Tensile Properties and Prediction Model of Recombinant Bamboo at Different Temperatures

The destruction of recombinant bamboo depends on many factors,and the complex ambient temperature is an important factor affecting its basic mechanical properties.To investigate the failure mechanism and stress–strain relationship of recombinant bamboo at different temperatures,eighteen tensile specimens of recombinant bamboo were tested.The results showed that with increasing ambient temperature,the typical failure modes of recombinant bamboo were flush fracture,toothed failure,and serrated failure.The ultimate tensile strength,ultimate strain and elastic modulus of recombinant bamboo decreased with increasing temperature,and the ultimate tensile stress decreased from 154.07 to 96.55 MPa,a decrease of 37.33%,and the ultimate strain decreased from 0.011 to 0.008,a decrease of 26.57%.Based on the Ramberg-Osgood model and the pseudo‒elastic design method,a predictive model was established for the tensile stress–strain relationship of recombinant bamboo considering the temperature level.The model can accurately evaluate the tensile stress–strain relationship of recombinant bamboo under different temperature conditions.

Tensile stress-strain behavior of metallic alloys

Tensile stress-strain curves of five metallic alloys,i.e.,SKH51,STS316L,Ti-6Al-4V,Al6061and Inconel600were analyzed to investigate the working hardening behavior.The constitutive parameters of three constitutive equations,i.e.,the Hollomon,Swift and Voce equations,were compared by using different methods.A new working hardening parameter was proposed to characterize the working hardening behavior in different deformation stages.It is found that Voce equation is suitable to describe stress-strain curves in large strain region.Meanwhile,the predicting accuracy of ultimate tensile strength by Voce equation is the best.The working hardening behavior of SKH51is different from the other four metallic alloys.

Effects of curing age on compressive and tensile stress-strain behaviors of ecological high ductility cementitious composites

To obtain the design parameters of the structure made by ecological high ductility cementitious composites(Eco-HDCC),the effects of curing age on the compressive and tensile stress-strain relationships were studied.The reaction degree of fly ash,non-evaporable water content and the pH value in pore solution were calculated to reveal the mechanical property.The results indicate that as the curing age increases,the peak compressive strength,peak compressive strain and ultimate tensile strength of Eco-HDCC increase.However,the ultimate compressive strain and ultimate tensile strain of Eco-HDCC decrease with the increase in curing age.Besides,as the curing age increases,the reaction degree of fly ash and non-evaporable water content in Eco-HDCC increase,while the pH value in the pore solution of Eco-HDCC decreases.Finally,the simplified compressive and tensile stress-strain constitutive relationship models of Eco-HDCC with a curing age of 28 d were suggested for the structure design safety.

MODELLING OF TENSILE STRESS-STRAIN CURVE OF WOVEN FABRICS

A general shape of tensile stress-strain curves of woven fabrics is first recognised by puttingtested and predicted results together.An exponential function with two parameters is then selectedfor the prediction of tensile stress-strain relationship.The predicted results by using the proposedfunction show excellent agreement with experimental data.

ANALYSIS OF THE LOCALIZATION OF DAMAGE AND THE COMPLETE (STRESS-STRAIN) RELATION FOR MESOSCOPIC HETEROGENEOUS ROCK UNDER UNIAXIAL TENSILE LOADING

The mechanical behavior of rock under uniaxial tensile loading is different from that of rock under compressive loads. A micromechanics-based model was proposed for mesoscopic heterogeneous brittle rock undergoing irreversible changes of their microscopic structures due to microcrack growth. The complete stress-strain relation including linear elasticity, nonlinear hardening,rapid stress drop and strain softening was obtained. The influence of all microcracks with different sizes and orientations were introduced into the constitutive relation by using the probability density function describing the distribution of orientations and the probability density function describing the distribution of sizes. The influence of Weibull distribution describing the distribution of orientations and Rayleigh function describing the distribution of sizes on the constitutive relation were researched. Theoretical predictions have shown to be consistent with the experimental results.

