Residual Tensile Strength of Plain Concrete Under Tensile Fatigue Loading

The functional relation between the residual tensile strength of plain concrete and number of cycles was determined. 99 tappered prism specimens of plain concrete were tested under uniaxial tensile fatigue loading. Based on the probability distribution of the residual tensile strength, the empirical expressions of the residual tensile strength corresponding to the number of cycles were obtained. The residual tensile strength attenuating curves can be used to predict the residual fatigue life of the specimen under variable-amplitude fatigue loading. There is a good correlation between residual tensile strength and residual secant elastic modulus. The relationship between the residual secant elastic modulus and number of cycles was also established.

Effect of the amount of lignin on tensile properties of single wood fibers

Chemical components are the main factors affecting the mechanical properties of wood fibers. Lignin is one of the main components of wood cell walls and has a critical effect on the mechanical properties of paper pulp and wood fiber based composites. In this study, we carried out tensile tests on single mature latewood tracheids of Chi- nese fir （Cunninghamia lanciolata （Lamb.） Hook.）, using three different delignified treatment methods to obtain different amounts of lignin. We applied single fiber tests to study the effect of the amount of lignin on mechanical tensile proper- ties of single wood fibers at the cellular level. The results show that in their dry state, the modulus of elasticity of single fi- bers decreased with the reduction in the amount of Iignin; even their absolute values were not high. The amount of lignin affects the tensile strength and elongation of single fibers considerably. Tensile strength and elongation of single fibers increase with a reduction in the amount of lignin.

Study on the Tangential Tensile Mechanical Properties of Moso Bamboo

In this work,we used tensile tests to analyze the tangential failure forms of raw bamboo and determine a relationship between tangential tensile strength,elastic modulus,position,density,and moisture content.We found that the tangential mechanical properties of the culm wall were mainly dependent on the mechanical properties of the basic structure of the thin wall.Formulas for calculating the tangential tensile strength of moso bamboo and adjusting the moisture content were also determined.The tangential tensile strength and the tangential tensile modulus of elasticity(TTMOE)followed:outer>middle>inner,and diaphragm>bamboo node>culm wall.Below the fiber saturation point,the tangential tensile strength and TTMOE values of the bamboo gradually decreased with increasing moisture content.When the moisture content was 15%,the tangential tensile strengths of the inner,middle,outer,culm wall,bamboo node,and diaphragm samples of the five-year-old moso bamboo were 3.17,3.29,3.31,3.24,3.67,and 8.85 MPa,respectively.Furthermore,their TTMOE values were 215.09,227.98,238.45,224.04,267.21,and 559.27 MPa,respectively.Hence,this study provides a theoretical basis for future research on bamboo cracking.

INFLUENCE OF FIBER COATING ON TENSILE BEHAVIOR OF UNIDIRECTIONAL C/Mg COMPOSITES

The mechanical properties and deformation mechanisms of unidirectional carbon fiber reinforced magnesium composites under tensile loading are studied. Two different materials are used as fiber coatings: a single silica and a gradient C/SiC/SiO[sb 2]. The results show that, under the same preparation conditions, composite with the former coating is broken in a non-cumulative mode and its failure stress is rather low. Conversely, the latter coating demonstrates much better efficiency and the corresponding composite is broken in a cumulative mode.

基于ANN的HVFAC拉伸性能预测评价

基于人工神经网络(ANN)预测混凝土拉伸性能,对研究混凝土开裂机制具有重要意义。基于团队实验数据获得不同粉煤灰掺量、骨胶比、水胶比和养护龄期下大掺量粉煤灰混凝土(HVFAC)的抗压强度、极限拉伸应变、抗拉强度和拉伸弹性模量数据,用均方根误差(RMSE)最小原则建立一种预测HVFAC拉伸性能的ANN模型,并用公开发表的文献数据对该预测模型可靠性进行分析评估。结果表明:模型预测结果与实验结果的相关系数均大于0.94,文献中的实验值与模型预测值的误差均在±20%以内,说明所建立的模型有较高的预测精度。基于ANN影响权重分析发现:骨胶比对HVFAC的抗压强度、极限拉伸应变和拉伸弹性模量的影响最大;对于HVFAC的拉伸性能,在早龄期时水胶比的影响程度较大,但随着龄期的延长,粉煤灰掺量的影响程度逐渐上升并超过水胶比。

