Research Projects

10. Experimental investigation of nanosecond laser ablation of advanced Engineering Materials 

Dr. Ma experimentally investigated nanosecond laser ablation of advanced engineering materials. e.g. carbon nanotubes (CNTs), Bulk Metallic glasses (BMGs), and Shape Memory Alloys. 

10.1 Laser ablation of CNTs. 

Carbon nanotubes (CNTs) have been a subject of development and investigation in the last two decades due to their superior physical and chemical properties, such as high electrical conductivity, high thermal conductivity, high mechanical and elastic properties, and relative inexpensiveness. Dr. Ma used nanosecond pulsed laser to ablate the CNTs grown on the Si/SiO2 substrate. SEM and Raman Spectroscopy are used to characterize the samples before and after ablation. Left image (upper) below shows a burned and damaged silicon substrate at the spot where the laser beam ablated the sample. No sign of CNTs was found neither inside the beam spot nor around it, as it is seen in left image (lower). This corroborates with the Raman Spectrum given in right image below. More images can be found in the full paper: https://doi.org/10.1115/IMECE2021-73390 

10.2 Laser ablation of Bulk Metallic Glasses (BMGs)

Bulk metallic glasses (BMGs) are a new group of metallic materials having amorphous microstructure that results in some preferable mechanical properties, e. g. high fracture toughness, superior tensile strength, desirably high rupture strength, super large elastic strain limit along with outstanding resistance to corrosion and wear. As a result, BMGs have been used in aerospace, optics, sports, and biomedical applications. Dr. Ma used nanosecond laser with 1064 nm wavelength is used to modify the surface of a Zr-based bulk metallic glass Vitreloy 1b. (Zr67Cul0.6Ni9.8Ti8.8Be3.8). optical microscope was used to measure the diameter of the craters formed by the laser. 3D surface profilometer was used to analyze the 3D profile of the fabricated craters and slots in addition to measuring the depth of individual crater. The scanning electron microscope (SEM) was used to analyze the surface topography and ripple formation on the craters and slots. The laser induced surface modification or composition changes on the laser treated BMG surface was investigated using the energy dispersive X-ray spectroscopy (EDS) analysis. 

Images below show 3D surface profile of craters and portion of slots machined under some different machining conditions.

10.3 Laser ablation of Shape Memory Alloy (BMGs)

Nickel-Titanium based Shape Memory Alloys (Ni-Ti SMAs), a group of special advanced engineering materials, are gaining popularity in industrial engineering and biomedical engineering for their superior properties. for example, amazing shape memory effects (SME), high strength, excellent corrosion and wear resistance, pseudoelasticity, outstanding biocompatibility and biodegradability. Dr. Ma used the Continuum Surelite Class III nanosecond laser system with 1064 nm wavelength and 5 nanosecond pulse width to modify the surface of a Nickel-Titanium based SMA. The effects of laser pulse energy level and lens-to-samples distance on the crater and slot forming are evaluated. 

10.4 Laser ablation of Silicon wafers

Silicon is a favorite material to be chosen to build semiconductor products, high performance sensors and others, because of its very special properties such as high melting temperature and hardness. However, because silicon is a very brittle and hard material, its machinability is very poor. Dr. Ma used nanosecond laser to ablate/machining silicon wafers. Images below are micrographs of the laser ablated slots obtained using optical microscope.

10.5 Laser ablation of 3D printed Carbon Fiber Reinforced Polymers (CFRPs)

This study aims to investigate the feasibility of using a nanosecond laser for machining single craters or blind holes and slots on 3D printed CFRP samples and understand the effects of important process parameters on feature dimensions, (i.e., crater diameter, slot width, crater/hole depth, and slot depth), heat affected zone (HAZ), and surface quality of the machined features. 

