reduced in length by cryogenic grinding. The compressive strength and fracture behaviour were examined. Fibre addition of up to 10 wt % had a significant effect on composite properties, with the energy absorbed during failure being significantly increased, although this tended to be accompanied with a slight drop in compressive strength. The fibre reinforcement mechanisms appeared to be crack bridging and fibre pull-out. The setting time of the CPC with fibre reinforcement was also investigated and was found to increase with fibre volume fraction.

Significant Improvement of Mechanical Properties in NiAl-Cr(Mo)/Hf Alloy by Suction Casting and Subsequent Hot Isostatic Pressing

The NiAl-28Cr-5.5Mo-0.5Hf eutectic alloy was prepared by the suction casting (SC) technique and subsequent hot isostatic pressing (HIP) treatment, and tested for compressive strength and fracture behavior in the temperature range of 300 to 1373 K. The microstructure of suction-cast alloy is characterized by fine interlamellar spacing, large area fraction of eutectic cell, and fine Heusler (Ni2AlHf) phase distributed semicontinuously at the cell boundaries. After HIP treatment, Ni2AlHf phase at the cell boundaries is transformed into Hf solid solution phase and distributed homogeneously within the NiAl matrix. Compared with the conventionally cast alloy, the room-temperature compressive strain and elevated temperature strength of suction-cast alloy are enhanced markedly after HIP treatment. The reason is that the HIP treatment causes Hf solid solution phase to distribute homogeneously and then strengthens the NiAl matrix.

Dynamic compressive deformation and failure behavior of Zr-based metallic glass reinforced porous tungsten composite

The dynamic compressive deformation and fracture behavior of the Zr-based metallic glass reinforced porous tungsten composite were investigated at room temperature by means of the Split Hopkinson Pressure Bar (SHPB). Both fracture stress and fracture strain increased significantly compared to the pure metallic glass phase. The deformation behavior of the composite was found to be dominated by the ductile W phase and the 3D net structure of the W phase. It was found that the composite appeared to exhibit some work hardening during the dynamic compressive deformation. The failure mode of the specimen is a mixture of one major shear band and axial splitting, and the shear plane inclined ∼56° with respect to the loading axis. Scanning election microscope (SEM) was used to evaluate damage initiation and propagation. It was found that the increase of fracture stress and fracture strain is due to the interaction between localized shear banding and axial splitting, promoting additional fracture surface area, and large volume fraction of ductile W phase. The dynamic compressive deformation and fracture behavior of the composite are discussed by taking the effect of the complex stress state within the composite into account.

Failure-mode dependence of the strengthening effect in Ti3AlC2/10 vol.% Al2O3composite

AbstractThe high-temperature mechanical properties of both Ti3AlC2and Ti3AlC2/10vol.%Al2O3composite, including compressive strength, bending strength, and fracture behavior, were investigated. The strengthening effect caused by Al2O3strongly depended on the mode of failure: significant enhancement in strength was only observed under the brittle mode of failure; whereas under the ductile mode of failure the strengthening effect was impaired due to Ti3AlC2matrix softening and stress relaxation.

Fracture behavior of seawater-absorbed carbon/epoxy laminated composites in the hydrostatic pressure condition

It was shown in the previous study that the fracture toughness of dried carbon/epoxy composites increased 38% as the applied hydrostatic pressure increased from 0.1 to 200 MPa. However, no research has been conducted on the fracture behavior of seawater-absorbed carbon/epoxy composites in a hydrostatic pressure environment. This work investigates the compressive fracture behavior of seawater-absorbed carbon/epoxy composites subjected to various hydrostatic pressures. Compressive fracture tests were performed under four hydrostatic pressure levels, 0.1 (atmospheric pressure), 100, 200, and 270 MPa. The compliance and fracture loads were determined from load–displacement curves as a function of hydrostatic pressure. Fracture toughness was determined from the elastic work factor approach. The results showed that compliance decreases but fracture load increases as the applied hydrostatic pressure increases. Fracture toughness increased with increasing pressure. Specifically, fracture toughness increased from 2.66 to 4.44 kJ/m 2, a 67% increase, as hydrostatic pressure increased from 0.1 to 270 MPa. Optical microscope examination of the fractured surface showed that local delaminations and microcracks are suppressed with increasing hydrostatic pressure. SEM examination showed that seawater-absorbed specimen shows a lot more epoxy fracture than the dried specimen.