高温蒸汽养护复掺混凝土力学性能时变特性与模型研究

为研究高温蒸汽养护下粉煤灰-矿粉机制砂混凝土(简称复掺混凝土)力学性能时变特性与模型,本文结合某高速公路高温蒸汽养护复掺混凝土预制梁项目,设计了蒸汽-标准养护、蒸汽-自然养护和标准养护三种养护方式,测试了不同阶段复掺混凝土的抗压强度、劈裂抗拉强度和弹性模量,探究了抗压强度与劈裂抗拉强度、弹性模量的关系。结果表明:合适的蒸汽养护方式能促进复掺混凝土抗压强度、劈裂抗拉强度和弹性模量更快增长,其中对抗压强度形成作用最显著,后期的力学性能不倒缩;蒸汽养护恒温阶段复掺混凝土的力学性能具有最大的增长率,其次是升温阶段,降温阶段力学性能增长率最小;蒸汽-标准养护方式下复掺混凝土的抗压强度时变模型可取对数或对数与幂函数复合函数,劈裂抗拉强度、弹性模量时变模型可取幂函数。

冻融循环后混凝土冲击劈拉强度预测模型

为预测混凝土材料冻融循环后冲击劈拉强度,本文对混凝土标准冻融试件和混凝土劈拉试件进行0、25、50、75、100次的冻融循环试验,通过动弹仪对混凝土标准冻融试件进行动弹性模量测试,采用电液伺服万能试验机和分离式霍普金森压杆系统分别在0.5和0.5×10^(6)、1.0×10^(6)、2.0×10^(6)kN/s的力加载速率下对劈拉试件进行劈拉试验,分析了冻融损伤以及力加载速率对混凝土冲击劈拉强度的影响。结果表明:随着冻融次数的增加,标准冻融试件的表观状况、质量、相对动弹性模量均不断劣化;当冻融次数一定时,随着力加载速率的提高,混凝土试件的冲击劈拉强度不断提升。在上述试验基础上,建立了冻融循环后混凝土冲击劈拉强度预测模型,该模型可为冻融循环后混凝土冲击劈拉强度的预测提供理论依据。

基于混凝土水化热效应的高地温水工隧洞衬砌结构温控防裂研究

为分析高地温水工隧洞衬砌结构温度应力特性,基于拉普拉斯变换推导出衬砌结构瞬态温度场的解析解,并借助弹性抗力法推导出衬砌结构的弹性温度应力分量。依托新疆布伦口水电站监测数据对衬砌结构瞬态温度场及应力场进行计算分析,并采用抗拉强度准则和裂缝尖端强度因子对衬砌结构破坏进行分析,提出合理的温控防裂措施。结果表明:1)衬砌温度场前期整体温度迅速上升,在第7天左右达到最大值,其中衬砌内壁温度可达到37℃,外壁温度可达到56℃。2)衬砌结构外墙环向应力可达到2.2 MPa,体现为拉应力状态;径向应力可达到2.7 MPa,呈现为压应力状态。3)衬砌结构强度的破坏主要受温度及结构本身稳定性2方面影响,可通过采用低热水泥、控制混凝土的入模温度以及严格监控施工过程来提高衬砌的稳定性。其中,采用低热水泥可降低衬砌结构的温升值,混凝土的最终水化热每降低50 k J/kg,衬砌结构内外壁的温差可降低1.85℃左右;适当提高入模温度可缩短水化热的放热周期及降低衬砌内外壁温差。

仿木材料抗拉强度与应力-应变曲线试验研究

仿木材料是以氯氧镁水泥为基体,植物纤维为增强体,并添加柠檬酸、酒石酸、六偏磷酸钠搅拌均匀后经高压静置固化成型的无机胶凝材料,为研究其抗拉强度和抗拉本构关系,制作了30个试件进行轴心受拉试验,共采集到22个试件的有效数据。结果表明:仿木材料的轴心抗拉强度为7.98 MPa,变异系数为0.121,抗拉弹性模量为3600 MPa,变异系数为0.089,轴心拉力作用下,材料达到峰值应力后应力迅速下降,试件脆性破坏;根据应力、应变测试结果,拟合得到了材料的轴心抗拉本构关系,可供材料非弹性应用时参考。

Effect of internal defects on tensile strength in SLM additively-manufactured aluminum alloys by simulation

