海洋大气环境对CFRP-钢界面粘结性能的影响

为研究长期海洋大气环境作用对碳纤维增强树脂复合材料(CFRP)-钢界面粘结性能的影响,设计并制作了36个CFRP-钢板双搭接试件,采用盐雾沉降量1～2 mL/80 (cm2·h)的盐雾箱来模拟海洋大气环境。对试件进行了疲劳加载后的静力拉伸试验,分析了环境作用时间(30、180、360天)、长期持续荷载和硅烷表面处理方式对CFRP-钢界面破坏模式和承载力的影响。研究结果表明：随着海洋大气环境作用时间增加,CFRP-钢双面搭接节点由胶层内破坏伴随CFRP层离破坏逐渐向钢-胶界面粘结失效转变。暴露360天后极限承载力最大下降了15.72%。硅烷表面处理对CFRP-钢界面耐久性提升作用较小。持续荷载导致短期环境作用下(30天)极限承载力下降了18.39%,但对长期环境作用影响很小,高应力预加疲劳导致CFRP-钢界面极限承载力最大下降了26.6%。采用Hart-Smith模型对CFRP-钢界面极限承载力进行计算,发现长期环境作用后的承载力预测值和试验值误差超过了30%。在考虑破坏模式变化对界面极限承载力的影响下进行了修正,将误差减小到最大为14.04%。     

纳米SiO2质量分数对胶粘碳纤维增强树脂复合材料板-钢搭接界面黏结性能的影响

胶黏剂力学性能对碳纤维增强树脂复合材料(CFRP)加固钢结构的界面黏结性能影响显著。基于研制的胶黏剂配比,分析了不同纳米SiO₂质量分数对胶黏剂常温固化后基本力学性能及微观结构的影响,制作了31个CFRP板-钢板双搭接试件,对其进行了常温固化后的承载能力、有效黏结长度、传力模式、黏结-滑移本构等试验研究,得出了纳米SiO₂质量分数对CFRP板-钢板搭接试件界面黏结性能的影响规律,并与常用商品胶黏剂进行了比较。研究结果表明:随纳米SiO₂质量分数的增加,胶黏剂应力-应变关系由线性转变为非线性,应变能、断裂伸长率及剪切强度分别最高提升了292.10%、202.88%和133.12%。微观结构分析表明纳米SiO₂的添加使断面粗糙度显著增加,形成了密集的塑性空穴,产生了更多的微裂纹,使胶黏剂的韧性大幅度提高。当纳米SiO₂质量分数从0增至1wt%,搭接试件破坏模式由界面破坏逐渐变为CFRP板层离破坏。掺入纳米SiO₂能显著增加搭接试件的极限承载力(提升256.96%)及界面有效黏结长度(提升3倍),提高CFRP表面的应变及界面剪应力峰值。纳米SiO₂质量分数为0与0.5wt%的搭接试件的黏结-滑移曲线为双线性三角形模型,纳米SiO₂质量分数为1wt%的搭接试件的黏结-滑移曲线为三线性梯形模型,黏结界面韧性大幅提升。CFRP-钢界面承载能力受胶黏剂拉伸强度与断裂伸长率的双重影响,非线性高强度(即具有较高应变能)胶黏剂对应的CFRP-钢搭接接头具有更好的界面性能。      

