FRP约束混凝土的基本力学性能

本文简述了ＦＲＰ约束混凝土柱的工作机理,并根据ＦＲＰ材料的破坏准则以及Ｍ．Ｊ．Ｎ．Ｐｒｉｅｓｔｌｅｙ提出的强度计算公式为基础,结合约束混凝土的单轴等效应力－应变关系,确定了ＦＲＰ约束混凝土的抗压强度,应力－应变关系和荷载－变形关系。     

Measuring Hydro-Static Dependent Constitutive Behaviour of Adhesives Using a Bend Specimen

A simple bend test and associated equations that determine, simultaneously, both the tensile and compressive uniaxial stress-strain behaviour of a bulk adhesive are presented. From this, the ratio of the flow stress in compression to tension (S) can be found. Such data are required if a meaningful elastoplastic stress analysis of an adhesive joint is to be carried out. Experimental results for both the tensile and compressive stress-strain data are obtained for an epoxy specimen using this technique. The tensile data are compared with the results from uniaxial tensile tests on flat dumbell specimens of the same material and the good correlation that is found indicates that this is a reliable technique. Values of the ratio (S) for this adhesive are calculated as a function of both strain hardening and work hardening parameters. These results indicate that this technique complements standard test techniques and provides an elegant method not only of obtaining the ratio (S) but also of deriving uniaxial stress-strain curves.     

Crack softening zone in plain concrete under static loading

Starting from the fictitious crack model the softening zone at the tip of a discrete crack in concrete is studied. Using a power relation for the stress distribution in the softening zone, the extension of this zone is a function of the exponent. If the fully softened cross-section is taken as a failure criterion, the exponent can be considered as a measure for the true strength of the material. Supporting the theory concrete plates were tested under uniaxial tensile loading. Since stress distribution cannot be measured the strain distribution around the crack was determined. Using the complete stress-strain relation the strains were translated into stresses. The test results are discussed and compared to the theoretical model. Further studies are encouraged to improve the accuracy of the experiments and to extend the model to cyclic loading.     

On the interrelation of rubber elastic stress-strain curves under different types of strain

With specially shaped samples it is possible to study the stress-strain relation σ(γ) in simple shear up to large shear deformation γ. Measurements of σ(γ) on synthetic polyisoprene, IR 305, differently crosslinked with dicumylperoxide, are reported and compared with those for uniaxial extension on the same materials. Using the simple deformation geometry including shearbands proposed in the meander model (1), both stress-strain relations can be converted into each other. These results favor the applied superstructural model and moreover show that the deformation behavior of rubbers is governed by one material law, σ(γ).     

Failure Assessment on a Strip Biaxial Tension Specimen for a HTPB-Based Propellant Material

This paper indicates the possibility of assessing the failure of a strip biaxial tension specimen from the non-linear stress-strain behaviour of a uniaxial tension specimen which is useful for characterizing the propellant material. In order to examine the adequacy of the analytical and finite element methods, test data existing on a HTPB-based propellant material is used. Failure predictions on a strip biaxial tension specimen are found to be in reasonably good agreement with test results.     

Stress-strain relations of steel fiber reinforced concrete under repeated compressive load

The purpose of the present paper is to examine the hysteretic stress-strain behavior of steel fiber reinforced concrete and steel fiber reinforced mortar under uniaxial compression and to propose mathematical expressions of stress-strain curves based on experimental data. The stress-strain relations are examined in terms of the volume fraction and the aspect ratio of steel fiber. It is indicated in this paper that the normalized stress - strain curves can be described by the proposed simple numerical model with a fairly good accuracy.     

EPDM/PA硫化共混物力学行为的模拟

采用Rivlin模型对EPDM／聚酰胺（PA）硫化共混物的单轴拉伸力学行为进行模拟。结果表明，2个参数的Ri。lin模型可以较好地描述PA用量不超过30份时EPDM／PA静态硫化共混物的应力-应变行为；3和5个参数的Rivlin模型在PA试验用量范围内对静态硫化共混物的拟合效果很好。3个参数的Rivlin模型可以很好地描述EP-DM／PA动态硫化共混物的应力-应变行为，但PA用量过大时，EPDM／PA动态硫化共混物显示出明显的塑料特征，拟合曲线与试验数据有所偏离。     

铝/丁羟胶粘接强度的率相关特性研究

参照试验标准设计了用于测量铝与端羟基聚丁二烯(丁羟胶)粘接强度的单轴拉伸试验,通过变换拉伸速率获得了粘接强度与拉伸速率的关系,随着拉伸速率的增大粘接强度不断升高。同时进行了丁羟胶片的单轴拉伸试验并获得了200%应变范围内的应力-应变曲线。结果发现,丁羟胶作为铝板的胶粘剂的粘接强度明显大于丁羟胶片自身的强度,且粘接时丁羟胶的伸长率明显下降。     

