碳／环氧层合板连接孔的损伤扩展特性

作者通过实验研究了碳纤维增强复合材料迭层板(CFRP)连接孔在温湿环境条件下的静强度和疲劳寿命,实验结果用图表和曲线加以描绘。对“失效”试件,利用“揭层技术”(Deply Tecnique),渗透剂增强的X射线图象法(TBE)以及扫描电镜方法(SEM)进行损伤检测分析,揭示了连接孔周围脱层和纤维断裂等损伤情况,对温湿条件下疲劳寿命降低等实验现象,在细观上进行损伤机理分析。本文并对各种损伤检测方法进行了比较。     

A technique to measure fatigue crack growth threshold

An experimental technique for determining fatigue crack growth threshold is presented. This experimental technique uses an increasing ΔK step loading procedure to determine threshold going from a no-growth to growth status. Stress relief annealing of the Ti-6AI-4V test specimens eliminates load history effects normally associated with the precrack, providing a measurement equivalent to what is achieved by a standard ASTM load shed test. In addition to measuring load history free thresholds, this increasing ΔK technique can be used to investigate different load history effects on threshold by using the threshold step measurement with different precrack histories and without the subsequent annealing process. Verification of the threshold step measurement is demonstrated by comparing measurements with standard ATSM load shed testing results.     

LANGMUIR—BLODGETT膜及其摩擦行为

本文回顾了Langmuir-Blodgett膜(简称LB膜)的发展简史,综述了各种类型LB膜的制备方法和利用其解决磁记录技术中超薄润滑问题的现状等,并且阐述了影响LB膜成膜质量的因素,论述了速度、负荷和LB膜之累积层数等对LB膜摩擦行为的影响。文章最后还提出了为把LB膜应用于摩擦学领域所必须深入研究的几个问题。作者认为,由于LB膜具有无与伦比的超薄和厚度容易控制,以及分子取向有序等诸多优点,故其除在磁记录技术中的应用外,对解决空间技术中的某些润滑问题及一些小负荷工况下的超薄润滑问题都将发挥重要作用。     

副翼铰链力矩脱机校准试验的简化方法及验证

飞机副翼铰链力矩飞行实测是新机定型的必要环节。采取传统的脱机载荷校准方法完成某新型民机副翼铰链力矩的校准试验需要自主研发专用实验台,难度大、成本高。本文提出了一种简化的副翼作动器脱机载荷校准试验方法,不需要研制专用实验台,仅使用一台拉压试验机,排空作动器中的液压油,将作动器直接安装在拉压试验机上进行拉压试验即可完成校准试验,建立载荷模型。通过两点和四点地面联机验证试验验证了载荷模型的正确性,其中四点加载时左右副翼载荷模型的误差分别为0.8%和0.3%。该方法为具有类似结构飞机活动面的脱机载荷校准试验提供了一种重要的技术途径。     

杆式冲击装置测定材料动态J积分

本文介绍了一种研究材料动态断裂韧度的实验技术。该方法采用冲击杆对常规三点弯曲试件进行动态加载。由于长杆条件下存在荷载、位移及冲击速度之间的定量关系,试验中只需对荷载的时间历程进行测定,就能间接地计算出位移和J积分值。与目前广泛使用的示波摆锤(落锤)冲击法相比,不仅测试过程明显简化,而且力学分析的基础也更为可靠。     

Development of a load-cell compensation system

When a materials testing machine is used dynamically, the force recorded by the load cell may differ from that experienced by the specimen. This error is caused by the mass of the load string, usually the grip, between the specimen and the load cell.The equations of motion for a testing machine are developed and the parameters affecting the error are identified. A system is described which removes the inertia error from the load-cell output by measurement of the acceleration of the mass. The effectiveness of the technique is assessed by the use of strain-gaged reference specimens, of different stiffnesses, for comparison with the load-cell output. Two methods for calibrating the system are used and their merits assessed.     

A Review of External Pressure Testing Techniques for Shells including a Novel Volume-Control Method

A review of conventional testing methods for applying external hydrostatic pressure to buckling-critical shells is presented. A new “volume-control” pressure testing method, aimed at preventing catastrophic specimen failures and improving control of specimen deformation near the critical load, is also introduced. The implementation of conventional and volume-control systems in an experimental program involving the destructive pressure testing of ring-stiffened cylinders is described. The volume control method was found to improve control of the specimen deformations, especially near the critical load, and catastrophic failures observed while using a conventional setup were avoided. The quasi-static tracking of post-collapse load-deformation relationships for snap-through buckling behaviour was possible while using a volume-control system, but precise control of dynamic shell deformations during buckling was not achieved for specimens failing with large buckling lobes. Expressions for estimating the available control over specimen deformations for pressure testing systems are presented.     

