Flexural vs. tensile strength in brittle materials

International audienceThe tests leading to the determination of the strength of brittle materials show a very wide scattering and a noticeable difference between flexural and tensile strengths. The corresponding statistics are usually described by the Weibull law, which only partly explained the observed difference. From a theoretical point of view, the coupled criterion reaches the same conclusion, the flexural strength is higher than the tensile one. It is shown that these two approaches complement to give a satisfying explanation of the difference between the flexural and tensile strengths. Moreover, according to the coupled criterion, the tensile strength appears to be the only material parameter

Effect of carbon nanotubes on the thermoelectric properties of CFRP laminate for aircraft applications

International audienceThe present paper focuses on the thermoelectric behavior of carbon nanotube-charged carbon fiber-reinforced polymer composite materials for aircraft applications. Two types of samples: Type A with carbon nanotube and Type B without carbon nanotube), and with two different stacking sequences (unidirectional-[0](8), cross orthogonal-[0/90](4)) were manufactured for the thermoelectric experiments, DC electrical current was injected through the specimens, and the temperature of the specimens was monitored simultaneously in order to deduce the effect of carbon nanotube on the electrical conductivity change of the specimen. During the test, transient and steady temperature fields were measured on the sample surfaces by infrared thermography, and real-time voltage measurements monitor the sample electrical resistance. The results show that the presence of carbon nanotube produces increasing values of longitudinal electric conductivity sigma(L) of about 10%. At 9 A, the maximum temperature value is around 95 degrees C for unidirectional and 145 degrees C for cross orthogonal samples. The presence of carbon nanotube tends to decrease the entire range of maximum temperatures, about 7% on average for the unidirectional and about 4% on average for cross orthogonal samples

Numerical simulation of the thermoelectric behavior of CNTs/CFRP aircraft composite laminates

International audienceThe present paper focuses on the development of a model for simulating the thermoelectric behavior of CNTs/CFRP Organic Matrix Composite (OMC) laminates for aeronautical applications. The model is developed within the framework of the thermodynamics of irreversible processes and implemented into commercial ABAQUS Finite Element software and validated by comparison with experimental thermoelectric tests on two types of composites materials, namely Type A with Carbon Nanotubes (CNT) and Type B without CNT. A simplified model, neglecting heat conduction, is also developed for simplifying the identification process. The model is then applied for FEM numerical simulation of the thermoelectric response of aircraft panel structures subjected to electrical loads, in order to discuss the potential danger coming from electrical solicitations. The structural simulations are performed on quasi-isotropic stacking sequences (QI) [45/-45/90/0](s) using composite materials of type A and type B and compared with those obtained on plates made of metallic material (aluminum). For both tested cases-transit of electric current of intermediate intensity (9A) and electrical loading on panels made of composite material-higher heating intensity is observed in composites materials with respect to the corresponding metallic ones

Experimental study to assess the effect of carbon nanotube addition on the through-thickness electrical conductivity of CFRP laminates for aircraft applications

International audienceThe present paper tests experimentally the through-thickness electrical conductivity of carbon fiber-reinforced polymer (CFRP) composites laminates for aircraft applications. Two types of samples were prepared: Type A samples with carbon nanotubes (CNTs) and Type B samples without CNTs. During the electrical experiments, electrical currents of several mA were injected through the specimens. Electrical resistance was monitored simultaneously in order to deduce the changes in the through-the-thickness electrical conductivity caused by the addition of CNTs. Improvement of electrical conduction by two orders of magnitude was achieved through the addition of 1 wt% carbon nanotubes as compared to classic CFRP without CNTs. For moisture saturated samples, the influence of moisture absorption on such measures was found to be negligible. (C) 2015 Elsevier Ltd. All rights reserved