Hypervelocity impact on CFRP: Testing,material modelling,and numerical simulation

This paper describes the derivation and validation of a numerical material model that predicts the highly dynamic behaviour of CFRP (carbon fibre reinforced plastic) under hypervelocity impact. CFRP is widely used in satellites as face sheet material in CFRP-Al/HC sandwich structures (HC = honeycomb) that can be exposed to space debris. A review of CFRP-Al/HC structures typically used in space was performed. Based on this review, a representative structure in terms of materials and geometry was selected for study in the work described here. An experimental procedure for the characterisation of composite materials is documented by Riedel et al. [ADAMMO – advanced material damage models for numerical simulation codes. ESA CR(P) 4397, EMI report I 75/03, Freiburg; October 31, 2003.]. The test results from the CFRP of the current study allow for the derivation of an experimentally based orthotropic continuum material model data set that is capable of predicting the mechanical behaviour of CFRP under hypervelocity impact. Such a data set was not previously available. In the work by Riedel et al. [Hypervelocity impact damage prediction in composites: part II – experimental investigations and simulations. International Journal of Impact Engineering, 2006;33:670–80.] an orthotropic material data set was used for modelling HVI on AFRP (aramid fibre reinforced plastic), which shows relatively high deformability before failure. The enhancements of the modelling approaches in previous studies [Riedel W, Harwick W, White DM, Clegg RA. ADAMMO – advanced material damage models for numerical simulation codes. ESA CR(P) 4397, EMI report I 75/03, Freiburg; October 31, 2003. Hiermaier S, Riedel W, Hayhurst C, Clegg RA, Wentzel C. AMMHIS – advanced material models for hypervelocity impact simulations. Final report, EMI report E 43/98, ESA CR(P) 4305, Freiburg; July 30, 1999.] necessary to model brittle CFRP are specified. An experimental hypervelocity impact campaign was performed at two different two-stage light gas guns which encompassed both normal and oblique impacts for a range of impact velocities and projectile diameters. Validation of the numerical model is provided through comparison with the experimental results. For that purpose measurements of the visible damage of the face sheets and of the HC core are conducted. In addition, the numerically predicted damage within the CFRP is compared to the delamination areas found in ultrasonic scans.     

Meso-scale modeling of hypervelocity impact damage in composite laminates

ObjectivesThis paper presents an approach to numerical modeling of hypervelocity impact on carbon fiber reinforced plastics (CFRP).MethodsThe approach is based on the detailed meso-scale representation of a composite laminate. Material models suitable for explicit modeling of laminate structure, including fiber-reinforced layers and resin-rich regions, are described. Two numerical impact tests with significantly different impact energies were conducted on thermoplastic AS4/PEEK materials with quasi-isotropic layups. Simulations employed both SPH and Finite element methods.ResultsResults of simulations are verified against experimental data available from the literature and demonstrate good correlation with the experiments.ConclusionsDeveloped modeling approach can be used in simulations where post-impact damage progression in composite material is of the main focus.     

复合材料低速冲击损伤研究及等效模型的应用

复合材料低速冲击损伤的特殊性及危害性使得对航空复合材料冲击损伤的评估尤为重要。该文通过建立数值计算模型并结合实验数据解决了4个方面的应用问题:1)在ABAQUS子程序VUMAT中引入损伤模式及损伤演化,结合层间连接单元对层合板低速冲击损伤进行了模拟;2)损伤容限设计方法要求对含缺陷结构的极限强度做出正确的评估,通过ABAQUS子程序USDFLD引入损伤模式及材料折减方案,得到了含圆孔的层合板极限拉压强度;3)通过ABAQUS子程序UMAT引入损伤模式及刚度折减方案,结合层间连接单元,模拟了含预制分层的层合板压缩失效问题;4)针对共用铺层结构的工程有限元计算问题,提出了力学等效模型,将该模型应用到结构级的静力实验模拟并拓展至结构冲击模拟。     

Hypervelocity impact damage to composites

This paper presents the results of hypervelocity impact tests conducted on graphite/PEEK laminates. Both flat plate and circular cylinders were tested using aluminum spheres of varying size, travelling at velocities from 2–7 km/s. The experiments were conducted at several facilities using light gas guns. Normal and oblique angle impacts were investigated to determine the effect of impact angle, particle energy and laminate configuration on the material damage and ejecta plumes. Correlations were established between an energy parameter and the impact crater size, spallation damage and debris cone angle. Secondary damage resulting from the debris plume on adjacent composite structures was studied using high-speed photography and witness plates. It was observed that for hypervelocity impacts, the debris plume particles have sufficient energy to penetrate adjacent structures and cause major structural damage as well.     