9. Investigation of correlation between complexity and mechanical recovery of metallic nanoarchitecture structures and composition influence on edge dislocation mobility in an FCC high entropy alloy (HEA) 

Dr. Ma and his collaborators also investigated the effect of complexity (four different suggested geometries with various levels of complexity) on the mechanical behavior and recovery of metallic nanoarchitecture structures using Molecular Dynamics simulations (MDS). The structures exhibited multiple degrees of self-recovery under compressive loading conditions at three temperatures, 300K, 400K, and 500K. The results demonstrated correlations between the complexity of the structures and their recovery ability and strength, and the geometric cell size and temperature. These insightful findings can guide the design of novel nanoarchitecture geometries for specific applications with tailored properties.

Dr, Ma and his collaborator also used Molecular dynamics simulations to investigate the mobility of edge dislocation on FeNiCrCoCu FCC High Entropy Alloy (HEA). The effects of temperature and stress on the dislocation velocity and evaluated the material’s drag coefficient were computed.

8. Numerical modeling of pure water jet machining of Ti-6Al-4V and Al 6061-T6 using ABAQUS and smoothed particle hydrodynamics

Dr. Ma's team used pure water jets to conduct nano-scale cutting of cut hard materials because the commonly used abrasive particles are typically in the micron range which is three orders of magnitude larger than sizes to be cut.  To ensure that it is possible to cut metals using a pure water jet, simulations at millimeter scale are conducted before downscaling to nano-scale. These simulations, using the smooth particle hydrodynamics (SPH) feature of ABAQUS, to model the machining of Al 6061-T6 and Ti-6Al-4V, 

Dr. Ma's team also developed a pulsed water jet simulation model of machining of Al 6061-T6 and Ti-6Al-4V using ABAQUS Smoothed Particle Hydrodynamics (SPH). This technique allows high precision machining of titanium that preserves the integrity of the machined material, reduces tool wear or even eliminates tooling entirely.

7.  Investigation of material removal in impact machining by loose abrasives 

This innovative nanomachining process is also known as Vibration Assisted Nano Impact machining by Loose Abrasives (VANILA). This process can overcome the shortcomings of the existing nanomachining processes that rely on lithographic and energy beam based methods which usually need cleanroom environments and huge capital investments and lead to a low cost alternative for nanomachining at room temperature. The new process can improve the nanomachinability of a wide variety of both conductive and nonconductive materials, and may have applications in biomedical, electronic, automotive, energy, and metal working industries. The following images show the in-house experimental setup for VANILA process,  experimental results obtained on aluminum coated silicon substrate, and schematic representation of VANILA process respectively. 

Dr. Ma and his team investigated the effects of different machining parameters at elevated operating temperatures in a novel nanomachining process, Vibration Assisted Nano Impact machining by Loose Abrasives (VANILA). Image below shows the ABAQUS FEM model for VANILA. The Drucker-Prager (D-P) constitutive model is employed in this research to describe the material behavior of the silicon workpiece [18] to capture the influence of hydrostatic pressure. 

FEM for the validation model used in VANILA process 

Images below present damage evolution of silicon from hit number 0 to hit number 25 with the impact velocity, impact angle, friction coefficient and temperature being 200 m/s, 900, 0.05, and 6000C, respectively. It illustrates that the damage region for which D equals 1.0 increases (red region) as the number of hits increases. 

Dr. Ma and his team also investigated the phase transformation experienced by the silicon workpiece and to study the effects of VANILA process parameters, such as impact speed, impact angle and coefficient of friction between the nanoabrasive and silicon workpiece, on the volume of phase transformation of silicon. Images below show the pressure and phase distribution/phase volume of silicon workpiece with impact speed of 200 m/s, impact angle of 90⁰, and friction coefficient of 0.05 when the pressure reaches the highest value before the particle moves away from workpiece. 

Dr. Ma and his team also used Molecular Dynamics Simulations to model VANILA process for silicon wafer. Images below are the MDS model and effect of impact angle on the material removal mechanisms.

6. Numerical investigation of non-traditional (EDM and Laser machining) machining processes

Dr, Ma and his team also used the commercial FEM software package Abaqus to numerically investigate the effects of EDM conditions on the crater size, phase transformation in HAZ, and the residual stress distribution in EDMing of Ti-6Al-4V. The phase transformations of Ti-6Al-4V alloy during EDM are modeled based on phase transformation kinetics and flow stress is described using the rule of mixtures. Experiments are conducted to validate FEM model, which are then used to predict crater size, phase transformation and residual stress for different discharge energy levels. SDV11 represents the status of the material points. The points that have SDV11 greater than 1.0 are molten material points and will not experience either phase transformation or residual stress. . These two images below present FEM model and thermal model for EDM, respectively.

