1,721,089 research outputs found
A quantitative investigation on the thermoelastic effect of cfrp laminates
No full textThe thermoelastic effect on CFRP laminates with various lay-ups is investigated. A
thick low crimp unidirectional fabric reinforcement is adopted. The measured
thermoelastic signal is compared with predictions from two analytical models based on the meso-mechanical bulk properties of the lamina and on assuming a strain witness
behaviour of the surface resin rich layer
A Quantitative Analysis of the Thermoelastic Effect in CFRP Composite Materials
No full textIn this study the thermoelastic signal from carbon fibre-reinforced plastic (CFRP)
laminates is investigated. A comparison between the theoretical and experimental values of the thermoelastic signal is reported, with the theoretical predictions obtained from two different quantitative models. These models are based on the classic thermoelastic effect law extended to the case of orthotropic materials (by using the mesomechanical or bulk approach), and the modified law assuming that the surface resin-rich layer behaves as a strain witness of the laminate. It is found that the theoretical predictions of the two models can be strongly and differently influenced by the intrinsic orthotropy of carbon fibres. Some effects are highlighted in particular such as the influence
of the laminate lay-up and the strong mismatch between the thermal expansion coefficients of the polymer matrix and the fibres. These influences are investigated analytically, predicting the thermoelastic
signal from various lay-ups and using strain-based and stress-based analytical models.
Experimental evidence of some theoretical findings is provided by reporting on tests performed on CFRP tensile samples manufactured from low-crimp unidirectional fabrics
Polycarbonate for frozen stress photoelasticity
No full textThe possibility of using polycarbonate in the frozen stress photoelastic technique is investigated. The results obtained from strip specimens made of laminated and extruded polycarbonate and from plates confirm this possibilit
Thermoelastic stress analysis of titanium components and simultaneous assessment of residual stress
Full text linkThe thermoelastic effect describes a linear relationship between change in body temperature and state of stress in the presence of adiabatic conditions. This approach considers the material properties constant with temperature, which is not correct for all materials. Experimental results and a review of the theory, especially for the titanium and some alloys of aluminium, have shown that the thermoelastic signal is also dependent of mean stress of the material. The use of titanium in various fields of application makes interesting use of thermoelastic technique as full field stress analysis technique. However, it is necessary to make a correction of the measure in relation to the mean stress. The possibility to measure the mean stress allows also an evaluation of residual stresses on the surface of titanium components
Application of thermal methods for characterization of steel welded joints
No full textDespite the large number of proposals in the field of fatigue prediction of welded joints, a globally accepted and unified theory, which applies easily to any load condition, does not exist. Real life components, indeed, differ in geometry and/or type of load from the structural design for which they are regarded by Standards, so that a lot of precautionary safety factors are used that lead to an underestimation of the actual fatigue life of joints. Infrared thermography has a great potential in this field, both from structural and thermomechanical points of view. It enables a full field stress analysis with a sufficient spatial resolution so that the complexity of the stress state at the weld toe and its time evolution are taken into account, emphasizing anomalies that may predict structural failure. A new methods for evaluation fatigue limit damage is presented in this paper and in particular interesting results derived from analysis of the evolution of thermoelastic signal phase. Variations in the value of signal phase indicate a not elastic behaviour and plastic dissipation in the material
Potenzialità dell'approccio basato sull'analisi del segnale termico per la caratterizzazione rapida di materiali ad alta diffusività
No full textCaratterizzazione a fatica con tecnica termografica di giunti Friction Stir Welding in AA5754-H111
No full textA novel signal processing method for TSA applications
No full textA novel development of the thermoelastic stress analysis (TSA) technique for testing mechanical components under the random load condition is presented. The method proposed does not need a reference signal to reduce the amount of noise in the thermoelastic images, allowing an easier application of the TSA to the real working condition of mechanical components. Noise is filtered out by means of a numerical algorithm based on the hypothesis that a random thermoelastic signal can be approximated with a harmonic signal. Some notched specimens under the pseudo-random load condition have been tested using either the proposed method or a commercial one (DeltaTherm. data processing procedure). Results obtained with both methods are in good agreement
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