双钢筋对拉度件搭接长度试验研究

通过四组不同搭接长度试件分析，得出合理的双钢筋搭接长度，为双钢筋构件的设计及施工提供了理论依据。并节约了钢材。     

胶膜连接碳纤维增强树脂复合材料板-钢搭接接头室温条件的力学性能试验

针对碳纤维增强树脂（CFRP）复合材料板-钢搭接接头连接的糊状胶黏剂粘层厚一致性控制较难、铅垂向成形可能不易等问题,将糊状胶黏剂换成胶膜,制作了胶膜连接的五种粘结长度共15个CFRP板-钢双搭接接头试件,并对该胶膜连接的CFRP板-钢搭接接头进行了室温条件下的破环模式、有效粘结长度、传力规律、粘结-滑移本构、承载力等的试验研究。结果表明:所用胶膜的连接强度略高于CFRP板层间强度（即碳纤维与树脂基体的黏聚强度）;室温下,所用胶膜连接的CFRP板-钢搭接接头有效粘结长度约为80 mm;加载初期,剪应力最大值位于接头钢板端;继续加载,其位置向接头CFRP板端移动;加载末期,其位置位于距接头钢板端20 mm （粘结长度不超过80 mm时）或者50 mm （粘结长度不小于120 mm时）处;胶膜连接的CFRP板-钢搭接接头界面粘结-滑移模型为近似梯形,不同于胶黏剂连接的CFRP板-钢搭接接头的近似三角形,胶膜连接接头的延性大为提升;所用胶膜连接接头界面峰值剪应力、断裂能、界面刚度等代表值（可视为准平均值）分别为四种典型商品胶黏剂连接接头的1.2~3.0倍、1.6~5.7倍和5.4~7.5倍;在粘结长度不小于有效粘结长度条件下,所用胶膜连接接头的抗拉承载力代表值为四种典型商品胶黏剂连接接头的1.25~2.39倍;胶膜连接接头的抗拉承载力、最大位移的变异系数与糊状胶黏剂连接接头相差不大。      

固化剂混掺对高温下CFRP板-钢板界面黏结性能的影响

针对单一固化剂难以兼顾耐热性和韧性的不足,研究了耐热性能较好的缩胺105和韧性较好的聚醚胺D230两种固化剂混掺对纳米SiO₂环氧胶黏剂玻璃转变温度及高温下基本力学性能的影响。按一定固化条件制作了30个胶黏剂拉伸试件、21个碳纤维增强树脂复合材料(CFRP)板-钢板双搭接试件,进行了高温及常温下的准静态拉伸试验、拉伸剪切试验,测试了相应胶黏剂的动态热机械性能,并与常用商品胶的耐热性能与力学性能进行比较,得到以下结论:随混掺固化剂中聚醚胺D230比重的增加,胶黏剂高温下的拉伸强度及弹性模量逐渐降低,断裂伸长率及应变能先增加后减小,缩胺105与聚醚胺D230两种固化剂混掺的推荐比例为1∶2。随固化温度的升高,具有固化剂混掺较佳比例的胶黏剂的玻璃转变温度有所提升,综合技术与经济因素,推荐(较佳)固化条件为90℃、2 h。推荐比例与推荐固化条件的纳米SiO₂环氧胶黏剂在环境温度20~70℃之间的拉伸强度及韧性均大大优于常用商品胶黏剂。基于推荐比例与推荐固化工艺的纳米SiO₂胶黏剂粘结的CFRP板-钢板搭接接头,在70℃服役温度下的荷载-位移曲线存在屈服段,承载能力(较采用单一缩胺105和单一聚醚胺D230固化剂的搭接试件分别提升了104.03%、64.43%)和延性(为采用单一缩胺105固化剂的搭接试件的2.5倍以上)均大幅提升。高温和常温下的黏结-滑移本构均为三线性四边形。胶黏剂在满足耐热性的同时,需尽可能提升其韧性,才能有效提升CFRP-钢搭接界面的力学性能。相比于常用商品胶黏剂,研制的推荐胶黏剂粘结的CFRP板-钢板搭接接头具有优越得多的承载能力和界面断裂能。      

搭接长度和铺层方式对CFRP复合材料层合板胶接结构连接性能和损伤行为的影响

针对不同搭接长度和铺层方式的碳纤维增强树脂（CFRP）复合材料层合板单搭胶接结构进行了拉伸试验,观察了试件的受力过程和失效形态,获得了载荷-位移曲线;同时基于连续损伤力学模型和三维Hashin失效准则模拟了CFRP复合材料层合板的层内损伤形成和演化,并利用内聚力模型来模拟层间及胶层的失效损伤,对CFRP复合材料层合板单搭胶接结构在拉伸作用下的失效强度和损伤机制进行了预测,通过对比验证了该数值方法的有效性;通过数值试验比较不同搭接长度和铺层方式的单搭胶接结构及双搭胶接结构的连接强度和损伤行为,并提出了一种优化的CFRP复合材料层合板胶接结构。结果表明:CFRP复合材料层合板胶接结构的极限失效载荷随着搭接长度的增大逐渐增加并趋于稳定值,且结构的失效形式逐渐从胶层自身剪切失效过渡到邻近胶层的层合板层间分层失效;CFRP复合材料层合板胶接结构的连接强度和损伤行为随着铺层方式的不同而改变,通过对3种铺层方式的对比和分析,得到性能最好的铺层方式是[0₃/90₃]_2S;在搭接长度为5~20 mm时,通过对搭接长度进行优化,得到单搭胶接结构的最优搭接长度是17 mm,双搭胶接结构的最优搭接长度是19.3 mm,与搭接长度为20 mm相比,单搭胶接结构和双搭胶接结构的连接强度分别提高了13.26%和0.43%。      