碳纤维层合板弹体冲击仿真方法研究

为了研究碳纤维增强复合材料层合机匣对高速撞击碎片的包容能力,通过LS-DYNA对圆柱弹体撞击BMS8-212层合增强复合材料进行动态仿真计算。有限单元计算模型中,层板材料采用连续损伤材料本构模型,层间采用固连失效接触模式。通过与试验结果的比较,验证了数值仿真方法的可靠性。发现,纤维增强复合材料层合板在弹体的横向高速撞击下主要的失效形式为纤维剪切、纤维和基体挤压、分层破坏、拉伸失效。     

Simulation of delamination–migration and core crushing in a CFRP sandwich structure

Following the onset of damage caused by an impact load on a composite laminate structure, delaminations often form propagating outwards from the point of impact and in some cases can migrate via matrix cracks between plies as they grow. The goal of the present study is to develop an accurate finite element modeling technique for simulation of the delamination–migration phenomena in laminate impact damage processes. An experiment was devised where, under a quasi-static indentation load, an embedded delamination in the facesheet of a laminate sandwich specimen migrates via a transverse matrix crack and then continues to grow on a new ply interface. Using data from this test for validation purposes, several finite element damage simulation methods were investigated. Comparing the experimental results with those of the different models reveals certain modeling features that are important to include in a numerical simulation of delamination–migration and some that may be neglected.     

Ballistic limit prediction using a numerical model with progressive damage capability

The ultimate objective of this study is to provide further understanding of the behaviour of laminated composites of varying lamina orientations and stacking sequences, when under high-velocity impact. Emphasis is placed on the determination of ballistic limits of these composites. To this end, an experimental program is carried out and a computational model, with progressive damage modeling capabilities, is developed using LS-DYNA. Experiments are performed whereby striking velocities are measured, via high-speed photography, to determine the ballistic limits of carbon fiber-reinforced polymer (CFRP) laminates of various stacking sequences. The results are reproduced closely by a numerical simulation, indicating that the numerical analysis conducted, including the choice of material model and contact definition, is an accurate means for modeling the high-speed impact characteristics of CFRP laminates. It is found that the use of static elastic and strength properties to describe the material is reasonable, since strain rate effects are found to be negligible. The kinetic energy of the projectile, plotted over the simulated impact duration, is used as the prime parameter to compare the experimental and numerical results. The numerical results accurately predict the experimental ballistic limit for six of the seven tested laminate stacking sequences. Failure due to delamination is found to play a vital role with respect to the energy absorbing ability and lamina stacking sequence of CFRP laminates.     

Inclusion of a thermoplastic phase to improve impact and post-impact performances of carbon fibre reinforced thermosetting composites — A review

Infusion processing methods have become a popular manufacturing alternative to the autoclave procedure to meet the increased demand for high-performance composites with shorter production times and lower cost. These processes are primarily limited to low viscosity, thermosetting matrices that are inherently brittle, and hence are susceptible to impact damage. It has been shown that introducing a thermoplastic modifier to create a “three-phase composite” can improve the ability of the laminate to resist damage formation and growth, and enhance a damaged laminate's structural performance. A comprehensive review is presented herein of the state-of-the-art on the incorporation of a thermoplastic phase into a fibre-reinforced thermosetting composite laminate to improve its damage resistance and tolerance properties when subjected to a low-energy impact. Several material properties govern the response of a laminate to an impact event, and for this reason, a discussion on the impact damage process and post-impact performance is also presented. Techniques from two main areas of toughening are considered — namely, bulk resin modification and interlaminar toughening. The improvements in laminate performance brought about by the thermoplastic additive are discussed, and each technique is assessed based on its suitability for inclusion in infusion manufacturing processes.     

