Peter Joyce

sometimes Graduate Research Assistant
sometimes Teaching Assistant
Materials Science & Engineering
ETC 6.120
University of Texas at Austin
Austin, TX 78712 U.S.A.

Email: pjj@mail.utexas.edu
Telephone: (512)/471-5723
Fax: (512)/471-8727
Informal Homepage

Last modified 6/3/97

I am a graduate research assistant in the Materials Science & Engineering Program at The University of Texas at Austin. I am also pursuing my Ph.D in Materials Science & Engineering.

What am I doing in the IMPACT lab

I am doing research on process-induced fiber waviness in composite materials. My research thus far has concentrated on trying to develop a characterization technique for detecting/measuring fiber waviness in fiber-reinforced composite materials. Our efforts have focused primarily on destructive techniques for use in qualifying the composite parts produced in our own lab. Ongoing research is aimed at demonstrating a feasible non-destructive technique for characterizing fiber/ply waviness that could ideally be used for in-situ process monitoring and control in applications where fiber waviness is critical. The principal thrust of my dissertation research is the investigation of thermo-mechanical mechanisms active at the microscale which cause the initiation and growth of fiber waviness in composite materials. For a brief summary of this work see the text of my dissertation proposal below

Background

I received a B.S. in Engineering Mechanics at the University of Illinois - Urbana/Champaign, in 1992, and and an M.S. in Materials Science and Engineering from the University of Texas at Austin, in 1994.

Professional Experience

Research Interests

My current research interests include the study of composite microstructures. I am specifically interested in experimental characterization of the fiber morphology in glass and carbon fiber composite laminates and cylinders. More generally my research interests include 1.) mechanical characterization of materials, 2.) characterization of composite microstructures using video microscopy and image analysis, 3.) process monitoring of composite materials using embedded sensors, 4.) mechanical behavior of composites with embedded sensors & actuators, 5.) advanced materials processing and performance.

Research Publications

Publications -- Journal Paper

• P. Joyce, D. Kugler, and T. Moon, "A Technique for Characterizing Process-Induced Fiber Waviness in Composite Laminates - Using Optical Microscopy", accepted for publication.

• D. Kugler, P. Joyce, and T. Moon, "Investigation of the Effect of Part Length on Process-Induced Fiber-Wrinkled Regions in Composite Laminates", accepted for publication.

Publications -- Conference Papers & Presentations

• P. J. Joyce, and T. J. Moon, ''Compression Strength Reduction in Composites with In-Plane Fiber Waviness,'' Seventh Symposium on Composites: Fatigue and Fracture (ASTM), St. Louis, MO, May 6-8, 1997, in preparation.
• P. J. Joyce, D. Kugler, M. S. Bhalerao and T. J. Moon, "The Effect of Fiber Waviness on Global Structural Performance," Proceedings of the Sixth International Conference on Marine Applications of Composite Materials (MACM `96). Cocoa Beach, FL, March 1996.
• P. Joyce, D. Kugler, and T. Moon, "Investigation of Process-Induced Fiber-Wrinkled Regions in Composite Laminates", Society of Engineering Science 31st Annual Technical Meeting, October 10, 1994, Texas A & M University, College Station, Texas (abstract only published by SES).
• T.J. Moon, M.S. Bhalerao, P.J. Joyce, and D. Kugler, "Polymer Composite Processing: Models and Experiments", 1995 NSF Design and Manufacturing Grantees Conference, January 4-6, 1995, University of California, San Diego, California (abstract only published by SME).

End professional information, return to

Dissertation Proposal to Graduate School (November 1994)

Continuous fiber-reinforced composite materials are an important class of engineering materials. They offer outstanding mechanical properties, excellent strength-to-weight ratios, and unique flexibility in design capabilities. The strength of composite materials depends not only on the strengths of the constituent materials but also on the processing history of the material. The load carrying capabilities of fiber-reinforced composites are very sensitive to the distribution and linearity of the fibers. In a unidirectional laminate composed of many plys or layers of composite prepreg, the fibers should be perfectly aligned with respect to one another, aligned from layer to layer, and, ideally, they should be linear. However, the fibers in real composite materials exhibit small angular imperfections which can be categorized as either fiber misalignment or fiber waviness.

An improved explanation of how this fiber waviness develops is necessary not only for the development of processing techniques which reduce fiber waviness, but also for the more accurate prediction of material strength. Past researchers have linked the existence of fiber waviness to a number of variables in the fabrication of composite parts. There is still a need to investigate the thermo-mechanical mechanisms at work at the microscale which really drive the initiation and growth of fiber waviness. A number of mechanisms have been postulated to be involved in driving the development of fiber waviness during autoclave processing. A better understanding of the mechanisms which lead to the development of fiber waviness and how these mechanisms are linked to the processing will enhance one's ability to predict the amount of waviness in a product without destructive testing and enable one to predict waviness levels before rigorous (and often expensive) experimental testing is required.

The objective of this thesis is to investigate the many phenomenae that occur leading up to the development of fiber waviness. It is proposed to conduct a series of model experiments which address the different waviness inducing mechanisms in isolation to study their various effects in the development of fiber waviness for an array of different composite material systems.

Past researchers have experienced difficulty quantifying fiber waviness throughout composite parts; therefore, there is a need to develop an improved method for characterizing fiber waviness for qualification and/or comparison purposes. The other objective then, of this experimental program is to establish a method for characterizing the process-induced fiber waviness found in unidirectional composite laminates. A major obstacle to investigating fiber waviness is determining how to quantify fiber waviness. Since sinusoidal models are frequently adopted or assumed, wavelength and amplitude are the traditional geometric parameters used to define waviness. However, even these relatively simple parameters are not easily measured when examining the entangled fibers in a real composite laminate. In a composite, each fiber may have its own amplitude and wavelength. Therefore, a statistical analysis describing the waviness distribution throughout the part yields the most comprehensive characterization available using sectioning and polishing techniques with optical microscopy. If a non-destructive test for local fiber waviness can be found that is applicable to the entire part this dependence on statistical sampling can be overcome.

An experimental methodology for characterizing the process-induced fiber waviness in thermoplastic (T300/P1700) composite laminates using computer assisted optical microscopy has been developed [see (Joyce et. al 1994)]. Several experiments are left to be performed that will help to characterize the fiber waviness in composite laminates using optical microscopy. More importantly a non-destructive evaluation (NDE) technique for detecting and measuring fiber waviness is desired. The secondary thrust of the proposed work is to seek after an appropriate NDE technique for characterizing fiber waviness in composite parts. I am looking specifically at ultrasonic inspection and x-ray computed tomography for their potential capability to detect/measure fiber waviness in composite parts. If a suitable NDE technique could be implemented on-line it would be a significant contribution to the quality assurance of composite parts in which the presence of fiber waviness plays a key role in failure.

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