Effect of Loading Rate on the Delamination Behavior of Carbon/Epoxy Laminated Composites

Previous studies show that fracture toughness of carbon/epoxy composite is affected by hydrostatic pressure. The fracture toughness of carbon/epoxy composite is also affected by strain rate. To date, no study has been made on the combined effects of hydrostatic pressure and strain rate on the fracture toughness of carbon/epoxy composite. This work investigates the compressive fracture behavior of carbon/epoxy composite subjected to low and high strain rates in the hydrostatic pressure environment. Compressive fracture tests were performed in the atmospheric pressure and hydrostatic pressure environment of 270MPa. The compliance and fracture load were determined from load-displacement curves as a function of applied strain rate. Fracture toughness was determined from the elastic work factor approach. The results showed that the compliance decreased as the applied strain rate increased. However, the fracture load is less affected by the strain rate. The toughness decreased with increasing strain rate. Specifically, for 270 MPa hydrostatic pressure environment, fracture toughness decreased from 4.64 kJ/m 2 to 4.05 kJ/m 2 (12.7% decrease) as the strain rate increased from 0.05% to 0.55%. The decrease of fracture toughness with an increase in the strain rate is due to the epoxy becoming brittle as there is not sufficient time for the stress to be relieved.

Effect of aspect ratio on the compressive deformation and fracture behaviour of Zr-based bulk metallic glass

The compressive deformation and fracture features of Zr59Cu20Al10Ni8Ti3 bulk metallic glassy samples with aspect ratios in the range of 0.67–2.00 have been investigated. The compressive plastic strain of the glass monotonically increases with decreasing aspect ratio, but the maximum strength almost maintains a constant value of 1.77–1.88 GPa. All the compressive shear-band angles are equal to ∼40° if modified by the rotation of the primary shear bands.

Mechanical and Fracture Behaviour of a SiC-Particle-Reinforced Aluminum Alloy at High Temperature

The compressive characteristics and fracture behavior of CW67 aluminum alloy and of a composite based on CW67 alloy were studied under unaxial compressive loading in the temperature range 25-400°C, at a constant strain rate of 1 - 3 10 4 . 2 s × . The yield strength values of the composite were higher than those of the monolithic alloy at all temperatures. The ultimate strength values of the composite were lower at room temperature, but higher at elevated temperatures when compared with those of the monolithic alloy. The composite exhibited lower ductility than the monolithic alloy in the entire temperature range. High concentration of SiC particles in the structure of CW67 composite affected its compressive properties. At higher temperatures, it behaved like a typical precipitation hardened alloy, in other words, with temperature increase the main influence on the mechanical properties occurred in its matrix. When temperature rises, the fracture process changes from particle cracking and particle agglomerate decohesion (at room temperature) to particle matrix debonding (at high temperature).

Ａｌ‐Ｍｇ‐Ｓｉ系合金押出形材の軸圧縮変形および破壊挙動

Axial compression and successive fracture behavior in Al–Mg–Si alloy extrusions has been investigated. Fracture after axial compression was caused by bending in macroscopic. And it was due to microcracking at the surface by tensile stress and the followed propagation in microscopic. The critical strain for cracking was corresponded with local strain in uni-axial tension. Fine graining was effective to prevent from fracture because of lowering the stress concentration value at grain boundaries. The value for 7 μm grain was a tenth of that for 130 μm. Over aging treatment was also a practical method through homogeneous deformation to lessen the effective stress at grain boundary to a fourth or a fifth of that of peak aged materials.

高温集塵フィルタ用多孔質セラミックスの熱サイクル疲労

A thermal cyclic fatigue testing method is proposed for hot gas tube filters made of SiC porous ceramics. The method simulates reverse pulse cleaning of the outer surfaces of the filters during dust removal. O-ring specimens cut from the ceramics were thermally shocked by cyclically blowing air outward through the specimens exposed to a high temperature flue gas. The inner subsurface layer of the specimens fractured preferentially as a result of the thermal tensile stress produced by the temperature difference between the inner and outer surfaces of the specimen. The thermal cyclic fatigue diagram was shown from the maximum thermal tensile stresses calculated on the basis of nonequilibrium thermal conduction, and the O-ring compression fracture behavior of the specimens after the thermal cyclic fatigue tests. The critical conditions that result in the fatigue fracture are given.

