Zhili Feng - Academia.edu (original) (raw)

Papers by Zhili Feng

Journal of Manufacturing and Materials Processing

The root cause of post-weld baking on the mechanical performance of Al-steel dissimilar resistanc... more The root cause of post-weld baking on the mechanical performance of Al-steel dissimilar resistance spot welds (RSWs) has been determined by machine learning (ML) and finite element modeling (FEM) in this study. A deep neural network (DNN) model was constructed to associate the spot weld performance with the joint attributes, stacking materials, and other conditions, using a comprehensive experimental dataset. The DNN model positively identified that the post-weld baking reduces the joint performance, and the extent of degradation depends on the thickness of stacking materials. A three-dimensional finite element (FE) model was then used to investigate the root cause and the mechanism of the baking effect. It revealed that the formation of high thermal stresses during baking, from the mismatch of thermal expansion between steel and Al alloy, causes damage and cracking of the brittle intermetallic compound (IMC) formed at the interface of the weld nugget during welding. This in turn re...

Transactions on Intelligent Welding Manufacturing, 2017

A master welder uses his sensory perceptions to evaluate the process and connect them with his/he... more A master welder uses his sensory perceptions to evaluate the process and connect them with his/her knowledge base to take the necessary corrective measures with his/her acquired skills to make a good weld. All these actions must take place in real time. Success depends on intuition and skills, and the procedure is labor-intensive and frequently unreliable. The solution is intelligent weld manufacturing. The ultimate goal of intelligent weld manufacturing would involve sensing and control of heat source position, weld temperature, weld penetration, defect formation and ultimately control of microstructure and properties. This involves a solution to a problem (welding) with many highly coupled and nonlinear variables. The trend is to use an emerging tool known as intelligent control. This approach enables the user to choose a desirable end factor such as properties, defect control, or productivity to derive the selection of process parameters such as current, voltage, or speed to provide for appropriate control of the process. Important elements of intelligent manufacturing are sensing and control theory and design, process modeling, and artificial intelligence. Significant progress has been made in all these areas. Integrated computational welding engineering (ICWE) is an emerging field that will aid in the realization of intelligent weld manufacturing. The paper will discuss the progress in process modeling, microstructure, properties, and process control and automation and the importance of ICWE. Also, control and automation strategies for friction stir welding will be discussed.

Objectives • Quantify and develop the knowledge base for hydrogen permeability and embrittlement ... more Objectives • Quantify and develop the knowledge base for hydrogen permeability and embrittlement of pipeline steels and their welds under high-pressure gaseous hydrogen exposure relevant to hydrogen gas transmission pipeline. • Optimize the base metal and weld metal composition and microstructure to avoid excessive hydrogen permeation and increase service performance of hydrogen pipelines. • Evaluate welding technologies suitable for joining high-pressure hydrogen pipelines. • Develop a risk assessment based approach to manage the integrity and safety of hydrogen pipelines including weld joints.

Objective • Develop the technological basis for friction stir welding and processing (FSW/P) of a... more Objective • Develop the technological basis for friction stir welding and processing (FSW/P) of advanced high-strength and lightweight materials for the automotive industry. • Gain fundamental understanding of the relationships between workpiece and tool material properties during FSW/P. • Characterize the mechanical properties and microstructures of joints. • Correlate the proprieties and microstructures produced by FSW/P to the process conditions.

Materials, 2020

Friction stir processing is a novel solid-state process to modify microstructures and their prope... more Friction stir processing is a novel solid-state process to modify microstructures and their properties by intense, localized plastic deformation. However, little research has been reported for microstructure evolutions of advanced high-strength steels during the process. The present work focuses on the study of transient microstructure changes and local mechanical properties for friction stir spot processed dual-phase (DP) 980 MPa grade steel (DP980) under different peak temperatures. A pinless silicon nitride ceramic tool was used to produce relatively simple material deformation and flow near the tool. Friction stir spot processed steel samples were characterized by optical and electron microscopies. Furthermore, Vickers microhardness and nano-indentation measurements were used to study local mechanical properties for correlation with microstructures. A swallow layer of refined grains (<0.6 µm) was obtained with a low peak temperature (under 400 °C), whereas higher peak tempera...

