Hongyong Jiang

Improvement of Progressive Damage Model to Predicting Crashworthy Composite Corrugated Plate

To predict the crashworthy composite corrugated plate, different single and stacked shell models are evaluated and compared, and a stacked shell progressive damage model combined with continuum damage mechanics is proposed and investigated. To simulate and predict the failure behavior, both of the intra- and inter- laminar failure behavior are considered. The tiebreak contact method, 1D spot weld element and cohesive element are adopted in stacked shell model, and a surface-based cohesive behavior is used to capture delamination in the proposed model. The impact load and failure behavior of purposed and conventional progressive damage models are demonstrated. Results show that the single shell could simulate the impact load curve without the delamination simulation ability. The general stacked shell model could simulate the interlaminar failure behavior. The improved stacked shell model with continuum damage mechanics and cohesive element not only agree well with the impact load, but also capture the fiber, matrix debonding, and interlaminar failure of composite structure.

Meso-Scale Progressive Damage Behavior Characterization of Triaxial Braided Composites under Quasi-Static Tensile Load

Based on continuum damage mechanics (CDM), a sophisticated 3D meso-scale finite element (FE) model is proposed to characterize the progressive damage behavior of 2D Triaxial Braided Composites (2DTBC) with 60° braiding angle under quasi-static tensile load. The modified Von Mises strength criterion and 3D Hashin failure criterion are used to predict the damage initiation of the pure matrix and fiber tows. A combining interface damage and friction constitutive model is applied to predict the interface damage behavior. Murakami-Ohno stiffness degradation scheme is employed to predict the damage evolution process of each constituent. Coupling with the ordinary and translational symmetry boundary conditions, the tensile elastic response including tensile strength and failure strain of 2DTBC are in good agreement with the available experiment data. The numerical results show that the main failure modes of the composites under axial tensile load are pure matrix cracking, fiber and matrix tension failure in bias fiber tows, matrix tension failure in axial fiber tows and interface debonding; the main failure modes of the composites subjected to transverse tensile load are free-edge effect, matrix tension failure in bias fiber tows and interface debonding.

Evaluations of failure initiation criteria for predicting damages of composite structures under crushing loading

The crushing behaviors of thin-walled composite structures subjected to quasi-static axial loading are comparatively evaluated using four different failure initiation criteria. Both available crushing tests of composite corrugated plate and square tube are used to validate the stiffness degradation-based damage model with the Maximum-stress criterion. Comparatively, Hashin, Maximum-stress, Stress-based Linde, and Modified criteria are respectively implemented in the damage model to predict crush behaviors of corrugated plate and square tube. To develop failure criteria, effects of shear coefficients and exponents in the Modified and Maximum-stress criteria on damage mechanisms of corrugated plate are discussed. Results show that numerical predictions successfully capture both of experimental failure modes and load–displacement responses. The Modified criterion and particularly Maximum-stress criterion are found to be more appropriate for present crush models of corrugated plate and square tube. When increasing the failure index, the crushing load is decreased, which also causes premature material failure. The shear coefficient and exponents have dramatic influence on the crushing load. Overall, an insight into the quantitative relation of failure initiation is obtained.

Microscale finite element analysis for predicting effects of air voids on mechanical properties of single fiber bundle in composites

Air voids produced in the manufacturing process have significant influence on the mechanical performances of single fiber bundle in carbon fiber-reinforced composites. The microscale finite element model of fiber bundle with voids is developed to predict mechanical properties and failure mechanisms. The failure responses of fiber and matrix in bundle are initiated by the maximum stress and Stassi failure criteria. The sudden stiffness degradation law is adopted to capture brittle behaviors. Both available theoretical models for voids and non-voids are used to validate the numerical model without voids and with different percentages of voids including 0.15, 0.5, 1, 2, 3, 4 and 5%. Effects of void contents on stress–strain responses of bundle are studied. The matrix damage development is studied regarding transverse compression and out-of-plane shear loading. The micro-stress analysis of matrix and voids in three-RUC model under different loadings is performed. The simulated elasticity and strength properties correlate well with theoretical results for voids and non-voids. The strengths and moduli gradually decrease with increasing void contents except longitudinal properties. The stress concentrations of bundle are mainly influenced by the loading direction.

