纤维增强复合材料层板高速冲击损伤数值模拟

推导了复合材料应变率相关三维本构关系, 并将其用于复合材料层板高速冲击损伤的数值模拟。该模型在复合材料层间引入界面单元模拟层间分层, 结合三维Hashin失效准则进行单层板面内损伤识别, 引入材料刚度退化, 采用非线性有限元方法, 研究了复合材料层板高速冲击的破坏过程及层板的损伤特性。数值分析结果表明, 剩余速度预报结果与实验结果吻合较好, 层板的主要损伤形式是层间分层、 基体微裂纹和纤维断裂, 减小弹体直径、 增大铺层角度和层板厚度能够有效降低层板损伤面积。      

Analytical and numerical investigation of polyurea layered aluminium plates subjected to high velocity projectile impact

This paper discusses on the penetration of high velocity projectiles through aluminium–polyurea composite layered plate systems. An analytical model has been proposed to predict the residual velocity of aluminium–polyurea composite plates, and validated with both experimental and numerical investigations. Full metal jacket (FMJ) projectiles (5.56 mm × 45 mm), corresponding to NATO standard SS109, were fired at the aluminium–polyurea composite layered plate systems from a distance of 10.0 m at a fixed velocity of 945 m/s. Four different composite plate configurations were used with thicknesses varying from 16 to 34 mm. Each configuration consisted of six specimens. Residual velocities for each individual test were recorded. Numerical simulations of the penetration process have been performed using advanced finite element code LS-DYNA®. The well-established Johnson–Cook and Mooney–Rivlin material models were used to represent the stress–strain behaviour of aluminium and polyurea in the numerical analysis. The analytical and numerical models provided good approximations for the residual velocities measured during the experimental tests. Polyurea layers contributed positively towards the reduction of residual velocity of the projectile in composite plate systems. In addition, ballistic limit curves for different composite systems have been established based on the validated models. As the results showed that polyurea contributes positively towards the reduction of residual velocity of projectiles, the findings of this study can be effectively used for the similar applications in future armour industry.     

复合材料加筋板低速冲击损伤的数值模拟

建立了复合材料加筋板在横向低速冲击载荷作用下的渐进损伤有限元模型.该模型考虑了复合材料加筋板受低速冲击时的纤维断裂、基体开裂及分层脱粘等五种典型的损伤形式,在层内采用应变描述的失效判据,结合相应的材料性能退化方案,通过编写VUMAT用户自定义子程序以实现相应损伤类型的判断和演化.在层间以及筋条与层板间加入界面元,模拟层间区域的情况,结合传统的应力失效判据和断裂力学中的能量释放率准则来判断分层损伤的起始和演化规律.通过对数值模拟结果与实验数据的比较,验证了模型的合理性和有效性.同时探讨了不同位置、不同冲击能量以及含初始损伤(脱粘)等因素对复合材料加筋板低速冲击性能的影响.     

复合材料层合板低速冲击的接触力和能量响应仿真

以连续介质损伤力学（CDM）为基础,提出了一个有效的数值分析模型来模拟碳纤维增强复合材料（CFRP）层合板低速冲击的接触力响应和能量响应。该模型考虑了不同的失效模式,引入了不可逆的损伤变量和新的刚度折减方式以考虑损伤造成的刚度变化,定义了耗散能的计算方式以考虑损伤造成的能量变化。通过在Abaqus/Explicit平台上编写VUMAT子程序具体实现模型,数值仿真与试验结果吻合较好,验证了该模型的有效性。此外,还综合考虑了Hashin准则与LaRC04准则各自的优缺点,用Hashin和LaRC04相混合得到的准则对低速冲击进行了模拟。结果表明：在冲击外载作用下当CFRP层合板中存在较多基体压缩失效时,采用混合的失效准则模拟得到的接触力响应和能量响应结果更接近试验结果,而使用纯Hashin准则得到的预测结果偏保守。     

复合材料加筋板低速冲击损伤的数值模拟

建立了复合材料加筋板在横向低速冲击载荷作用下的渐进损伤有限元模型。该模型考虑了复合材料加筋板受低速冲击时的纤维断裂、基体开裂及分层脱粘等五种典型的损伤形式, 在层内采用应变描述的失效判据, 结合相应的材料性能退化方案, 通过编写VUMAT用户自定义子程序以实现相应损伤类型的判断和演化。在层间以及筋条与层板间加入界面元, 模拟层间区域的情况, 结合传统的应力失效判据和断裂力学中的能量释放率准则来判断分层损伤的起始和演化规律。通过对数值模拟结果与实验数据的比较, 验证了模型的合理性和有效性。同时探讨了不同位置、不同冲击能量以及含初始损伤(脱粘)等因素对复合材料加筋板低速冲击性能的影响。     

Efficient computational modelling of carbon fibre reinforced laminated composite panels subjected to low velocity drop-weight impact

This paper reports on the actual and virtual low velocity impact response of carbon fibre composite laminates. It utilises the contribution of through-thickness stresses, in the prediction of the onset of internal damage created by this type impact scenario.The paper focuses on the damage imparted by the flat nose impactor since this induces a different type of damage and structural response compared to that of the standard test method of using a round nose impactor.Vulnerability of the fibrous composites to vertical drop-weight impact can result in premature failure which is a major concern in their widespread usage. The topic has been of intense research to design more damage tolerant and resistant materials. However, due to materials’ anisotropic and three-dimensional nature and complicated damage mechanisms no standard model could have been achieved. Designers predict consequences of a local impact within the global structural context without full-scale testing.Majority of the existing simulation models neglect through-thickness stresses that are regarded as the major cause of catastrophic failures. Efficient and reliable investigations are required to reduce testing and include through-thickness stresses. Drop-weight impact simulation models were developed herein using ABAQUS™ software. Simulations were carried out to compute in-plane stresses subjected to flat and round nose impacts on laminates of differing thicknesses. These stresses once computed were numerically integrated employing the equilibrium equations to efficiently predict through-thickness stresses. The predicted stresses were then utilised in failure criteria to quantify the coupled and embedded damage. This provides a quick insight into the status and contribution of through-thickness stresses in failure predictions. The computed values were compared to the experimental results and found to be in good agreement.     

