Research On Characteristics Of Damage Behavior And Dynamic Response Of Fibre-metal Laminate Under Impact Load

Fibre-Metal Laminate (FML) is one kind of hybrid composite composed ofalternatively laminated thin sheets of metal and plies of fibre reinforced composites.FML owes many advantages such as high specific strength, low density, hightoughness and excellent fire, impact and corrosion resistance, etc. Nowadays, FMLhas been successfully applied on some aircrafts of Boeing or Airbus and it showsgreat application foreground on the aircraft industry. Simultaneously, impactdamage resulting from bird impact, hail, runway debris and dropped tools, etc. isone important type of damage for fuselage structures in aircrafts. According to therequirements of safety and stability for aircraft structures, impact resistanceassessment has become one important standard for the design of civil and militaryaircrafts. Meanwhile, research on the impact mechanical characteristics of FML hasbecome a worldwide hot spot.Research on the impact mechanical characteristics of FML is mainly conductedusing experimental and numerical simulation methods. So far, the material modelthat can exactly describe the complex damage patterns and failure processes ofcomposite layers is still a fundamental work for the finite element numericalsimulation about FML under impact load, it is also a key and difficult point. Theusebility of composite material models in numerical simulation modeling of FMLunder impact load has not yet been discussed. Moreover, the data involving theinfluences on the damage behavior and dynamic response characteristics under low-velocity impact load of FML by “material parameters” and “event parameters” isstill in lack, and datas involving the effect on the damage behavior and dynamicresponse characteristics of FML under high-velocity impact load by “materialparameters” and “event parameters” are even rare, which need future studies.Based on the background mentioned above, this paper firstly established a2-Dcontinuum damage mechanics model and a3-D progressive damage model for thecomposite layers in FML.Material parameters were obtained combined withexperiments and the models were coded into VUMAT (user defined materialsubroutines); combining the material models with dynamic explicit algorithm, thefinite elements numerical simulation about FML under impact load was conducted,experimental results were used to verify the numerical simulation method, and theapplicability of material models in the numerical simulation was discussed; in theend, with a combined method of both experiment and simulation, the low-velocityand high-velocity impact mechanical characteristics of FML were systematically investigated, especially for the influences of “material parameters” and “eventparameters” on the damage behavior and dynamic response characteristics of FMLunder impact load. The investigation contents of this paper show below:Firstly, establish a2-D continuum damage mechanics model for compositeincluding fiber tensile damage evolution, differences of elastic moduluses betweentension and compression and in-plane shear plasticity. Based on the continuumdamage mechanics theory, considering fiber tensile damage evolution, differences ofelastic modulues between tension and compression in fiber and transverse directionas well as in-plane shear plasticity, two continuum damage mechanics models forcomposites under in plane stress condition were established, which ignored the in-plane shear plasticity and considered the in-plane shear plasticity, respectively. Tookthe composite layers in FML——S2-Glass/Epoxy laminates for example,parameters obtaining problems of the two material models were investigated. At last,the material models were coded into VUMAT subroutines and verified.Secondly, establish a3-D progressive damage model for composite describedwith strain components including nonlinear shear behavior, shear damage initiationcriteria and differences of elastic moduluses between tension and compression.Based on Hashin criteria described with stress components, considering thenonlinear shear mechanical bahvior and differences of elastic moduluses betweentension and compression of composite, shear damage initiation criteria was supplied,a3-D damage initiation criteria described with strain components was established;then the damage evolution equations were set up with strain components.Furthermore, a3-D progressive damage model which can describe the damageinitiation and evolution of composite was established; at last, the material modelwas coded into VUMAT subroutine and verified.Thirdly, discuss and analyze the applicability of composite material models onthe finite elements numerical simulation about FML under impact load. Combinethe dynamic explicit algorithm, use the2-D continuum damage mechanics modeland3-D progressive damage model of composites set up before and other materialmodels in ABAQUS, numerical simulation on drop weight or ballistic impact testswere completed. In this way, the validity of the numerical simulation method wasverified through experimental results and the applicability of composite materialmodels was specially analyzed. The results show that the2-D continuum damagemechanics model can describe the failure behavior of composite layers in FMLunder low impact energy, but if the impact energy is higher which will result inperforation or critical perforation in FML,2-D material model could no longer beapplicable as it can’t truly represent the dynamic response or failure processes of composite layers in FML under impact load. On the other hand, the3-D progressivedamage model can well predict the dynamic response and failure processes ofcomposite layers in FML under low-velocity and high-veloctiy impact load.Fourthly, use a combined method of both experiment and simulation toinvestigate the low-velocity impact mechanical characteristics of FML. Thedynamic response characteristics and damage patterns of FML under low-velocityimpact were obtained through drop weight impact tests and the damage mechanismswere investigated. The influences of repeated impact, temperature environment andmetal layer’s material performance on the damage behavior and dynamic responsecharacteristics of FML under impact load were also obtained; the influences ofimpactor’s dimension on the damage behavior and dynamic response characteristicsof FML under impact load was obtained through numerical simulation method.Fifthly, use a combined method of both experiment and simulation toinvestigate the ballistic impact mechanical characteristics of FML. The damagepatterns and ballistic limit equations of FML under ballistic impact were obtainedthrough high-velocity impact experiments with light gas gun, the influences ofimpact conditions as impact angle, repeated impact, etc. were obtained; theinfluence mechanism of boundary effect on the damage behavior and dynamicresponse characteristics of FML under ballistic impact load was investigated by acombined method of both experiment and simulation; the influence of each layer’sthickness and stacking configuration of FML on the ballistic impact mechanicalcharacteristics of FML was obtained by simulation method.This paper is aimed at the characteristics of damage behavior and dynamicresponse of FML under impact load, a2-D continuum damage mechanics model anda3-D progressive damage model for the composite layers in FML were establishedrespectively, the usebility of composite material models in numerical simulationmodeling of FML under impact load was analyzed. Based on the research, the low-velocity and high-velocity impact mechanical characteristics of FML werecomprehensively investigated, and the influences of “material parameters” and“event parameters” on the damage behavior and dynamic response characteristics ofFML under impact load were studied. The results can provide a technical guidanceto the development and design of newly FMLs, as well as impact damage riskassessment or optimal design of FML structures in aircraft fuselage.