轴压与偏压状态下混凝土损伤全过程声发射特征参数分析

声发射技术可以评估混凝土的损伤演化过程。为合理描述混凝土的受压损伤演化过程,开展了轴压和偏压状态下混凝土损伤全过程的声发射试验,分析了轴压和偏压状态下混凝土损伤全过程声发射特征参数的演化规律,进而合理遴选了描述混凝土损伤演化过程的声发射特征参数,揭示了混凝土应力-应变曲线特征点与声发射特征参数特征点之间的对应关系。分析表明:振铃计数、持续时间、幅值、信号强度和平均频率可以较好地表征轴压与偏压状态下混凝土损伤的演化规律;混凝土试件受压破坏过程中声发射特征参数特征点与应力-应变曲线特征点之间具有高度的相关性,其中声发射特征参数特征点中的第一个分界点对应于应力-应变曲线弹性阶段的起点,第二个分界点对应于应力-应变曲线的峰值应力点,信号强度的最大突变点对应于应力-应变曲线的开裂点。     

结构异性煤体单轴/三轴冲击动力学性能研究

井下深孔爆破致裂是提高低渗煤层渗透率的重要措施之一,但由于煤层层理因素影响,在不同方向上的爆破致裂效果存在显著差异.采用分离式霍布金森压杆实验装置,对从垂直于层理方向和平行于层理方向进行取芯的煤样,分别进行冲击荷载为0.1,0.15,0.2,0.3,0.5 MPa的单/三轴SHPB冲击实验,分析结构异性煤体的冲击动力学...     

HTPB推进剂的低温力学性能

通过低温和低温恢复常温单轴拉伸试验,考察了低温条件下HTPB推进剂力学性能的变化情况,用SEM扫描电镜观察了推进剂拉伸断面形貌,分析了所得HTPB推进剂的拉伸应力-应变曲线和力学性能特性。结果表明,在低温拉伸条件下,HTPB推进剂主要表现为基体撕裂和颗粒脆断,而在低温恢复常温拉伸条件下,主要以"脱湿"破坏为主。推进剂的低温拉伸曲线具有明显的屈服现象发生,说明推进剂的屈服现象与低温有关。推进剂在低温和低温恢复常温条件下的最大抗拉强度、弹性模量和延伸率等力学性能呈现出不同的变化规律。     

受冻融混凝土动态抗压特性试验研究

通过对受冻融混凝土试件进行单轴动态抗压试验,分析了冻融次数(0、25、50和75次)及应变速率(10-5 s-1、10-4 s-1和10-3 s-1)对混凝土抗压强度、峰值应变和应力-应变曲线的影响.结果表明:不同应变速率下受冻融混凝土的破坏特点有所差异,随着应变率的提高,试件断面更加平整,有较多粗骨料发生破坏;相同冻融次数下,随着应变率的增大,抗压强度明显增加,而峰值应变减小,应力-应变全曲线的峰值点呈前移和上升的趋势,曲线上升段斜率逐渐增大且长度也随之增大,下降段越为陡峭,表现明显的脆性特点;相同应变率下,随着冻融次数的增加,抗压强度均有所降低,而峰值应变逐渐增大,应力-应变全曲线的峰值点表现为明显下降和后移的趋势,其曲线下包面积减小,吸收能量的能力变差;通过对试验结果分析,建立了考虑应变率影响的受冻混凝土受压应力-应变曲线方程.     

Continuous damage model for load-response estimation of concrete

Estimation of the stress-strain relationship for concrete in uniaxial tension is done by means of a semiempirical damage model. The damage is a measure of the relative portion of pores and cracks in the material. The model is related to stress-strain curves published by Evans and Marathe (3).     

Behavior of high strength concrete with and without steel fiber reinforcement in triaxial compression

Based on an extensive experimental program, this paper studies the behavior of high strength concrete and steel fiber reinforced high strength concrete under uniaxial and triaxial compression. Triaxial stress-strain relations and failure criteria are used to evaluate the effect of steel fiber reinforcement on the mechanical properties of high strength concrete in triaxial compression, which is found to be insignificant.     

The large strain compression,tension, and simple shear of polycarbonate

Polymeric materials subjected to large strains undergo an evolution in molecular orientation. The developing orientation and corresponding strengthening are highly dependent on the state of strain. In this paper, we examine and compare the very different stress-strain results of polycarbonate produced from four types of mechanical testing: uniaxial compression, plane strain compression, uniaxial tension, and simple shear. These tests produce different states of orientation within the material and, in the case of simple shear, the principle axes of orientation rotate during the deformation. The ability of the recent constitutive model of Arruda and Boyce (1992) to predict the to predict the observed behavior is evaluated. The model has been incoporated into a finite element code in order to properly simulate the material behavior during the inhomogenous deformations of tension (cold drawing) and simple shear. The material properties of the model are obtained from the uniaxial compression test and the model is then found to be truly predictive of the other states of deformation demonstrating its fully three dimensional capability. The disadvantages of the tensile and simple shear tests for obtaining the data needed to accurately quantify the large strain material behavior of polymers are shown and discussed.     

