Multiscale Study on Low Temperature Crack Resistance Mechanism of Steel Slag Asphalt Mixture

The objective of this paper was to study low temperature crack resistance mechanism of steel slag asphalt mixture(SAM).Thermal stress restrained specimen test(TSRST)and three-point bending test were carried out to evaluate the low-temperature crack resistance of SAM and basalt asphalt mixture(BAM).Based on the digital image correlation technique(DIC),the strain field distribution and crack propagation of SAM were analyzed from the microscopic point of view,and a new index,crack length factor(C),was proposed to evaluate the crack resistance of the asphalt mixture.The crystal phase composition and microstructure of steel slag aggregate(SA)and basalt aggregate(BA)were studied by X-ray diffraction(XRD)and scanning electron microscopy(SEM)to explore the low-temperature crack resistance mechanism of SAM.Results show that the low-temperature crack resistance of SAM is better than that of BAM;SAM has good integrity and persistent elastic deformation,and its bending failure mode is a hysteretic quasi-brittle failure;The SA surface is evenly distributed with pores and has surface roughness.SA has the composition phase of alkaline aggregate-calcite(CaCO3),so it has good adhesion to asphalt,which reveals the mechanism of excellent low-temperature crack resistance of SAM.

A review on evaluation of crack resistance of asphalt mixture by semi-circular bending test

Although there are many kinds of fracture tests to choose from in evaluating the crack resistance of asphalt mixture,the semi-circular bending(SCB)test has attracted a lot of attention in the academic road engineering community because of its simplicity,stability,and flexibility in testing and evaluation.The SCB test has become a common method to study the cracking resistance of asphalt mixture in recent years.This paper mainly summarizes the overview of the SCB test,summarizes some research results and common characterization parameters of the SCB test method in monotone test and fatigue test in recent years,and predicts and suggests the research direction of the SCB test in the future.It is found that the research on the monotonic SCB test is more comprehensive,and the research on the SCB fatigue test needs to be further improved in the aspects of loading mode,characterization parameter selection,and so on.Researchers can flexibly adjust the geometric dimensions and the test parameters of semi-cylindrical specimens,and conduct comprehensive analysis combined with the results of numerical simulation.The crack resistance of asphalt mixture can be comprehensively evaluated by fracture energy,fracture toughness,stiffness,flexibility index and other fracture indicators,combined with the crack propagation of the specimen.The analysis of numerical simulation can confirm the test results.In order to standardize the setting of fatigue parameters for future application,it is necessary to standardize the setting of bending performance.

Study of Cracking Mechanism and Wear Resistance in Laser Cladding Coating of Ni-based Alloy

Nickel-based alloy coatings were widely used for the remanufacturing of dies and moulds by laser cladding,but the crack sensitivity would be increase due to the higher strength and hardness,which reduced the wear resistance of Ni-based alloys.In this paper,Ni-based coatings with the addition of a plastic phase(an austenitic stainless net)were prepared using laser cladding technology,and the CeO_(2)was added in cladding layers.The cracking mechanism,microhardness,microstructure,phase composition,and wear properties were investigated.The relationship between thermal stress and the elastic and plastic fracture had been developed from the standpoint of fracture mechan-ics and thermal elastic fracture mechanics.The fracture criterion of the nickel-based coating was obtained,and the study has shown that the crack sensitivity could be reduced by decreasing the thermal expansion coefficientΔα.Thus,a new method was proposed,which the stainless steel nets were prefabricated on the substrate.It was found that the number of cracks reduced significantly with the addition of stainless steel net.When the stainless steel net with 14 mesh was added in Ni-based coatings,the average microhardness of nickel composite coating was 565 HV_(0.2),which was 2.6 times higher than that of the 45 steel substrate.Although the rare earth oxide 4 wt.%CeO_(2)and stainless steel net were added in the Ni-based coating reducing the microhardness(the average microhardness is 425 HV_(0.2)),the wear resistance of it improved substantially.The wear volume of Ni-based composite coating was 0.56×10^(−5) mm^(3)·N^(−1)·m^(−1),which was 85.1%lower than that of 45 steel.The experiment results have shown that the Nickel-based composite coating is equipped with low crack sensitivity and high abrasive resistance with austenitic stainless net and the rare earth oxide 4 wt.%CeO2.This research offers an efficient solution to produce components with low crack susceptibility and high wear-resistance coatings fabricated by laser cladding.