An ultrasonic technique for nondestructive testing of butt-welded steel plate in ship hulls

This paper proposes an ultrasonic nondestructive testing (NDT) method for underwater-diver inspection of shiphull welds. The specimens used were prepared with various induced cracks in the vicinity of the welds. The type of flow considered is a transverse crack in the heat-affected zone in a butt-welded seam. An automated data analysis is developed to scan, locate and characterize cracks using the pulse-echo technique with a single focus transducer. Specimens and probes were submerged in sea water as an additional exercise in simulating operating conditions. Calibration of the NDT characterization was established by first heat tinting to register the size of the induced crack and subsequently to load the specimen to failure so as to examine the crack. The results show that the actual crack length and the maximum load to failure for each cracked specimen were comparable with the test data obtained from the NDT. presently at mechanical Engineering Department, King Abdulaziz University, P.O. Box 9027, Jeddah 21413, Saundi Arabia.     

Investigation of Impact Response of Composites with Projection Moiré Enhancement

As a method for measuring full-field out-of-plane displacement, projection moiré provides high measuring quality with simple experimental setup. Based on an image processing program developed by Heredia and Patterson, this article presents the implementation of projection moiré in low-velocity impact testing. Results from projection moiré agree reasonably well with those obtained from the commonly used load cell method. In an attempt to better document composite response to impact loading, the possibility of correlating the external out-of-plane displacement measurement with the internal delamination is discussed. The technique is further applied to composites with various microstructures, including laminated, two-dimensional woven and quasi-three-dimensional (Q3D) woven composites. Projection moiré is able to provide some insights of the delamination propagation of the composites under impact loading.     

中应变率下材料动态拉伸关键参数测试方法

通过高速液压伺服材料试验机进行金属材料的中等应变率动态拉伸力学性能测试。为获取精确的动态拉伸载荷数据,提出了一种拉伸载荷的间接测量方法,在不改变试验机原有结构的情况下,解决了试验机自带载荷传感器测试数据在塑性段振荡导致材料真正动力学行为被掩盖的问题;通过数字图像相关的非接触测量方式进行动态拉伸应变的测量。实验验证表明,提出的载荷和应变测试方法可实现金属材料动态拉伸试验中的力学性能参数测试。     

Crack-length measurement by compliance in fracture-toughness testing

The experimental evaluation of crack length in the elastic unloading compliance technique for fracture-toughness testing of compact tension (CT) specimens is discussed with reference to the accuracy required for the digital acquisition of the load and displacement data. In addition, the influence of nonlinearity in the clip-gage output with displacement is considered. The use of a second-order polynomial calibration function is described and discussed.     

High-speed stochastic fatigue testing

Good stochastic fatigue tests are difficult to perform. One of the major reasons is that ordinary servohydraulic loading systems realize the prescribed load history accurately at very low testing speeds only. If the speeds used for constant amplitude testing are applied to stochastic fatigue testing, quite unacceptable errors are introduced. Usually this problem is solved by running the tests at very low speeds and by editing the load history in order to reduce the duration of the test. In this paper a new method for control of stochastic fatigue tests is proposed. It is based on letting the analog control device remain as the basic control mechanism in the system, but distorting the input signal by computer in order to minimize the errors of the load history extremes. The principle proves to be very efficient to reduce all kinds of system errors and has shown to be able to increase the allowable speed by a factor from 10 to 30.     

单向双筋板结构件共振疲劳试验及分析

航空航天领域广泛存在着振动疲劳问题,严重危及飞行器结构的安全可靠性。本文首先设计了激振器直接作用于试件的力激励振动疲劳试验系统,并提出了跟踪结构共振频率的频带激励共振疲劳寿命测试方法;而后利用试件进行了频带激励下的定应变共振或定载荷共振结构振动疲劳试验;最后针对试验结果分析与讨论了可能影响结构振动疲劳寿命的各种因素。结论表明,试验结构件的边界条件、初始条件以及结构动力学特性等都可能是影响振动疲劳寿命的关键因素。频带激励共振疲劳试验方法为振动疲劳寿命曲线的测试积累了经验。     

Obtaining a Wide-Strain-Range True Stress–Strain Curve Using the Measurement-In-Neck-Section Method

Background

Measuring true stress–strain curve over a large-strain-range is essential to understand mechanical behavior and simulate non-linear plastic deformation. The digital image correlation (DIC) technique, a non-contact full-field optical measurement technique, is a promising candidate to obtain a long-range true stress–strain curve experimentally.