An experimental investigation of the large-strain tensile behavior of neat and rubber-toughened polycarbonate

The large-strain tensile behavior of polycarbonate and polycarbonate filled with several volume fractions (f) of rubber particles is studied via an optical technique. Digital image correlation is used to determine, in two dimensions, the local displacement gradients and full-field displacements during a uniaxial tension test. Full-field strain contours, macroscopic true stress-strain behavior, and local volumetric strain are reduced from the raw test data. Full-field strain contours exhibit a decreasing degree of localization with increasing f. The true stress-strain results show a decrease in modulus, yield stress, post-yield strain softening, and subsequent strain hardening with increasing f. The volumetric strain decreases with increasing f as well. In the case of the neat polymer, comparisons are made to a three-dimensional finite element simulation.     

砂的颗粒级配对SHCC抗拉性能的影响

本文研究了颗粒级配不同的同批次砂对应变硬化水泥基复合材料(SHCC)抗拉性能的影响。在前期试验基础上,通过流动扩展度试验得到了具有最佳流动性的SHCC;通过对哑铃型试件进行单轴拉伸试验,获得采用不同颗粒级配砂配制的SHCC的应力-应变曲线。结果表明,采用最大粒径为0.3mm的级配砂比最大粒径为0.6mm和1.18mm级配砂所配制出的SHCC能够更好地实现应变硬化和多点开裂,且极限拉应变可达5.8%左右。本文所得结论可为SHCC的科研和工程应用提供理论依据。     

水泥土力学性能的试验研究

利用内蒙古河套粉质粘土拌制水泥土,掺入比分别取5%、10%、15%、20%、25%,养护龄期取7 d、28 d、60 d、90 d,通过单轴受压试验,取得了水泥土无侧限抗压强度、应力-应变关系的变化规律,并分析了对其影响的因素,提出了这种水泥土的单轴受压下应力-应变全曲线本构方程,定量的分析了龄期、水泥掺入比对水泥粘土的力学性能的影响,为其应用于实际工程提供实验依据.     

玄武岩纤维混凝土应力应变关系及孔结构分析

为了探究纤维掺量对玄武岩纤维混凝土宏、微观性能的影响规律,采用数字图像相关方法与微观气孔结构分析仪对不同纤维掺量的混凝土试件进行试验研究,通过数据回归建立了纤维掺量与平均峰值应力之间关系,给出了玄武岩纤维混凝土单轴受压应力-应变曲线上升段表达式;结合微观孔结构,建立了平均峰值应力与含气量、平均气泡弦长、气孔间距、比表面积相关公式,同时采用分形维数定量描述微观孔结构与玄武岩纤维混凝土抗压强度、弹性模量的关系.结果表明:玄武岩纤维的加入能够提高混凝土平均峰值应力和峰值应变,对试件应力-应变关系曲线上升段改变不明显;玄武岩纤维的加入能够减少混凝土内部缺陷,降低混凝土含气量、减小平均气泡弦长,使混凝土内部孔结构得到优化,孔隙分布较为均匀,抗压强度提高,割线模量有所下降.     

Impact of characteristic length and loading rate upon dynamic constitutive behavior and fracture process in alumina ceramics

Understanding the impact performance of ceramic materials requires accurate corresponding relationship between mechanical response and fracture behavior. In this study, constitutive behaviors of alumina ceramics were successfully determined via split-Hopkinson pressure bar (SHPB) system coupled with high-speed camera to track the deformation and failure process. Failure strength of alumina demonstrated a strong dependency on strain rate beyond a critical value (namely transition strain rate). Inelastic deformation in the dynamic stress-strain curves implied that degradation of modulus does occur. The incorporating such degradation (damage evolution) in modulus enabled a more accurate evaluation of transition strain rate as a function of characteristic length of specimen. On-line observation revealed that longitudinal cracks dominated the failure process of alumina with negligible interfacial friction. However, interfacial friction became significant with the decreased characteristic length, thus the inclined cracks dominated fracture in alumina. It was found that the effect of interfacial friction can be minimized by lowering the impact velocity to maintain the uniaxial loading status in SHPB loads. Finally, it is suggested that an aspect ratio of 1.0 for the specimen should be suitable for alumina due to its insensitivity to interfacial friction within the achievable strain rate.