Evaluation of Cracking Resistance of Copper-Bearing Age Hardening Steel Weldment

The weldability of a low-carbon copper-bearing age hardening steel was evaluated using cracking suscepti- bility calculation, HAZ maximum hardness measurement, and Y-groove cracking evaluation test. The results show that the hardenability characteristics and cold cracking susceptibility of the steel are very low. The results also indicate that a crack-free weldment can be obtained during the welding of this type of steel even at an ambient temperature as low as -5 ℃ as well as in an absolute humidity lower than 4 000 Pa without any preheat treatment. A slight preheat treatment can prevent the joint from cracking when welding is carried out at lower ambient temperature or higher absolute humidity.

Effect of RE on Cracking Resistance and Microstructure of Coatings Formed by Plasma Jet Surface Metallurgy

Metallurgical coatings of iron-based alloy with RE oxide were prepared on low-carbon steel using a home-made DC-plasma jet surface metallurgy equipment. Scanning electron microscope (SEM), energy dispersive X-ray (EDX) microanalysis and X-ray diffraction analysis (XRD) were employed to observe the microstructure and analyze the chemical compositions of coatings. And the cracking susceptibility of coatings was studied in terms of RE addition. Experimental results show that addition of RE oxide (La_2O_3 and CeO_2) can refine and purify the microstructure, and can reduce the cracking susceptibility of coatings.

Evaluation method of cracking resistance of lightweight aggregate concrete

The cracking behavior of lightweight aggregate concrete(LWAC) was investigated by mechanical analysis, SEM and cracking-resistant test where a shrinkage-restrained ring with a clapboard was used. The relationship between the ceramsite type and the cracking resistance of LWAC was built up and compared with that of normal-weight coarse aggregate concrete(NWAC). A new method was proposed to evaluate the cracking resistance of concrete, where the concepts of cracking coefficient ζt(t) and the evaluation index Acr(t) were proposed, and the development of micro-cracks and damage accumulation were recognized. For the concrete with an ascending cracking coefficient curve, the larger Acr(t) is, the lower cracking resistance of concrete is. For the concrete with a descending cracking coefficient curve, the larger Acr(t) is, the stronger the cracking resistance of concrete is. The evaluation results show that in the case of that all the three types of coarse aggregates in concrete are pre-soaked for 24 h, NWAC has the lowest cracking resistance, followed by the LWAC with lower water absorption capacity ceramsite and the LWAC with higher water absorption capacity ceramsite has the strongest cracking resistance. The proposed method has obvious advantages over the cracking age method, because it can evaluate the cracking behavior of concrete even if the concrete has not an observable crack.

Improvement of Cracking-resistance and Flexural Behavior of Cement-based Materials by Addition of Rubber Particles

By ring test and bend test, the improvement of waste tire rubber particles on the crack- resistance and flexural behaviors of cement-based materials were investigated. Test results show that the cracking time of the ring specimens can be retarded by the incorporation of rubber particles in the cement paste and mortar. The improvement in the crack-resistance depended on the rubber fraction. When the rubber fraction was 20% in volume, the cracking time was retarded about 15 h for the paste and 24 d for the mortar respectively. Flexural properties were evaluated based on the bend test results for both mortar and concrete containing different amount of rubber particles. Test results show that rubberized mortar and concrete specimens exhibit ductile failure and significant deformation before fracture. The ultimate deformations of both mortar and concrete specimen increase more than 2-4 times than control specimens.

