Abstract This paper presents a study on the interlaminar fracture of filament wound composites. M... more Abstract This paper presents a study on the interlaminar fracture of filament wound composites. Mode II End Notched Flexure (ENF) tests were performed on flat glass/polyester specimens. The tested specimens had asymmetric [±θ] 4 angle-ply stacking-sequences. ...
Numerical and experimental studies of end-notched flexure (ENF) fracture tests were performed to ... more Numerical and experimental studies of end-notched flexure (ENF) fracture tests were performed to obtain mode II R curves for maritime pine (Pinus pinaster Ait.) wood in the radial-longitudinal (RL) crack propagation system. Three-(3D) and two-dimensional (2D) finite element analyses were conducted to determine the mode II release rate of the critical strain energy (G IIc ). The 3D analysis revealed that a small spurious mode III component did not affect G IIc measurements and that the 2D model was very accurate. A new scheme for data reduction based on the equivalent crack concept is proposed to overcome the difficulties related to accurate crack length measurement during propagation. This method does not require previous experimental tests to obtain the elastic modulus, which varies markedly for different wood specimens. Experimental ENF tests were performed to verify the numerical results. The results demonstrate the accuracy of the data reduction method proposed.
ABSTRACT In this work, a new approach is suggested for predicting the open-hole tensile strength ... more ABSTRACT In this work, a new approach is suggested for predicting the open-hole tensile strength of quasi-isotropic [0°/±45°/90°]ns laminates. The well known size dependency of the layer longitudinal tensile strength is explicitly taken into account. The interest in such an approach lies in avoiding material-dependent empirical parameters, e.g. characteristic distances, whose physical meaning is not always clear. In situ fibre strengths were estimated by using longitudinal stresses obtained from finite-element models and experimental data available in the references. The estimated size-dependent fibre strengths were found to be consistent with typical Weibull distributions. It is also worth emphasising that mixed 2D/3D finite-element models were used in this work, since the common 2D models proved to be significantly inaccurate.
... The exact position of the crack front and the stress state in its vicinity are a complex frac... more ... The exact position of the crack front and the stress state in its vicinity are a complex fracture mechanics problem. ... The solution of (7) is (8) where C and D are integration constants that must be determined from the ... The circumferential stress (3) can then be expressed as (9). ...
ABSTRACT This paper presents a closed-form micromechanical equation for predicting the transverse... more ABSTRACT This paper presents a closed-form micromechanical equation for predicting the transverse modulus, E2, of continuous-fibre-reinforced polymers. The equation was derived from a relatively simple mechanics-of-materials analysis of a repeating square cell. The assumptions made concerning the stress distributions and the typical matrix and fibre properties enabled the derivation of a closed-form expression. The present equation is in good agreement with a 3D finite-element hexagonal cell model and with Aboudi's method-of-cells equation, both complex approaches known to provide accurate predictions. Furthermore, combining the equation developed with other well-known equations, enables the calculation of the ν23 transverse Poisson ratio, thus completing the set of layer elastic constants needed for 3D stress analyses.
Composites Part A: Applied Science and Manufacturing, 2013
ABSTRACT Torsion tests were conducted on unidirectional carbon/epoxy laminated plates. Preliminar... more ABSTRACT Torsion tests were conducted on unidirectional carbon/epoxy laminated plates. Preliminary finite element analyses showed that the specimen geometry selected avoided pronounced geometric non-linearity and ensured that a significant volume of material would be under a high fraction of the maximum shear stress. Furthermore, the clear prevalence of in-plane shear stresses allowed the development of a simplified data analysis model. Calculated shear-stress strain curves were consistent with the results of tensile tests on angle-ply coupons, despite lower failure stresses that may have been caused by surface defects or by spurious transverse tensile stresses. Nevertheless, the unidirectional plate torsion test is worthy of further research, given the structural relevance of torsional loads and the problems of in-plane shear tests methods.