This research investigates the effect of internal defects on the tensile strength of Selective Laser Melting(SLM)additively-manufactured aluminum alloy(AlSi10Mg)test parts used for civil aircraft light weight design.A Finite Element Analysis(FEA)model containing internal defects was established by combining test data and the stress concentration factor comparison method.The effect of variation in the number,location and shape of defects on the finite element results was analyzed.Its results show that it is reasonable to use spherical defect modeling.The finite element modeling and analysis methods are also applied to the study of the effect of internal defects on tensile strength in additive manufacturing of other metallic materials.According to the FEA results of single defects at different scales,the formula for calculating the weakening degree of tensile strength applicable to the defective area of less than 15%was established.The result of the procedure is reliable and conservative.This research results can guide the selection of process parameters for the additive manufacturing of aluminum alloys.Further,the research results can promote the application of metal additive manufacturing in designing light-weight civil aircraft structures.

各向异性PCL/明胶复合人工心脏瓣膜瓣叶材料的制备及性能

为制备模拟人体原生瓣膜层状结构及力学各向异性的人工心脏瓣膜瓣叶材料,采用静电纺丝技术,以不同质量配比的聚己内酯(PCL)和明胶为原料,通过调整各层纤维膜的纤维排列情况,顺序堆叠纺制3层结构的PCL/明胶复合支架。结果表明,PCL质量体积比为10%时,随着明胶质量分数增加,纤维直径和复合支架厚度随之增加,复合支架的弹性模量和极限抗拉强度减小。其中,PCL和明胶质量配比为5∶3的复合支架在两个相互垂直方向上的弹性模量分别为(26.98±3.01)MPa和(3.39±0.36)MPa,各向异性比约为7.96,接近原生主动脉瓣的力学各向异性比,其体外脉动流测试显示有效开口面积(EOA)为1.79 cm^(2)、平均跨瓣压差(MPD)为1.67 kPa(即12.52 mmHg)、反流分数(RF)为24.22%。同时,制备的复合支架溶血率均小于5%,细胞相对增殖率均大于80%,具有良好的血液相容性和细胞相容性,有望应用于人工心脏瓣膜瓣叶材料。

机制砂细粉含量对混凝土力学性能影响研究

设置5种不同机制砂细粉含量,在相同配合比条件下,研究混凝土强度及弹性模量受机制砂细粉含量影响规律。研究表明,机制砂细粉含量对机制砂混凝土强度和弹性模量均存在显著影响,且弹性模量对细粉含量的响应更为显著。随着机制砂细粉含量的增加,混凝土抗压强度和劈裂抗拉强度均呈先升后降的变化趋势,混凝土弹性模量则随细粉含量的增加呈持续降低趋势。细粉含量为5%时,抗压强度增幅4.91%,劈裂抗拉强度增幅7.91%,均达到最大值。细粉含量为20%时,混凝土弹性模量降幅高达14.7%。基于细粉含量对混凝土物理力学特性影响规律,机制砂细粉含量为5%时混凝土强度增益效果较佳。

大掺量粉煤灰对UHPC性能影响研究

采用粉煤灰取代分别为0、25%、50%、75%水泥配制UHPC,研究粉煤灰不同取代率对UHPC工作性能、力学性能的影响规律。研究表明,粉煤灰取代率增加,UHPC抗压强度、抗劈拉强度逐渐降低,但取代率为25%时UHPC强度发展较为理想,个别龄期强度甚至超过了基准混凝土的强度,所以粉煤灰掺量为25%时工作性能、力学性能最为理想。

HF-QF膨胀纤维抗裂防水剂对混凝土劈裂抗拉性能的影响研究

本文研究HF-QF膨胀纤维抗裂防水剂对C35普通混凝土劈裂抗拉强度的影响,并通过劈裂抗拉破坏形态、轴心抗压强度、弹性模量和应力-应变曲线充分的分析出了HF-QF膨胀纤维抗裂防水剂在提升混凝土劈裂抗拉性能过程中的实际作用效果。试验结果表明:HF-QF膨胀纤维抗裂防水能够提高C35普通混凝土的劈裂抗拉强度,最佳掺量为30 Kg/m^(3),较空白试样增加了35.50%;掺加HF-QF膨胀纤维抗裂防水剂的混凝土破坏形式为中心开裂破坏并伴随局部受压破坏;HF-QF膨胀纤维混凝土的应力-应变曲线显示了其易于发生脆性破坏的特性。

