Impact Damage In CFRP Laminates Research Articles

Nonlinear Lamb Wave Imaging for Low Energy Impact Damage of CFRP Laminates

Nonlinear Lamb Wave Imaging for Low Energy Impact Damage of CFRP Laminates

Probabilistic ultrasound C-scan imaging of barely visible impact damage in CFRP laminates

Ultrasonic pulse-echo C-scan imaging is a widespread method for detecting and characterizing defects in fiber reinforced polymer composites. However, the accurate assessment of a complex distributed damage cluster, like barely visible impact damage, in multi-layer and heterogeneous composites is not straightforward. For reliably estimating the remaining load carrying capacity and/or remaining useful lifetime of a damaged composite, a proper and complete damage assessment is of utmost importance.In this paper, a statistical time-energy gating approach is proposed in view of obtaining improved ultrasonic pulse-echo imaging of impacted composites. The majority of virgin A-scan signals are first clustered by analyzing their back-wall echoes. Next, using the principle of maximum likelihood, a Rice distribution is matched to the instantaneous amplitude in order to estimate the natural variability in the local energy of the virgin response signals. The resulting time-varying reliability interval provides an effective means to identify signals coming from defects or inhomogeneities, and as such to robustly assess defect parameters. The proposed probabilistic imaging procedure is demonstrated on various carbon fiber reinforced polymer laminates with barely visible impact damage. The obtained results are benchmarked by conventional ultrasonic C-scan imaging in through-transmission mode as well as in pulse-echo mode using the classical time gating approach. In contrast to the classical time gate method, the proposed statistical time-energy gating procedure successfully extracts and quantifies the full extent of the complex impact damage cluster. Further, the good noise resistance of the proposed probabilistic imaging method is demonstrated for a wide range of signal-to-noise ratios.

Experimental Research on Medium Leakage of CFRP Laminates after Impact

The effects of thickness and impact energy on the medium leakage of composite laminates were discussed in this paper. Impact tests for the composite laminates with the size of 600 mm×700 mm with three different thicknesses were subjected to impact energy levels from 5 J to 40 J. The medium leakage and the damaged area were investigated according to different energy levels and stacking sequences. The damage area was evaluated by visual inspection and three-dimensional microscope. The experimental results reveal that the impact damage of CFRP laminates with three different thicknesses tends to be more severe as impact energy increases. The impact area and the crater depth increases with increasing impact energy. The impact area and the crater depth decreases with increasing thickness for the same impact energy.

Experimental Research on CFRP Laminates with Different Impact Energy Levels

The effects of thickness and impact energy on the impact damage of CFRP laminates were studied in this paper. Impact tests for the CFRP laminates with the size of 600 mm×700 mm with five different thicknesses were subjected to impact fatigue loading at different energy levels from 5 J to 65 J. The crater depth and matrix length were investigated according to different energy levels and different thicknesses. The impact damage was evaluated by visual inspection, three-dimensional microscope. The experimental results reveal that the crater depth and the crack length increase with the increasing impact energy. For the same impact energy, the crater depth and the crack length decreased with the increasing thickness of specimens.

Experimental Research on the Impact Damage of Composite Laminates at Different Energies

The effects of the impact energy on the impact damage of CFRP laminates were studied in this paper. Impact tests for the CFRP laminates with the size of 600 mm×700 mm were subjected to different the impact energy levels from 5 J to 50 J. The matrix length was investigated according to different energy levels. The experimental results reveal that the crack length increases linearly with the increasing impact energy. The impact damage of CFRP laminates tends to be more severe as impact energy increases, and the impact area and crater depth increases with increasing impact energy. The surface of impact dent of specimen looks like W shape.

Experimental Research on the Effects of Dimension on the Impact Damage of CFRP Laminates

The effects of thickness on the impact damage of composite laminates were discussed in this paper. Impact tests for the composite laminates with the size of 600 mm×700 mm with three different thicknesses were subjected to impact energy levels from 5 J to 40 J. The crater depth and matrix length were investigated according to different energy levels and different thicknesses. The impact damage was evaluated by visual inspection, three-dimensional microscope. The experimental results reveal that the crater depth and the crack length increase with the increasing impact energy. The thickness had the negative effects on the impact damage of the specimens at the same impact energy.

Threshold of Impact Energy on the Medium Leakage of CFRP Laminates

The effects of the thickness and the impact energy on the medium leakage of CFRP laminates were discussed in this paper. Impact tests for CFRP laminates with the size of 600 mm×700 mm with three different thicknesses were subjected to impact energy levels from 5 J to 65 J. The medium leakage and the damaged area were investigated according to different energy levels and thicknesses. The damage area was evaluated by visual inspection and three-dimensional microscope. The experimental results reveal that the impact damage of CFRP laminates tends to be more severe as the impact energy increases, and the impact area and the crater depth increases with the increasing impact energy. For the same impact energy, the impact area and the crater depth decrease with the increasing thickness.

