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Biaxial tensile testing of sheet metals is becoming increasingly popular for sheet metal forming. Determining equivalent stresses in biaxial tensile specimens is more complicated than in conventional uniaxial tensile specimens. In the present study, we compare four different approaches to calculate effective stresses during biaxial tensile loading of a cruciform specimen: (a) partial unloading method,...
High‐throughput, high‐accuracy determination of thermal deformation and coefficient of thermal expansion (CTE) of carbon fibre–epoxy composites using 2D‐digital image correlation (2D‐DIC) is described. With the aid of a specially designed ultra‐stable and high fidelity imaging system, which integrates a high‐quality bilateral telecentric lens with monochromatic blue light illumination, surface images...
The crystallinity of stretched crystallizable rubbers is classically investigated using X‐ray diffraction. In this study, we propose a new method based on temperature measurement and quantitative calorimetry to determine rubber crystallinity during mechanical tests. For that purpose, heat power density are first determined from temperature variation measurements and the heat diffusion equation. The...
This paper presents a calorimetric approach to the measurement of mechanical dissipation in specimens subjected to cyclic tensile tests. Mechanical dissipation, that is, the heat power produced by the material due to mechanical irreversibility, can potentially be deduced from the temperature changes captured on the specimen surface by infrared thermography. However, a difficulty arises for long‐term...
The ability of alloy 70Ni‐27.5Fe‐2.5Cr to form an ordered crystalline structure upon application of elevated temperature and the resulting effects on a variety of physical properties such as magnetism, strength, electrical resistance, and specific heat are well known. This paper demonstrates that strain gages made with 70Ni‐27.5Fe‐2.5Cr foil with an ordered crystalline structure have both high gage...
The paper presents a strain measurement technique to be applied on repetitive knitted nets. The application of the procedure is focused on large deployable reflectors used in space applications. Manufacturing of these structures involves knitting of thin metallic wires. Besides space antennas, the method herein developed is advantageous for many other types of knitted tissues such as elastic coatings,...
The tensile properties of a polymer‐bonded explosive (PBX) were systematically studied by using quasi‐static and dynamic experiments. A non‐linear constitutive relation was developed to describe the tensile behaviour of the PBX. The tensile properties of the PBX under different strain rates and temperatures were measured in quasi‐static tests. The tensile behaviour of the PBX was found to exhibit...
This paper uses the Continuous Wavelet Transform Analysis on mode shapes for damage identification. The wavelet analysis is applied to the difference in the mode shapes between a healthy and a damaged state. The paper also includes a novel methodology for estimating the level of noise of the experimental mode shapes based on a standard Signal to Noise Ratio (SNR). The estimated SNRs are used for identifying...
The process and mechanism of impact fractures in sandstone were investigated under equal biaxial static compression. The cracking process was captured by a high‐speed video camera. The results indicate that the main crack propagates along the circumference and finally forms a crater‐shaped failure zone. The size of the crater‐shaped failure zone increases as the static stress and impact velocity increase...
A methodology for finding the yield point of epoxy resins, both neat and particulate toughened, is described. Trends of the effect that particulate filling has on the time dependent response of these materials were constructed from observations made with stereo‐based digital image correlation (3D–DIC), namely, creep and stress relaxation at constant load. The use of 3D–DIC also enabled the observation...
An extensive series of compression tests with birch plywood specimens is conducted in the out‐of‐plane direction. Various experimental conditions are tested with different temperatures and strain rates. To this end, a specially designed Split Hopkinson pressure bar protocol is defined, and the specimen dimensions are validated from quasi‐static EN789 standards experiments. Temperatures are ranging...
Current trends in aircraft design are to increase the economic efficiency by integrating different features in multifunctional materials. One strategy is to embed resistance heater elements between glass‐fibre epoxy layers in (heated) fibre metal laminates and to use them as anti or de‐icing devices in leading edges of wings. Heated glass fibre reinforced aluminium (GLARE) is an example of such a...
Digital shearography is an interferometric technique, which is often used for defect detection on composite structures. The measurement is fast and non‐destructive and thus suitable for the application to cultural heritage. However, a major drawback of the technique is the indirect measurement, because surface strain is used to detect subsurface defects. So the determination of depth, size, and type...
The hardening behaviour of metals is generally described in terms of a stress‐strain curve derived from experiments. In this paper, a linear method to identify the stress‐strain curve starting from full‐field measurement data is presented. This method can be applied to any stress state using a generic yield function, the only requirement is that the full‐field measurement is extended up to the border...
Cultural heritage conservation is an active field of research, where there is an ever‐growing demand for nondestructive and noninvasive diagnostic techniques, for performing remote analysis and diagnosis of the condition of historical structures and pieces of art, often of very high cultural and historical value. In this context, holographic interferometry is a very well‐established optical technique...
In this work, warm white (3,000 K) LEDs were used for investigating accelerated ageing of different classes of natural terpenoid compounds. In particular, colophony, sandarac, shellac, and mastic resins were considered. Maximum total irradiance of 80 Mlxh was used, which can be compared to about 130 years of exposure in recommended museum conditions. Moreover, another set of the same resins was kept...
A MATLAB‐based graphical user interface for simplified comparisons of nuclear magnetic resonance depth profiles or other 1‐dimensional datasets was developed. It allows for the application and combination of 3 statistical methods for computing and visualising similarities. The methods included in the program are principal component analysis, linear discriminant analysis, and dynamic time warping....
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