高性能混凝土高温力学及热变形试验研究

本文探究了高性能混凝土在高温环境下的宏观特征、力学性能以及热变形情况。采用对照试验的方法,分别使用素混凝土和掺入了聚丙烯纤维的高性能混凝土制作了试件,使用两种试件分别进行了高温试验、高温后的力学试验以及热应变试验。结果表明,随着试件温度的升高,素混凝土试件率先出现裂隙,最后完全剥落,而高性能混凝土试件出现裂隙的时间较晚,只有少许剥落;高性能混凝土的抗拉性能和弹性模量均优于素混凝土,在800℃高温下高性能混凝土试件的抗拉强度损失率为75.5%,弹性模量损失率为94.2%,均低于塑性混凝土试件;加热相同时间下,高性能混凝土的热应变值始终低于素混凝土。

浅谈干挂石材用胶粘剂的性能和使用

本文简述了目前干挂石材用胶粘剂的行业现状,通过检测数据分析了干挂胶各项检测参数反映的产品特性及使用过程中的注意事项,强调了在新材料、新工艺、新配方不断发展的时代背景下工程检测的必要性和重要性。

高性能气缸套材料及其热处理工艺研究

为了满足气缸套的高爆发压力,对材料的强度和弹性模量有了更高的要求,因此进行了灰铸铁的合金化及热处理试验研究,获得了合适的化学成分和热处理工艺;使灰铸铁的抗拉强度超过600 MPa,弹性模量大于140 GPa。

门窗用未增塑聚氯乙烯型材的产品优化和性能研究

综合型材性能和生产成本的双重因素,将生产中的废料进行回收再利用,对门、窗用未增塑聚氯乙烯型材中的白色通体型材的外可视面进行改良优化,并对其各项力学性能的变化进行研究。分别对改良后的型材外可视面和内可视面的拉伸屈服强度、断裂标称应变、弯曲弹性模量、密度和维卡软化温度进行对比,结果表明:改良后的外可视面拉伸屈服强度增加了4.00%,弯曲弹性模量增加了8.25%,拉伸断裂应变降低了7.34%,密度降低了0.587%,维卡软化温度降低了0.984%。经过分析说明:加工改良后的型材产品性能得到优化,刚性明显增强,关键性能得到提升,不但节约了生产成本,也减少了废料对环境的污染。

A cation-dipole-reinforced elastic polymer electrolyte enabling long-cycling quasi-solid-state lithium metal batteries

The application of ionic liquids(IL)in polymer electrolytes represents a safer alternative to the currently used organic solvents in lithium batteries due to their nonflammability and thermal stability.However,as a plasticizer,it is generally agreed that the introduction of ionic liquid usually leads to a trade-off between ion transport and mechanical properties of polymer electrolyte.Here we report the synthesis of an IL-embedded polymer electrolyte with both high ionic conductivity(2.77×10^(-4)S cm^(-1)at room temperature)and excellent mechanical properties(high tensile strength up to 11.4 MPa and excellent stretchability of 387%elongation at break)achieved by strong ion–dipole interactions between polymer electrolyte components,which was unveiled by the DFT calculation.Moreover,this polymer electrolyte also exhibits nonflammability,good thermal stability and the ability to recover reversibly from applied stress,i.e.,excellent elasticity.This highly viscoelastic polymer electrolyte enables tight interfacial contact and good adaptability with electrodes for stable lithium stripping/plating for 2000 h under a current density of 0.1 mA cm^(-2).By coupling with this polymer electrolyte,the LiFePO_(4)/Li cells exhibit outstanding cycling stability at room temperature as well as the reliability under extreme environmental temperature or being abused.

土木工程中组合再生混凝土材料性能分析

为探讨组合再生混凝土材料性能,制备了4种掺杂不同有机纤维的组合再生混凝土材料,分别测试其抗压强度、劈拉强度及抗折强度。结果表明,掺入有机纤维会降低材料的抗压强度,但会提高其劈拉强度及抗折强度。在此基础上制备了20种含有不同骨料的组合再生混凝土材料并计算其弹性模量。计算结果表明,不同骨料会对材料的弹性模量产生不同的影响(如硅灰的掺入会增强材料的弹性模量,钢纤维的掺入会降低材料的弹性模量)。