This report summarizes recent post-welding activities on irradiated alloys at the Irradiated Mate... more This report summarizes recent post-welding activities on irradiated alloys at the Irradiated Materials Examination and Testing (IMET) and the Low Activation Materials Development and Analysis (LAMDA) facilities at Oak Ridge National Laboratory. Equipment and capabilities were developed jointly by the U.S.

Materials, 2019

Transient distortion of thin plate in the welding process usually has a complicated mode and larg... more Transient distortion of thin plate in the welding process usually has a complicated mode and large magnitude. Quantitative measurement and prediction of full-field distortion are challenging and rarely reported up to now. In this study, the out-of-plane distortion of a thin plate during the Tungsten Inert Gas (TIG) welding process was measured using the digital image correlation (DIC) method. A simulation model based on thermal elastic–plastic finite element method (FEM) and DIC measured geometric imperfection were developed for accurate prediction of the transient welding distortion. The numerical results and experimental data agreed very well in both out-of-plane deformation modes and magnitudes of the plate at different stages of welding. The maximum out-of-plane distortion was larger than 4 mm during welding which can cause instability of arc length and heat input. The distance change between welding torch and plate surface was investigated under different initial deflections of...

The residual stress distribution in a GTA spot welded HSLA-100 steel disk was analyzed using ther... more The residual stress distribution in a GTA spot welded HSLA-100 steel disk was analyzed using thermomechanically uncoupled and semi-coupled finite element (FE) formulations and measured with the neutron diffraction technique. The computations used temperature-dependent thermophysical and mechanical properties of the base metal. The thermal analysis was based on the heat conduction formulation with the Gaussian heat input from the arc. The semi-coupled approach is an effective alternative to the fully coupled approach in which the incompatibility in the thermal and mechanical time increments often leads to numerical convergence difficulties. Convergence was achieved in the semi-coupled approach where a larger time increment for temperature calculation was automatically divided into some sub-intervals for the thermal stress calculation. The temperature, deformation configurations, and state variables were updated at the end of the temperature increment. The predictions from the FE models are in very good agreement with the neutron measurement results in the far heat-affected zone (HAZ) and in the base metal. Both models over-predicted the residual stress field in the fusion zone and near HAZ as measured by the neutron diffraction method. The discrepancy could be attributed to the changes in microstructures and material properties in the HAZ and fusion zone due to phase transformations during the welding thermal cycle. The formation of cracks in the fusion zone is another factor that possibly contributes to the lower measured residual stress values. Residual stresses develop in a material during welding due to the uneven distribution of inelastic strains caused by the localized heating from the welding heat source and the subsequent uneven cooling of the material. Solidification shrinkage of the weld metal and local thermal expansion and

Solid-state welding of oxide-dispersion-strengthened (ODS) alloy MA956 sheets using friction stir... more Solid-state welding of oxide-dispersion-strengthened (ODS) alloy MA956 sheets using friction stir welding (FSW) was investigated. Butt weld was successfully produced. The weld and base metals were characterized using optical microscopy, scanning electronic microscopy, transmission electronic microscopy, and energy dispersion x-ray spectrum. Microhardness mapping was also conducted over the weld region. Analyses indicate that the distribution of the strengthening oxides was preserved in the weld. Decrease in microhardness of the weld was observed but was insignificant. The preliminary results seem to confirm the envisioned feasibility of FSW application to ODS alloy joining. For application to Gen IV nuclear reactor heat exchanger, further investigation is suggested.

SAE International Journal of Materials and Manufacturing, 2012

ABSTRACT Friction stir spot welding was used to join two advanced high-strength steels using poly... more ABSTRACT Friction stir spot welding was used to join two advanced high-strength steels using polycrystalline cubic boron nitride tooling. Numerous tool designs were employed to study the influence of tool geometry on weld joints produced in both DP780 and a hot-stamp boron steel. Tool designs included conventional, concave shouldered pin tools with several pin configurations; a number of shoulderless designs; and a convex, scrolled shoulder tool. Weld quality was assessed based on lap shear strength, microstructure, microhardness, and bonded area. Mechanical properties were functionally related to bonded area and joint microstructure, demonstrating the necessity to characterize processing windows based on tool geometry.

