Session: 16-01-01: Government Agency Student Poster Competition

Paper Number: 151006

151006 - Dynamic Mixed-Mode I/ii Fracture Criterion of 3-D Printed Abs With Computer Vision Assisted Crack Initiation Determination 

This research project used three-point bending of single edge notch beam (SENB) specimens to study fracture toughness of fusion deposition modeling (FDM) 3D printed acrylonitrile butadiene styrene (ABS) material in 4 different raster orientations in dynamic mode-I, mixed-mode, and mode-II loading conditions. Computer vision was used to enhance visual analysis of crack initiation.

FDM printing with ABS filament, a strong thermoplastic polymer widely used in engineering and structural applications, can be used to fabricate structural materials on-the-fly that can be used for repairs on marine vessels and in other environments where a temporary solution is needed. Existing research is limited to determining fracture toughness in quasi-static pure mode-I loading conditions which does not adequately represent the conditions these materials are subjected to under practical application.

A split-Hopkinson bar was modified for dynamic testing of the specimens. An apparatus for 3-point bending was designed and positioned so that the impulse through the incident bar directly transferred to the movable part of the structure that housed the two supports. The impulse accelerated the two supports which generated a force on the specimen resting between the two supports and the midpoint, behind which a force sensor sent load data to a digital oscilloscope. The three point bending structure had one stationary and one vertically adjustable support. The adjustable support was set to different distances from the midpoint line to generate pure mode-I opening, pure mode-II shearing, and mixed-mode loading conditions. A high-speed camera was also connected to the oscilloscope and set to trigger when the force reading on the oscilloscope went over a certain threshold. A computer vision algorithm with a visual noise filter was used by an image processing program to find the crack edges and graphically represent the crack length as a function of time.

Dynamic mode-I fracture toughness for 45°- and 90°-degree raster orientations were found to be higher than that of 0° and 0°/90° degree raster orientations. The 0°/90° orientation was found to be very similar to the 0° orientation, with a small but observable increase. Additionally, dynamic fracture toughness values for all these orientations were higher than static counterparts. The experiments are in progress to determine the fracture toughness values for pure mode-II and several mixed mode conditions to develop a rate dependent mixed-mode fracture criterion.

Due to how rapidly the crack initiation was occurring (typically under 100µS and under 50 frames), visually determining the initiation point by looking frame-to-frame was open to interpretation and was inconsistent between observers. This began a sub-project of implementing a computer vision algorithm for this problem. Computer vision resolved the observer issue by generating a graphical representation of the entire progression of the crack over time. The use of computer vision allowed for increased objectivity in determining initiation points, at-a-glance analysis of many specimens at once, and it illuminated trends in crack behaviors that were not apparent through the manual visual analysis method. This method was particularly useful because in cases like this one, no other objective metric of determining crack initiation was available, such as piezoelectric sensing, as ABS material is non-conductive. Future research should further explore the application of computer vision as a reliable and replicable determination of crack initiation

Presenting Author: Anya Zakhour Community College of Rhode Island/University of Massachusetts, Dartmouth

Presenting Author Biography: Anya Zakhour is a rising sophomore at the Community College of Rhode Island in the joint admissions program with the University of Rhode Island in the area of Mechanical Engineering. She previously participated in bat wing morphology research in the Swartz Aeromechanics and Evolutionary Morphology Lab at Brown University, and has been an officer of the Engineering Student's Association at the Community College of Rhode Island. She is currently completing a REU internship at the University of Massachusetts, Dartmouth in Vijaya Chalivendra's Dynamic Materials Characterization lab. Her research interests include materials science, mechanics, and woman-centered design.

Authors:

Anya Zakhour Community College of Rhode Island/University of Massachusetts, Dartmouth
Zhuoyuan Leng University of Massachusetts, Dartmouth
Vijaya Chalivendra University of Massachusetts, Dartmouth