高延性水泥基复合材料高温作用后的拉伸性能

高温是高延性水泥基复合材料(ECC)在服役过程中可能面临的最不利工况之一,对比研究了聚乙烯醇纤维增强ECC(PVA-ECC)与钢纤维/聚乙烯醇纤维混杂增强ECC(HyECC)在常温以及200℃、400℃、600℃高温作用后的拉伸性能。研究发现,常温下利用钢纤维等量替代PVA纤维将劣化PVA-ECC的拉伸应变硬化能力。高温对PVA-ECC和HyECC的拉伸强度和拉伸韧性均有明显的劣化作用,高温作用后均已不具备拉伸应变硬化能力;PVA-ECC的拉伸强度与拉伸韧性随温度呈指数型衰减,钢纤维可以减缓HyECC拉伸强度与拉伸韧性的衰减速率;高温作用改变了PVA-ECC和HyECC的微观结构,PVA纤维在200℃时的软化以及400℃后的分解是2种ECC材料拉伸性能高温劣化的主要原因。     

不同赋存深度岩石的动态断裂韧性与拉伸强度研究

按照国际岩石力学学会试验规范以及工程岩体试验方法标准(GB/T50266-99),对不同赋存深度的玄武岩试件分别进行动态断裂韧性测试和单轴拉伸强度测试,得到动态断裂韧性与拉伸强度之间可能存在一定的关系;并从岩石破坏的力学机制角度,分析动态断裂韧性与拉伸强度之间存在联系的根本原因:两者均是由于岩石内部微裂纹受到拉应力作用而引起微裂纹的扩展、互相贯通,从而导致岩石的破坏。根据动态断裂韧性与拉伸强度之间可能存在的关系,可以由拉伸强度的测试结果推测试件的动态断裂韧性值,将大大简化动态断裂韧性测试的繁琐性。     

大粒径钢纤维混凝土劈拉性能研究

基于水利工程中对大粒径混凝土的防裂增韧要求,进行了二级配骨料钢纤维混凝土试件的劈拉试验,探讨了钢纤维体积率(钢纤维掺量)对混凝土劈拉强度的影响,提出丁提高钢纤维对混凝土劈拉强度影响系数的思路和劈拉强度的计算公式.结果表明:钢纤维对二级配混凝土劈托强度有良好的增强效果.     

橡胶粉对C60 HPC高温后力学性能的影响

为研究橡胶粉对C60高性能混凝土高温后断裂性能的影响,对橡胶粉掺量为5％和8％的C60 HPC进行高温试验,测定不同高温后试件的抗压强度及劈裂抗拉强度,并基于双K断裂理论对试件进行三点弯曲断裂试验,计算断裂参数,绘制起裂韧度、失稳韧度随温度的变化曲线.结果表明,随着温度上升,C60 HPC抗压强度和劈裂抗拉强度呈下降趋...     

基于半圆弯拉试验的煤样抗拉及断裂性能研究

 为研究准静态加载条件下煤的抗拉及断裂性能,采用巴西圆盘劈裂法和半圆弯拉法对煤样进行抗拉性能对比测试;并开展不同切缝深度的半圆弯拉煤样断裂性能测试分析,探讨平面应变断裂韧度KIC和J积分断裂韧度对评价煤的断裂性能的适用性,研究切缝深度对半圆弯拉煤样的2种断裂韧度测定结果的影响;并结合受载过程中煤样表面应变监测和破坏后试样的工业CT扫描图像分别对煤样受载变形特征和破坏后裂纹展布规律进行分析。研究表明：半圆弯拉试验更适于测定煤的抗拉强度;当量纲一化的切缝深度 = 0.28时半圆弯拉煤样平面应变断裂韧度KIC离散度最小;煤样的J积分断裂韧度离散度更小,且更适用于评价煤的断裂性能。     

