Elastic Wave Scattering From a Partially Debonded Elastic Cylindrical Inclusion

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设沥青夹层水泥混凝土路面早龄期力学行为与作用效应研究

基于水泥混凝土路面早龄期三维有限元力学分析程序,对设沥青夹层面板结构早龄期阶段力学行为和性状形成的结构效应、沥青夹层效应进行了研究。研究发现,早龄期阶段固化温度、混凝土的徐变和硬化历程与环境场叠加作用,会引起面板更大的早期板角翘曲和脱粘,以往传统分析理论忽略了此方面影响。设沥青夹层结构比无夹层直接加铺路面脱粘面积小、翘曲变形更大。沥青夹层面板早龄期增大翘曲、脱粘的结构效应与特定重载交通共同作用下可能产生对路面板疲劳寿命不利的影响。对设沥青夹层加铺结构建议采用刚度较大的基层,夹层厚度宜在30 mm以内,沥青夹层混合料模量宜选低值。     

Real-time frequency determination of acoustic emission for different fracture mechanisms in carbon/epoxy composites

Carbon/epoxy material in the form of a unidirectional composite was loaded under different conditions to determine the frequency content of acoustic emission signals. Special specimens, designed to fail under well-defined modes such as matrix cracking, debonding, fibre pull-out and fibre failure, were tested from zero load to failure. Real-time analysis of the acoustic signals was performed with a Dantec burst spectrum analyser permitting the detection of frequencies in a wide band around a certain central frequency. The signals analyzed ranged from 50 to 600 kHz and were distinguished as being released from four special types of failure. By using different types of specimen it was concluded that matrix cracking released frequencies between 90 and 180 kHz, fibre failure frequencies above 300 kHz, debonding frequencies between 240 and 310 kHz and pull-out frequencies between 180 and 240 kHz. A comparison with published values shows agreement with the frequency bands determined for matrix and fibre failure, while for the debonding and pull-out mechanisms the frequency bands turned out to be interchanged. It can still be concluded that these failure mechanisms generate frequencies between those of matrix failure and fibre fraction.     

层合复合材料由于纤维—基体脱胶引起刚度下降的估算

本文根据显微结构图,建立了纤维-基体界面脱胶的力学模型,采用有限元法,计算了玻璃/环氧 及硼/环氧两种单向纤维增强的复合材料的刚度降。计算结果表明,界面脱胶对刚度降有相当大的影响,并且纤维断裂对脱胶产生一定的影响,这是前人估算由于脱胶而产生的刚度降所没有计及的。     

Thermal loading of a thin layer with circular debonding over a substrate

By using techniques appropriate to mixed boundary value problems, this study addresses the determination of stress intensity factors for a circular interface debonding between a thin layer and a substrate subjected to nearly uniform temperature change. The solution method involves three-dimensional equilibrium equations of thermo-elasticity under axisymmetry conditions. The stress intensity factors are obtained by solving the resulting pair of coupled singular integral equations numerically. This revised version was published online in August 2006 with corrections to the Cover Date.     

FRP与砌体节点的粘结性能

用FRP加固的无筋砌体墙的面外弯曲和面内剪切性能经常受剥离破坏机理的控制。因而,需要定量确定基本的界面粘结滑移模型,这个模型能够描述FRP与砖砌体粘结界面性能。给出了29个采用外包和嵌入式加固FRP的拔出试验结果,试验变量包括:表面处理方式,几何尺寸,FRP(相对于节点和核心的)位置,基础节点的砌筑方法(砂浆快速干砌),玻璃纤维布的粘结方式,FRP种类。讨论了试验结果,初步给出了实际应用的建议。通过试验数据验证预测界面开裂剥离抗力的模型。该模型在外包和嵌入式加固技术应用中具有普遍的意义。这个一般性模型对所研究的29个拔出试验的极限强度具有很高的预测精度。     

碳纤维布加固混凝土梁的剥离破坏

碳纤维布加固混凝土结构中剥离破坏是一种重要的破坏形式,通过九根碳纤维布加固混凝土梁的模型试验,考察了剥离承载力及剥离模式。根据试验结果和力学理论知识,对碳纤维布加固混凝土梁的剥离破坏进行了极限应力分析,建立了极限状态的判据和相应的碳纤维布剥离承载力计算方法,在计算方法中考虑了粘结正应力与剪应力的综合作用以及U形箍的横向剪切变形,与试验结果的比较表明,方法具有较高的精度,完善了碳纤维布加固混凝土梁的设计理论。     

Double bridge circuit for self‐validated structural health monitoring strain measurements

In structural health monitoring (SHM) applications, sensor faults and structural damage need to be assuredly discriminated. A self‐diagnosis strain sensor operating in a continuous online SHM scenario is considered. The strain sensor is based on full electric resistance strain gauge Wheatstone bridges. The state of the art shows that such a sensor has not yet been developed. The loop current step response (LCSR) is a well‐known method to detect strain gauge debonding. However, applying the LCSR method to a full strain gauge Wheatstone bridge has some limitations analysed in this paper. To enable the use of the LCSR method in an online SHM scenario, the double bridge circuit is proposed in this work. Two new strain gauge debonding fault detection methods and a new debonding fault isolation method—based on the double bridge circuit measurements—are proposed and evaluated. Two new sensor fusion weighting approaches are also proposed and evaluated—to achieve strain gauge debonding fault tolerance on the double bridge circuit. The experimental results show that the proposed methods can detect, isolate, and tolerate a strain gauge grid debonding fault and can be applied in an online SHM self‐diagnosis sensor scenario.     

Evaluation of Fracture Surfaces in Carbon Fiber/Epoxy Composites

We have investigated carbon fiber/resin debonding mechanisms using wetting force scanning to examine the fracture surfaces. The wettability of the site of a resin microdroplet (50-150 μm long) on a fiber after debonding is compared with that of the original fiber surface by scanning along the fiber with an appropriate probe liquid. For an HMS/Epon828 system, debonding seems to involve removal of a layer of carbon fiber, while for an AS4/Epon828 system, there is evidence for adhesive failure as well as cohesive failures in both fiber and resin. These contrasting failure mechanisms are consistent with the morphological structures of the carbon fibers studied.     

CFRP加固混凝土结构剥离损伤识别试验研究

碳纤维增强复合材料(CFRP)由于强度高、重量轻、适应面广等特点,成为土木工程修复和加固工程中引人注目的替代材料.剥离破坏是CFRP加固结构时常见的破坏方式,一旦发生剥离破坏,将达不到预期的加固效果,不仅造成材料浪费,而且被加固结构也存在安全隐患.可以采用无损检测(NDT)的方法对剥离损伤进行识别.利用压电陶瓷对CFRP加固的混凝土柱的剥离损伤进行试验研究,以确定损伤的位置和程度.将一组压电陶瓷(如镐钛酸铅,简称PZT)预埋在小体积混凝土中,制成“智能骨料”,并将其预埋在混凝土柱内的指定位置.柱表面进行CFRP加固处理,在指定位置设置人工模拟剥离损伤.将另一组PZT片粘贴在具有人工剥离损伤处的表面.利用扫频波对具有预先设定剥离区域的CFRP加固混凝土试件进行试验,其中三个预埋的“智能骨料”作为作动器,表面粘贴的PZT作为传感器.对接收到的检测信号,利用傅里叶频谱分析与定义的两个基于小波包分析的损伤指标进行计算,不但成功检测到模拟的剥离区域,而且可以看出损伤指标对试件剥离损伤程度具有足够的灵敏度.