Neutron diffraction was used to measure the residual stress distribution in an FeAl weld overlay ... more Neutron diffraction was used to measure the residual stress distribution in an FeAl weld overlay on steel. It was found that the residual stresses accumulated during welding were essentially removed by the post-weld heat treatment that was applied to the specimen; most residual stresses in the specimen developed during cooling following the post-weld heat treatment. The experimental data were compared with a plasto-elastic finite element analysis. While some disagreement exists in absolute strain values, there is satisfactory agreement in strain spatial distribution between the experimental data and the finite element analysis.

• Develop the technological basis for friction stir welding and processing (FSW/P) of advanced hi... more • Develop the technological basis for friction stir welding and processing (FSW/P) of advanced high-strength and lightweight materials for the automotive industry.

Science and Technology of Welding and Joining, 2007

The evolution of temperature and thermal stresses during friction stir welding of Al6061-T6 was i... more The evolution of temperature and thermal stresses during friction stir welding of Al6061-T6 was investigated by means of in situ, time resolved neutron diffraction technique. A method was developed to deconvolute the temperature and stress from the lattice spacing changes measured by neutron diffraction. The deep penetration capability of neutrons made it possible for the first time to obtain the temperature and thermal stresses inside a friction stir weld.

Microscopy and Microanalysis, 2012

Extended abstract of a paper presented at Microscopy and Microanalysis 2012 in Phoenix, Arizona, ... more Extended abstract of a paper presented at Microscopy and Microanalysis 2012 in Phoenix, Arizona, USA, July 29 – August 2, 2012.

Metallurgical and Materials Transactions A, 2009

LA-UR-fY{-{) I~J Approved for public release; distribution is unlimited.

Journal of Manufacturing and Materials Processing

The root cause of post-weld baking on the mechanical performance of Al-steel dissimilar resistanc... more The root cause of post-weld baking on the mechanical performance of Al-steel dissimilar resistance spot welds (RSWs) has been determined by machine learning (ML) and finite element modeling (FEM) in this study. A deep neural network (DNN) model was constructed to associate the spot weld performance with the joint attributes, stacking materials, and other conditions, using a comprehensive experimental dataset. The DNN model positively identified that the post-weld baking reduces the joint performance, and the extent of degradation depends on the thickness of stacking materials. A three-dimensional finite element (FE) model was then used to investigate the root cause and the mechanism of the baking effect. It revealed that the formation of high thermal stresses during baking, from the mismatch of thermal expansion between steel and Al alloy, causes damage and cracking of the brittle intermetallic compound (IMC) formed at the interface of the weld nugget during welding. This in turn re...

Transactions on Intelligent Welding Manufacturing, 2017

A master welder uses his sensory perceptions to evaluate the process and connect them with his/he... more A master welder uses his sensory perceptions to evaluate the process and connect them with his/her knowledge base to take the necessary corrective measures with his/her acquired skills to make a good weld. All these actions must take place in real time. Success depends on intuition and skills, and the procedure is labor-intensive and frequently unreliable. The solution is intelligent weld manufacturing. The ultimate goal of intelligent weld manufacturing would involve sensing and control of heat source position, weld temperature, weld penetration, defect formation and ultimately control of microstructure and properties. This involves a solution to a problem (welding) with many highly coupled and nonlinear variables. The trend is to use an emerging tool known as intelligent control. This approach enables the user to choose a desirable end factor such as properties, defect control, or productivity to derive the selection of process parameters such as current, voltage, or speed to provide for appropriate control of the process. Important elements of intelligent manufacturing are sensing and control theory and design, process modeling, and artificial intelligence. Significant progress has been made in all these areas. Integrated computational welding engineering (ICWE) is an emerging field that will aid in the realization of intelligent weld manufacturing. The paper will discuss the progress in process modeling, microstructure, properties, and process control and automation and the importance of ICWE. Also, control and automation strategies for friction stir welding will be discussed.

