Decrease In Fracture Energy Research Articles

Relationship between Defects of Recycled Aggregate and Mechanical Properties of Recycled Aggregate Concrete

This paper presents an experimental research on the influence of defects of recycled coarse aggregate on mechanical properties of recycled aggregate concrete (RAC). Concretes at two water/binder ratios (0.255 and 0.586) were broken into recycled aggregate (RA). A type of thermal treatment, i.e. heating to target temperature 620 °C, which was maintained for 3 hr, was employed to remove mortar from gravel in RA. Tests were conducted on RA and natural aggregate to measure their water absorption and crushing values, and on RAC and natural aggregate concrete (NAC) to measure compressive strength, tensile splitting strength, and fracture energy. The experimental results revealed that both gravel damage and mortar attached can significantly influence the water absorption and crushing value of RA, as well as strength and fracture energy of RAC. The mechanical properties RAC were obviously lower than those of NAC at an identical mix proportion. Moreover the removal of mortar caused additional change in mechanical properties of RA, which might be a decrease in mechanical properties in the case of low water/binder ratio, but might be an increase in mechanical properties in the case of high water/binder ratio. As to RAC at a low water/binder ratio, gravel damage was a main factor governing the decrease in fracture energy, which means a decrease in cracking resistance of hardened RAC, whereas the mortar attached had only a slight influence on fracture energy. However, as to RAC at a high water/binder ratio, mortar attached could significantly cause a greater decrease in cracking resistance of RAC than that caused by gravel damage.

Photoactive Polyesters Containing o-Nitro Benzyl Ester Functionality for Photodeactivatable Adhesion

The fabrication of modern microelectronic silicon devices mechanically challenges these thin silicon substrates during manufacturing operations. Melt and solution polyesterification enabled the synthesis of polyesters containing photoreactive o-nitro benzyl ester units for use as a potential photocleavable adhesive. Melt transesterification provided a solvent-free method for synthesis of 2-nitro-p-xylylene glycol (NXG)-containing polyesters of controlled molecular weights. 1H NMR spectroscopy confirmed the chemical composition of the photoactive polyesters. Size exclusion chromatography (SEC) determined the number-average molecular weights (Mn) of the polyesters synthesized in the range of 6000 to 12000 g/mol. 1H NMR spectroscopy confirmed increasing levels of photocleavage of the o-nitro benzyl ester functionality with increasing exposure to broad wavelength UV irradiation, and exposure levels ranged from 0–187 J/cm2 UVA. Photocleaveage of approximately 90% of the o-nitro benzyl ester (ONB) units within the backbone of the polymer occurred at maximum dosage. Wedge fracture testing revealed approximately a two-fold decrease in fracture energy upon UV irradiation, suggesting that these structural adhesives offer potential for commercial “flip bonding” applications.

The Concrete Fracture Performance Response to the Interface Transition Zone Parameters Based on Mesoscopic Simulation

The interface transition zone (ITZ) has a significant impact on the concrete’s mechanical properties and fracture modes. For the influence of ITZ’s strength and elastic modulus, the extended finite element method (XFEM) is adopted to simulate the mesostructure failure process by virtue of random aggregate model under uniaxial tension. The results show that ITZ’s strength and elastic modulus have a certain effect on the mechanical properties and fracture modes. With the tensile strength of ITZ increasing, the fractured modes transit from single coalescent crack to multiple non-coalescent cracks and the fracture energy increases, the ductility of concrete is enhanced. With the elastic modulus of ITZ increasing, the concrete’s elastic modulus increases, the tensile strength and the fracture energy decrease.

OS0114 ポリジメチルシロキサン共重合ポリカーボネートの衝撃強度におよぼす負荷速度の影響

Polycarbonate was one of the materials which has the highest impact strength in the high polymer materials. However, there was a problem that impact strength decreased in low-temperature environment. S In order to solve this problem, PC which copolymerized the poly dimethyl siloxane was developed. In this study, change by the load rate of impact strength was verified about PDMS-PC. By preserving ductile fracture, PDMS-PC had controlled the decrease in fracture energy.