PVA纤维混凝土弯折性能试验研究浅析

混凝土是一种脆性材料，其抗裂性能较差，在其中掺入合成纤维，可增加其韧性、提高早期和极限抗拉强度以及局部强度。本文利用正交原理，从现成的试验数据中挑选出具有代表性的数据。分别以初裂荷载、弯折抗拉、初裂挠度、极限荷载、极限抗拉、极限挠度为考核指标，对PVA纤维掺量和龄期等因素进行极差和方差分析。分析结果表明：无论哪种龄期，PVA纤维混凝土梁的韧性要比普通混凝土梁高，且随纤维含量的增加而增大；龄期对混凝土梁的韧性影响不明显。     

Influence of steel fibres on strength and ductility of normal and lightweight high strength concrete

This paper presents the results of a series of experiments conducted to investigate the effectiveness of fibre inclusion in the improvement of mechanical performance of concrete with regard to concrete type and specimen size. Lightweight aggregate concrete and limestone aggregate concrete with and without steel fibres were used in the study. The compressive strength of the concrete mixes varied between 90 and 115 MPa and the fibre content was 1% by volume. Splitting tests on prisms and three-point bending test on notched beams were carried out on specimens of varying sizes to examine the size effect on splitting strength, flexural strength and toughness.

The experimental findings indicate that the low volume of fibre has little effect on compressive strength but improve remarkably splitting tensile strength, flexural strength and toughness. The increase in splitting tensile strength, flexural strength and toughness index for lightweight concrete seems much higher than that of normal aggregate concrete.

The size effect on prism splitting tensile strength is not significant beyond a critical (transition) size. There are apparent size effects on flexural strength and toughness index. As the specimen size increases, splitting and flexural strengths appear to decrease, and fracture behaviour tends to be more brittle.     

Effects of limestone crusher dust and steel fibers on concrete

Effects of crusher dust content in aggregate on properties of fresh and hardened concrete are not very well known. On the other hand, it is known that short discrete fibers delay the propagation of microcracks and improve some properties of concrete. In this research, the effect of crusher dust replacement levels of fine aggregate and hooked-end steel fibers with different aspect ratios and different volumes on some properties of concrete was investigated. All mixes were tested for compressive and splitting tensile strength, water penetration, flexural toughness energy and impact energy. Relations such as compressive strength/splitting tensile strength/water penetration depth/flexural toughness energy/impact energy-dust replacement level-fiber reinforcement index were also determined.     

钢纤维混凝土劈拉及弯曲强度和韧性研究

通过钢纤维混凝土劈拉强度、弯曲强度和弯曲韧性的实验,研究了混凝土的劈拉强度、弯曲强度和弯曲韧性随着钢纤维掺量的增加有不同幅度的增长,同时钢纤维的长径比和钢纤维根数对钢纤维混凝土的性能也有重大影响。     

Fracture mechanics analysis of cracked discs of anisotropic rock using the boundary element method

This paper is the second of a series of two papers dealing with the determination of the deformability, tensile strength and fracturing of anisotropic rocks by diametral compression (Brazilian test) of discs of rock. It is shown how a new formulation of the Boundary Element Method (BEM), proposed recently by the authors, can be used to determine the stress intensity factors (SIFs) and the fracture toughness of anisotropic rocks from the results of diametral compression tests on initially cracked discs. Crack initiation angles and propagation paths can also be predicted using a numerical procedure based on the BEM and maximum tensile stress criterion. Numerical examples of calculation of mixed mode SIFs are presented for both isotropic and anisotropic media. The calculated SIFs for the special isotropic case are found to be in good agreement with those reported by previous authors. Diametral loading tests were conducted on Cracked Straight Through Brazilian Disc (CSTBD) specimens of a shale in order to evaluate its fracture toughness, the angle of crack initiation and the path of crack propagation. It was found that the numerical simulations of crack initiation and propagation in the CSTBD specimens of the shale were in good agreement with the experimental observations.     