Bird strike damage analysis in aircraft structures using Abaqus/Explicit and coupled Eulerian Lagrangian approach

The subject of this paper is numerical prediction of bird strike induced damage in real aeronautical structures using highly detailed finite element models and modern numerical approaches. Due to the complexity of today’s aeronautical structures, numerical damage prediction methods have to be able to take into account various failure and degradation models of different materials. A continuum damage mechanics approach has been employed to simulate failure initiation and damage evolution in unidirectional composite laminates. Hashin’s failure initiation criteria have been employed in order to be able to distinct between four ply failure modes. The problem of soft body impacts has been tackled by applying the Coupled Eulerian Lagrangian technique, thereby avoiding numerical difficulties associated with extensive mesh distortion. This improvement in impactor deformation modelling resulted in a more realistic behaviour of bird material during impact. Numerical geometrical and material nonlinear transient dynamic analyses have been performed using Abaqus/Explicit. The main focus of the work presented in this paper is the application of the damage prediction procedure in damage assessment of bird impact on a typical large airliner inboard flap structure. Due to the high cost of gas-gun testing of aircraft components, experimental testing on the real flap structure could not have been performed. In order to evaluate the accuracy of the presented method, the bird and composite damage model have been validated against experimental data available in the literature.     

Hybrid approach in bird strike damage prediction on aeronautical composite structures

This paper deals with the problem of numerical prediction of bird strike induced damage on aeronautical structures. The problem of soft body impacts has been tackled by applying a hybrid Eulerian Lagrangian technique, thereby avoiding numerical difficulties associated with extensive mesh distortion. Eulerian modeling of the bird impactor resulted in a more realistic behavior of bird material during impact, which has lead to an enhanced response of the impacted structure. The work presented in this paper is focused on damage modeling in composite items of aeronautical structures. The bird impactor model and damage modeling approaches have been validated by comparison with experimental gas gun results available in the open literature, while the complete damage prediction procedure has been demonstrated on a complex airplane flap structure finite element model.     

Hybrid approach in bird strike damage prediction on aeronautical composite structures

This paper deals with the problem of numerical prediction of bird strike induced damage on aeronautical structures. The problem of soft body impacts has been tackled by applying a hybrid Eulerian Lagrangian technique, thereby avoiding numerical difficulties associated with extensive mesh distortion. Eulerian modeling of the bird impactor resulted in a more realistic behavior of bird material during impact, which has lead to an enhanced response of the impacted structure. The work presented in this paper is focused on damage modeling in composite items of aeronautical structures. The bird impactor model and damage modeling approaches have been validated by comparison with experimental gas gun results available in the open literature, while the complete damage prediction procedure has been demonstrated on a complex airplane flap structure finite element model.     

Low-velocity impact analysis of composite laminates under initial in-plane load

In this paper, low-velocity impact response and damage of composite laminates is analytically investigated. A modified displacement field of the plate considering initially loaded in-plane strain is proposed. From the displacement field, a finite element equation on the structural behavior of composite laminate is newly induced and a computational program is coded. Numerical results using the FEM code is compared with the numerical ones from reference. Additional numerical analysis is performed on another impact condition, and the effect of initial in-plane load is investigated. Potential delamination damage area in the first inter-ply surface from the bottom of the laminate is approximately estimated, and the effect of the initial in-plane load and the impact condition are also investigated. Consequently, it may be concluded that the initial in-plane load of the laminate does not affect so much on the impact damage area of the laminate.     

空间碎片高速撞击的数值模拟方法评述

计算机数值模拟是实现空间碎片撞击效应地面模拟的重要手段之一。撞击速度增加,撞击的物理机制和效应将发生改变,计算机数值模拟方法也应随之丰富和全面。介绍了基于有网格和无网格方法的高速撞击数值模拟发展历程,并针对数值模拟中常用的有限元法和SPH法进行了分析比较,阐述了高速撞击计算机模拟中无网格法的计算优势,并提出量子力学在未来无网格法数值模拟中的可能应用。为空间碎片高速撞击更加真实可靠的数值模拟提供参考。     

Experimental investigation of impact on composite laminates with protective layers

This paper presents an experimental study of low energy impacts on composite plates covered with a protective layer. In service, composite materials are subjected to low energy impacts. Such impacts can generate damage in the material that results in significant reduction in material strength. In order to reduce the damage severity, one solution is to add a mechanical protection on composite structures. The protection layer is made up of a low density energy absorbent material (hollow spheres) of a certain thickness and a thin layer of composite laminate (Kevlar). Energy absorption ability of these protective layers can be deduced from the load/displacement impact curves. First, two configurations of protection are tested on an aluminium plate in order to identify their performance against impact, then the same are tested on composite plates. Test results from force–displacement curves and C-scan control are compared and discussed and finally a comparison of impact on composite plates with and without protection is made for different configurations.     