Objectives • Quantify and develop the knowledge base for hydrogen permeability and embrittlement ... more Objectives • Quantify and develop the knowledge base for hydrogen permeability and embrittlement of pipeline steels and their welds under high-pressure gaseous hydrogen exposure relevant to hydrogen gas transmission pipeline. • Optimize the base metal and weld metal composition and microstructure to avoid excessive hydrogen permeation and increase service performance of hydrogen pipelines. • Evaluate welding technologies suitable for joining high-pressure hydrogen pipelines. • Develop a risk assessment based approach to manage the integrity and safety of hydrogen pipelines including weld joints.

Objective • Develop the technological basis for friction stir welding and processing (FSW/P) of a... more Objective • Develop the technological basis for friction stir welding and processing (FSW/P) of advanced high-strength and lightweight materials for the automotive industry. • Gain fundamental understanding of the relationships between workpiece and tool material properties during FSW/P. • Characterize the mechanical properties and microstructures of joints. • Correlate the proprieties and microstructures produced by FSW/P to the process conditions.

Materials, 2020

Friction stir processing is a novel solid-state process to modify microstructures and their prope... more Friction stir processing is a novel solid-state process to modify microstructures and their properties by intense, localized plastic deformation. However, little research has been reported for microstructure evolutions of advanced high-strength steels during the process. The present work focuses on the study of transient microstructure changes and local mechanical properties for friction stir spot processed dual-phase (DP) 980 MPa grade steel (DP980) under different peak temperatures. A pinless silicon nitride ceramic tool was used to produce relatively simple material deformation and flow near the tool. Friction stir spot processed steel samples were characterized by optical and electron microscopies. Furthermore, Vickers microhardness and nano-indentation measurements were used to study local mechanical properties for correlation with microstructures. A swallow layer of refined grains (<0.6 µm) was obtained with a low peak temperature (under 400 °C), whereas higher peak tempera...

This report summarizes recent post-welding activities on irradiated alloys at the Irradiated Mate... more This report summarizes recent post-welding activities on irradiated alloys at the Irradiated Materials Examination and Testing (IMET) and the Low Activation Materials Development and Analysis (LAMDA) facilities at Oak Ridge National Laboratory. Equipment and capabilities were developed jointly by the U.S.

Materials, 2019

Transient distortion of thin plate in the welding process usually has a complicated mode and larg... more Transient distortion of thin plate in the welding process usually has a complicated mode and large magnitude. Quantitative measurement and prediction of full-field distortion are challenging and rarely reported up to now. In this study, the out-of-plane distortion of a thin plate during the Tungsten Inert Gas (TIG) welding process was measured using the digital image correlation (DIC) method. A simulation model based on thermal elastic–plastic finite element method (FEM) and DIC measured geometric imperfection were developed for accurate prediction of the transient welding distortion. The numerical results and experimental data agreed very well in both out-of-plane deformation modes and magnitudes of the plate at different stages of welding. The maximum out-of-plane distortion was larger than 4 mm during welding which can cause instability of arc length and heat input. The distance change between welding torch and plate surface was investigated under different initial deflections of...

