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W Blum - One of the best experts on this subject based on the ideXlab platform.
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a simple dislocation model of the influence of high angle boundaries on the Deformation behavior of ultrafine grained materials
Journal of Physics: Conference Series, 2010Co-Authors: W Blum, Philip EisenlohrAbstract:The Deformation Resistance of ultrafine-grained (UFG) materials is modelled on the basis of the evolution of the average dislocation density with strain in the course of glide and recovery of dislocations. In contrast to materials with conventional grain size (CG), dislocations are stored and annihilated solely at the high-angle boundaries, where screw dislocations glide and edge dislocations climb towards annihilation sites. The high-angle boundaries enhance both the rates at which dislocations are stored and recovered. Depending on the spacing of high-angle boundaries, temperature and strain rate, UFG materials are softer or harder than their CG counterparts.
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evolution of dislocation structure and Deformation Resistance in creep exemplified on single crystals of caf2
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2009Co-Authors: P Sadrabadi, Philip Eisenlohr, G Wehrhan, J Stablein, L Parthier, W BlumAbstract:Abstract Single crystals of CaF 2 oriented along 〈 111 〉 for glide on three equally stressed slip systems were used to study the evolution of the dislocation structure during Deformation at temperatures from 873 to 1315 K. Structure quantification was done by the etch pit method using atomic force microscopy for high resolution. Evolution begins with free dislocations forming a cellular structure. The average spacings of free dislocations and of cell boundaries are generally close to their stress-dependent steady state values. The subgrain structure develops more slowly with strain. As it superimposes on the free dislocations, the crystals work harden and the creep rate decreases. The rates of change of the characteristic spacings of subgrain and cell boundaries, of free dislocations and of dislocations in subgrain boundaries are formulated as functions of stress, strain and the empirical steady state values of spacings. Combining the laws of structure evolution with those of Deformation kinetics in the framework of the composite model, the creep behavior is modeled in a large range of homologous temperatures in consistence with the general picture of plasticity of crystalline materials.
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a simple dislocation model of Deformation Resistance of ultrafine grained materials explaining hall petch strengthening and enhanced strain rate sensitivity
Acta Materialia, 2009Co-Authors: W Blum, X H ZengAbstract:A model is presented where the properties of ultrafine-grained (UFG) materials are explained in terms of the influence of high-angle boundaries on the rates at which dislocations are stored and recovered at the boundaries. The model reproduces the experimental observations that UFG materials reach a steady state where the Deformation Resistance is independent of strain, that the strain rate sensitivity of flow stress is relatively high and that the steady-state flow stress increases inversely with the square root of grain size. The model results are compared to experimental data for UFG Cu and nanostructured Ni.
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evolution of microstructure and Deformation Resistance in creep of tempered martensitic 9 12 cr 2 w 5 co steels
Acta Materialia, 2006Co-Authors: R Agamennone, W Blum, C K Gupta, J K ChakravarttyAbstract:Abstract The microstructural evolution during creep at 923 K of four tempered martensite 9–12%Cr-steels modified with 2%W and 5%Co was quantified by electron microscopy. Coarsening of subgrains with strain towards the stress dependent steady state was confirmed. The evolution of the precipitate structure is similar with regard to M23C6 (M: metallic element, X: N, C) and Laves phase (Fe,Cr)2(W,Mo) but differs strongly with regard to V-bearing precipitates. Low temper temperatures promote precipitation of V as M2X instead of VX. This appears to be critical in causing anomalously fast breakdown of initially high creep Resistance. Dissolution of small V-bearing precipitates and corresponding loss of precipitation hardening in the subgrain interior is proposed to be the reason for this breakdown. The dissolution is caused by fast coarsening of M2X precipitates and precipitation of Z-phase at subgrain boundaries. Large M2X precipitates at subgrain boundaries are proposed to be nucleation sites of Z-phase.