Acoustic structural health monitoring of composite materials : Damage identification and evaluation in cross ply laminates using acoustic emission and ultrasonics

The characterisation of the damage state of composite structures is often performed using the acoustic behaviour of the composite system. This behaviour is expected to change significantly as the damage is accumulating in the composite. It is indisputable that different damage mechanisms are activated within the composite laminate during loading scenario. These “damage entities” are acting in different space and time scales within the service life of the structure and may be interdependent. It has been argued that different damage mechanisms attribute distinct acoustic behaviour to the composite system. Loading of cross-ply laminates in particular leads to the accumulation of distinct damage mechanisms, such as matrix cracking, delamination between successive plies and fibre rupture at the final stage of loading. As highlighted in this work, the acoustic emission activity is directly linked to the structural health state of the laminate. At the same time, significant changes on the wave propagation characteristics are reported and correlated to damage accumulation in the composite laminate. In the case of cross ply laminates, experimental tests and numerical simulations indicate that, typical to the presence of transverse cracking and/or delamination, is the increase of the pulse velocity and the transmission efficiency of a propagated ultrasonic wave, an indication that the intact longitudinal plies act as wave guides, as the transverse ply deteriorates. Further to transverse cracking and delamination, the accumulation of longitudinal fibre breaks becomes dominant causing the catastrophic failure of the composite and is expected to be directly linked to the acoustic behaviour of the composite, as the stiffness loss results to the velocity decrease of the propagated wave. In view of the above, the scope of the current work is to assess the efficiency of acoustic emission and ultrasonic transmission as a combined methodology for the assessment of the introduced damage and furthermore as a structural health monitoring tool.     

Hypervelocity impact damage prediction in composites: Part II—experimental investigations and simulations

The extension of damage in composites during hypervelocity impact (HVI) of space debris is controlled by failure thresholds and subsequent energy consumption during damage growth. Characterisation and modelling of the material under partially and fully damaged states is essential for the prediction of HVI effects on fibre-composite structures. Improved experimental and numerical analysis techniques have been developed and are summarised in an accompanying paper. The present paper deals with the establishment of two precise damage experiments under HVI conditions as a validation basis for numerical simulations: The first type consists of space debris impact configurations optimised for damage evaluation and the second experiments reproduce HVI strain rates and compressions in plate impact. Coupling of damage analysis techniques (visual, ultrasonic, residual strength) to quantify different aspects of failure has been achieved. Numerical simulations using the commercial hydrocode AUTODYN in mesh-based and SPH formulations are presented using the material model and data described in the accompanying paper.     

Numerical simulation of hypervelocity impact on CFRP/Al HC SP spacecraft structures causing penetration and fragment ejection

A representative carbon fiber reinforced plastic/aluminum honeycomb sandwich panel (CFRP/Al HC SP) spacecraft structure has been modeled in the hydrocode AUTODYN using the state-of-the-art ADAMMO material model [Riedel W, Harwick W, White D, Clegg R. Advanced material damage models for numerical simulation codes. ESA CR(P) 4397, 2003] to study the performance of the structure during impact events that cause perforation and fragment ejection. A new procedure combining a series of existing theoretical methods has been developed and applied to derive a full set of coarse material data. The data set has been implemented in AUTODYN, and the results of the numerical simulation have been compared to experimental impact test data. For impact tests performed near the structural ballistic limit, quantitatively accurate results were obtained over a range of impact velocities and angles. A further increase in the projectile size resulted in significant destruction of the sandwich panel front face-sheet and diversion from the experimental damage measurements. Inspection of the numerical model has shown non-localized propagation of inter-laminar delaminations, possibly caused by an under-prediction of the laminate dynamic inter-laminar tensile strength. The effects of the delamination propagation occur over an extended time scale and were not found to affect the state and trends of the fragment cloud ejected into the satellite interior. Accordingly, experimental trends of fragment cloud dispersion have been qualitatively reproduced.     

Numerical simulation of impact tests on GFRP composite laminates

The design of advanced composite structures or components subjected to dynamic loadings requires a deep understanding of the damage and degradation mechanisms occurring within the composite material. The present paper deals with the numerical simulation of low-velocity impact tests on glass fabric/epoxy laminates through the LS-DYNA Finite Element (FE) code. Two laminates of different thickness were subjected to transverse impact at different energy levels and modeled by FE. Solid finite elements combined with orthotropic failure criteria were used to model the composite failure and stress based contact failure between plies were adopted to model the delamination mechanism. The final simulation results showed a good correlation with experimental data in terms of both force–displacement curves and material damage.