Biaxial tensile properties and elastic constants evaluation of envelope material for airship

This paper presents an experimental study to determine the tensile properties of the envelope fabric Uretek3216L under biaxial cyclic loading.First the biaxial cyclic tests were carefully carried out on the envelope material to obtain the stress-strain data and the corresponding nonlinearity and orthotropy of the material were analyzed. Then for some determination options with different stress ratios the least squares method minimizing the strain terms was used to calculate the elastic constants from the experimental data.Finally the influences of the determination options with different stress ratios and the reciprocal relationship on the elastic constants were discussed.Results show that the orthotropy of the envelope material can be attributed to the unbalanced crimp of their constitutive yarns in warp and weft directions and the elastic constants vary noticeably with the determination options as well as the normalized stress ratios.In real design practice it is more reasonable to use constants determined for specific stress states in particular stress ratios depending on the project＆#39;s needs.Also calculating the structures with two limitative sets of elastic constants instead of using only one set is recommendable in light of the great variety of the constant＆#39;s values.

Nucleation potency prediction of LaB_6 with E2EM model and its influence on microstructure and tensile properties of Al-7Si-0.3Mg alloy

The edge-to-edge matching(E2EM)crystallographic model was used to predict the orientation relationships(ORs)between LaB6 and Al.Three different possible ORs can be predicted between LaB6 and Al,which are(100)Al||(100)LaB6,[001]Al||[001]LaB6;(110)Al||(110)LaB6,[001]Al||[001]LaB6;and(111)Al||(111)LaB6,[011]Al||[011]LaB6.The prediction results are perfectly confirmed through TEM analysis and prove the nucleation potency of LaB6.The refining efficacy of Al-2La-1B refiner and its influence on the tensile properties were investigated in the as-cast Al-7Si-0.3Mg alloy.According to the results,LaB6 has higher nucleation potency than TiB2,leading to better grain refining efficacy of Al-2La-1B refiner in the as-cast Al-7Si-0.3Mg alloy.Regarding the mechanical performances,tensile properties of the as-cast Al-7Si-0.3Mg casting alloy are prominently improved after addition of Al-2La-1B refiner,due to the refined microstructures.

Stress-Strain Relationship and Failure Criterion for Concrete after Freezing and Thawing Cycles

The research of the failure criterion and one-dimensional stress-strain relationship of deteriorated concrete were carried out. Based on the damage mechanics theory, the dsmage which reflects the alternation of internal state of material were introduced into the formula presented by Desayi and Krishman and the weighted twin-shear strength theory. As a nondestructive examination method in common use, the ultrasonic technique was adopted in the study, and the ultrasonic velocity was used to establish the damage variable. After that, the failure criterion and one-dimensional stress-strain relationship for deteriorated concrete were obtained. Eventually, tests were carried out to study the evolution laws on the damage. The results show that the more freezing and thawing cycles are, the more apparently the failure surface shrinks. Meanwhile, the comparison between theoretical data and experimental data verifies tile rationality of tile damage-based one-dimensional stress-strain relationship proposed.

Stress-strain relationship of unsaturated cohesive soil

A moisture-content based constitutive model was proposed based on the hyperbolic model as an attempt to move towards the implementation of unsaturated soil mechanics into routine geotechnical engineering practice. The stress-strain behavior of in-situ soil at a depth of 5 m was investigated by conducting undrained triaxial compression tests using the remolded soil samples. The test results show that the stress-strain relationship of unsaturated cohesive soil is still hyperbolic. The values of parameters a and b given in the model decrease with increasing the confining pressure for soil samples with the same moisture content and increase with increasing the moisture content for soil samples under the same confining pressure. The relationships between parameters a, b and moisture content were studied for confining pressures of 100, 150, 200 and 250 kPa. The comparison between the measured and predicted stress-strain curves for an additional group of soil samples, having a moisture content of 25.4%, shows that the proposed moisture content-dependent hyperbolic model provides a good prediction of stress-strain behavior of unsaturated cohesive soil.