Deformation Behavior in Pipe Production Process for New High Strength Microalloyed Steel

The influence of forming process on mechanical properties and microstructure of high strength microalloyed steel has been studied in this research. All samples selected from 90º and 180º of pipes in transverse and longitudinal orientations after UOE forming. The steel was supplied as a hot rolled plate with accelerated cooling. Microstructure of the micro alloy steel was various combinations of acicular ferrite, granular ferrite and M/A phases. Charpy impact fracture toughness tests were carried out in -50 °C to 0 °C. Minimum and maximum yield strength appears in the 180º and 90º of pipe in longitudinal and transverse orientations respectively. Increasing in the yield strength related to minimum amount was about 5.8 % after UOE forming. Comparison between yield strength after and before forming appears increased about 6.9 % due to forming. With decreasing in the test temperature from -50 °C to 0 °C, fracture energy decrease up to 0.9 % that it’s very little and relinquishment. However for samples that fractured in the temperature of -50 °C difference between highest and lowest energy was about 5.9 %. Charpy test results appear that fine M/A phase not a major factor on decrease of upper shelf energy, if homogenize distributed in the acicular ferrite matrix.

Fracture properties of geopolymer paste and concrete

Geopolymers are an emerging type of cementitious material purported to provide an environmentally friendly alternative to Portland cement-based concrete. This paper reports the results of experimental research on fracture properties (fracture energy and brittleness) of fly ash based geopolymer concrete and paste with various mix parameters. The characteristic length of the geopolymer concrete was approximately three times less than that of ordinary Portland cement (OPC) concrete, due to an increase in tensile splitting strength of about 28%, a decrease in elastic modulus of about 22% and a decrease in fracture energy of about 24%. The difference in characteristic length is similar to that reported between high-strength and normal-strength OPC concretes, indicating that the geopolymer concrete exhibits higher brittleness than its OPC counterpart. This trend was found to be consistent between pastes and concretes, implying that the difference between geopolymer and OPC concrete is due to the type of matrix formation (geopolymerisation or hydration). For geopolymer concretes made with different mix parameters, fracture properties are closely correlated to their compressive strength.

Influence of Anisotropy Behavior in UOE Process for X80 Micro Alloy Steel

The anisotropy of tensile properties and charpy impact fracture toughness and its relationship with UOE pipe forming has been study on X80 micro alloy steel. All samples selected from 90º and 180º of pipes in transverse and longitudinal orientations after UOE forming. The steel was supplied as a hot rolled plate with accelerated cooling. Microstructure of the micro alloy steel was various combinations of acicular ferrite, granular ferrite and M/A phases. Charpy impact fracture toughness tests were carried out in -50 °C to 0 °C. Minimum and maximum yield strength appears in the 180º and 90º of pipe in longitudinal and transverse orientations respectively. Increasing in the yield strength related to minimum amount was about 5.8 % after UOE forming. Comparison between yield strength after and before forming appears increased about 6.9 % due to forming. With decreasing in the test temperature from -50 °C to 0 °C, fracture energy decrease up to 0.9 % that it’s very little and relinquishment. However for samples that fractured in the temperature of -50 °C difference between highest and lowest energy was about 5.9 %. Charpy test results appear that fine M/A phase not a major factor on decrease of upper shelf energy, if homogenize distributed in the acicular ferrite matrix.

Influence of temperature and strain rate on cohesive properties of a structural epoxy adhesive

Effects of temperature and strain rate on the cohesive relation for an engineering epoxy adhesive are studied experimentally. Two parameters of the cohesive laws are given special attention: the fracture energy and the peak stress. Temperature experiments are performed in peel mode using the double cantilever beam specimen. The temperature varies from −40 to + 80°C. The temperature experiments show monotonically decreasing peak stress with increasing temperature from about 50 MPa at −40°C to about 10 MPa at + 80°C. The fracture energy is shown to be relatively insensitive to the variation in temperature. Strain rate experiments are performed in peel mode using the double cantilever beam specimen and in shear mode, using the end notch flexure specimen. The strain rates vary; for peel loading from about 10−4 to 10 s−1 and for shear loading from 10−3 to 1 s−1. In the peel mode, the fracture energy increases slightly with increasing strain rate; in shear mode, the fracture energy decreases. The peak stresses in the peel and shear mode both increase with increasing strain rate. In peel mode, only minor effects of plasticity are expected while in shear mode, the adhesive experiences large dissipation through plasticity. Rate dependent plasticity, may explain the differences in influence of strain rate on fracture energy between the peel mode and the shear mode.

