Ainullotfi Abdul-Latif

Failure in composite laminates: overview of an attempt at prediction

Abstract Success with the high strain rate testing of polymer composites has been limited by the ability to isolate the inherent inertial disturbances attributed to the test system. This necessitated the development of a technique for the prediction of high strain rate material property data. The resulting data were used in a finite element analysis (FEA) to simulate impact behaviour of glass fibre reinforced composites. High strain rate properties obtained by extrapolating results of experiments conducted at low to intermediate strain rates were used in the FEA of a simple three-point bend beam impact. Three point bend impact tests were performed on the laminates, and comparisons were made of the results predicted from this analysis and actual impact test data. The results show that the finite element model created may be used to predict the behaviour of woven glass laminates. However, the inclusion of flexible post-failure degradation rules to allow for progressive damage, will improve the accuracy of the analysis.

Reynolds number effects on flow topology above blunt-edge delta wing VFE-2 configurations

This paper discusses further the effects of Reynolds number, angle of attack and leading edge bluntness on the flow topology above delta wing VFE-2 configurations. In this project two delta wing models differentiated by its leading edge radius to the mean aerodynamics chord ratio of 0.15 and 0.3, namely the medium and large radius wing, were tested in Universiti Teknologi Malaysia wind tunnel. The relationship between the leading edge primary vortex and the occurrence of a secondary vortex called the inner vortex on the round-edged delta wings are discussed. The effects of leading edge bluntness, angle of attack and Reynolds number on both vortex systems are further discussed in this paper. The tests in this study were performed at speeds of 18.0 m/s, 36.1 m/s, and 54.2 m/s representing Reynolds numbers of 1×106, 2×106 and 3×106 and based on the mean aerodynamic chord. Two measurement techniques were employed on the models i.e. steady force balance and surface pressure data. The current experiments showed that an increase in leading edge bluntness and Reynolds number can delay the formation of the primary vortex towards the aft portions of the wing.

Aerodynamic damping and stiffness determination for aircraft wing flutter speed analysis

The modeling of aircraft wing flutter using statically determined aerodynamic derivatives may not accurately represent the actual aeroelastic system. This paper presents an experimental method for estimating the transient aerodynamic derivatives relative to the airspeed for four 3D airfoil models. The transient aerodynamic derivatives are used to represent the aerodynamic damping and stiffness in aeroelastic equation of motion to determine the flutter speed of the models. An oscillating dynamic aeroelastic test rig with constraint to pitch motion is developed for the wind tunnel test. A set of wing models with NACA 0010, NACA 0012, NACA 0014 and NACA 0018 airfoils respectively, with a wing span of 0.36m and chord of 0.16m (i.e. AR=2.25) are tested in UTM Low Speed Tunnel with the reduced frequencies range from 0.04 to 0.4. From the experiment, the time responses of the wing models during wind-off and wind-on conditions allow the transient aerodynamic damping and stiffness of the wing aeroelastic system to be determined. By varying the stiffness of the mechanical springs attached to the test rig, the effects of dynamically determined aerodynamic damping and stiffness on aircraft wing flutter speed prediction are observed. It is discovered that the aeroelastic equation of motion gives more realistic flutter speed estimation of the models with the inclusion of aerodynamic damping and stiffness with respect to the airspeed which can not be determined from static test. The differences between the computed wing flutter speeds and the referred wing flutter speeds show that this method gives better estimation of aircraft wing flutter speed for both thin and thick airfoils compared to Theodorsen’s method.

Inclusion of Strain-Rate Effects in Low Velocity Impact Simulation of Laminated Composites

Composite materials are widely used in aircraft, automotive, marine and railway applications and are exposed to impact loads, in particular low velocity impact. As material properties of composites are affected by strain-rate [, finite element analysis (FEA) by using static properties would not predict their impact behaviour accurately. Thus, the objective of this study was to include strain-rate effects in the simulation of composite laminates under low velocity impact. This was achieved using ABAQUS anisotropic damage model (ADM) by taking account of material properties changes as a function of log strain-rate using user-defined ABAQUS/VUSDFLD subroutine Strain-Rate Dependent ADM (SRD ADM). Results obtained from SRD ADM were validated using simple tensile test done by Okoli [. Subsequently a three-point bending impact event of a simple composite laminate beam by a cylindrical steel impactor was simulated using both the original ABAQUS Static ADM and the user-defined SRD ADM, and compared with experimental impact test results done by [. The results show that reductions in errors of predicted maximum impact reaction force (compared to experimental data) were achieved from 29% using Static ADM to 14% using SRD ADM and from 35% using Static ADM to 15% using SRD ADM respectively for impactor speeds of 2 ms-1 and 5 ms-1.