Changes of Stress-Strain Relationship of Rabbit Femoral Vein after Simulated Weightlessness

Objective: To observe the effect of simulated weightlessness on stress-strain relationship and the structural change of rabbit femoral vein. Methods: After seting up the Head-Down Tilt (-20°) (HDT) model to simulate weightlessness, 24 healthy male New-Zealand Rabbits were randomly divided into HDT-21d group, HDT-10d group and control group, with 8 in each. Femoral venous strips and rings were used to make uniaxial tensile test of the longitudinal and circumferential specimens of the vessels. At last we observed the microstructure of femoral vein wall in 3 groups. Results : With the increasing of load stress, both longitudinal and circumferential strains of vein samples from 3 groups increased significantly (P<0. 01). With the decrease of unload stress, strains decrease obviously (P<0. 01). The unloaded longitudinal and the circumferential strain from 3 groups increased much than those of the loaded. Under the same stress (longitudinal 0-2. 0 g, circumferential 0. 5-1. 0 g) , HDT-21d group and HDT-10d group increased obviously in tlie longitudinal or circumferential strain (load and unload) than control, and HDT-21d increased much than that of HDT-10d. The contents and structures of femoral vein walls of HDT-rabbits changed significantly. Some endotheli-um cells of femoral vein became short, columnar or cubic even fell off. Smooth muscle layers became thinner. Conclusion:The compliance of femoral venous increased significantly after weightlessness-simulation and increased much obviously after 21d-HDT than that of 10 d. The structure of femoral vein wall changed obviously. The changes may be one reason for the increase of femoral vein compliance.

Tensile bond anchorage properties of Australian 500N steel bars in concrete

In order to investigate the tensile bond anchorage properties of Australian 500N steel bars in concrete, 111 pullout tests were conducted. The precise bond slip values have been gained by using the laser displacement sensor with high resolution, including the complete bond-slip curves. How the main anchorage factors such as concrete strength, bar diameter （8, I0, 12, 16, 20, 24, 28, 32 and 36 mm） the concrete covered, embedded length and transverse reinforcement influencing the bond anchorage properties was studied under tensile condition. The process of the tensile force-slip failure for Australian 500N reinforcing steel can be divided into five stages： elastic stage, local slip stage, slip in ascent stage, slip in descent stage and remnant stage. The formula for calculating the tensile bond strength of Australian 500N reinforcing bar in concrete was proposed according to the test results, including the consistent model for tensile bond-slip relationship.

Nonlinear model characterizing stress-strain relationship and permeability change of contact compression fracture at closing stage

Understanding the stress-strain relationship and permeability change for contact compression fracture at closing stage has been a hot issue for a long time.Previous investigations of this topic were mainly focused on experimental tests;however,theoretical approaches were rarely reported.Based on this,this paper focuses on the contact fracture at closing stage when rock is uniaxially loaded,and then a theoretical model is proposed.Based on the change of fracture elasticity modulus,it shows that as crack apertures are gradually reduced in the loading process,the permeability of rock sample will decrease progressively.This scenario shows that theoretical computation matches well with the experimental results.Finally,the effects of ratio of sample size to fracture aperture(n).pore pressure(P),and initial aperture(b) on stress-strain relationship and permeability change for contact compression fracture at closing stage are analyzed.

A novel binary effective medium model to describe the prepeak stressstrain relationship of combined bodies of rock-like material and rock

Combined bodies of rock-like material and rock are widely encountered in geotechnical engineering,such as tunnels and mines.The existing theoretical models describing the stress-strain relationship of a combined body lack a binary feature.Based on effective medium theory,this paper presents the governing equation of the“elastic modulus”for combined and single bodies under triaxial compressive tests.A binary effective medium model is then established.Based on the compressive experiment of concretegranite combined bodies,the feasibility of determining the stress threshold based on crack axial strain is discussed,and the model is verified.The model is further extended to coal-rock combined bodies of more diverse types,and the variation laws of the compressive mechanical parameters are then discussed.The results show that the fitting accuracy of the model with the experimental curves of the concretegranite combined bodies and various types of coal-rock combined bodies are over 95%.The crack axial strain method can replace the crack volumetric strain method,which clarifies the physical meanings of the model parameters.The variation laws of matrix parameters and crack parameters are discussed in depth and are expected to be more widely used in geotechnical engineering.