Abstract This paper presents a study on the interlaminar fracture of filament wound composites. M... more Abstract This paper presents a study on the interlaminar fracture of filament wound composites. Mode II End Notched Flexure (ENF) tests were performed on flat glass/polyester specimens. The tested specimens had asymmetric [±θ] 4 angle-ply stacking-sequences. ...
Numerical and experimental studies of end-notched flexure (ENF) fracture tests were performed to ... more Numerical and experimental studies of end-notched flexure (ENF) fracture tests were performed to obtain mode II R curves for maritime pine (Pinus pinaster Ait.) wood in the radial-longitudinal (RL) crack propagation system. Three-(3D) and two-dimensional (2D) finite element analyses were conducted to determine the mode II release rate of the critical strain energy (G IIc ). The 3D analysis revealed that a small spurious mode III component did not affect G IIc measurements and that the 2D model was very accurate. A new scheme for data reduction based on the equivalent crack concept is proposed to overcome the difficulties related to accurate crack length measurement during propagation. This method does not require previous experimental tests to obtain the elastic modulus, which varies markedly for different wood specimens. Experimental ENF tests were performed to verify the numerical results. The results demonstrate the accuracy of the data reduction method proposed.
ABSTRACT In this work, a new approach is suggested for predicting the open-hole tensile strength ... more ABSTRACT In this work, a new approach is suggested for predicting the open-hole tensile strength of quasi-isotropic [0°/±45°/90°]ns laminates. The well known size dependency of the layer longitudinal tensile strength is explicitly taken into account. The interest in such an approach lies in avoiding material-dependent empirical parameters, e.g. characteristic distances, whose physical meaning is not always clear. In situ fibre strengths were estimated by using longitudinal stresses obtained from finite-element models and experimental data available in the references. The estimated size-dependent fibre strengths were found to be consistent with typical Weibull distributions. It is also worth emphasising that mixed 2D/3D finite-element models were used in this work, since the common 2D models proved to be significantly inaccurate.
... The exact position of the crack front and the stress state in its vicinity are a complex frac... more ... The exact position of the crack front and the stress state in its vicinity are a complex fracture mechanics problem. ... The solution of (7) is (8) where C and D are integration constants that must be determined from the ... The circumferential stress (3) can then be expressed as (9). ...
ABSTRACT This paper presents a closed-form micromechanical equation for predicting the transverse... more ABSTRACT This paper presents a closed-form micromechanical equation for predicting the transverse modulus, E2, of continuous-fibre-reinforced polymers. The equation was derived from a relatively simple mechanics-of-materials analysis of a repeating square cell. The assumptions made concerning the stress distributions and the typical matrix and fibre properties enabled the derivation of a closed-form expression. The present equation is in good agreement with a 3D finite-element hexagonal cell model and with Aboudi's method-of-cells equation, both complex approaches known to provide accurate predictions. Furthermore, combining the equation developed with other well-known equations, enables the calculation of the ν23 transverse Poisson ratio, thus completing the set of layer elastic constants needed for 3D stress analyses.
Composites Part A: Applied Science and Manufacturing, 2013
ABSTRACT Torsion tests were conducted on unidirectional carbon/epoxy laminated plates. Preliminar... more ABSTRACT Torsion tests were conducted on unidirectional carbon/epoxy laminated plates. Preliminary finite element analyses showed that the specimen geometry selected avoided pronounced geometric non-linearity and ensured that a significant volume of material would be under a high fraction of the maximum shear stress. Furthermore, the clear prevalence of in-plane shear stresses allowed the development of a simplified data analysis model. Calculated shear-stress strain curves were consistent with the results of tensile tests on angle-ply coupons, despite lower failure stresses that may have been caused by surface defects or by spurious transverse tensile stresses. Nevertheless, the unidirectional plate torsion test is worthy of further research, given the structural relevance of torsional loads and the problems of in-plane shear tests methods.
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Papers by Alfredo Morais