The first three images show the distributions of SDV11, SDV1, and von Mises stress, respectively. The last image presents the residual stress of sigmaxx for four different energy levels.

Below are two animation files for EMDing of Ti alloy.

Dr. Ma and his team also used the finite element method (FEM) to model the craters formed during the micro-EDM of metallic glass (Vitreloy 1 alloy (Zr67Cu l0.6Ni9.8Ti8.8Be3.8 (wt%)) ). The model showed various phases in a single crater including molten layer followed by a crystalline layer. The developed model was able to successfully predict the crater sizes, as the experimental crater sizes matched closely with those predicted by the FEM simulation. The images below present 2D FEM model and heat flux and boundary conditions of EDM model of BMG. 

The images below show phase distribution of EMDing of BMG and comparison of crater size between experimental and simulation results, respectively.

Dr. Ma and his team also used finite element method (FEM) commercial software package Abaqus to simulation the film burst process during Femtosecond laser ablation of gold thin film on the front and backside of silicon to guide the selection of laser parameters for the backside ablation process. Maximum nominal stress criterion is used to describe damage initiation of the cohesive elements, 

5. Investigation of influences of innovative microtextured/microbumped cutting tools on machining

Dr. Ma and his team numerically Investigating influences of innovative microtextured/microbumoed cutting tools and cutting tools with with restricted contact area on cutting force, chip thickness, phase changes, grain size and dislocation density distribution during machining processes using coupled Eulerian-Lagrangian (CEL) FEM model based on Abaqus FEM software package with Arbitrary-Lagrangian-Eulerian (ALE) technique and AdvantEdge FEM. The images below show insert that has laser-made microgrooves and tool-chip contact area between regular and microgrooved tool in experiment and simulation using AdvantEdge FEM. 

Dr. Ma also used the commercial FEM software package Abaqus to investigate the effects of microgrooved cutting tools in high speed orthogonal cutting of AISI 1045 steel. Microgrooves are designed and fabricated on the rake face of cemented carbide (WC/Co) cutting inserts. A coupled Eulerian-Lagrangian (CEL) finite element model is developed based on Abaqus to solve the evolution of the cutting temperature, chip morphology, cutting force, and phase constitutes simultaneously. Images below show the CEL model and mesh, respectively.

Below images show comparison of temperature distribution between results available in literature and numerical results obtained using our CEL model.

Below images show temperature distribution, the von Mises stress distribution and phase distribution for non-microgrooved regular tool and phase distribution for one microgrooved tool when machining AISI 1045, respectively.

Below are several animation files (temperature and FV1-phase transformation) for CEL modeling of AISI1045.

Dr. Ma and his team also developed a coupled Eulerian-Lagrangian (CEL) finite element model based on FEM software package Abaqus to investigate the evolution of the dislocation density and grain size simultaneously in orthogonal cutting of pure titanium . Below images show the distributions of dislocation density and grain size when machining pure Titanium.  

Below are several animation files (temperature, SDV15-dislocation density, and SDV22-grain size) for CEL modeling of CPTI.

4. ·Numerical investigation of ductile regime machining of nanocrystalline hydroxyapatite bioceramic 

FEM is used to model 2D laser assisted machining process of the newly developed nano-HA to gain insight of the cutting conditions (critical depth of cut) under which ductile regime machining of this material can be achieved. The materials were modeled by using the Drucker-Prager Thermal Expansion constitutive model to account for thermal expansion of the workpiece and tool as heating occurred and to satisfy the need for a pressure-sensitive yield criterion. Different cutting conditions (different rake angles, different thermal boundary temperatures, and different edge radii/depths of cut) are tested. First image below shows how to identify the critical depth of cut-when pressure greater than or equal to the hardness of the workpiece at the given temperature. Second image below shows relation between critical depth of cut and machining conditions. 