On the Mechanical and Physical Properties of Recycled Polymer Matrix Composites Reinforced with Cooper Powder

The influence of cooper powder as reinforcing phase on the main mechanical and physical properties of recycled polyethylene matrix composites has been investigated. The obtained elastic modulus increases up to the upper adopted reinforcing level (∼10 [vol. %]), while elongation and fracture energy decrease. The UTS values remain quite constant within the reinforcing content interval. Electrical resistivity proved to depend, to a great extent, on the reinforcing particle distribution inside the polymer matrix. It has a sudden drop when a continuous electrical conductive path is formed at a critical volume fraction of metal particles. At a lower content, instead, it slowly decreases as reinforcing powder content increases. Both the mechanical properties and values for electrical resistivity are similar to those published for polymers obtained directly from monomers.

Low Temperature Thermal Stability of Quaternary Al-Li-Cu-Mg Alloys

Combined copper and magnesium additions have been made to a base Al-1.7wt%Li alloy to investigate their effect on the microstructural stability of Al-Li-Cu-Mg alloys. Alloys have been given a standard age of 24h at 150°C, followed by a second ageing treatment of 1000h at 70°C to stimulate low temperature exposure under service conditions. Exposure at 70°C resulted in a decrease in fracture energy and an increase in proof stress. The magnitude of these changes in mechanical properties were larger than those observed in binary Al-Li and ternary Al-Li-Cu alloys. TEM, DSC and electrical resistivity measurements have been used to establish the microstructural changes and precipitation kinetics that cause this increased level of exposure embrittlement. It is proposed that in Al-Li-Cu-Mg alloys Cu/Mg co-clusters or GPB zones form during the 150°C pre-age and these act as nucleation centres for δ' (Al 3 Li) formation during the 70°C exposure. This produces enhanced kinetics of δ' precipitation and therefore a larger volume fraction of δ' forms during the exposure treatment.

Size Effect in Fracture of Concrete Specimens and Structures: New Problems and Progress

Presented is a concise summary of recent Northwestern University studies of six new problems. First, the decrease of fracture energy during crack propagation through a boundary layer, documented by Hu and Wittmann, is shown to be captured by a cohesive crack model in which the softening tail slope depends on the distance from the boundary (which causes an apparent size effect on fracture energy and implies that the nonlocal damage model is more fundamental than the cohesive crack model). Second, an improved universal size effect law giving a smooth transition between failures at large cracks (or notches) and at crack initiation is presented. Third, a recent renewed proposal that the nominal strength variation as a function of notch depth be used for measuring fracture energy is critically examined. Fourth, numerical results and a formula describing the size effect of finite-angle notches are presented. Fifth, a new size effect law derivation from dimensional analysis coupled with asymptotic matching is given. Finally, an improved code-type formula for shear capacity of R.C. beams is proposed.

SHIP-deficient mice are severely osteoporotic due to increased numbers of hyper-resorptive osteoclasts.

The hematopoietic-restricted protein Src homology 2-containing inositol-5-phosphatase (SHIP) blunts phosphatidylinositol-3-kinase-initiated signaling by dephosphorylating its major substrate, phosphatidylinositol-3,4,5-trisphosphate. As SHIP(-/-) mice contain increased numbers of osteoclast precursors, that is, macrophages, we examined bones from these animals and found that osteoclast number is increased two-fold. This increased number is due to the prolonged life span of these cells and to hypersensitivity of precursors to macrophage colony-stimulating factor (M-CSF) and receptor activator of nuclear factor-kappa B ligand (RANKL). Similar to pagetic osteoclasts, SHIP(-/-) osteoclasts are enlarged, containing upwards of 100 nuclei, and exhibit enhanced resorptive activity. Moreover, as in Paget disease, serum levels of interleukin-6 are markedly increased in SHIP(-/-) mice. Consistent with accelerated resorptive activity, 3D trabecular volume fraction, trabecular thickness, number and connectivity density of SHIP(-/-) long bones are reduced, resulting in a 22% loss of bone-mineral density and a 49% decrease in fracture energy. Thus, SHIP negatively regulates osteoclast formation and function and the absence of this enzyme results in severe osteoporosis.

