Strength criterion for crystalline rocks considering grain size effect and tensile-compressive strength ratio

The macroscopic mechanical properties of rocks are significantly influenced by their microstructure.As a material bonded by mineral grains,the grain morphology of crystalline rock is the primary factor influencing the strength.However,most strength criteria neglect the strength variations caused by different grain characteristics in rocks.Furthermore,the traditional linear criteria tend to overestimate tensile strength and exhibit apex singularity.To address these shortcomings,a piecewise strength criterion that considers the grain size effect has been proposed.A part of an ellipse was employed to construct the envelope of the tensive-shear region on the meridian plane,to accurately reproduce the low tensile-compressive strength ratio.Based on the analysis of experimental data,both linear and exponential modification functions that account for grain size effects were integrated into the proposed criterion.The corresponding finite element algorithm has been implemented.The accuracy and applicability of the proposed criterion were validated by comparing with the experimental data.

新型捕收剂PJ-9在某硫化铜矿浮选中的应用

针对某铜矿山在高碱条件下采用丁基铵黑药进行强压强拉选铜,存在的铜回收率偏低、选矿药剂成本高等问题,在不改变现场工艺流程结构及磨矿细度的前提下,仅通过采用新型铜捕收剂PJ-9,在低碱条件下就实现了该矿山铜硫矿物的有效分离,闭路试验获得铜精矿含铜25.22%、金4.60g/t、银90.80g/t,铜回收率92.03%、金回收率39.51%、银回收率49.41%,比相同条件下采用丁基铵黑药作捕收剂时,铜精矿铜品位高2.77%、铜回收率高2.15个百分点,石灰用量减少800g/t,具有良好的工业应用前景。

大兴安岭岔路口钼尾矿分选试验研究

为了解决大兴安岭岔路口钼矿资源利用效率较低的问题,以钼尾矿为研究对象,通过全优先浮选试验和混合浮选试验、单独浮选试验,考察铅锌回收效果。试验结果表明:与其他三种试验效果相比,钼尾矿过滤-强压强拉全优先浮选试验的效果更好,可以得到品位为60. 70%、回收率为0. 02%的铅精矿,同时可以得到品位为37. 44%、回收率为66. 59%的锌精矿。

Compressive and tensile strength of polymer-based fiber composite sand

Traditional soil additives like Portland cement and lime are prone to cause the brittle fracture behavior of soil,and possibly,environmental impacts.This study explores the potential use of polyurethane organic polymer and sisal fiber in improving the mechanical performance of sand.The effects of polymer content,fiber content,and dry density on the unconfined compressive strength(UCS)and direct tensile strength(DTS)of the polymer-fiber-sand composite were evaluated.The results showed significant increase in UCS and DTS of the reinforced sand with the increase of polymer content,fiber content,and dry density.At high dry density condition,a single peaked stress−strain curve is often observed.Higher polymer content is beneficial to increasing the peak stress,while higher fiber content contributes more to the post-peak stress.The combined use of polymers and fibers in soil reinforcement effectively prevents the propagation and development of cracks under the stress.Scanning electron microscopy(SEM)test was also performed to investigate the micro-structural changes and inter-particle relations.It was found through SEM images that the surface coating,bonding,and filling effects conferred by polymer matrix greatly enhance the interfacial interactions,and hence provide a cohesive environment where the strength of fibers could be readily mobilized.

Static mechanical properties and ductility of biomedical ultrafine-grained commercially pure titanium produced by ECAP process

Equal channel angular pressing(ECAP)is one of the most effective processes to produce ultra-fine grain(UFG)and nanocrystalline(NC)materials.Because the commercially pure titanium exhibits excellent biocompatibility properties,it has a significant potential to be utilized as an implant material.The low static and dynamic strengths of the pure titanium are one of the weaknesses of this material.This defect can be removed by applying the ECAP process on the pure titanium.In this work,the commercially pure titanium Grade2(CP-Ti of Grade2)was pressed at room temperature by the ECAP process via a channel angle of135°for3passes.The microstructural analysis and mechanical tests such as tensile test,hardness test,three-point bending test and Charpy impact test were all carried out on the ECAPed CP-Ti through3passes.The microstructural evolution reveals that by applying the ECAP process,coarse grain(CG)structure develops to UFG/NC structure.Moreover,the results of the mechanical tests show that the process significantly increases the yield and ultimate tensile strengths,bending strength,hardness and fracture toughness of the commercially pure titanium so that it can be used as a replacement for metallic alloys used as biomaterials.