Effect of RE Oxide on Cracking Resistance of Hardfacing Metal

The crack morphologies of hardfacing metal were observed by means of optical microscope and scanning electron microscope. Meanwhile, the cracking resistances of hardfacing metal were investigated. The results show that the solidification cracking and quench hardened cracking are the main forms of cracking in hardfacing metal. The cracking resistance of hardfacing metal can be improved by adding rare earth oxide in the coat of electrode.

Environmental Stress Cracking Resistance of Halloysite Nanoclay-Polyester Nanocomposites

The environmental stress cracking resistance of halloysite nanoclay-polyester nanocomposites was investigated using fracture mechanics approach. The incorporation of halloysite nanoclay was found to improve the environmental stress cracking resistance of the nano-composites. The storage modulus of nano-composites measured by dynamic mechanical analysis increased remarkably as a function of halloysite nanoclay content. At 0.7 wt% nanoclay, the Tg improved from 72°C to 76°C. The fracture toughness increased up to 33% and time to failure improved 155% with the addition of 0.7 wt% of halloysite nanoclay. The maximum microhardness was found 119% higher for the same nano-filler concentration compared to monolithic polyester. The reinforcement with 1 wt% showed lower fracture toughness due to agglomerations of nanoclay which act as flaws. The presence of agglomerates weakened the bond between nano-particles and matrix hence reduces the environmental stress cracking resistance by halloysite nanoclay reinforcement.

Effects of alloy elements on microstructure and crack resistance of Fe-C-Cr weld surfacing layer

Effects of alloy elements on the microstructure and crack resistance of Fe-C-Cr weld surfacing layer were investigated. The results show that microstructures of the layer mainly consist of carbides and austenite matrix. Increasing C and Cr contents impair the crack resistance of the layer due to increased amount of brittle carbides. The addition of Ni, Nb or Mo improves the crack resistance of Fe-C-Cr weld surfacing layer by increasing the amount of austenite and forming fine NbC or M 7C 3 carbides in the layer. But, the excessive Nb (>2.50wt%) or Mo (>1.88wt%) impairs the crack resistance of the layer, which has relation with increased carbides or carbide coarsening and austenite matrix solid solution strengthening. The proper combination of C, Cr, Ni, Nb and Mo can further improve not only the crack resistance of Fe-C-Cr weld surfacing layer but also the erosion resistance as a result of fine NbC and M 7C 3 carbides distributing uniformly in austenite matrix. The optimal layer compositions are 3.05wt%C, 20.58wt%Cr, 1.75wt%Ni, 2.00wt%Nb and 1.88wt%Mo.

Application of New Heavy Metals Resistant Porous Binder Material Used in Fluid Catalytic Cracking Reaction

A novel porous binder was obtained from acid-treated kaolin. This new binder possessed abundant meso/macropores, good hydrothermal stability and heavy metal resistance. The prepared catalyst using new binder featured low attrition index and large pore volume. The catalysts were contaminated with Ni, V, and tested in a fixed-fluidized bed reactor unit. In comparison with the reference sample, the oil conversion achieved by the above-mentioned catalyst increased by 3.50 percentage points, and heavy oil yield decreased by 2.86 percentage points, while the total liquid yield and light oil yield increased by 2.82 percentage points and 0.79 percentage points, respectively. The perfect pore structure, good hydrothermal stability and heavy metal resistant performance of new binder were the possible causes leading to its outstanding performance.

Experimental and Numerical Analysis of Restrained Early Age Cracking based on Electrical Resistivity Using Eccentric Sample

Crack potential and hydration processes of the cement pastes were monitored using an upto-date eccentric steel cracking frame(ESCF), associated with the non-contact electrical resistivity apparatus, independently. The objective of employing the ESCF is to give a new method determining cracks of concrete at early age. The findings indicate that the lowest water-cement ratio paste reveals highest resistivity values, compasses an earlier inflection point and obtained higher stress. The eccentric restrained cracking test exhibited that lower water-cement ratio paste cracked at the earliest time, accordingly confirms cracking tendency is the highest. Tensile strength test and stresses utilizing ABAQUS simulation was performed. The crack initiation ages obtained are consistent with the experimental program results, which indicates that ABAQUS numerical analysis can well be utilized to predict the crack tendency of cement.

