• Proceedings of the Korean Society For Composite Materials Conference
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• 2001.10a
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• pp.174-178
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• 2001

The piezoelectric thin film sensor can be used to interpret variations in structural and material properties, e.g. for structural integrity monitoring and assessment. To illustrate one of this potential benefit, PVDF film sensors are used for monitoring impact damage initiation in Gr/Ep composite panel. Both PVDF film sensors and strain gages are surface mounted to the Gr/Ep specimens. A series of impact test at various impact energy by changing impact mass and height is performed on the instrumented drop weight impact tester. The sensor responses are carefully examined to predict the onset of impact damage such as matrix cracking, delamination, and fiber breakage, etc. Test results show that the particular waveforms of sensor signals implying the damage initiation and development are detected above the damage initiation impact energy. As expected, the PVDF film sensor is found to be more sensitive to impact damage initiation event than the strain gage.

• Proceedings of the KSR Conference
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• 2011.10a
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• pp.2661-2665
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• 2011

In order to evaluate the structural integrity of a GFRP composite bogie frame due to flying railway ballast, the low velocity impact test and compressive test after impact was conducted for glass fiber/epoxy 4-harness satin woven laminate composites applied to skin part of a bogie frame. The impact test was performed using a instrumented impact testing system with energy levels of 5J, 10J and 20J and the designed impactor based on typical railway ballast shapes such as sphere, cube and cone to simulate the ballasted track environments. The compressive strength was tested to according to ASTM D7137 to evaluate the degradation of mechanical property of impact damaged laminate composites. The results showed that the damage area and the degradation of compressive strength after impact for laminate composites was increased with increase in impact energy for all ballast shapes and was particularly most influenced by cone ballast shape.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2005.11a
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• pp.264-267
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• 2005

Impact damages are very important in the perspective of residual strength of composite structures such as aircrafts, ships, and trains because those damages are sometimes not visible on the surface of the point of impact and the impact resistance of laminated composites is usually not so high. Thus, the impact characteristics of laminated composites should he investigated for the safety of composite structures. This paper investigates the low-velocity impact and damage detection conducted on woven carbon/epoxy laminates. Experimental results show that the type of damage is dependent on the impact energy level and the delamination area becomes larger as the impact energy increases.

• Structural Monitoring and Maintenance
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• v.4 no.2
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• pp.133-151
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• 2017

The paper describes the results of an experimental and numerical investigation into the structural and damage response of sandwich composites to low-velocity impact. Sandwich panels consisting of laminated composite skins with three different layups bonded to a PVC foam core were subjected to impact at various energy levels corresponding to barely visible impact damage (BVID) in the impacted skins. Damage assessment analyses were performed on the impacted panels to characterise the extent and the nature of the major failure mechanisms occurring in the skins. The data collected during the experimental analyses were finally used to assess the predictive capabilities of an FE tool recently developed by the authors for detailed simulation of impact damage in composite sandwich panels. Good agreement was observed between experimental results and model predictions in terms of structural response to impact, global extent of damage and typical features of individual damage mechanisms.

• Proceedings of the KSR Conference
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• 2002.10a
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• pp.86-91
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• 2002

Glass/phenolic composite laminates have been used in the field of non-flammable light rail transit and their applications have expanded more widely. Low velocity impact tests have been used to evalute the effect of temperature and acceleration aging on low velocity impact response of phenolic matrix composites reinforced with woven E-glass fabric. The damage of matrix cracking and delamination are suddenly reduced the compressive strength after impact. The damage area increases with increasing temperature and impact energy. UT C-scan is used to determine damage areas by impact loading. Therefore, all this observations indicate reduced impact damage resistance and damage tolerance of the laminates at elevated temperature.

• Composites Research
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• v.20 no.4
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• pp.42-50
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• 2007

This paper describes the results of experiments and numerical simulation studies on the low-velocity impact damage of two different sandwich composite panels for application to bodyshell and floor structure of the BIMODAL tram vehicle. Square test samples of 100mm sides were subjected to low-velocity impact loading using an instrumented testing machine at four impact energy levels. Part of this work presented is focused on the finite element analysis of low-velocity impact response onto a sandwich composite panels. It is based on the application of explicit finite element (FE) analysis codes LS-DYNA 3D to study the impact response of sandwich structures under low-velocity impact conditions. Material testing was conducted to determine the input parameters for the metallic and composite material model, and the effective equivalent damage model for the orthotropic honeycomb materials. Numerical and experimental results showed a good agreement for damage area and the depth of indentation of sandwich composite panels created by the impact loading.