Fatigue properties of rolled AZ31B magnesium alloy plate

Fatigue strength,crack initiation and propagation behavior of rolled AZ31B magnesium alloy plate were investigated. Axial tension-compression fatigue tests were carried out with cylindrical smooth specimens.Two types of specimens were machined with the loading axis parallel(L-specimen)and perpendicular(T-specimen)to rolling direction.Monotonic compressive 0.2%proof stress,tensile strength and tensile elongation were similar for both specimens.On the other hand,monotonic tensile 0.2%proof stress of the L-specimen was slightly higher than that of the T-specimen.Moreover,monotonic compressive 0.2%proof stresses were lower than tensile ones for both specimens.The fatigue strengths of 107cycles of the L-and T-specimens were 95 and 85 MPa,respectively. Compared with the monotonic compressive 0.2%proof stresses,the fatigue strengths were higher for both specimens.In other words, the fatigue crack did not initiate and propagate even though deformation twins were formed in compressive stress under the cyclic tension-compression loading.The fatigue crack initiated at early stage of the fatigue life in low cycle regime regardless of specimen direction.The crack growth rate of the L-specimen was slightly lower than of the T-specimen.Consequently,the fatigue lives of the L-specimen were longer than those of the T-specimen in low cycle regime.

Simulation of rock deformation and mechanical characteristics using clump parallel-bond models

To properly simulate hard rock with a high ratio of the uniaxial compressive strength to tensile strength(UCS/TS) and realistic strength-failure envelope,the rock deformation and mechanical characteristics were discussed in detail when the particle simulation method with the clump parallel-bond model(CPBM) was used to conduct a series of numerical experiments at the specimen scale.Meanwhile,the effects of the loading procedure and crack density on the mechanical behavior of a specimen,which was modeled by the particle simulation method with the CPBM,were investigated.The related numerical results have demonstrated that:1) The uniaxial compressive strength(UCS),tensile strength(TS) and elastic modulus are overestimated when the conventional loading procedure is used in the particle simulation method with the CPBM; 2) The elastic modulus,strength and UCS/TS decrease,while Poisson ratio increases with the increase of the crack density in the particle simulation method with the CPBM; 3) The particle simulation method with the CPBM can be used to reproduce a high value of UCS/TS(>10),as well as a high friction angle and reasonable cohesion strength; 4) As the confining pressure increases,both the peak strength of the simulated specimen and the number of microscopic cracks increase,but the ratio of tensile cracks number to shear cracks number decreases in the particle simulation method with the CPBM; 5) Compared with the conventional parallel-bond model,the CPBM can be used to reproduce more accurate results for simulating the rock deformation and mechanical characteristics.

Rock strength interval analysis using theory of testing blind data and interval estimation

The concepts of rock strength intervals are presented in this work, furthermore, central values of intervals and their corresponding credibility are provided using two-case study based on blind data theory and fuzzy interval estimation. 60 granite specimens are first tested, the compressive strength interval and tensile strength interval are [ 103.68, 219.6 l ] and [7.53, 11,86] MPa, while the tested mean values of compressive strength and tensile strength are 152.86 and 10.14 MPa, the credibilities are less than 58.4% and around 70.4%, respectively, the credibility of shear strength is between 40% and 60%. Then 70 other rock specimens are designed and tested, the similar conclusions can be reached. The results show that the conventional definite values are the particular values within the intervals, and the credibility of them often fails to reach the high-precision engineering requirement. The results demonstrate the feasibility and application potential of this proposed algorithm for the engineering practice. The references for engineering value selection of rock strength under different credibility or according to frequency distribution of central values are provided to increase the reliability and precision of calculation.

Correlations between direct and indirect strength test methods

The difficulties associated with performing direct compression strength tests on rocks lead to the development of indirect test methods for the rock strength assessment. Indirect test methods are simple, more economical, less time-consuming, and easily adaptable to the field. The main aim of this study was to derive correlations between direct and indirect test methods for basalt and rhyolite rock types from Carlin trend deposits in Nevada. In the destructive methods, point load index, block punch index, and splitting tensile strength tests are performed. In the non-destructive methods, Schmidt hammer and ultrasonic pulse velocity tests are performed. Correlations between the direct and indirect compression strength tests are developed using linear and nonlinear regression analysis methods. The results show that the splitting tensile strength has the best correlation with the uniaxial compression strength.Furthermore, the Poisson's ratio has no correlation with any of the direct and indirect test results.

Concrete Containing Marginal Aggregates for Use in Concrete Pavement

The study presented an analysis accessing the feasibility of using concrete containing marginal aggregates in concrete pavement slabs. The physical properties of aggregates were first determined and concrete was produced from them. Marginal aggregates were found to have higher fines, absorption, soundness loss, micro-Deval abrasion loss, LA （Los Angeles） abrasion loss and lower specific gravity and unit weight when compared with standard aggregates. Workability of concrete containing marginal aggregate was found to be similar to concrete containing normal aggregates when Shilstone mix design method was used to optimize the concrete mixes. The compressive strength, splitting tensile, flexural strength and modulus of elasticity of concrete containing marginal aggregates were determined and found to be generally lower than concrete containing standard aggregates. A typical concrete pavement in Florida was modeled in FEACONSIV （finite element analysis of concrete slab） software developed at the University of Florida. Laboratory determined mechanical and thermal properties of concrete were inputted in FEACONS IV and analyzed for maximum induced stresses. Critical stress to strength ratios, i.e., ratio between maximum computed stresses obtained from FEACONS IV to modulus of rupture （strength） of concrete, was used as evaluation criterion for different concrete pavement mixes. It was found that, in general, concrete containing marginal aggregates have higher stress to strength ratios as compared with concrete containing standard aggregates.