Compressive properties of zone-directionally solidified β-NiAl and its off-eutectic alloys with chromium and tungsten

The ordered intermetallic compound β-NiAl and its pseudo-binary off-eutectic alloys with 1 at.% tungsten and 9.7 at.% chromium were directionally solidified (DS) in the ‘floating-zone’ mode, and tested for compressive strength and fracture behavior in the temperature range 300–800 K. The dual-phase structures created by the DS of ternary NiAl alloys led to improvements in both the compressive strength and the ductility. The room-temperature (300 K) 0.2% compressive yield strength (CYS) of DS NiAl(W) (623 MPa) is larger than the CYS of DS NiAl(Cr) (565 MPa) and DS NiAl (435 MPa). The CYS of the three alloys dropped with increasing test temperature, and at 800 K, the CYS values for the three materials were comparable (356, 315 and 344 MPa for NiAl, NiAl(W) and NiAl(Cr), respectively). All the DS alloys exhibited greater than near-zero ductility of polycrystalline β-NiAl at room-temperature, with the fracture strain being the largest for the DS NiAl(Cr) (16.6%), followed by DS NiAl(W) (9.8%) and DS NiAl (7.33%). The strength and ductility data and fractography of test specimens suggest that ductile-phase toughening and second-phase strengthening are responsible for the observed improvements in the ductility and strength of NiAl. Limited tensile tests on the DS NiAl and DS NiAl(Cr) indicate that the CYS is greater than the tensile yield strength.

Hydrostatic Pressure Effect on the Fracture Toughness of Unidirectional (0-deg) Graphite/Epoxy Laminated Composites

Previous studies show that hydrostatic pressure affects elastic modulus, strength, and strain of fiber-reinforced composites. However, no work has been done to understand the compressive fracture behavior of laminated composites under hydrostatic pressure. This work is an experimental study of the hydrostatic pressure effects on the compressive fracture behavior of fiber-reinforced composites. Compressive fracture tests were conducted under various hydrostatic pressures from 0.1 MN/m2 (atmospheric pressure) to 200 MN/mi2 (2 Kbar). Test specimens used were unidirectional (0-deg) graphite/epoxy laminated composites with a single delamination at the center of specimen. First, compression load-displacement curves were determined as a function of hydrostatic pressure and delamination length. Second, the compressive fracture toughness was determined from the compliance method based on the load-displacement curves as a function of hydrostatic pressure. The results showed that compliance, fracture load, and fracture toughness were significantly influenced by hydrostatic pressure. The fracture load increases as hydrostatic pressure increases. The compliance decreases linearly with increasing pressure. Particularly, fracture toughness increased from 3.45 N-mm/mm2 to 4.53 N-mm/mm2 (32% increase) as hydrostatic pressure increased from 0.1 MN/mm2 to 200 MN/mm2. Apparently the increase of fracture toughness is due to the suppression of local delamination with increasing hydrostatic pressure.

406 炭素繊維強化樹脂/アラミドハニカムサンドイッチ材の衝撃・圧縮破壊特性と水環境効果(GS-11 複合材料(2))

406 炭素繊維強化樹脂/アラミドハニカムサンドイッチ材の衝撃・圧縮破壊特性と水環境効果(GS-11 複合材料(2))

Hydrostatic Pressure Effect on the Fracture Toughness of Unidirectional (0-deg) Graphite/Epoxy Laminated Composites

Previous studies show that hydrostatic pressure affects elastic modulus, strength, and strain of fiber-reinforced composites. However, no work has been done to understand the compressive fracture behavior of laminated composites under hydrostatic pressure. This work is an experimental study of the hydrostatic pressure effects on the compressive fracture behavior of fiber-reinforced composites. Compressive fracture tests were conducted under various hydrostatic pressures from 0.1 MN/m2 (atmospheric pressure) to 200 MN/mi2 (2 Kbar). Test specimens used were unidirectional (0-deg) graphite/epoxy laminated composites with a single delamination at the center of specimen. First, compression load-displacement curves were determined as a function of hydrostatic pressure and delamination length. Second, the compressive fracture toughness was determined from the compliance method based on the load-displacement curves as a function of hydrostatic pressure. The results showed that compliance, fracture load, and fracture toughness were significantly influenced by hydrostatic pressure. The fracture load increases as hydrostatic pressure increases. The compliance decreases linearly with increasing pressure. Particularly, fracture toughness increased from 3.45 N-mm/mm2 to 4.53 N-mm/mm2 (32% increase) as hydrostatic pressure increased from 0.1 MN/mm2 to 200 MN/mm2. Apparently the increase of fracture toughness is due to the suppression of local delamination with increasing hydrostatic pressure.

Failure Prediction Technique for Compression Loaded Carbon Fibre-Epoxy Laminate with Open Holes

The inplane compressive fracture behaviour of a carbon fibre-epoxy laminate containing a single hole is examined. Failure is due to 0° fibre microbuckling surrounded by delamination. The microbuckled zone initiates at the hole boundary. It extends stably under increasing load before becoming unstable at a critical microbuckle length of 2–3 mm. The damage propagation and failure of the orthotropic laminate is analysed by a cohesive zone model, in which damage around the open hole is represented by a line crack loaded on its faces. Good agreement between experimental and predicted notched strength is observed for the chosen material and lay-up.