Xinran Xiao

A METHODOLOGY FOR PRACTICAL CUTTING FORCE EVALUATION BASED ON THE ENERGY SPENT IN THE CUTTING SYSTEM

This paper presents a methodology for practical estimation of cutting force and cutting power. Based on a previously proposed definition, the power spent in metal cutting is the summation of four components: the power spent on the plastic deformation of the layer being removed by both major and minor cutting edges, the power spent on the tool-chip interface, the power spent on the tool-workpiece interface, and the power spent in the formation of new surfaces (cohesive energy). This paper provides a complete list of mathematical expressions needed for the calculation of each energy mode and demonstrates their utility for turning operation of two work materials: AISI bearing steel E52100 and aerospace aluminum alloy 2024 T6. The calculated cutting forces were in fairly good agreement with the experimental results. Energy partition in the cutting system and relative impact of the parameters of the machining regime are discussed. For the first time, a simple and practical method is available for the calculation of the total cutting power and the evaluation of the relative contributions of each individual component of the cutting system.

A vibration method for measuring mechanical properties of composite, theory and experiment

This paper presents a method for identifying elastic and damping properties of composite laminates by using vibration test data. The analysis model is established based on a finite element model which considers the effect of transverse shear deformation and hysteretic damping. The reduced elastic constants and material loss factors are selected as the updated parameters. Since the damping mainly causes a change of the imaginary part in eigenvalues and eigenvectors, the complex modal parameters are measured. The selected parameters are identified by minimizing an error function containing the deviations of eigenvalues and responses between experiment and analysis. The numerical study shows that satisfactory results including transverse shear moduli can be obtained by designing a suitable plate specimen. Experimental results demonstrate the efficiency of the proposed method. In principle, the present method allows all elastic constants and damping factors to be determined simultaneously.

Compression Response of 2D Braided Textile Composites: Single Cell and Multiple Cell Micromechanics Based Strength Predictions

This article is concerned with the development of a finite element (FE) based micromechanics model for the prediction of compressive strength and post-peak compression response of 2D triaxial braided carbon fiber polymer matrix composites (2DTBC). This micromechanics based study was carried out on a series of single and multiple representative unit cell (RUC) 3-D FE models. The uniaxial compressive response, including unstable equilibrium paths, was studied using an arc-length method in conjunction with the ABAQUS commercial FE code. In the reported study, explicit account of the braid microstructure (geometry and packing) and the measured inelastic properties of the matrix (the in-situ properties) are accounted for via the use of the FE method. This enables accounting for the different length scales that are present in a 2DTBC. The computational model provides a means to assess the compressive response of 2DTBC and its dependence on various microstructural parameters. The model provides a means to compute the compression strength allowable for a 2DTBC structure. In particular, the dependence of compressive strength on the axial fiber tow properties and axial tow geometrical imperfections is discussed and shown to be significant in capturing the mechanism of damage development. Results are presented for 1, 4, 9, and 16 RUC representations of the 2DTBC, enabling to examine the dependence of compressive strength (or lack thereof) on the size of the region that is modeled. The predicted results are found to compare favorably against experiment.

Modeling Energy Absorption with a Damage Mechanics Based Composite Material Model

The Matzenmiller—Lubliner—Taylor (MLT) model, a continuum damage mechanics (CDM) based model, was used in modeling energy absorption of composite structures in crashworthiness applications. It was found that the assumption of linear elastic unloading and reloading in MLT model resulted in a lower calculated energy absorption in thin wall composite tube axial crush simulations. A modification to compressive unloading was proposed and tested in an MLT-based user material model. The modified model improved the stability of the tube crush simulation and the simulation results. This study demonstrates the importance of properly representing the unloading response of damaged composites in energy absorption prediction.The Matzenmiller—Lubliner—Taylor (MLT) model, a continuum damage mechanics (CDM) based model, was used in modeling energy absorption of composite structures in crashworthiness applications. It was found that the assumption of linear elastic unloading and reloading in MLT model resulted in a lower calculated energy absorption in thin wall composite tube axial crush simulations. A modification to compressive unloading was proposed and tested in an MLT-based user material model. The modified model improved the stability of the tube crush simulation and the simulation results. This study demonstrates the importance of properly representing the unloading response of damaged composites in energy absorption prediction.

Processing and Modelling of Resistance Welding of APC-2 Composite

The process for resistance welding of APC-2 composite has been devel oped with the aid of thermal analysis using two-dimensional finite element modelling. The numerical prediction was used as a guide for selecting the processing parameters. Single- lap shear testing and microstructure viewing were employed for bonding evaluation. Re sistance welded joints achieved a shear strength 33.9 ± 2.3 MPa and retained this strength after hot-wet conditioning. The fibre orientation adjacent to the bondline layer was found to have an influence on the failure mode and thus the shear strength.

Modeling of Load Frequency Effect on Fatigue Life of Thermoplastic Composites

This paper presents a simple prediction scheme correlating fatigue life to the thermal degradation of fatigue strength. Shifting factors similar to the time-temperature shifting in viscoelastic media were employed to account for the effect of temperature on fatigue strength and an iso-strength plot was introduced for fatigue life prediction under non-isothermal conditions. The scheme presented in this paper can predict the load frequency effect associated with hysteretic heating from limiting basic material information. The load frequency effect on the fatigue life of an AS4/PEEK ±45 thermoplastic composite laminate was investigated at 1 Hz, 5 Hz and 10 Hz. Fatigue life prediction for 5 Hz and 10 Hz based on S-N data at 1 Hz was also demonstrated. The predictions agreed reasonably with the experimental data.