The Fracture Behavior of Rubbery Vulcanizates: I. Single Component Versus Blend Systems

Abstract The tear energy and heat build up of NR, SBR and BR vulcanizates and their corresponding blends were measured at several temperatures via modified trouser tear and Goodrich flexometer experiments. In all single component samples, by increasing temperature from -10 to 125 °C, the fracture energy decreases, goes through a minimum and increases again. Nevertheless, in SBR and BR, a level off and a level off followed by second drop occur at higher temperatures, respectively. On the other hand, for aforementioned samples the heat build up decreases monotonically by raising the temperature. For two-component blends, the fracture energy and heat build up show different dependencies on temperature in comparison to single component systems. The fracture energy either increases, does not change at first and then decreases, or does not change as the temperature increases. While the heat build up is more or less constant by raising the temperature up to a certain point and then decreases but by a different path from single component vulcanizates. These peculiar behaviors are attributed to the competition between residual stress release and reduction of viscose loss term, while the temperature increases.

Influence of crack speed on fracture energy in amorphous and rubber toughened amorphous polymers

To study the influence of the crack speed at initiation on measurements of the toughness of amorphous polymers such as polycarbonate (PC) and rubber toughened poly(methyl methacrylate) (RTPMMA), ‘compact tension’ specimens were tested at a medium loading rate (0·6 m s-1 ). The specimens were equipped to allow location of the position of the crack tip and to trigger a photograph on passage of the crack. The experimental procedure was validated using PC for which the crack speed was found to change suddenly over very short distances, owing to stick–slip propagation. Conversely, fracture tests on RTPMMA showed that the acceleration of the crack tip, due to the decrease in fracture energy with crack speed, is controlled by a process zone, the size of which did not allow the systematic use of linear elastic fracture mechanics. The rapid crack propagation regime in RTPMMA corresponds to a propagation stabilised at the macroscopic crack branching velocity. This constant crack speed corresponds to frustrated microbranching and leads to non-unique values of the fracture energy at the macroscopic branching velocity.

Reduction of Toughness in Aluminium-Lithium Alloys Caused by Long Term Exposure at Low Temperatures

An Al-1.7%Li alloy has been aged 24 h at 150°C and then subjected to long term exposure at 100°C which resulted in an increase in proof stress and a decrease in fracture energy. The δ' solvus temperature of the alloy has been measured as 220°C and this result has been used to establish a reversion heat treatment that would dissolve δ' precipitates without the formation of δ phase. By carrying out reversion heat treatment on the exposed alloy it has been shown that the exposure embrittlement arises entirely from the formation of a fine dispersion of δ' phase. There is no contribution to embrittlement from the formation of δ phase at the grain boundaries.

Chemo-Mechanical Effects in Mortar Beams Subjected to Water Hydrolysis

Reliable predictions of the long-term behavior of concrete structures require both an accurate knowledge of the various degradation mechanisms that affect the structures over their lifetime and the use of simulation tools. Leaching due to aggressive water can be responsible for a loss of mechanical properties and stability of concrete structures. This paper focuses on coupled chemo-mechanical effects on concrete structures subjected to aggressive water inducing calcium leaching. Experimental investigations on mortar bending beams and their analysis are detailed. The response of leached mortar beams is deduced from these tests. It is found that the stiffness of mortar decreases, along with its strength, as the chemical attack progresses. The size effect on geometrically similar bending beams at various stages of degradation is studied experimentally. Due to leaching, the brittleness of the structures is increased and the fracture energy decreases.