锈蚀对钢板表面特性及CFRP板-锈蚀钢板界面黏结性能的影响

为研究锈蚀对钢板表面特性及碳纤维增强树脂复合材料(CFRP)板-锈蚀钢板界面黏结性能的影响,开展了6批次锈蚀钢板表面特性测试及22个CFRP板-锈蚀钢板双搭接试件的拉伸试验,揭示了锈蚀对钢板表面形貌与粗糙度、表观接触角与表面自由能以及CFRP板-钢板黏结界面破坏模式、有效黏结长度、极限荷载的影响.研究结果表明:随着腐蚀...     

双材料界面端附近奇异应力场消除几何条件研究

基于Bogy特征值方程,分析了消除界面端奇异应力场的几何条件,给出了平面应力和平面应变条件下的接合角组合曲线.应用有限单元法对上述结果进行了验证,并对消除应力奇异性后的界面应力进行了分析与讨论;结果表明:采用刚好使奇异性消失的接合角会获得最均匀的界面应力分布.     

钛板表面质量对钛-钢复合界面的影响

通过测试爆炸钛-钢复合板结合强度和分析钛板表面质量情况,研究了复合板中钛层产生分层、碎边和皱褶缺陷的原因。结果表明,钛板上残留的冶金缺陷、板形不良和不均匀的边部致密氧化层残留,会造成复合板界面的结合不牢。针对复合时界面结合不牢的问题,提出了对钛板的质量管控和表面处理的适宜措施。     

火灾条件下16Mn钢的力学性能试验研究

对建筑工程常用的16Mn钢在火灾条件下的力学性能进行了测试,获得了16Mn钢的屈服强度、极限强度、弹性模量和伸长率等力学性能随火灾温度变化的规律,并对影响16Mn钢力学性能的因素进行了分析。     

碳纤维复合材料补强混凝土界面温度应力分析

碳纤维片材的热膨胀系数与混凝土的热膨胀系数相差很大,因而,在环境温差作用下,补强碳纤维片材和混凝土界面处将产生界面温度应力.正确地分析界面温度应力,揭示界面温度应力的变化规律,对补强结构设计和安全评价具有重要意义.建立了碳纤维片材补强混凝土梁的界面温度应力定量计算公式,并通过实验测试验证了定量分析理论的合理性.研究结果表明:界面温度应力分布及大小与补强复合材料的刚度和作用温差有较大关系,与基底混凝土的刚度关系不大.     

CFRP-钢界面粘结性能试验与数值模拟

碳纤维增强聚合物基复合材料（CFRP）与钢板的界面粘结性能为CFRP加固钢结构的关键问题之一。开展了17个CFRP板-钢板单搭接试件的拉伸剪切试验,研究了不同环氧粘结剂与CFRP材料的CFRP-钢界面力学行为和破坏模式;分析了粘结剂类型和CFRP材料对界面粘结滑移本构和界面剪切性能的影响,讨论了其承载力计算方法。结果表明：采用不同的粘结剂或CFRP材料,界面破坏形式和抗剪承载力均差异较大。采用Sika 330、Lica粘结剂的试件为CFRP板或钢板与胶层的界面破坏,采用Araldite粘结剂的试件为CFRP板浅表层离,采用Sika 30粘结剂的试件为胶层内聚破坏,采用SF（Sika S512/80）碳板的试件为CFRP板深层层离;Araldite试件的抗剪承载力为其他试件的1.7~2.9倍。Sika 330、Araldite及Lica试件粘结滑移曲线无明显下降段,属脆性破坏,而Sika 30与SF试件存在缓坡下降段,失效前有一定征兆;SF试件的粘结滑移本构可简化为三折线模型,其余试件则可简化为双线性模型。SF试件抗剪承载力需用Xia-a模型表征,其余试件则可用Xia-b模型表征。基于粘聚力模型对界面力学行为进行了数值模拟,结果表明,粘聚力模型可以较好地模拟界面的非线性力学行为,剥离应力对本单搭接试件的界面粘结强度影响很小。     