Effect of Rare Earth Elements on Quenching Crack Resistance of Steel 9Cr2Mo

The effect of rare earth elements on quenching crack resistance of steel 9Cr2Mo was investigated by means of scanning electron microscopy (SEM) and optical microscopy. Experimental results show that, by adding RE elements to steel 9Cr2Mo, the number of quenching for crack initiation is increased. Meanwhile the propagation of quenching cracks is postponed and the paths of crack propagation are changed. Therefore, quenching crack resistance can be improved by adding RE elements to steel 9Cr2Mo.

Ballistic resistance and energy dissipation of woven-fabric composite targets:Insights on the effects of projectile shape and obliquity angle

This study aims at investigating the ballistic resistance and energy absorption in woven E-glass composite panels,considering different projectile nose shapes and oblique incidence angles.To that scope,three-dimensional finite element(FE)models of both projectiles and the laminated target are developed and numerical investigations are carried out using Abaqus Explicit solver.The composite damage model’s constitutive law encompasses nonlinear material response,material properties degradation,progressive failure,and an element deletion strategy.The cohesive surface technique is used to represent the interface between two adjacent plies in the laminate,and the traction-separation law is used to characterize the behaviors of interlaminar degradation and failure.Material responses attributable to fiber rupture,matrix cracking,and plasticity caused by micro-matrix cracking due to shear loading are taken into account with suitable damage evolution laws.The computational framework is first validated against the experimental results reported in the literature by performing ballistic impact tests on the target laminate with conical,hemispherical and blunt-ended projectile,and the numerical results showed a good comparison in terms of residual velocity.Subsequently the framework is explored in simulating more complex failure mechanisms,with particular emphasis on the influence of the impact angle of obliquity,a parameter that is not usually analyzed in the literature.In that regard,the effects of normal and oblique impact on the damage morphologies and ballistic behavior of the fabric composite target in terms of energy absorption,impact contact force,and projectile residual velocity are conducted and analyzed,comparatively.The findings showed that the ballistic impact behavior of target composite is substantially influenced by projectile nose shape and incidence angle obliquity.

Corrosion Resistance of Steel in Cracked Reinforced Concrete after Electro-depositon Treatment

An electro-deposition method has been recently proposed to repair cracked reinforced concrete. To evaluate the corrosion resistance of the reinforcing steel in cracked concrete, three different parameters including type of auxiliary electrode, electrode distance, and current density were studied. Tafel polarization curve was used to evaluate the corrosion resistance of the steel. Self-corrosion potential and corrosion current of the steel were tested. The results indicate that the corrosion resistance improvement of the reinforcing steel is optimal as prism titanium mesh is applied as auxiliary electrode, followed by the flaky titanium mesh and the column titanium bar. When the electrode distance is 60 mm, the corrosion resistance improvement of the reinforcing steel is optimal, and with 80 mm electrode distance, the corrosion resistance improvement is the poorest. The property falls in between them when 40 mm electrode distance is used. Moreover, the corrosion resistance improvement of the reinforcing steel increases as the current density goes up.

Preparation of High Impermeable and Crack-resistance Chemical Admixture and Its Mechanism

A kind of high impermeable and crack-resistance chemical admixture ( HICRCA) was prepared , which is a compound chemical admixture composed of an expansion ingredient, density ingredient, and organic hydrophobic poreblocking ingredient. The results of the experiments indicate that the addition of HICRCA improves mortar and concrete in the following performances: (1) perfect workability: slump is more than 22cm, theslump afar 3h is about 16cm; (2) high impermeability:for the mortar, the pervious height under a water pressure of 1.5MPa is 1.5cm,for the concrete, the pervious height under a water pressure of 5.0MPa is 2. 2cm;(3) high crack-resistance: there is a micro-expansion at the age of 90d; (4) high compressivestrength: compared with the controlled concrete, the compressive strengths at the age of 3d and 2Sd are improved by 66.4% and 62.0% , respectively. At the same time, the effects of different curing condition on mortar and concrete expansive andshrinkage performance were studied. In addition, the impermeable and crack-resistance mechanism, was investigatedin the present paper.