Investigation of meso-failure behaviors of Jinping marble using SEM with bending loading system

In this study, the meso-failure mechanism and fracture surface of Jinping marble were investigated by means of scanning electron microscope(SEM) with bending loading system and laser-scanner equipment. The Yantang and Baishan marbles specimens from Jinping II hydropower station were used. Test results show that the fracture toughness and mechanical behaviors of Yantang marble were basically higher than those of Baishan marble. This is mainly due to the fact that Baishan marble contains a large percentage of dolomite and minor mica. Crack propagation path and fracture morphology indicated that the direction of tensile stress has a significant effect on the mechanical behaviors and fracture toughness of Baishan marble. For Yantang and Baishan marbles, a large number of microcracks around the main crack tip were observed when the direction of tensile stress was parallel to the bedding plane.Conversely, few microcracks occurred when the direction of tensile stress was perpendicular to the bedding plane. The presence of a large number of microcracks at the main crack tip decreased the global fracture toughness of marble. The results of three-point bending tests showed that the average bearing capacity of intact marble is 3.4 times the notched marble, but the ductility property of the defective marble after peak load is better than that of the intact marble. Hence, large deformation may be generated before failure of intact marbles at Jinping II hydropower station. The fractal dimension of fracture surface was also calculated by the cube covering method. Observational result showed that the largest fractal dimension of Yantang marble is captured when the direction of tensile stress is parallel to the bedding plane. However, the fractal dimension of fracture surface of Yantang and Baishan marbles with tensile stress vertical to the bedding plane is relatively small. The fractal dimension can also be used to characterize the roughness of fracture surface of rock materials.     

利用测井资料预测深部地层岩石断裂韧性

涉及在石油开发的深层岩土工程中,岩石断裂韧性参数的获取,对工程 设计有着重要的意义。但以往通常采取深井岩芯以获取岩石断裂韧性,成本昂贵,加之在无围压条件下测试,不能反映深部地层的真实性质。在有围压岩石断裂韧性测试数据的基础上,发现断裂韧性与岩石抗拉强度之间存在较好的统计关系,据此利用测井数据建立了预测深部地层岩石断裂韧性的模型。     

钢纤维膨胀混凝土力学性能试验研究

对钢纤维膨胀混凝土抗压强度、抗拉强度、抗折强度及抗折韧性进行了试验研究,试验结果表明：钢纤维和膨胀剂的联合作用,大大提高了混凝土的抗压强度、劈拉强度及抗折初裂强度,并在一定程度上提高了混凝土的极限抗折强度及抗折韧性。     

纤维加筋土的动力特性试验研究

研究用聚丙烯纤维加筋粘性土抵抗静动荷载作用下土体发生张拉裂缝的功能。试验研究结果表明，纤维加筋土的静动力抗张拉、抗断裂性质，诸如极限拉应力、极限技应变、动强度、动模量、临界断裂韧度等，与素土相比都有很大的提高。由此说明纤维加筋粘性土是一种比较理想的土坝防渗抗震填料。     

水作用下砂岩断裂力学效应试验研究

 消落带是库岸边坡稳定的敏感地带,在库水位反复升降作用下,岩石的断裂韧度变化规律对库岸边坡的稳定性十分关键。以三峡库区典型库岸边坡砂岩为研究对象,针对库岸边坡消落带的实际赋存环境,设计长期浸泡和浸泡–风干循环作用2种试验方案。试验结果表明：(1) 长期浸泡和浸泡–风干循环作用下砂岩试样有明显“变软”的趋势,其断裂韧度、抗拉强度和抗压强度劣化趋势基本一致,劣化幅度在试验初期较为明显,后期逐渐趋于平缓;(2) 各力学参数劣化的幅度差别较大,其中,断裂韧度劣化最快,抗拉强度次之,抗压强度劣化相对较慢;(3) 比较而言,在浸泡–风干循环作用下,砂岩的各力学参数劣化趋势更加明显,说明在模拟库岸边坡消落带水–岩作用时,浸泡–风干循环作用是不可忽略的因素。研究成果对大量存在的库岸边坡稳定性分析具有重要参考价值,同时,相关试验方法也可以为类似试验提供参考。     