Tensile behaviors of ecological high ductility cementitious composites exposed to interactive freeze-thaw-carbonation and single carbonation

To explore the tensile property parameters in the structural design of bridge deck link slabs made by ecological high ductility cementitious composites (Eco-HDCC), the tensile properties of Eco-HDCC exposed to interactive freeze-thaw-carbonation cycles and single carbonation cycles were studied. The carbonation front of Eco-HDCC was determined by X-ray diffraction and differential scanning calorimetry-thermal gravimetric methods. Results indicate that the carbonation front of Eco-HDCC after interaction tests is deeper than that of Eco-HDCC after single carbonation tests. In addition, the ultimate tensile strength for Eco-HDCC shows an increasing trend after the interaction of 1 to 5 cycles compared with that of virgin specimens, while the ultimate tensile strength decreases after the interaction of 10 to 15 cycles. For single carbonation tests, the ultimate tensile strength of Eco-HDCC increases as cycles increase. After being subjected to interaction and single carbonation environments, both the ultimate tensile strain and tensile strain energy of Eco-HDCC decrease as cycles increase, and the decrease degrees of Eco-HDCC after interaction cycles are larger than those of Eco-HDCC after single carbonation. For general consideration, the tensile stress-strain relationship of Eco-HDCC after the interaction of 15 cycles can be adopted in the design of bridge deck link slabs for the purpose of safety.

Effect of Engineering Character on Stress-Strain Relationship in Post-Peak Area

Constitutive experiments are the base of all rock mechanics works. The effect of engineering character on constitutive law is a new problem of rock mechanics. The results of series specimens based on the uniaxial and plane strain compression experiments were presented and discussed. It is found that engineering or experiment character has obvious effects on stress-strain relationship and especially on mechanic parameters in post-peak area. And the law of size effect of softening materials was also discussed.

UHPC直拉试验方法与本构关系研究

超高性能混凝土(Ultra-high performance concrete, UHPC)单轴拉伸(直拉)试验是分析UHPC抗拉性能和直拉本构关系的基础性试验,经过对其试件形状与尺寸的优化,试验成功率已得到了较大提升。但由于试件连接方式和局部加强方式的差异,各机构试验成功率参差不齐。为进一步保证直拉试验成功率,采用试验研究和数值模拟的方法系统分析了常见的四种试件连接方式和三种试件局部加强方式对试验成功率的影响,比选出最优试验方法。结果表明:面内夹持装置具有连接可靠、操作简单的优点,适合推广。但夹具的尺寸加工误差或微变形可能导致其与试件的接触面变窄、加剧夹持引发的试件应力集中,致使主裂纹位于测距范围之外;试件与夹具的接触区域进行柔性加强(粘贴碳纤维布)和刚性加强(粘贴铝片)均能有效解决上述问题,提高试验成功率。此外,采用比选的直拉试验方法,探究了钢纤维长径比和体积率对UHPC直拉损伤本构关系的影响。通过声发射(Acoustic emission, AE)监测探究了UHPC在直拉荷载作用下的损伤演化规律,利用声发射参数(累积计数比)构建损伤因子,得到了考虑钢纤维影响的UHPC直拉损伤本构关系。

Stress-strain relationship for reactive powder concrete with recycled powder under uniaxial compression