Characterization of high-velocity impact damage in CFRP laminates: Part II – prediction by smoothed particle hydrodynamics

High-velocity impact damage in CFRP laminates was studied experimentally and numerically. Part I of this study observed and evaluated near-perforation damage in the laminates and characterized the damage pattern experimentally. Part II predicts the extension of high-velocity impact damage based on smoothed particle hydrodynamics (SPH), which facilitates the analysis of large deformations, contact, and separation of objects. A cross-ply laminate was divided into 0° and 90° layers, and virtual interlayer particles were inserted to express delamination. The damage patterns predicted on the surfaces and cross-sections agreed well with the experiments. The analyzed delamination shape was similar to that resulting from a low-velocity impact, consisting of pairs of fan-shaped delaminations symmetric about the impact point. Finally, the mechanisms of high-velocity impact damage in CFRP laminates are discussed based on the observations and numerical analyses.

Characterization of high-velocity impact damage in CFRP laminates: Part I – Experiment

This study investigated mechanisms of the extension of high-velocity impact damage in CFRP laminates. To this end, damage states due to near-perforation impact were studied in detail. This study consists of two parts. Part I presents the experiment results of high-velocity impact tests for CFRPs with specified stacking sequences. A crater and splits were observed on the impacted surface, while multiple splits with fiber breaks extended on the back surface. The cross-section beneath the impact point included catastrophic ply failure with extensive fiber breaks. Impacted specimens also exhibited a particular delamination pattern consisting of pairs of symmetric fan-shaped delaminations emanating from to the impact point and elongated delamination along the cracks in the bottom ply. These damage patterns were common to all of the stacking sequences. Part II of this study presents a numerical analysis of high-velocity impact based on smoothed-particle hydrodynamics and discusses damage extension mechanisms.

Effect of Material Properties on High-velocity Impact Damage in CFRP Laminates

Effect of Material Properties on High-velocity Impact Damage in CFRP Laminates

PS12 高速衝撃を与えたCFRP積層板の損傷解明

PS12 高速衝撃を与えたCFRP積層板の損傷解明

Detection of impact damage in CFRP laminates by means of electrical potential techniques

Quasi-isotropic samples of carbon fibre reinforced polymer composite 2mm thick were manufactured and instrumented with an array of electrodes. The electrodes were used to introduce a DC current and to measure the resultant potential distribution on the top and bottom surfaces of the laminate. Instrumented samples were impacted at energies between 2 and 12J, and the potential fields measured before and after the impact. The impact damage caused significant changes in local values of potential. Indications of the extent and severity of the impact damage could be best obtained by representing the data as contours of equi-potential change. There was excellent correlation between regions of potential change and impact damage as measured by ultrasonic C scan. The results of finite element calculations of potential change distribution on the surface of current carrying quasi-isotropic laminates containing delaminations of a range of sizes and locations were qualitatively similar to those obtained experimentally, but differed in detail. Results are discussed in terms of the differences between real impact damage and that which was simulated, and the likely performance of a damage detection system based on this principle.

Impact Damage in CFRP Laminates under High Temperature.

In the present study, impact damage in CFRP laminates under high temperature is considered through experimentation. For carbon fiber/epoxy (type A) and carbon fiber/PEEK (type P) laminates having the stacking sequence [0°/90°]SYM, the impact damage is generated under environments from room temperature to 150°C, by the collision of a steel ball launched from an air gun. The total area of delamination is proportional to impact energy for both laminates. When the environmental temperatures are higher, critical energies of generating delaminations are larger for type A specimens and constant for type P specimens, though energies of developing delaminations are constant up to the glass transition temperature for type A specimens, and lower for type P specimens. Residual strengths of impacted specimens are estimated by static three-point bending test. It is shown that the residual strengths are reduced with decreasing total area of delamination.

Delaminations of barely visible impact damage in CFRP laminates

CFRP laminates were impacted by projectiles of low masses, accelerated in an air gun, to have barely visible impact damage (BVID) to simulate damage to aircraft by runway debris. The delamination damage on individual interfaces was revealed by the destructive method of thin strips. In sub-BVID and BVID specimens, the damage was confined mostly to the front 30% of the laminate thickness. Delamination areas in the BVID specimens were found to be considerable — the largest dimension exceeding 12 mm on several interfaces. Nucleation of delamination damage was observed in interfaces adjacent to the mid plane in BVID specimens. At higher impact energies, about 110 to 150% more, the delamination damage was observed on almost all the interfaces with no sign of spalling at the rear surfaces. In comparison with a lightweight projectile of aluminium (4·4 g), a higher density steel projectile (11·8 g) caused more delamination damage for the same impact energy and an identical geometry of projectiles.

Detection of impact damage in CFRP laminates

The initiation and propagation of damage in carbon fibre composites subjected to impact loading has been investigated. High velocity impact tests were conducted on a variety of stacking configurations using a nitrogen operated gas gun. The damage processes were characterised using X-radiography, ultrasonic C-scanning, optical microscopy and the deply technique. The merits and weaknesses of applying such damage detection techniques to the monitoring of impact damage in composites are discussed. The consequence of the various fracture mechanisms on residual tensile strength is also considered.