Experimental study on the dynamic compressive mechanical properties of concrete at elevated temperature

Strain rate effect and temperature effect are two important factors affecting the mechanical behavior of concrete. Each of them has been studied for several years. However, the two factors usually work together in the engineering practice. It is necessary to understand the mechanical responses of concrete under high strain rate and elevated temperature. A self-designed high temperature SHPB apparatus was used to study the dynamic compressive mechanical properties of concrete at elevated temperature. The results show that the dynamic compressive strength and specific energy absorption of concrete increase with strain rate at all temperatures. The elastic modulus decreases obviously with strain rate at room temperature and stabilizes at a level with slightly decrease at elevated temperature. The dynamic compressive strength of concrete at 400 °C increases by nearly 14% compared to the room temperature. However, it decreases at 200 °C, 600 °C and 800 °C with the decrease ratio of 20%, 16% and 48%, respectively. The dynamic elastic modulus decreases largely subjected to elevated temperature. The specific energy absorption at 200 °C, 400 °C and 600 °C is higher than room temperature and decreases to be lower than room temperature at 800 °C. Formulas are established under the consideration of mutual effect of strain rate and temperature.     

Finite element interface models for the delamination analysis of laminated composites: mechanical and computational issues

The finite element analysis of delamination in laminated composites is addressed using interface elements and an interface damage law. The principles of linear elastic fracture mechanics are indirectly used by equating, in the case of single‐mode delamination, the area underneath the traction/relative displacement curve to the critical energy release rate of the mode under examination. For mixed‐mode delamination an interaction model is used which can fulfil various fracture criteria proposed in the literature. It is then shown that the model can be recast in the framework of a more general damage mechanics theory. Numerical results are presented for the analyses of a double cantilever beam specimen and for a problem involving multiple delamination for which comparisons are made with experimental results. Issues related with the numerical solution of the non‐linear problem of the delamination are discussed, such as the influence of the interface strength on the convergence properties and the final results, the optimal choice of the iterative matrix in the predictor and the number of integration points in the interface elements. Copyright © 2001 John Wiley & Sons, Ltd.     

A study on the mechanical properties of self-compacting concrete at high temperature and after cooling

Self-compacting/consolidating concrete (SCC) is certainly one the most innovative material used today by the construction industry, because of its astonishing workability and low permeability, both properties being ensured by the large amounts of fine aggregates, the special additives and the fillers, that characterize SCC??s mix compared to traditionally-vibrated concrete (VC). Since many of the structures where SCC is used (like tunnel linings, off-shore structures, containment shells, bridge decks, slabs on grade) are often required to face severe environmental conditions, such as fire, information on SCC??s behavior at high temperature is badly required, because SCC??s more dense or compact microstructure, with smaller and less connected pores, may in principle make this material more heat-sensitive than VC, as occurs in high-performance/high-strength concrete. While the thermal effects on VC have been extensively investigated in the last 20?years and several studies have been devoted to SCCs spalling in fire, only in the last few years due attention has been paid to the mechanical properties of SCCs at high temperature (??hot?? properties) and/or after cooling (??residual?? properties). The few of papers on this subject, however, give limited information on the stress?Cstrain curves in compression and on the tensile behavior, that are the first objective of this project, with reference to three self-compacting ??limestone?? concretes (target strength f _c?=?50, 80 and 95?MPa). The second objective is to synthesize the test results available in the literature and to make systematic comparisons, something that is not as simple as one may expect, because of the different heating rates, specimen types, and procedures in data treatment and presentation. The agreement, however, is more than satisfactory and confirms what has been more or less overtly indicated in previous studies, that the thermal and mechanical behavior of SCC at high temperature is hardly different from that of VC, at least in quasi-static thermal conditions and uniaxial loading.     

