Name : Yunpeng Ren

Associate Professor; MSSupervisor

Address : Room B101School of Mechanical Engineering

Phone: (86) 15716106320

E-mail: coolim515@163.com

Education

2008-2012Ph.D, Mechanical and Aerospace Engineering, University of Missouri-Columbia,US

2005-2008 MS, Materials Science, China University of Petroleum, China

2001-2005 BS, Materials Science and Engineering, China University of Petroleum, China

Professional Experience

2015- AssociateProfessor, MS Supervisor, Jiangsu University, China

2013-2014 Assistant Professor, Guangzhou Institute of Advanced Technology, China

2013-2013 PostDoc, Mechanical and Aerospace Engineering, University of Missouri-Columbia, US

Research interests

1. Interaction between ultra-fast laser and (metallic) materials. Ultra-fast laser has extremely high peak power by which it can treat materials with very high precision. Currently, most of the processing is using low energy pulses to guarantee precision by reducing heat affected zone (HAZ). However, the processing speed is pretty low by using low energy pulses. Considering the multi-photon absorption effect, it is possible to realize very high processing precision that even less than diffraction limit by modulating the high energy ultra-fast laser pulses in the center part of the laser spot. Meanwhile, the processing speed can be significantly improved due to much higher pulse energy. But the treatment process is involving complicated optics, mechanism, and thermodynamics. It is critical to get deep understanding of these physics to realize fast precise processing by ultra-fast lasers. This research is intending to build a Critical Point Model which can describe the optical properties of metals such as gold, copper, and aluminum both at room temperature and very high temperature. By incorporating this model into the Two-Temperature Model, the interactions between metals and ultra-fast lasers can be described and the non-thermal ablation induced by low energy pulses and thermal ablation induced by high energy pulses can be studied. Besides, the ultra-fast crystallization process driven by “under-cooling” will be investigated based on phase field model to reveal how the laser parameters influence microstructure of the materials. Based on this model, how the ablation process and crystallization are influenced by laser parameters will be studied to provide direction of using ultra-fast lasers in more fields.

Change of optical properties and melting process of metal induced by femtosecond laser

2. Theoretical study of 3D printing process (SLM technology).The 3D printing parts have defects such as deformation, crack, low density, low mechanical properties, and high residual stress. These defects could be eleminated by changing parts' designs, optimizing printing parameters and scanning strategies. However, these attempes will lead a very high cost of time and money which results in that the advantages of 3D printing are losing compared to the traditional maching methods. This problem will be solved by simulating the 3D printing process mathematically. The designs will be optimized before printing to remove the ones containing stress concentration. The temperature and thermal stress development will be investigated during process of printing and the printing parameters will be optimized to find the best ones for printing.

Heat transfer during 3D printing

Teaching Courses

Engineering Materials and Shaping Foundation

Precise and Special Processing

Principles and Applications of Rapid Prototyping

Main Research Projects

1. Study of ultra-fast ablation dynamics and crystallization of metallic materials induced by ultra-fast lasers, NSFC, 2016-2018

2. Study of laser shock 3D auto cool shaping technology and application on Chinese big planes, Jiangsu Province, 2015-2018

3. Study of theory and processing of precise laser cuttingof metal sheets, Yangzhou City, 2015-2018

Main Scientific Publications

1. S. Y. Wang, Y. Ren, K. P. Chang, C. W. Cheng, J. K. Chen, D. Y. Tzou, Ablation of copper by a single ultrashort laser pulse, Journal of Laser Micro/Nanoengineering, 9, 88, 2014.

2. C. Zhang, Y. Ren, X. Chen. The development situation of selective laser melting metal powder based on 3D printing, Advanced Materials Research, 518, 12, 2014.

3. Y. Ren, C. W. Cheng, J. K. Chen, Y. Zhang, D. Y. Tzou, Thermal ablation of metal films by femtosecond laser bursts, International Journal of Thermal Science, 70, 32, 2013.

4. S. Y. Wang, Y. Ren, C. W. Cheng, J. K. Chen, D. Y. Tzou, Micromachining of copper by femtosecond laser pulses, Applied Surface Science, 265, 302, 2013.

5. Y. Ren, Y. Zhang, J. K. Chen, Z. C. Feng, Inverse estimation of front surface temperature of a 3-D finite slab based on back surface temperature measured at course grids, Numerical Heat Transfer, Part B: Fundamentals, 63, 1, 2013.

6. Y.Ren, J. K. Chen, Y.Zhang, Heat transfer in metal films irradiated by combined nanosecond laser pulse and femtosecond pulse train, Frontiers in Heat and Mass Transfer, 3, 023001, 2012.

7. Y.Ren, J. K. Chen, Y. Zhang, Modeling of ultrafast phase changes in metal films induced by an ultrashort laser pulse using a semi-classical two temperature model, International Journal of Heat and Mass Transfer, 55, 1620, 2012.

8. Y.Ren, J. K. Chen, Y.Zhang, Optical properties and thermal response of copper films induced by ultrashort-pulsed lasers, Journal of Applied Physics, 110, 113102, 2011.

9.Y. Ren, J. K. Chen, Y.Zhang, J. Huang, Ultrashort laser pulse energy deposition in metal films with phase changes, Applied Physics Letters,98, 191105, 2011.

10. D. Jia, A. Ba, Y.Ren, Mechanism of acceleration effect of Ni in WC synthesizing process, Superhard Material Engineering, 20, 23, 2008.

11.Y.Ren, Y. Lu, Q. Lou, Theory study on the behavior of CO chemisorption on low-index Platinum surface, ActaPhysico-ChimicaSinica, 23, 1728, 2007.

12. W. Miao, Y. Lu, Y. Ren, Y. Liu, Q. Lou, Thermal mechanical alloying synthesis of tungsten carbide-metal composites, Ordnance Material Science and Engineering, 30, 31, 2007.

13.S. Y. Wang, Y. Ren, K. P. Chang, C. W. Cheng, J. K. Chen, D. Y. Tzou, Ablation of copper by a single ultrashort laser pulse, Proceedings of LPM2013 – the 14^th International Symposium on Laser Precision Microfabrication, Toki Messe, Nigata, Japan, July 23-26, 2013.

14. Y. Ren, J. K. Chen, Y, Zhang, Transient optical and thermal response of metal films induced by ultrashort-pulsed lasers, Proceedings of ASME 2012 Summer Heat Transfer Conference, Puerto Rico, July 8-12, 2012.

15.S. Y. Wang, C. W. Cheng, W. C. Shen, Y. Ren, J. K. Chen, D. Y. Tzou, Y. Zhang, Femtosecond laser induced surface nanostructures on copper, Proceedings of LPM2012 - the 13^th International Symposium on Laser Precision Microfabrication, Washington DC, June 12-15, 2012.

Plan for Overseas Master & Ph. D

One master