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creep Deformation mechanisms in high pressure die cast magnesium aluminum base alloys
Metallurgical and Materials Transactions A-physical Metallurgy and Materials Science, 2005Co-Authors: W Blum, X H Zeng, P Zhang, B Von Grosmann, C HaberlingAbstract:Creep of die-cast Mg alloys is described as an integral part of their plastic Deformation behavior in terms of stress-strain-rate-strain relations. Creep tests yield information on yield stress, work hardening, maximum Deformation Resistance (minimum creep rate), and work softening. Testing in compression avoids influences by fracture. Data on the alloy AJ52 (5Al, 2Sr) in the temperature range between 135 °C and 190 °C are presented and compared to those for AZ91 and AS21. Die-cast Mg-Al alloys consist of fine grains with a grain boundary region containing intermetallic precipitates. Transmission electron microscopic observations indicate that basal glide is the dominant mechanism of Deformation being supplemented by nonbasal glide and twinning to maintain compatiblity between the grains. The Deformation Resistance can be modeled with a composite approach assuming that the grain boundary region is relatively hard due to precipitation of intermetallic phases. The differences in long-term creep Resistance at low stress are explained in terms of different strength and stability of precipitates in the different alloys.
Zongwu Chen - One of the best experts on this subject based on the ideXlab platform.
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function investigation of stone mastic asphalt sma mixture partly containing basic oxygen furnace bof slag
Journal of Applied Biomaterials & Functional Materials, 2016Co-Authors: Zongwu Chen, Ling Pang, Jun XieAbstract:AIMS In this paper, the effect of the size gradations of basic oxygen furnace (BOF) slag on the functional performances of stone mastic asphalt (SMA) mixture including skid and Deformation Resistances was investigated. METHODS The industrially produced BOF slag coarse aggregates (BSCA) with size gradations of 4.75-9.5 mm and 9.5-16 mm were used. SMA mixtures were designed according to Marshall procedure. British pendulum number (BPN), indicating the skid Resistance of asphalt mixture, was measured by a British pendulum skid Resistance device. Flow number (FN) and Marshall quotient (MQ), reflecting the Deformation Resistance of asphalt mixture, were determined, respectively, based on the results of dynamic creep test and Marshall test (stability and flow value). RESULTS Showed that BSCA with a size gradation of 9.5-16 mm performed better in improving the skid and Deformation Resistance of SMA mixture than BSCA with a size gradation of 4.75-9.5 mm. Furthermore, BSCA with combined size gradations, namely, 4.75-16 mm, worked the best. CONCLUSIONS These conclusions would benefit the future extensive utilization of BSCA in asphalt pavement.
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utilization of gneiss coarse aggregate and steel slag fine aggregate in asphalt mixture
Construction and Building Materials, 2015Co-Authors: Zongwu Chen, Jin Wen, Meiling Zhao, Jiuming WanAbstract:Abstract Natural resource shortage and environmental pollution issue have promoted the recycling of inferior natural resources and solid wastes in asphalt pavement. While steel slag fine aggregate and inferior gneiss aggregate are rarely used in asphalt mixture in China due to some poor performances. The primary objective of this research was to explore the feasibility of simultaneously using gneiss coarse aggregate and steel slag fine aggregate in asphalt mixture. A new method to improve the quality of steel slag fine aggregate was proposed first. Raw material characteristics directly related to asphalt adhesion and absorption were fully detected then. Performances of asphalt mixture including Marshall stability and quotient, crack Resistance, moisture susceptibility, volume stability and Deformation Resistance were evaluated finally. Results showed that modified WSFA (Weathered Steel Slag Fine Aggregate) presented lower asphalt absorption than original WSFA. Asphalt mixture consist of gneiss coarse aggregate and modified WSFA obtained better crack Resistance, moisture Resistance, volume stability and Deformation Resistance.
