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.     

Simulation of orbital debris impact on the Space Shuttle wing leading edge

A series of three dimensional hypervelocity impact simulations has been performed to study the effects of orbital debris impact on the Space Shuttle wing leading edge. The simulations employed an improved hybrid particle-finite element method and an orthotropic elastic-plastic material model recently developed for reinforced carbon–carbon. The simulation results are consistent with the available experimental data, and suggest the use of momentum scaling to estimate damage effects for impact conditions outside the range of current light gas gun technology. Projectile shape and orientation effects appear to be modest for flat plate projectiles at impact velocities above the ballistic limit.     

Hypervelocity impact of small masses on large surfaces of piezoelectric ceramics

The hypervelocity impact of small masses on large surface piezoceramics was investigated to study the impact behavior of hypervelocity projectiles. From a linear elastic model obtained at lower velocities, solutions were found for the hypervelocity case which determine both the size and the momentum of impacting projectiles from the rising slope of the charge signal generated by the impact. The results lead to the development of a new generation of impact detectors for small masses at hypervelocities which consists only of a plate of piezoceramic material.     

Comparison study of MPM and SPH in modeling hypervelocity impact problems

Due to the high nonlinearities and extreme large deformation, the hypervelocity impact simulation is a challenging task for numerical methods. Meshfree particle methods, such as the smoothed particle hydrodynamics (SPH) and material point method (MPM), are promising for the simulation of hypervelocity impact problems. In this paper, the material point method is applied to the simulation of hypervelocity impact problems, and a three-dimensional MPM computer code, MPM3D, is developed. The Johnson–Cook material model and Mie–Grüneisen equation of state are implemented. Furthermore, the basic formulations of MPM are compared with SPH, and their performances are compared numerically by using MPM3D and LS-DYNA SPH module.     

The application of the integral theory of impact to model penetration of hypervelocity impact

The Integral Theory of Impact (ITI) (Swanson and Donaldson, 1978) is a unique formulation of the equations of motions of projectiles to describe the penetration process. The model requires only basic material properties, no empirical data is needed. The original model was modified to divide the penetration process into three consecutive phases. The new model has successfully modeled impacts over a wide range of velocities, at normal or oblique impact, for infinite or finite targets. In order to better match the experimental observations of impacts in the hypervelocity range, it was necessary to include a thermal softening effect on flow stress. For finite targets, the back-face effect is proposed to be a function of both penetration velocity and the speed of sound, extending the model's applicability to hypervelocity penetration.     

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.     

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.     

Historical overview of hypervelocity impact diagnostic technology

The ability to understand hypervelocity impact phenomena and to validate predictive models of material behavior is largely dependent on the diagnostic tools available to the experimenter. These tools range from simple, post-impact examination of targets to extremely sophisticated and complex techniques, which simultaneously measure a myriad of impact parameters on a time scale of nanoseconds to milliseconds. This wide range of available techniques represents the challenge and opportunity if hypervelocity impact experimentation.

There has been a continual challenge to develop diagnostic techniques with ever-increasing resolution, as higher velocities and pressures are achieved. Today's techniques provide the experimenter the means of measuring most hypervelocity impact parameters, including velocity, displacement, temperature, radiation, volumetric change, impluse, stress, and strain of the materials involved. However, the prospective quantum leap in impact velocities to be produced by electromagnetic and electrothermal launchers will require corresponding advances in diagnostic systems.

This paper examines the capabilities and limitations of the major diagnostic techniques for hypervelocity impact experimentation and traces their evolvement as useful laboratory tools.     

Ballistic limit evaluation of advanced shielding using numerical simulations

The advanced shielding concept employed for the Columbus module of the International Space Station consists of an aluminum bumper and an intermediate shield of Nextel and Kevlar-epoxy. Until recently, the lack of adequate material models for the Nextel cloth and Kevlar-epoxy has precluded the practical usage of hydrocodes in evaluating the response of these shields to hypervelocity impact threats. Recently hydrocode material models for these materials have been proposed [1,2] and the further development and completion of this model development is reported in this paper. The resulting models, now implemented in AUTODYN-2D and AUTODYN-3D, enables the coupling of orthotropic constitutive behavior with a non-linear (shock) equation of state. The model has been compared with light gas gun tests for aluminum spheres on the advanced shield at impact velocities between 3.0 and 6.5km/s [3]. Reasonable correspondence has been obtained at these impact velocities and thus the models have been used to perform preliminary assessment of predicted ballistic limits at velocities from 7 to 11km/s. The predicted ballistic limits are compared with ballistic limit curves derived on the basis that damage is proportional to projectile momentum     

Material characterization and development of a constitutive relationship for hypervelocity impact of 1080 Steel and VascoMax 300

The area of hypervelocity impact and associated high energy is one of extreme interest in the research community. A specific example of this emphasis is the US Air Force test facility at Holloman Air Force Base which specializes in the field of hypervelocity impact testing. This Holloman AFB High Speed Test Track (HHSTT) is currently working to increase the speed of their test vehicle to above Mach 10. As the test sled's speed has increased into the Mach 8.5 range, a material interaction has developed which causes “gouging” in the rails or the sled's “shoes” and this starts a process that can result in catastrophic failure. In the tests that do not structurally fail, the rails and shoes are damaged. Previous efforts in investigating this event have resulted in a choice of the most suitable computer code (CTH), and a model of the shoe/rail interaction. However, the specific materials present in this impact problem were not available in CTH. In this work, the specific materials present at the HHSTT (VascoMax 300 and 1080 Steel) will be characterized using the Split Hopkinson Bar Test and a Johnson–Cook constitutive model will be developed. The model will then be validated by comparison to a series of Taylor impact tests. The coating materials utilized on the rails at the HHSTT will also be evaluated using a Taylor impact test.     