The recycled powder(RP)from construction wastes can be used to partially replace cement in the preparation of reactive powder concrete.In this paper,reactive powder concrete mixtures with RP partially replacing cement,and natural sand instead of quartz,are developed.Standard curing is used,instead of steam curing that is normally requested by standard for reactive powder concrete.The influences of RP replacement ratio(0%,10%,20%,30%),silica fume proportion(10%,15%,20%),and steel fiber proportion(0%,1%,2%)are investigated.The effects of RP,silica fume,and steel fiber proportion on compressive strength,elastic modulus,and relative absorption energy are analyzed,and theoretical models for compressive strength,elastic modulus,and relative absorption energy are established.A constitutive model for the uniaxial compressive stress-strain relationship of reactive powder concrete with RP is developed.With the increase of RP replacement ratio from 0% to 30%,the compressive strength decreases by 42% and elastic modulus decreases by 24%.

不同冷却方式对高温后600MPa级高强钢筋拉伸性能的影响

为了评估火灾后高强钢筋的性能演化规律,文章研究了空气中冷却、炉内冷却和浸水冷却3种方式对高温作用后高强钢筋应力-应变曲线的影响,分析了屈服强度、极限强度、强屈比、弹性模量和断后伸长率等力学参数的变化规律。结果表明:1)高强钢筋经历高温后在气冷、炉冷和水冷作用下,其应力-应变曲线仍表现出明显的屈服台阶;2)与常温时相比,极限强度和屈服强度均呈现出下降趋势,而强屈比变化并不显著;3)不同冷却方式对高强钢筋的弹性模量和断后伸长率影响程度不同,其中水冷作用对钢筋的弹性模量影响最大,炉冷作用对钢筋的断后伸长率影响最大。此外,通过建立不同冷却方式下高强钢筋的拉伸本构关系,为高强钢筋在抗火结构中的应用提供依据。

Mechanical Properties and Stress Strain Relationship Models for Bamboo Scrimber

In order to investigate the basic mechanical properties and stress strain relationship model for bamboo scrimber manufactured based on a new technique,a large quantities of experiments have been carried out.Based on the analysis of the test results,the following conclusions can be drawn.Two main typical failure modes were classified for bamboo scrimber specimens both under tension parallel to grain and tension perpendicular to grain.Brittle failure happened for all tensile tests.The slope values for the elastic stages have bigger discreteness compared with those for the specimens under tensile parallel to grain.The failure modes for bamboo scrimber specimens under compression parallel to grain could be divided into four.Only one main failure mode happened both for the bending specimens and the shear specimens.With the COV values of 28.64 and 25.72 respectively,the values for the strength and elastic modulus under tensile perpendicular to grain have the largest discreteness for bamboo scrimber.From the point of CHV values,the relationship among the mechanical parameters for bamboo scrimber were proposed based on the test results.Compared with other green building materials,bamboo scrimber manufactured based on a new technique has better mechanical performance and could be used in construction area.Three stress strain relationship models which are four-linear model,quadratic function model,and cubic function model were proposed for bamboo scrimber specimens manufactured based on a new technique.The latter two models gives better prediction for stress strain relationship in elastic plastic stage.

珊瑚-陶粒混凝土力学性能试验研究

为了促进轻骨料混凝土在沿海及岛礁建设中的应用,以珊瑚骨料部分替代陶粒,配制珊瑚-陶粒混合骨料混凝土。通过轴心受压试验和劈裂抗拉试验,分析了不同取代率下珊瑚-陶粒混凝土的抗压强度、劈裂抗拉强度、峰值应变、弹性模量和延性等力学性能,建立了强度换算关系式,探讨了不同的本构关系模型。结果表明:随着珊瑚骨料取代率的增大,珊瑚-陶粒混凝土的抗压强度和劈裂抗拉强度逐渐降低,但是相比全陶粒混凝土的降低幅度不大;峰值应变先上升后下降,取代率大于75%时显著降低;弹性模量先减小后增大,取代率为50%时最小。所建立的抗压强度和劈裂抗拉强度换算关系式的计算结果与试验结果能较好吻合。