EFFECTS OF LASER MACHINING ON STRUCTURE AND FATIGUE OF 316LVM BIOMEDICAL WIRES

Recent advances in minimally invasive surgical techniques and an increasing need to miniaturize medical devices has led to a surge in developing advanced manufacturing techniques. In order to meet the functional needs of such small devices as cardiovascular stents, guide wires, and needles, the use of new materials and delicate geometries has increased creating a new challenge for manufacturing and machining. Some applications often include fine details that are impossible to achieve with rotary tool machining. Laser machining is one tool harnessing an enormous potential for the manufacture of such finely detailed devices as well as providing a means for improving the local material effects as a result of processing. However, thermal damage caused by laser machining can affect the performance of the components. As devices continue shrinking in size, there is a greater need for “athermal” manufacturing methods that have no adverse effect on performance. In this study, Nd:YAG and femtosecond lasers with different pulse widths were used to machine AISI 316LVM biomedical grade wires. The mechanical behavior of these materials were evaluated in uniaxial tension, and in cyclic strain-controlled fatigue with the use of a flex tester operated to provide fully reversed bending fatigue. All the fatigue testing was conducted in air over a range of cyclic strains to determine both the high-cycle and low-cycle fatigue regimes. The effects of laser input energy and pulse width on surface quality, heat affected zone (HAZ), and subsequent mechanical response are reported Baseline fatigue data on 316LVM wires in the annealed and hard conditions revealed that the hard wires exhibited better high cycle fatigue behavior than exhibited by the annealed wires. However, the low cycle fatigue behavior of the annealed wires was better than that obtained on the hard wires. This was successfully modeled using the Coffin-Manson-Basquin approach. Mixed results were obtained on the fatigue behavior of laser-treated wires. Low power Nd:YAG laser-treated 316LVM annealed wires exhibited better fatigue performance in both high cycle fatigue and low cycle fatigue compared to the annealed 316LVM wires. In contrast, high power Nd:YAG laser-treated annealed wires exhibited poorer fatigue performance in both high cycle and low cycle fatigue. Nd:YAG laser-treated 316LVM hard wires exhibited poorer fatigue performance in both high cycle fatigue and low cycle fatigue compared to the 316LVM hard wires. The femtosecond laser-machined annealed wires exhibited better fatigue life in both high cycle and low cycle fatigue compared to the annealed wires. In contrast, the femtosecond laser-machined hard wires exhibited lower fatigue life in both the high cycle fatigue and low cycle fatigue regimes compared to hard wires. Attempts at modeling the fatigue behavior of the laser-treated wires was unsuccessful using the Coffin-Manson-Basquin approach, likely due to localized surface conditions that dominated the fatigue behavior of the laser-treated wires.

Name thesis:degree_name

Doctor of Philosophy

Level thesis:degree_level

doctoral

Discipline thesis:degree_discipline

Materials Science and Engineering

Grantor dc:publisher

Case Western Reserve University School of Graduate Studies

Year dc:date

2013

Author dc:creator

• Lavvafi, Hossein

Contributors dc:contributor

• Lewandowski, John J.

• Materials Science
• 316LVM
• medical device
• laser machining
• microfabrication
• flex bending fatigue
• femtosecond laser
• stent
• Nd:YAG nanosecond laser
• Coffin-Manson-Basquin
• fatigue-life
• heat exchanger
• heat-affected zone

Statement dc:rights

• unrestricted
• This thesis or dissertation is protected by copyright: all rights reserved. It may not be copied or redistributed beyond the terms of applicable copyright laws.

Language dc:language

English

Repository record dc:identifier

http://rave.ohiolink.edu/etdc/view?acc_num=case1352743353

OAI identifier oai:identifier

oai:etd.ohiolink.edu:case1352743353