• Advanced Composite Materials
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• v.18 no.2
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• pp.121-134
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• 2009

The present study investigated, both experimentally and numerically, the improvement of low-velocity impact damage resistance of carbon fiber reinforced plastic (CFRP) laminates due to through-the-thickness stitching. First, we conducted drop-weight impact tests for stitched and unstitched laminates. The results of damage inspection confirmed that stitching did improve the impact damage resistance, and revealed that the improvement effect became greater as the impact energy increased. Moreover, the stitching affected the through-the-thickness damage distribution. Next, we performed FEM analysis and calculated the energy release rate of the delamination crack using the virtual crack closure technique (VCCT). The numerical results revealed that the stitching affected the through-the-thickness damage distribution because the stitch threads had a marked effect on decreasing both the modes I and II energy release rate around the bottom of the laminate. Comparison of the results for models that contained delaminations of various sizes revealed that the energy release rate became lower as delamination size increased; therefore the stitching improved the impact resistance more effectively when the impact energy was higher.

• Structural Engineering and Mechanics
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• v.68 no.3
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• pp.325-334
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• 2018

The Nonlinear dynamic response of a sandwich plate subjected to the low velocity impact is theoretically and experimentally investigated. The Hertz law between the impactor and the plate is taken into account. Using the Extended High Order Sandwich Panel Theory (EHSAPT) and the Ritz energy method, the governing equations are derived. The skins follow the Third order shear deformation theory (TSDT) that has hitherto not reported in conventional EHSAPT. Besides, the three dimensional elasticity is used for the core. The nonlinear Von Karman relations for strains of skins and the core are adopted. Time domain solution of such equations is extracted by means of the well-known fourth-order Runge-Kutta method. The effects of core-to-skin thickness ratio, initial velocity of the impactor, the impactor mass and position of the impactor are studied in detail. It is found that these parameters play significant role in the impact force and dynamic response of the sandwich plate. Finally, some low velocity impact tests have been carried out by Drop Hammer Testing Machine. The results are compared with experimental data acquired by impact testing on sandwich plates as well as the results of finite element simulation.

• Steel and Composite Structures
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• v.17 no.2
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• pp.199-213
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• 2014

The damage characters of scarf repaired composite laminates subjected to low-velocity impact with various energy levels at different locations are studied experimentally. The results are compared with those of the original laminates which have no initial damage and don't need repair. The impact load-time history of the specimens, the velocity-time curves of the impactor, the post impact compressive strength of the specimens and the C-scan photographs of the damaged regions are obtained. The delamination threshold load and damage character of the specimen section at impact point are also studied. The results have shown that the impact response of a repaired composite laminate is sensitive to the location of the impact. The impact load and the delamination threshold load have shown different characters for specimens with different impact locations. The debonding characters of the adhesive and compressive strength after impact of the specimens are also influenced by impact locations.

• Steel and Composite Structures
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• v.50 no.2
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• pp.159-181
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• 2024

In the present study, the effect of geometrical parameters of two different types of aluminum thin-walled structures on energy absorption under three-bending impact loading has been investigated experimentally and numerically. To evaluate the effect of parameters on the specific energy absorption (SEA), initial peak crushing force (IPCF), and the maximum crushing distance (δ), a design of experiment technique (DOE) with response surface method (RSM) was applied. Four different thin-walled structures have been tested under the low-velocity impact, and then they have simulated by ABAQUS software. An acceptable consistency between the numerical and experimental results was obtained. In this study, statistical analysis has been performed on various parameters of three different types of tubes. In the first and the second statistical analysis, the dimensional parameters of the cross-section, the number of holes, and the dimensional parameter of holes were considered as the design variables. The diameter reduction rate and the number of sections with different diameters are related to the third statistical analysis. All design points of the statistical method have been simulated by the finite element package, ABAQUS/Explicit. The final result shows that the height and thickness of tubes were more effective than other geometrical parameters, and despite the fact that the deformations of the cylindrical tubes were around forty percent greater than the rectangular tubes, the top desirability was relevant to the cylindrical tubes with reduced cross-sections.