Search results for "Transports"
showing 10 items of 485 documents
A methodology for the rapid characterization of Mode II delamination fatigue threshold in FRP composites
2019
Abstract A new methodology to measure the Mode II interlaminar fracture in fatigue for FRP composites is developed. The proposed methodology uses a Modified Transvers Crack Tensile (MTCT) specimen and is able to characterize the near threshold behavior in a robust, easier and significantly faster way than standard procedures. Analytical formulae, able to link the crack growth rate to the load or strain amplitudes, were found and verified, and their importance was explained, in particular, for what concerns the characterisation of the near threshold behavior. Experiments were performed both in load and strain control, while the delamination growth was monitored using different techniques inc…
Robustness of Empirical Vibration Correlation Techniques for Predicting the Instability of Unstiffened Cylindrical Composite Shells in Axial Compress…
2020
Thin-walled carbon fiber reinforced plastic (CFRP) shells are increasingly used in aerospace industry. Such shells are prone to the loss of stability under compressive loads. Furthermore, the instability onset of monocoque shells exhibits a pronounced imperfection sensitivity. The vibration correlation technique (VCT) is being developed as a nondestructive test method for evaluation of the buckling load of the shells. In this study, accuracy and robustness of an existing and a modified VCT method are evaluated. With this aim, more than 20 thin-walled unstiffened CFRP shells have been produced and tested. The results obtained suggest that the vibration response under loads exceeding 0.25 of …
An experimental method for the investigation of rigid polyurethane foams in shear
2018
Widespread applications of rigid polyurethane and plastic foams lead to shear deformations. Therefore, methods for ensuring shear using experimental investigations are necessary, including the possibility of determining the shear modulus, strength and limit angle. Therefore, a device that allows investigating the shear properties of highly porous plastic foams was developed. The proposed device comprises a clip-on extensometer, commonly exploited in uni-axial compression/tension tests, for the determination of the shear displacement directly on the foams’ sample, on a measurement zone of certain dimensions and location. An innovative construction of the extensometer’s legs is elaborated, p…
Model of delamination propagation in brittle-matrix composites under cyclic loading
2001
A model of interlaminar fatigue crack growth based on damage accumulation ahead of the crack is proposed. Linear cumulative assumption is used for damage estimation, and a quadratic failure criterion is applied for complex interlaminar loading. Model parameters are determined from mode I and mode II fatigue tests, and used to predict mixed-mode delamination propagation rate. Comparison of theoretical prediction with mixed-mode test results for different brittle graphite FRP at several mode- and load ratios show reasonable agreement.
Effects of the indentation process on fatigue life of drilled specimens: optimization of the distance between adjacent holes
2016
The generation of permanent compressive stresses around the holes is recognized as a valuable mean to delay the onset and propagation of the defects and to extend the fatigue life of the mechanical components. In the work, a bilateral indentation process, performed on each side of the component, is widely used in order to create a residual circumferential stress field around the area to be drilled and that persists after the drilling operation. In order to evaluate the process parameters and to identify optimal geometric solutions, several static and fatigue tests are conducted on AW 6082-T6 aluminum alloy specimen where two holes are created. In particular, experimental tests on only drill…
Flexural vibrations of discontinuous layered elastically bonded beams
2018
Abstract This paper addresses the dynamic flexural behavior of layered elastically bonded beams carrying an arbitrary number of elastic translational supports and rotational joints. The beams are referred to as discontinuous for the discontinuities of response variables at the application points of supports/joints. The Euler-Bernoulli hypothesis is assumed to hold for each layer separately, and a linear constitutive relation between the horizontal interlayer slip and the interlaminar shear force is considered. Based on the theory of generalized functions to handle the discontinuities of response variables due to supports/joints, exact beam modes are obtained from a characteristic equation b…
Influence of Rotor Suspension Anisotropy on Oil Film Instability
2018
A crucial problem of turbomachinery is the oil film instability on increasing the angular speed, which is correlated with the asymmetry of the bearing stiffness matrix and resembles the hysteretic instability somehow. As a beneficial effect is exerted on the latter by the anisotropy of the support stiffness, some favorable effects have been recently found by the author also for the former, whence a systematic analysis has been undertaken. The instability thresholds may be detected by the usual conventional methods, but a detailed analysis may be carried out by closed-form procedures in the hypothesis of symmetry of the rotor-shaft-support system, which condition approaches the real working …
Salt spray fog ageing of hybrid composite/metal rivet joints for automotive applications
2017
Abstract The present experimental investigation aims to investigate the effect of salt-fog exposition on the mechanical behaviour of composite/metal riveted joints. To this aim, two kinds of joint were exposed to salt-fog environmental conditions according to ASTM B117 standard, for fifteen weeks. In particular, two composite laminates (i.e. glass fibre and carbon fibre/epoxy composites) were used as composite substrate joined with the metal substrate (i.e. aluminium alloy Al 6060). Single-lap shear tests were carried out in order to evaluate the evolution of the mechanical performances and the damage mechanisms of the riveted joints during the ageing exposition. The results evidence that t…
Thermal effects of continuous laser treatment on Ti-6 Al(wt%)-4V(wt%) titanium alloy
2008
A titanium alloy Ti-6 Al(wt%)-4V(wt%) was treated in air by Nd:YAG laser radiation (wavelength of 1.064 %m) in continuous mode. Targets were irradiated globally with different levels of energy (accumulated fluence) at constant power. Different focal lengths and beam displacement velocities were used. Cross section microstructural observations were carried out by scanning electron microscopy. Backscattered electron imaging reveals microstructural modifications in samples. A structural phase transformation of beta (bcc) to alpha prime (hcp) phase was observed. The depth of the transformed zone observed by phase transformation is dependent on the treatment parameters. Conformity between micros…
Effect of the loading rate on ultimate strength of composites. Application: Pressure vessel slow burst test
2013
International audience; The strength of unidirectional elastic fibre composites is shown to depend on the loading rate as the viscoelastic nature of the matrix results in a fall in breaking load as the rate is reduced. The simulation of the accumulation of fibre breaks leading to failure, takes into account all physical phenomena involved fibre failure, including the stochastic nature of fibre strength, stress transfer through the matrix between reinforcements, interfacial debonding and the viscoelastic nature of the matrix. The kinetics of composite failure are seen to involve the initial formation of random fibre breaks which at higher loads coalesce into clusters of broken fibres. The ra…