Effect of cyclic loading on interfacial shear stress in SiC–CAS glass ceramic matrix composite

Mechanical fatigue has been observed to occur in the Nicalon–CAS continuous fibre reinforced glass ceramic matrix composite under cyclic loading at room temperature, and both microcrack proliferation and propagation are induced. In situ fibre push down tests within a scanning electron microscope have then been used to assess changes in interfacial properties as a result of this mechanical cyclic loading. Both the interfacial shear stress and the interfacial fracture energy decrease when specimens are subjected to mechanical cyclic loading. It is deduced that a decrease in interfacial shear stress is the most likely mechanism driving stable and progressive microcrack propagation.

Interfacial reactions and adhesion strength of metal/ceramic composites

The interfacial fracture energy of Ti/Al2O3 composites was measured with and without a diffusion barrier at different bonding temperatures by using four-point bending tests. It was found that the interfacial fracture energy increases with increasing bonding temperature up to 950 °C. When the bonding temperature was further raised to 1000 °C, the interfacial fracture energy drops. The decrease of the interfacial fracture energy is due to the formation of the continuous intermetallic compound, Ti3Al, at the interface between Ti and Al2O3. By using a diffusion barrier, the interfacial fracture energy decreases from 25.4 to near O J/m2 and 32.9 to 8.7 J/m2 for applied bonding temperatures of 800 and 900 °C, respectively. This is because the diffusion barrier reduced the diffusion of Al across the interface and into the Ti, thereby preventing a strong chemical bond at the interface. For the composite bonded at 900 °C, the crack propagation was found to occur at the interface between the Ti and Al2O3. The interfacial failure was found to be in the Ti3Al reaction layer for the composite processed at 1000 °C. With a diffusion barrier, the crack propagation path follows several interfaces. Evaluation of the processing temperature on the mechanical properties of the Ti was also obtained by using a nanoindentation technique.

Influence of heat treatment and hot working on fracture toughness of cast aluminium base composites

AbstractEvaluation of toughness in terms of the fracture energy E*, obtained using Charpy impact testing and the fracture toughness KIc obtained from bend tested specimens, has been carried out for various cast particle reinforced aluminium base composites, namely, A356–SiC, A357–SiC, 6061–Al2O3, and 2014–Al2O3. In practice, the first two are used in the as cast foundry condition and the last two in the cast and extruded condition. Hot extrusion or rolling to reduction ratios between 2 : 1 and 50: 1 was conducted on the 6061 and 2014 composites to characterise the influence of working processes. Heat treatment conditions considered included the as cast (or as worked), solid solution treated, and T6 temper. The results show that extrusion or rolling can markedly improve the toughness, but on thermal aging the toughness is reduced. The increase in total fracture energy by hot working is mainly caused by the increase of initiation energy, whereas the decrease of fracture energy by artificial aging is control...

Effect of M7C3→M23C6transformation on fracture behaviour of cast ferritic stainless steels

The fracture behaviour of three 29 wt-%Cr ferritic steels, two containing zirconium and titanium respectively, has been investigated in the as cast condition and after annealing at 660°C for different times up to 2210 h. The fracture energy and the mode of fracture depend on both the morphology and the nature of the eutectic, which consists of carbides and ferrite. In the as cast condition, fracture is predominantly transgranular cleavage and it can be associated with the discontinuous morphology of the M7C3 carbides present in the eutectic as coarse particles surrounded by the eutectic ferrite. After prolonged heating, the ambient fracture energy decreases and the interdendritic mode of fracture is enhanced. This change in fracture mechanism is associated with transformation of the M7C3 to M23 C6 carbides. The M23 C6 carbides, unlike the coarse M7C3 carbides, form a continuous network within the eutectic mixture and constitute an easy path for crack propagation. The zirconium and titanium additions result in a more massive morphology of the carbides in the eutectic mixture and accelerate the M7C3 to M23C6 transformation during the heat treatments, enhancing the interdendritic mode of fracture both in the as cast and in the annealed condition.MST/1734