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recycling of flue gas desulfurization residues in gneiss based hot mix asphalt materials characterization and performances evaluation
Construction and Building Materials, 2014Co-Authors: Zongwu Chen, Juyong Chen, Zhehuan Qin, Ling PangAbstract:Abstract On the one hand, huge amount of Flue Gas Desulfurization (FGD) residues, produced during scrubbing flue gas, is discarded as solid waste. Such solid waste would cause serious environmental problems. One the other hand, high quality aggregates, such as limestone and basalt, are running out due to the rapid development of highway construction. Ungraded aggregates such as gneiss are therefore considered in China to replace the high quality aggregates. The application of FGD residues as a filler in gneiss based asphalt mixture has benefits both in environmental and economic sides. The main objective of this research was to visualize the raw materials characterization and evaluate the effect of FGD residues on the performance of gneiss based asphalt mixture. X-ray diffraction (XRD), X-ray fluorescence (XRF), Scanning Electron Microscope (SEM), Differential Scanning Calorimetric & Thermal gravimetric (DSC–TG) were used to investigate the features of raw materials. The performance of gneiss based asphalt mixture including high-temperature Deformation Resistance, low-temperature crack Resistance and moisture-induced damage Resistance were evaluated. Dynamic creep test, three-point bending test, Retained Marshall Stability (RMS), Tensile Strength Ratio (TSR), Indirect Tensile (IDT) strength and Resilient Modulus (MR) test were conducted and analyzed. Dissipated Creep Strain Energy to fracture (DCSEf) ratio, fracture energy and model analysis were also used to evaluate moisture Resistance, crack Resistance and Deformation Resistance of asphalt mixture respectively. Research results indicate that FGD residues can partly improve the moisture Resistance and crack Resistance of gneiss asphalt mixture, while it might worse the high-temperature Deformation Resistance.
Kwang W Kim - One of the best experts on this subject based on the ideXlab platform.
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framework for developing a static strength test for measuring Deformation Resistance of asphalt concrete mixtures
Construction and Building Materials, 2007Co-Authors: Young S Doh, Kyong Ku Yun, Serji N Amirkhanian, Kwang W KimAbstract:Abstract This study deals with a strength property which is showing high correlation with rutting Resistance of asphalt mixtures. The test procedure was developed by applying a load to the compacted asphalt samples and calculating the strength by using the Deformation of the mixture at the failure point. To evaluate the validity of this test, various mixtures were prepared with two aggregates and seven binders using four loading head types at the loading speed of 50.8 mm/min at 60 °C. Maximum load and Deformation were recorded for each test and Deformation strength, S D , was calculated using a newly developed equation. For the same mixture, wheel tracking test was performed and two rut parameters, depth of rut and dynamic stability were obtained. The relationship between S D and rut parameters was evaluated using regression analyses. In most cases, R 2 values were found to be over 0.9. This test procedure is still under development; however, current results indicate that it might be a simple test to predict the Deformation Resistance of asphalt mixtures at high temperatures.
Hussai U Ahia - One of the best experts on this subject based on the ideXlab platform.
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enhancement of permanent Deformation Resistance of modified asphalt concrete mixtures with nano high density polyethylene
Construction and Building Materials, 2020Co-Authors: Alaa H Abed, Hussai U AhiaAbstract:Abstract The present research was carried out to inspect the influence of Nano-High Density Polyethylene (Nano-HDPE) particles and Styrene-Butadiene-Styrene (SBS) on the rheological characteristics of modified asphalt binders and performance of modified asphalt concrete mixtures. In this study, the base asphalt binder of the PG (64-16) grade was modified with Nano-HDPE and SBS polymers at a concentration of 3% and 5% by weight of total asphalt binder content. The Superpave dynamic shear rheometer (DSR), rolling thin film oven (RTFO), rotational viscosity (RV), pressure aging vessel (PAV) and bending beam rheometer (BBR) were conducted to evaluate performance grade of base and modified asphalt binders, also gyratory compactor was used to find optimum asphalt content. Roller compactor and wheel track tests were utilized to assess the rutting performance of modified asphalt mixture with Nano and SBS polymers, and the Indirect Tension Test (IDT) was used to assess the strength of mixtures before and after water conditioning. The results of the study show that Nano-HDPE particles have a considerable influence on improving Performance Grade (PG) of the binder, but at an equal concentration of polymer, it is not as effective as the SBS. However, the HDPE shows a significant advantage in keeping the viscosity of the modified binder at significantly lower levels and thus allowing much lower mixing and compaction temperatures as determined by the equ-viscous standard procedure. Although the PG grades of the binders showed the SBS to be more effective in improving the high-temperature grade than the HDPE, the mixture rutting performance shows that the HDPE modified binders provide better rutting Resistance at 3% and 5% than the SBS modified binders. This finding shows that binder testing of G*/sin δ only could give a misleading indication of the true contribution of modified binders to rutting Resistance as polymers could improve mixtures in different mechanisms than what is measure with binder PG testing. The IDT testing also shows that the strength of the mixtures produced with the modified binders at 25 °C is superior to the control mixture, with the HDPE providing slightly higher strength values before and after water conditioning. The overall results of the study show that HDPE can be used as a viable modifier requiring lower mixing and compaction temperature and equal or significantly better rutting and strength performance than conventional SBS Modifier. The study also highlights the need to check mixture performance when using specialty modifiers and not depend on only DSR testing as specified in the Superpave PG grading.