Effect of aluminum silicate fiber modification on crack-resistance of a ceramic mould

To improve the crack-resistance of the mould for silica sol bonded quartz based ceramic mould casting,aluminum silicate fibers with the diameter ranging from 5 μm to 25 μm and the length about 1 mm were dispersed in the ceramic mould.The effect of the aluminum silicate fibers on the tensile strength,shrinkage rate and the cracking trend of the ceramic mould were investigated.In the ceramic slurry,quartz sand was applied as ceramic aggregate,silica sol containing 30% silicon dioxide as bonder,and the weight ratio of quartz sand to silica sol was 2.69;the dispersed fibers changed from 0 to 0.24vol.%.The mould samples were formed after the slurry was poured and gelled at room temperature,and then sintered at different temperatures ranging from 100 to 800 ℃ to measure the tensile strength and shrinkage rate.The results show that,with the aluminum silicate fiber addition increasing from 0 to 0.24vol.%,the tensile strength increases linearly from 0.175 MPa to 0.236 MPa,and the shrinkage rate decreases linearly from 1.75% to 1.68% for the ceramic mould sintered at 400 ℃,from 1.37% to 1.31% for the ceramic mould at room temperature.As the sintering temperature was raised from 100 ℃ to 800 ℃,the tensile strength increases,and the shrinkage rate decreases at all temperatures,compared with those without fiber dispersion,but their variation patterns remain the same.Furthermore,the cracking trend of the mould and its decreasing proportion were defined and analyzed quantitatively considering both effects of the fiber dispersion on the strength and shrinkage.The cracking trend appears to decrease linearly with increasing fiber content and to reach the maximum reduction of 28.8% when 0.24vol.% fiber was dispersed.Therefore,the investigation proposes a new method to improve the crack-resistance of the ceramic mould,i.e.,inorganic fiber dispersion into the ceramic mould.

EFFECT OF Na,K AND Ce ON CRACK PROPAGATION RESISTANCE FOR ALLOY 8090

The crack propagation resistance for alloy 8090 sheet decreases with the increase of content of Na and K impurities.An improvement over the fracture toughness and crack initiation resist- ance for the alloy containing Na and K within certain limit may be made by adding 0.05% Ce.This beneficial modification would not be manifested if the alloy contained more Na and K.One of the reasons why Na and K injure the toughness of the alloy might be due to that they cause the precipitation of T_1 phase along grain and subgrain boundaries and accelerate the abnormal growth of recystallized grains.

ROUGHNESS-INDUCED SHEAR RESISTANCE OF MODE Ⅱ CRACK GROWTH

It is obtained in this paper that the fatigue threshold value of mode H was 1.9 times of that of mode Ⅰ in dual-phase steel(DPS),and the normal stress intensity factor range oJ mode Ⅱ branch crack tip was 2.2 times of that of mode Ⅰ.Above results illustrate that the resistance of mode Ⅱ crack growth was higher than that of mode Ⅰ,the former resulting from roughness-induced shear resistance,the latter,crack closure. The mode Ⅱ component can play two important roles in near-threshold fatigue crack growth:(1)increasing crack tip plasticity which accelerates the crack growth and(2)intro- ducing crack surface contact and rubbing to reduce the crack propagation rate.By means of crack closure,the quantity of shear resistance was easily solved in this paper.The friction shear stress strength factor range of mode Ⅱ,K_,is still much higher than the closure stress strength factor range of mode Ⅰ,K_(Ⅰ,cl).This illustrated that the roughness enlarged the second role and played a role of shielding crack tip from mode Ⅱ crack.