Effects of Matrix Microcracking on the Response of 2D Braided Textile Composites Subjected to Compression Loads

This article is concerned with the implementation of a coupled damage-elastic-plastic constitutive model for the matrix material of a 2D triaxial braided carbon fiber composite (2DTBC) subjected to compression loads. Damage in the matrix of 2DTBC is in the form of matrix microcracking which is observed in laboratory experiments of 2DTBC coupons subjected to cyclic loading. In the model, the matrix is treated as a continuously evolving solid governed by a coupled elastic-plastic damage theory which is modified from the classical elasto-plastic theory. With this description of the matrix, the response of 2DTBC to compression loading is studied through the adoption of a representative unit cell that consists of a progressively damaging matrix and elastic-plastic progressively damaging fiber tows. Results from the analysis are compared against a model without evolving damage and also against available experimental data to understand the significance of matrix damage and its influence on compression load bearing capability.

A Coupled Damage-plasticity Model for Energy Absorption in Composite

Predicting the energy absorption of composite structures requires a constitutive model that is capable of representing post-peak softening and irreversible strains, i.e., a coupled damage-plasticity model. The development of such models requires a general damage-plasticity framework. This article examines the merits and limitations of the continuum damage mechanics (CDM) framework and the plasticity framework. Based on the physical evidence of damage accumulation process in composites and the fundamentals of the two theories, a simple coupling method was proposed. This method employs a perfect plastic flow rule within a CDM framework. The capability of this method was examined by incorporating plasticity into the Matzenmiller-Lubliner-Taylor (MLT) model, a classic CDM model for composites. The coupled MLT-plasticity model was implemented as a user defined material law in explicit finite element code LS-DYNA®, and subsequently numerical tests were conducted. It was demonstrated that the proposed method can extend an existing composite CDM model into a coupled damage-plasticity model seamlessly with only a few extra parameters, while retaining its computational efficiency. The capability of the coupled CDM-plasticity model in energy absorption prediction was validated in axial impact simulations of a composite tube reinforced with 1-ply carbon fiber tri-axial braid.Predicting the energy absorption of composite structures requires a constitutive model that is capable of representing post-peak softening and irreversible strains, i.e., a coupled damage-plasticity model. The development of such models requires a general damage-plasticity framework. This article examines the merits and limitations of the continuum damage mechanics (CDM) framework and the plasticity framework. Based on the physical evidence of damage accumulation process in composites and the fundamentals of the two theories, a simple coupling method was proposed. This method employs a perfect plastic flow rule within a CDM framework. The capability of this method was examined by incorporating plasticity into the Matzenmiller-Lubliner-Taylor (MLT) model, a classic CDM model for composites. The coupled MLT-plasticity model was implemented as a user defined material law in explicit finite element code LS-DYNA, and subsequently numerical tests were conducted. It was demonstrated that the proposed method can extend an existing composite CDM model into a coupled damage-plasticity model seamlessly with only a few extra parameters, while retaining its computational efficiency. The capability of the coupled CDM-plasticity model in energy absorption prediction was validated in axial impact simulations of a composite tube reinforced with 1-ply carbon fiber tri-axial braid.

A multilayer composite separator consisting of non-woven mats and ceramic particles for use in lithium ion batteries

Battery separator is a porous membrane that is placed between the positive and negative electrodes to avoid their electric contact, while maintaining a good ionic flow through the liquid electrolyte filled in its pores. Non-woven mats have been evaluated as battery separators due to their highly porous structures. In this study, composite non-woven mats were fabricated through electrospinning and lamination with a ceramic layer, and evaluated as lithium ion battery separators. The lamination with the ceramic layer provides not only improved separator dimensional stability at elevated temperatures but also the potential to increase the production rate of electrospun separators. The electrospun mats keep ceramic particles from dropping avoiding the non-uniform current density distribution caused by the loss of the ceramic particles. The composite separators enabled good ionic conductivity when saturated with a liquid electrolyte. Coin cells with this type of separators showed not only stable cycling performance but also good rate capabilities at room temperature.

A New Rectangular Plate Element for Vibration Analysis of Laminated Composites

In this paper, a higher order rectangular plate bending element based on a Higher Order Shear Deformation Theory (HSDT) is developed. The element has 4 nodes and 20 degrees of freedom. The transverse displacement is interpolated by using an optimized interpolation function while the additional rotation degrees offreedom are approximated by linear Lagrange interpolation. The consistent element mass matrix is used. A damped element is introduced to the finite element model. The proposed FEM is used to calculate eigenfrequencies and modal damping of composite plates with various boundary conditions and different thicknesses. The results show that the present FEM gives excellent results when compared to other methods and experiment results, and is efficient and reliable for both thick and thin plates. The proposed finite element model does not lock in the thin plate situation and does not contain any spurious vibration mode, and converges rapidly. It will provide a good basis for the inverse analysis of vibration of structure.