Papers by Keyword: Impact Damage (ID)

Abstract: The paper presents some aspects concerning the use of infrared thermography (IRT) in the evaluation of composite pipes integrity. Composite pipelines made up of glass fibres reinforced epoxy resins are increasingly used, especially in oil and gas industry, for their good mechanical properties, combined with reduced weight and excellent behaviour under hostile environment conditions. Taking into account that high reliability is required for such pipe networks, it is mandatory to choose reliable non-destructive inspection (NDI) methods to achieve efficient structural health monitoring. The main advantages of the IRT inspection are: non-contact and non-dangerous examination. In order to characterize the integrity of composites pipes, first of all the researches were interested in obtaining a set of reference images and then to examine the samples before and after the impact stress test. The conclusions point out the schemes and the optimal parameters of evaluation as well as the application limits of thermographic inspection

Abstract: Composite stiffened panels are widely used in the modern aircraft structure with the advantages of light weight, structural efficiency and good crack performance. But the stiffened panels have poor performance at thickness direction, especially for low-velocity impact. First of all, compressive tests were investigated and analyzed for two types of composite stiffened panels, which are integrated specimens and post-impact specimens. And the effect of low-velocity impact to the supporting capacity of composite stiffened panels was researched. Secondly，the finite element model was established to simulate the CAI (Compression After Impact)strength with the equivalent hole method. It is found that the analyze results match the experimental results well. According to the experimental results, structural damage and the maximum load caused by impact energy are scattering. Then the imperfect factors were introduced to reflect the initial imperfection, namely the initial deflection at thickness direction. The effect of different imperfect factors to the maximum load was discussed.

Abstract: The ultimate objective of the current work is to examine the effect of thickness on fiberglass reinforced epoxy matrix subjected to high velocity impact loading. The composite material chosen for this research was from type C-glass/epoxy 200 g/m² and type C-glass/epoxy 600 g/m². This material is used as a composite reinforcement in high performance applications since it provides certain advantages of specific high strength and stiffness as compared to metallic materials. This study investigates the mechanical properties, damage characterisation and impact resistance of both composite structures, subjected to the changes of impact velocity and thickness. For mechanical properties testing, the Universal Testing Machine (UTM) was used while for the high velocity impact, a compressed gas gun equipped with a velocity measurement system was used. From the results, it is found that the mechanical properties, damage characterisation and impact resistance of type C-glass/Epoxy 600 g/m² posses better toughness, modulus and penetration compared to type C-glass/Epoxy 200 g/m². A general trend was observed on the overall ballistic test results which indicated that as the plate specimen thickness continues to increase, the damage at the lower skin decreases and could not be seen. Moreover, it is also found that, as the plate thickness increases, the maximum impact load and impact energy increases relatively. Impact damage was found to be in the form of perforation, fibre breakage and matrix cracking. Results from this research can be used as a reference in designing structural and body armour applications in developing a better understanding of test methods used to characterise impact behaviour.

Abstract: This paper studied factors influencing AU detection results on different damage specimens, including simulation frequency, transducer modes and transducer location. Correlation between acousto-ultrasonic parameters (AUP1, AUP2) and impact damage severity in composite was investigated. The results showed that as damage severity increased, AUP1 and AUP2 of three different transducers decreased. Applying low frequency transducer, the variation of AUP1 may indicate a more rapid detection prospect. In addition, applying S1-transducer and WD-transducer, AUP2 was more effective for the early damage detection. Varying transducer’s location, S1-transducer applying 500khz simulation frequency presented a valuable results.

Abstract: This paper presents the finite element damage simulation of laminated plates induced by low-velocity transverse impact. The solid elements are used to model the laminae, and the solid-shell interface elements are employed to characterize the behavior of the interfacial layers of the laminated plates. The material properties of the adhesive layers are used in the solid-shell interfacial elements for the damage prediction. The simulated damage propagation agrees well with the experimental results. Therefore, the numerical results show that the solid-shell interface element is a good computational model for the interfacial layer modeling in the damage simulation.

Abstract: The propagation characteristic of Lamb waves activated by Piezoelectric actuators and collected by sensors in a stiffened panel has been investigated. A network of actuators is used to scan the structure before and after the presence of damage. A diagnostic imaging algorithm has been developed based on the probability of damage at each point of the structure measured by the signal reading of sensors in the benchmark and damaged structure. A damage localization image is then reconstructed by superimposing the image obtained from each sensor-actuator path. Three-dimensional finite element model with a transducer network is modeled. Damage is introduced as a small softening area in the stiffened panel. Applying the imaging algorithm, the damage location was predicted with good accuracy. This method proves to be suitable for stiffened panels, where the complicated geometry and boundary reflections make the signal processing more complicated.

Abstract: Kinetic equation of dumping geo-container is considered, ALE dynamic mesh technique of finite element is applied, and strength and failure problem in the process of geo-container hitting the bottom is discussed. The finite element model of dynamic meshing is established, and the motion state, stress and strain of the geo-membrane of the large geo-container during the process of dumping are analyzed and calculated. By comparing with the results of the flume model experiment and dynamics calculation, the results verify the FEM model of fluid-structure coupled dumping geo-container; during the dumping, the tensile stress on the geo-membrane is the largest at the first 0.24 seconds after the geo-container hitting the bottom, and the maximum is 6.936 MPa at node 397 in the geo-container; after the failure analysis of the geo-membrane, the breaking strength is 27.050 MPa, which is less than the allowable strength, and meets with the strength requirements.

Abstract: Carbon fiber reinforced polymer (CFRP) composites have been used extensively because of their excellent performance, but they are susceptible to the impact damages, such as the impact of birds, runway stones and tools off can cause the failure of CFRP composites. Therefore, nondestructive testing of CFRP composites is necessary to promote the failure control and prevention. Ultrasonic burst phase thermography (UBP) developed a few years ago is a defect-selective and fast imaging tool for damage detection. This paper describes the principle of UBP, gives some UBP testing results of impact damages in five CFRP laminated boards. The shape and position of the damages are shown in the phase images visualized and the relationship between the damage areas and impact energy is discussed. The flash pulse thermography (PT) results and ultrasonic C-scan results are also shown as comparison. It is concluded that all of the three NDT methods have their own characteristics and the comparison verifies the feasibility of CFRP impact damage detection using ultrasonic burst phase thermography.

Abstract: In order to research the aircraft impact damage, one symbolic fitting method for analyzing and forecasting the damage data is proposed based on genetic programming (GP). The method can be used to forecast the impact damage by recognizing the rule in some groups of actual data including impact parameters and damage hole size. The principle of GP symbolic fitting method is briefly introduced. The fitting model is created with some sample data respectively for training and testing from Sorenson experiential equation. The computation with Matlab program indicates the model has a good performance to fit and forecast the damage data with avoiding the noise. The application of GP symbolic fitting method can help to decrease the times of fire experiments. Since the method can recognize the complicated nonlinear relationship between the impact parameters and damage data, it is more applicable than theoretical analysis and experiential equation to forecast the aircraft impact damage.

Abstract: The damage ‘freezing’ test of concrete was carried out with the static load and SHPB testing technique, so the relatively loss ultimate bearing capacity could express the damage in macro-level. The result showed that the dynamic damage of the concrete increased with the increasing strain or strain rate and the dynamic damage had a certain strain threshold. Based on the damage evolutive law of concrete whose probability density was distributed Weibul1 distribution, the impact damage factor equation was put forward. Besides, the unified equation which described the whole stress-strain process of the concrete after impact damage were established. Compared with the testing data, it showed that the experiment and theoretical results were in good agreement.