The residual stress distribution in a GTA spot welded HSLA-100 steel disk was analyzed using ther... more The residual stress distribution in a GTA spot welded HSLA-100 steel disk was analyzed using thermomechanically uncoupled and semi-coupled finite element (FE) formulations and measured with the neutron diffraction technique. The computations used temperature-dependent thermophysical and mechanical properties of the base metal. The thermal analysis was based on the heat conduction formulation with the Gaussian heat input from the arc. The semi-coupled approach is an effective alternative to the fully coupled approach in which the incompatibility in the thermal and mechanical time increments often leads to numerical convergence difficulties. Convergence was achieved in the semi-coupled approach where a larger time increment for temperature calculation was automatically divided into some sub-intervals for the thermal stress calculation. The temperature, deformation configurations, and state variables were updated at the end of the temperature increment. The predictions from the FE models are in very good agreement with the neutron measurement results in the far heat-affected zone (HAZ) and in the base metal. Both models over-predicted the residual stress field in the fusion zone and near HAZ as measured by the neutron diffraction method. The discrepancy could be attributed to the changes in microstructures and material properties in the HAZ and fusion zone due to phase transformations during the welding thermal cycle. The formation of cracks in the fusion zone is another factor that possibly contributes to the lower measured residual stress values. Residual stresses develop in a material during welding due to the uneven distribution of inelastic strains caused by the localized heating from the welding heat source and the subsequent uneven cooling of the material. Solidification shrinkage of the weld metal and local thermal expansion and

Solid-state welding of oxide-dispersion-strengthened (ODS) alloy MA956 sheets using friction stir... more Solid-state welding of oxide-dispersion-strengthened (ODS) alloy MA956 sheets using friction stir welding (FSW) was investigated. Butt weld was successfully produced. The weld and base metals were characterized using optical microscopy, scanning electronic microscopy, transmission electronic microscopy, and energy dispersion x-ray spectrum. Microhardness mapping was also conducted over the weld region. Analyses indicate that the distribution of the strengthening oxides was preserved in the weld. Decrease in microhardness of the weld was observed but was insignificant. The preliminary results seem to confirm the envisioned feasibility of FSW application to ODS alloy joining. For application to Gen IV nuclear reactor heat exchanger, further investigation is suggested.

SAE International Journal of Materials and Manufacturing, 2012

ABSTRACT Friction stir spot welding was used to join two advanced high-strength steels using poly... more ABSTRACT Friction stir spot welding was used to join two advanced high-strength steels using polycrystalline cubic boron nitride tooling. Numerous tool designs were employed to study the influence of tool geometry on weld joints produced in both DP780 and a hot-stamp boron steel. Tool designs included conventional, concave shouldered pin tools with several pin configurations; a number of shoulderless designs; and a convex, scrolled shoulder tool. Weld quality was assessed based on lap shear strength, microstructure, microhardness, and bonded area. Mechanical properties were functionally related to bonded area and joint microstructure, demonstrating the necessity to characterize processing windows based on tool geometry.

Neutron diffraction was used to measure the residual stress distribution in an FeAl weld overlay ... more Neutron diffraction was used to measure the residual stress distribution in an FeAl weld overlay on steel. It was found that the residual stresses accumulated during welding were essentially removed by the post-weld heat treatment that was applied to the specimen; most residual stresses in the specimen developed during cooling following the post-weld heat treatment. The experimental data were compared with a plasto-elastic finite element analysis. While some disagreement exists in absolute strain values, there is satisfactory agreement in strain spatial distribution between the experimental data and the finite element analysis.

• Develop the technological basis for friction stir welding and processing (FSW/P) of advanced hi... more • Develop the technological basis for friction stir welding and processing (FSW/P) of advanced high-strength and lightweight materials for the automotive industry.

Science and Technology of Welding and Joining, 2007

The evolution of temperature and thermal stresses during friction stir welding of Al6061-T6 was i... more The evolution of temperature and thermal stresses during friction stir welding of Al6061-T6 was investigated by means of in situ, time resolved neutron diffraction technique. A method was developed to deconvolute the temperature and stress from the lattice spacing changes measured by neutron diffraction. The deep penetration capability of neutrons made it possible for the first time to obtain the temperature and thermal stresses inside a friction stir weld.

Microscopy and Microanalysis, 2012

Extended abstract of a paper presented at Microscopy and Microanalysis 2012 in Phoenix, Arizona, ... more Extended abstract of a paper presented at Microscopy and Microanalysis 2012 in Phoenix, Arizona, USA, July 29 – August 2, 2012.

Metallurgical and Materials Transactions A, 2009

LA-UR-fY{-{) I~J Approved for public release; distribution is unlimited.