纳米SiO2对钢纤维/混凝土高温后力学性能及微观结构的影响

研究了掺纳米SiO2的钢纤维混凝土(NSFC)、钢纤维混凝土(SFRC)和普通混凝土(NC)三种材料在不同加热温度后的抗压、劈裂和抗折强度等力学性能,对不同温度热处理后的微观结构进行了SEM分析,对钢纤维与过渡区界面的相结构进行了XRD分析.结果表明:在测试温度范围内,NSFC的抗压、劈裂和抗折强度均高于SFRC和NC的强度,且在400℃时达到最大值.在常温下,NSFC的抗压、劈裂和抗折强度较NC分别提高27.01％、63.28％和54.12％,400℃高温热处理后比NC分别高35.09％、84.62％和87.23％; SEM分析表明,在钢纤维与过渡区的界面处,致密度提高,显微硬度提高.由于固相反应,使界面区结构发生变化,在钢纤维表层形成扩散渗透层(白亮层),即化合物层,呈锯齿状,XRD分析证明,白亮层主要由FeSi2和复杂的水化硅酸钙组成,从而增强了钢纤维与基体的粘结力,提高了混凝土的高温力学性能.     

Experimental study on mechanical properties and fracture toughness of structural thick plate and its butt weld along thickness and at low temperatures

The thick plate induces the variation of mechanical properties and fracture toughness, especially in cold regions. At the low temperature, the brittle behaviour of steel becomes worse. A series of tests (such as uniaxial tensile test and three‐point bending test) were carried out at low temperature to investigate the mechanical properties and fracture toughness of structural steel plates of Q345B with thickness of 60 to 150 mm, as well as the fracture toughness of 150 mm thick butt welded plate. The test specimens are all manufactured from plates along thickness with small size, and the tensile test specimens included through‐thickness specimens additionally. The ductility index (percentage reduction of area) and the fracture toughness index (critical CTOD values) all decrease with the temperature decreases and the distance from plate surface increases. The results obtained in this paper provide technical basis for preventing brittle fracture of thick plate steel structures in cold regions.     

高温环境下碳纤维增强树脂复合材料的层间力学性能老化行为与失效预测

为了研究碳纤维增强树脂(CFRP)复合材料层间力学性能在高温环境中的老化失效行为,设计了CFRP复合材料层间拉伸和层间剪切实验,在高温(80℃)环境中进行0(未老化)、 120 h、 240 h、 360 h、 480 h、 600 h和720 h的老化测试,分析CFRP层间失效强度和失效形式随老化时间的变化规律,得到随高温老化的二次应力准则响应面。建立CFRP复合材料层间力学性能预测模型,得到不同老化衰减系数下的退化模型,并通过CFRP复合材料层间仿真模型进行了验证。结果表明:随着高温老化时间的增加,层间拉伸和层间剪切强度总体上都发生了一定程度的退化,层间拉伸时更容易发生碳纤维丝剥离,层间剪切发生局部的树脂剥离,纤维之间的分层更加明显,高温老化使树脂与纤维丝的界面结合力显著下降。通过CFRP复合材料层间力学性能随高温老化的二次应力准则,计算不同老化时间后的内聚力模型参数,预测CFRP复合材料在高温老化条件下的层间强度,发现仿真与实验误差小于10%,说明了CFRP复合材料层间失效预测模型的准确性。     

Experimental study on the mechanical properties and microstructure of chopped basalt fibre reinforced concrete

With high ductility and sufficient durability, fibre reinforced concrete (FRC) is widely used. In this study, the effects of the volume fraction and length of basalt fibre (BF) on the mechanical properties of FRC were analyzed. Coupling with the scanning electron microscope (SEM) and mercury intrusion porosimeter (MIP), the microstructure of BF concrete was studied also. The results show that adding BF significantly improves the tensile strength, flexural strength and toughness index, whereas the compressive strength shows no obvious increase. Furthermore, the length of BF presents an influence on the mechanical properties. Compared with the plain concrete, the compressive, splitting tensile and flexural strength of concrete reinforced with 12 mm BF increase by −0.18–4.68%, 14.08–24.34% and 6.30–9.58% respectively. As the BF length increasing to 22 mm, corresponding strengths increase by 0.55–5.72%, 14.96–25.51% and 7.35–10.37%, separately. A good bond between the BF and the matrix interface is observed in the early age. However, this bond shows degradation to a certain extent at 28 days. Moreover, the MIP results indicate that the concrete containing BF presents higher porosity.