3.    FEM Modeling of non-pneumatic tire interaction with sand 

Dr. Ma conducted research in NASA funded project optimizing the next generation non-pneumatic NASA tire using Finite Element Method (Abaqus) for NASA missions. Images below show two different non-pneumatic tire modes and their interaction with soil along with contact pressure distribution.  

2. Developing In-house Finite Element Method (FEM):

For efficient and fair comparison between Meshless Integral Method (MIM) and traditional Finite Element Method (FEM), Dr. Ma developed in-house FEM to analyze elastic problems with small deformation, elastoplastic problems with small deformation, and elastoplastic problems with large deformation. When compared with commercial FEM software packages (e.g. Abaqus and ANSYS), numerical tests show that the in-house FEM method is stable and accurate and could generate comparable numerical results. This FEM method has incorporated elasticity with small deformation, Tresa/von Mises yield criteria, Mohr-Coulomb, Drucker-Prager yield criterion, modified Cam-Clay yield criterion, capped Drucker-Prager yield criterion, viscoplasticity, damage mechanics, and anisotropic finite plasticity (single crystals), along with contact/friction and large deformation. This in-house FEM  is implemented using C++ language. This FEM program could be expanded based on customs' needs. 

Images below show contour plots for infinite plate with a circular hole solved using this in-house FEM program.

Images below show contour plots for beam solved using this in-house FEM program.

1. Developing In-house Meshless Integral Method (MIM):

Dr. Ma developed truly meshless integral method (MIM) to analyze elastoplastic problems with large deformation. This method is based on the regularized boundary integral equation to overcome the problems that the traditional Finite Element Method (FEM) has trouble to solve, e.g. large deformation, moving boundary and changing geometry. Numerical tests show that the MIM is stable and accurate and appears remarkably promising and it lays the foundation for modeling and simulation of metal cutting processes and tire-soil interaction and other processes which are characterized by large deformation and moving boundary and changing geometry. This meshless method has incorporated Tresa/von Mises yield criteria, Mohr-Coulomb, Drucker-Prager yield criterion, modified Cam-Clay yield criterion, capped Drucker-Prager yield criterion, viscoplasticity, damage mechanics, and anisotropic finite plasticity (single crystals), along with contact/friction. This in-house meshless integral method is implemented using C++ language. 

In addition,  a pre-processor and pixel-based post-processor (Meshless2D) has been developed using Java to generate input files for MIM solver and analyze and visualize the meshless results for both elastic and elastoplastic problems.  

Images show the domains in meshless integral method.

Images below show high color resolution contour plots via Meshless2D for infinite plate with a circular hole solved using MIM

Images below show low color resolution contour plots via Meshless 2D for infinite plate with a circular hole solved using MIM.

Images below show problem of edge crack under mode I solved using MIM

Images below show metal forming problem solved using MIM with large deformation.

Image shows the interface of Meshless2D software. This software has functionalities of pre-processor and post-processor. The pre-processor is used to define the data and discretization scheme for meshless analysis. This includes support for the geometric model, as well as definition of material, boundary conditions, and other parameters for the meshless method.

The post-processor provides a convenient graphical user interface for visualization of numerical solutions obtained from the meshless solver. Generally, the post-processors that are designed for use with finite element packages use the idea of an element to produce contours of the desired field variable. The problem domain is usually traversed element by element, and a coloring scheme for the element under consideration is synthesized, based upon the values of the field variable of interest within that element. This approach works very well when the domain has been discretized into elements, but the discretization that is done in a meshless method has no elements and so this approach is inapplicable. Instead, we have developed two truly element free methods for generating the desired color contours. One method is purely node-based and results in the generation of coarse color contours using a computationally lean algorithm; the second method is pixel-based and generates fine color contours using a method that is computationally more intensive. Please see the contour plots via Meshless2D for infinite plate with a hole above.

Image below shows Interfaces for setting model information, essential boundary conditions, and natural boundary conditions in Meshless2D software.

Images below show internal nodal refinement, nodal refinement on boundary, and nodal refinement dialog, respectively in Meshless2D Software.