Objective

This paper proposes a method for measuring true stress–strain curves over a large-strain-range during tensile testing using DIC.

Methods

The wide-strain-range true stress–strain curves of dual-phase and low carbon steels were extracted on the transverse direction in the neck region. The axial strain on the neck section was estimated by averaging the inhomogeneous deformation on the cross-section of the tensile specimen. The true stress was calculated from the engineering stress and the cross-sectional area of the neck.

Results

The validity of the proposed method was assessed by comparing the experimental load–displacement responses during tensile testing with the finite element method (FEM) simulation results. The stress and strain on the neck section estimated using the FEM and DIC, respectively, were proven to satisfy the uniaxial condition and successfully obtained.

Conclusions

The experimental results agree well with the FEM results. The proposed concept can be applied to various deformation modes for accurately measuring long-range true stress–strain curves.

     

微负荷摩擦测试系统

研究了采用浮力原理施力，用高灵敏度应变传感器测力的微负荷摩擦试验方法。测试结果表明，微负荷摩擦测试系统具有较高的分辨率和测试精度。     

用电子散斑干涉法进行结构内部微小缺陷检测的研究

本文应用电子散斑干涉法和相移技术对结构内部缺陷测试进行了试验研究,研究中采用气压加载,获得了相同气压载荷作用下不同试件的变形图,由此计算得到的结果表明,有缺陷的试件和无缺陷的试件在相同的气压载荷作用下变形不同,同时,相同载荷作用下,缺陷尺寸不同时,试件的变形不同.该试验证明了电子散斑干涉法在研究结构内部缺陷在气压载荷作用下的微小变形的有效性,进一步对缺陷影响的定量研究将为预知缺陷的尺寸及位置,结构的安全和检测提供帮助,同时将该方法应用进一步的推广和改进,将为结构无损检测提供依据.     

微小缺口/孔洞的激光衍射无损检测

基于裂纹和孔洞的小尺寸特征,提出了微小缺口/孔洞的激光衍射无损探测技术,给出了解析表达式.通过这一技术,对单向拉伸试件中所含单边缺口和中心孔洞在外载作用下的演化过程进行了实时原位检测,获得了缺口/孔洞孔径随载荷的变化曲线及模拟裂纹时裂纹的张开位移、裂纹开裂长度及应力强度因子等一系列断裂参数.     

大准铁路黄河特大桥钢桁梁静载试验

大准铁路黄河特大桥钢桁梁为 96 132 96m三跨连续式、无竖杆刚性桁梁柔性拱组合系结构。运营十年后进行了静载试验,并将测试结果与数值计算进行了对比。钢桁梁在中 -活载和恒载作用下,轴向总应力最大的杆件为A17E18,其总应力为 142. 083MPa。在中 -活载作用下,边跨中和中跨中的挠度,分别为 76. 23mm和 63. 94mm,其挠跨比分别为 1 /1259和 1 /2064。由此可以看出该桥承载力和竖向刚度符合设计标准,满足使用要求,且承载力和竖向刚度安全储备较大。上下游两片主桁受力均匀性较好。测试方法和结果可供类似工程参考。     

A Piezoelectric Technique for Evaluation of Crack Closure

The ability of the piezoelectric materials to work as sensors and actuators was employed in a technique for monitoring the degree of crack closure and to detect the crack opening load. The technique is demonstrated through experiments with a cracked beam. It consists in exciting the specimen with a piezoelectric actuator and recording the electromechanical response of piezoelectric sensors placed near the crack mouth, while applying a bending moment to open the crack. The sensors in the neighborhood of the crack present a reduction in the amplitude response signal due to the progressive decrease of the dynamic strains near the crack, as the bending load causes the crack to open, reducing the contact between the surfaces of the fatigue crack and the load transmission through the contact area. The results show that the method has a high sensitivity to the state of crack closure, allowing for the direct determination of the crack opening load.     

The cracking behavior of brick walls with steel-stud backup

The results of an experimental and analytical program designed to evaluate the performance of brick veneer walls with metal-stud backups are reported. Particular reference is made to the performance of the walls after a crack develops in the brick veneer. The project included testing of wall ties, flexural testing of full-scale wall systems, and water-permeance testing. Six full-scale walls were tested. three with positive pressure and three with negative pressure. The walls were tested to load levels up to three times the load recommended by the metal-stud manufacturers. The lateralload test results are reported in the form of deflection profiles at various load levels. Test results show that a large proportion of the lateral load is transferred to the metal-stud backup after a crack develops in the brick veneer.