Damage and perforation resistance behaviors induced by projectile impact load on bonding-patch repaired and scarf-patch repaired composite laminates

A three-dimensional continuum damage model is proposed to analyze the damage and perforation resistance behaviors of bonding-patch and scarf-patch repaired composite laminates under projectile impact load. Coupling with modified 3D-Hashin failure criteria, a linear-exponential law due to fiber pull-out failure and an exponential law are used to predict tensile and compressive softening processes of materials, respectively. A cohesive interaction based on triangle traction–separation law and mixed-mode fracture energy method is applied for interface debonding damages between patch/lamina, patch/patch and lamina/lamina. Comparisons are made between numerical results and several available test data for different impact offsets. The perforation resistance and interface debonding damage mechanisms are extensively discussed using finite element analysis. Further, perforation resistance behaviors of laminate with six different patch-repair patterns are assessed. Effects of initial velocity of projectile on residual velocity and energy-absorption are discussed. A residual velocity error within 7.3% and energy-absorption error within 9.2% is found between simulations and tests. Consistent failure modes including fiber fracture, matrix cracking, delamination and interface debonding are also identified. As the projectile invades patches, interface debonding damage in patches is accumulated rapidly, especially for larger impact offset. The combined patch-repairs show a reduction of at the most 48.3% in velocity and higher ballistic limit velocities which implies better perforation resistance capacity. The energy-absorption almost increases with increasing the initial velocity and a decreasing trend in average energy-absorption is found with the increase of impact offset.

Sensitivity analysis-based variable screening and reliability optimisation for composite fuselage frame crashworthiness design

ABSTRACT During the impact process, fuselage frame structures often experience severe crushing-induced kinematic deterioration. To improve cabin safety, this paper developed an analysis and design algorithm to optimise 2D triaxially-braided composite (2DTBC) frame under dynamic crush-type load. The design methodology integrates three concepts coming from several different communities including numerical simulation, sensitivity analysis-based variable screening and reliability optimisation. Based one continuous medium mechanics theory, a basic finite element (FE) model coupled with multiple failure modes is built at the macroscopic level previously. Afterwards, the Sobol’ global sensitivity analysis is performed to derive a design variable importance hierarchy. Finally, differential evolution (DE) algorithm is implemented to identify the optimum frame geometry that has maximum energy-absorption capacity. The investigation demonstrates that appropriate redistribution of shape parameters of the frame could enhance its design reliability and crashworthiness, and the higher number of design variables often performs better from the energy-absorption viewpoint.

Multi-Scale Progressive Damage Model for Analyzing the Failure Mechanisms of 2D Triaxially Braided Composite under Uniaxial Compression Loads

Based on continuum damage mechanics (CDM), a multi-scale progressive damage model (PDM) is developed to analyze the uniaxial compression failure mechanisms of 2D triaxially braided composite (2DTBC). The multi-scale PDM starts from the micro-scale analysis which obtains the stiffness and strength properties of fiber tows by a representative unit cell (RUC) model. Meso-scale progressive damage analysis is conducted subsequently to predict the compression failure behaviors of the composite using the results of micro-scale analysis as inputs. To research the free-edge effect on the local failure mechanisms, meso-scale models of different widths are also established. The stress-strain curves obtained by numerical analysis are verified with the experimental data. Results show that fiber and matrix compression failure inside the fiber tows are the major failure modes of the composite under axial compression. For transverse compression, the dominated failure modes are recorded for matrix compression failure inside the fiber tows. It is also presented that the free-edge effect plays an important role in the transverse mechanical response of the composite, and the failure behaviors of the internal fiber tows are strongly influenced as well.