A wave propagation model for the high velocity impact response of a composite sandwich panel

A solution methodology to predict the residual velocity of a hemispherical-nose cylindrical projectile impacting a composite sandwich panel at high velocity is presented. The term high velocity impact is used to describe impact scenarios where the projectile perforates the panel and exits with a residual velocity. The solution is derived from a wave propagation model involving deformation and failure of facesheets, through-thickness propagation of shock waves in the core, and through-thickness core shear failure. Equations of motion for the projectile and effective masses of the facesheets and core as the shock waves travel through sandwich panel are derived using Lagrangian mechanics. The analytical approach is mechanistic involving no detail account of progressive damage due to delamination and debonding but changes in the load-bearing resistance of the sandwich panel due to failure and complete loss of resistance from the facesheets and core during projectile penetration. The predicted transient deflection and velocity of the projectile and sandwich panel compared fairly well with results from finite element analysis. Analytical predictions of the projectile residual velocities were also found to be in good agreement with experimental data.     

复合材料层合板低速冲击损伤的有限元模拟

建立了用于预测复合材料层合板在低速冲击作用下损伤的3D有限元模型。采用应变描述的失效判据来判断铺层层内的各类损伤, 如纤维断裂、 纤维挤压、 基体开裂、 基体挤裂, 并结合相应的刚度折减方案对失效单元进行刚度折减。使用界面元模拟层间区域, 结合传统的应力失效判据和断裂力学中的能量释放率准则来定义分层损伤的起始和演化规律, 提出了一种界面元损伤起始强度沿厚度方向的分布函数。通过对数值仿真结果和实验结果的比较, 验证了模型的合理性和准确性。      

Strain rate dependent low velocity impact response of layerwise 3D-reinforced composite structures

The performance evaluation of a novel layerwise 3D-reinforced glass-fibre composite material under low velocity impact loading conditions is presented. Firstly, strain rate dependent material properties are determined, for which the experimental procedure is explained in detail on the example of polypropylene and epoxy matrix based composite configurations. The gained orthotropic property-profile provides the input parameters for a numerical low velocity impact analysis of a demonstrator structure. This complex shaped bucket structure, manufactured within a VARTM process, is subjected to various impact scenarios, for which a fully instrumented drop tower testing rig has been designed and utilised. The numerical results are compared with the experimentally observed impact response. The predictive capability of the proposed multidisciplinary evaluation approach for composites subjected to impact loading conditions is finally discussed.     

Specimen size effect on the residual properties of engineered cementitious composites subjected to high temperatures

In this study, size effect on the residual properties of Engineered Cementitious Composites (ECC) was investigated on the specimens exposed to high temperatures up to 800 °C. Cylindrical specimens having different sizes were produced with a standard ECC mixture. Changes in pore structure, residual compressive strength and stress–strain curves due to high temperatures were determined after air cooling. Experimental results indicate that despite the increase of specimen size, no explosive spalling occurred in any of the specimens during the high temperature exposure. Increasing the specimen size and exposure temperature decreased the compressive strength and stiffness. Percent reduction in compressive strength and stiffness due to high temperature was similar for all specimen sizes.     

High strain rate effects on direct tensile behavior of high performance fiber reinforced cementitious composites

Direct tensile behavior of high performance fiber reinforced cementitious composites (HPFRCCs) at high strain rates between 10 s⁻¹ and 30 s⁻¹ was investigated using strain energy frame impact machine (SEFIM) built by authors. Six series of HPFRCC combining three variables including two types of fiber, hooked (H) and twisted (T) steel fiber, two fiber volume contents, 1% and 1.5%, and two matrix strengths, 56 MPa and 81 MPa, were investigated. The influence of these three variables on the high strain rate effects on the direct tensile behavior of HPFRCCs was analyzed based on the test results. All series of HPFRCCs showed strongly sensitive tensile behavior at high strain rates, i.e., much higher post cracking strength, strain capacity, and energy absorption capacity at high strain rates than at static rate. However, the enhancement was different according to the types of fiber, fiber volume content and matrix strength: HPFRCCs with T-fibers produced higher impact resistance than those with H-fibers; and matrix strength was more influential, than fiber contents, for the high strain rate sensitivity. In addition, an attempt to predict the dynamic increase factor (DIF) of post cracking strength for HPFRCCs considering the influences of fiber type and matrix strength was made.     

Effects of shape memory alloys on low velocity impact characteristics of composite plate

The effects of shape memory alloy thin films embedded in composite plates for improving damage resistance of composite structures under low velocity impact were investigated numerically. Analysis model for SMA thin film was developed based on Lagoudas’ model and implemented using the user defined material subroutine of the ABAQUS/Explicit finite element program. Composite damage model based on the Chang–Chang failure criteria was also implemented to consider progressive damage behavior. The finite element simulation of low velocity impact behavior of a shape memory alloy hybrid composite plate was performed using the ABAQUS/Explicit program. Parametric studies were performed to investigate the effect of shape memory alloys for improving damage resistance of composite plate.