Yanli Huang - One of the best experts on this subject based on the ideXlab platform.
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characterizations of macroscopic Deformation and particle crushing of crushed gangue particle material under cyclic loading in solid backfilling coal mining
Powder Technology, 2019Co-Authors: Yanli Huang, Zhongwei Chen, Jixiong Zhang, Haiqiang Jiang, Yuanchao ZhangAbstract:Abstract In solid backfilling coal mining (SBCM), the Deformation Resistance of crushed gangue particle material (CGPM) is critical for controlling overburden strata movement and ground surface subsidence. In engineering practice, CGPM is generally circularly compacted first by the compaction machine to reduce its compressibility. However, a systematic approach to guide the compaction practices does not appear to be available. This study implemented an experimental approach to investigate the macroscopic Deformation and particle crushing characteristics of CGPM during constant amplitude cyclic loading (CACL) and continuously loading again after CACL (CL-CACL). At the same time, the influence mechanism of particle crushing on macroscopic Deformation of CGPM was also revealed. The results show that the residual compression ratio increased with the cyclic loading times in CACL experiments, but in CL-CACL experiments, the final compression ratio decreased with the cyclic loading times that the samples have borne before, which indicates that cyclic loading can significantly improve the Deformation Resistance of CGPM. It is also shown that the crushing ratio (Bg) increased with the cyclic loading times in CACL experiments. However, it was opposite in CL-CACL experiments. There existed a piecewise linear relationship between the residual compression ratio and the crushing ratio, which indicates the particle crushing is a key factor to leads macroscopic Deformation of CGPM. The research can reveal the influence mechanism of particle crushing on macroscopic Deformation of CGPM and provide a systematic approach to guide the compaction engineering practices in SBCM.
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effects of water soaked height on the Deformation and crushing characteristics of loose gangue backfill material in solid backfill coal mining
Processes, 2018Co-Authors: Yanli Huang, Ming Qiao, Zhongwei Chen, Tianqi Song, Guoqiang Kong, Huadong Gao, Lei GuoAbstract:In solid backfill coal mining (SBCM), loose gangue backfill material (LGBM) is used to backfill the goaf after coal resources are exploited from the underground mines. Under certain geological conditions, LGBM with a certain height may be soaked in the water, and then becomes saturated, significantly altering its mechanical properties. The confined compression experiments were used in this paper to analyze the Deformation and the crushing characteristics of LGBM with varying water soaked heights in coal mines. The results showed that a large number of small holes that were distributed in the gangue blocks were the main reason why the material absorbed water and was softened. The crushing ratio and the maximum axial strain of LGBM samples gradually increased with the water soaked heights of the samples. In addition, there was a strong linear correlation between the crushing ratio and the maximum axial strain. When LGBM was used as a solid backfill material in SBCM, its Deformation Resistance would significantly decrease after it was soaked in the water. Higher water soaked height of LGBM led to lower Deformation Resistance and greater influence on the quality of backfilling. This research has great significance in getting a deep and better understanding of the mechanical properties of LGBM, as well as guiding engineering practice.