珍珠岩基相变骨料混凝土断裂特性试验与分析

先以硬脂酸丁酯为相变材料,膨胀珍珠岩为基体材料,石灰石粉末为表面改性材料制备珍珠岩基相变骨料（PBPCA）,再用其等体积取代混凝土中的部分砂制备珍珠岩基相变骨料混凝土（PBPCAC）;通过三点弯曲梁试验和立方体试块拉压比,研究PBPCA掺量不同时PBPCAC的断裂特性和韧性.结果表明：PBPCAC的断裂过程分为裂缝产生、裂缝发展和裂缝失稳3个阶段;其裂缝产生阶段较普通混凝土长,裂缝失稳阶段较普通混凝土短;PBPCAC的临界有效裂缝长度、起裂断裂韧度和失稳断裂韧度与普通混凝土大致相同;PBPCA的掺加未明显改变混凝土的延性和韧性;PBPCAC具有较好的抗断裂性能.     

混杂钢-聚丙烯纤维混凝土弯曲韧性试验研究

普通混凝土具有易开裂,延性差、抗拉强度低的特点.针对混凝土这一系列缺点,采用不同体积掺量的钢纤维和聚丙烯纤维混合掺人混凝土中.采用ASTM-C1018评价体系综合评定混凝土的弯曲韧性指标,试验研究表明:在混凝土中掺入混杂纤维后显著提高了混凝土的弯曲韧性.其中加入聚丙烯纤维能够提高小梁试件的初裂挠度和初裂点的荷载,而钢纤...     

Mechanical properties of high strength flowing concrete with hybrid fibers

This study investigates the mechanical properties of hybrid fiber as 2 vol.% fraction. The researchers tested hybridizations of steel fibers-, palm fibers-, and synthetic fibers (Barchip) by incorporating them with high strength flowing concrete (HSFC) to determine the density, compressive strength, splitting tensile strength, static modulus of elasticity-, flexural strength, toughness indices, and impact-load test for all the mixes. The results demonstrate that the hybridizations of such fibers enhance the flexural toughness and tensile strength of the HSFC. Increasing the content of hybrid fibers has led to the increase of impact load resistance and thus the first crack and the post-crack strength respectively.     

Influence of admixtures on the cracking sensitivity of mortar layers applied to a mineral substrate

Mortar layers used as renderings or adhesives can be exposed to conditions of temperature and humidity that can induce considerable dimensional variations. As these mortar layers are applied to an adhesive substrate, the dimensional variations are restrained and can thus produce significant tensile stress inside the mortar. If such stresses exceed the tensile strength, cracking can occur. This paper proposes a methodology for analysing the sensitivity of mortars to cracking in relation with the characteristics of the substrate. A new test method named the “de-bonded length” test was designed, developed and validated. The effect of both polymeric admixtures (type and quantity) and substrate conditions on the cracking time was analysed. The mechanical characteristics of the mortar were also determined by means of a three-point bending test. Moreover, the cracking time was analysed in regard to flexural strength, flexural modulus and flexural toughness. It follows that the cracking sensitivity depends on the flexural toughness, whatever the quantity and type of polymeric admixtures or the humidity of the substrate at the time of mortar casting.     

基体强度对合成纤维混凝土力学性质的影响

在纤维体积掺量为1.5%的基础上,研究了基体强度对合成纤维混凝土力学性质的影响.结果表明:随着基体抗压强度的增大,劈拉强度和抗折强度增大,弯曲韧性在抗压强度小于一定程度时也随之增大,但超过此范围后反而有逐渐降低的倾向.