Characterization of prompt flash signatures using high-speed broadband diode detectors

Impact flash is a brief, intense flash of light released when a target is impacted by a hypervelocity particle. It is caused by emissions from a jet of shocked material which is thrown from the impact site. Impact flash phenomenology has been known for decades, and is now being considered for applications where remote diagnostics are required to observe and diagnose impacts on satellites and space craft where micrometeoroid and orbital debris impacts are common. Additionally, this phenomena and remote diagnostics are under consideration for missile defense applications. Currently, optical signatures created from hypervelocity impact can be utilized as the basis for detectors (spectrometers, pyrometers), which characterize the material composition and temperature. More recent interest has focused on study of hypervelocity impact generated debris and the physics of the associated rapidly expanding and cooling multiphase debris cloud. To establish this capability technically in the laboratory, we have conducted a series of experiments on a two-stage light gas gun at impact velocities ranging from 6 to 19 km/s, which is representative for light emissions resulting from hypervelocity impacts in space. At these high impact velocities jetting is no longer the dominant mechanism for observed impact flash signatures. The focus of this work is to develop fast, inexpensive photo-diodes for use as a reliable prompt flash, and late time radiating debris cloud diagnostic to: (a) characterize material behavior in the shocked and expanding state when feasible; (b) ascertain scaling of luminosity with impact velocity; (c) determine the temperature of the impact flash resulting from radiating emissions when multiple silicon diodes are used in conjunction with narrow band pass filtering at specific wavelengths as a pyrometer. The results of these experiments are discussed in detail using both a metallic target, such as aluminum, and an organic material such as Composition-B explosive.     

A study of damage in composite panels produced by hypervelocity impact

A phenomenological observation of the damage in graphite fiber (AS4/3501-6) composite panels caused by hypervelocity impact was made in this study. The panels have a nominal thickness of 2.54, 4.83, 6.6 and 17 mm. The impacts were made with nylon and aluminum projectiles of dimension 1.75 mm (dia) × 1.88 mm (length) with velocity from 3–7.5 km/sec. It was observed that the damage in the plate was caused by multiple breakage and delamination of the laminae and matrix material. The crater or hole area in all panels are approximately 7 to 9 times the area of projectiles for the velocity range used in the testing. The area of multiple breakage and delamination of layers in the panels are much larger than the corresponding crater or hole area, and they increase with the panel thickness and impact velocity.     

Nomex Kevlar平纹织物超高速撞击本构模型开发

为了研究Nomex-Kevlar平纹织物对空间碎片的超高速撞击力学特性, 运用LS-DYNA本构模型二次开发技术开发了Nomex-Kevlar平纹织物在超高速撞击条件下的带最大应力失效标准的线弹性正交各向异性本构模型, 并定义了Nomex-Kevlar平纹织物在超高速撞击条件下的Gruneison状态方程参数。运用光滑粒子流体动力学方法和有限元方法建立了与NASA试验工况相同的Al-2017-T4球形弹丸以6.84km/s速度斜向30°撞击Nomex-Kevlar平纹织物的数值分析模型。仿真结果与试验结果的比较表明, 本文中开发的本构模型以及建立的数值分析模型可以准确描述Nomex-Kevlar平纹织物的超高速撞击力学特性。      

Hypervelocity impact computations with finite elements and meshfree particles

The ability of computations to model characteristics of hypervelocity impact is demonstrated using an algorithm for the automatic conversion of distorted finite elements to meshfree particles. The Lagrangian formulation tracks material boundaries and properties without the errors typical in an Eulerian formulation as the material traverses large distances. A computation of a sphere impacting a bumper is shown to reproduce three regions in the debris cloud that are observed in tests: a front region composed of droplets of melted projectile and target, a middle region of fragmented projectile, and a back region of spalled projectile. Additional computations reproduce the observed traits that result from variations in the projectile shape and obliquity. The computation of a projectile impacting spaced plates demonstrates the ability of the method to model the damage to the rear plate of a Whipple shield for spacecraft protection.     

纤维织物FEM-SPH耦合单胞模型及超高速碰撞特性

目前,对纤维织物超高速碰撞过程中的变形、断裂、破碎等力学行为已有较广泛的研究,但对碰撞过程中纱线间接触问题的分析尚未见公开文献报道。考虑纱线间的相互作用,建立了纤维织物的FEM-SPH耦合单胞模型,该模型不仅能够进行纤维织物超高速碰撞过程中的穿孔断裂、破碎、碎片云扩展等损伤行为分析,还能够进行纱线间的接触作用过程分析。结果表明,该模型分析结果与试验结果具有较好的一致性。      

The production and evolution of impact-generated magnetic fields

The production of magnetic fields within impact-generated plasma may explain magnetic fields that have been observed during hypervelocity impact experiments at the NASA Ames Vertical Gun Range. The effect of impact angle on the production and subsequent evolution of impact-generated magnetic fields is assessed using magnetic field data obtained during macroscopic hypervelocity impacts conducted within two ambient magnetic field environments. The configuration and duration of spontaneous impact-generated magnetic fields are round to have a strong dependence on impact angle, exhibiting a smooth transition from a cylindrically symmetric field configuration at vertical incidence to a strong bilaterally anti-symmetric field configuration at high obliquity; hence, crater-related paleomagnetic fields may yield a diagnostic signature of impact angle where other clues (shape, ejecta pattern) are absent or ambiguous. As direct result of some surprising experimental results, a first-order model of field generation during the cavitation regime of high incidence angle hypervelocity impacts is explored. A possible consequence of this model is that magnetic fields produced during hypervelocity impacts (especially those that form large craters) may be an important component of planetary magnetism—especially lunar magnetism during the last 3.6 billion years.