New Method for Continuous Production of Continuous Fiber Metal Matrix Composite Precursors

Thomas R. Bieler, Department of Materials Science and Mechanics

We have developed a new technique for manufacture of precursors for making continuous fiber metal matrix composite (CFMMC) materials using fine fiber tows. The use of fine diameter fiber tows provides a reduction in the size of features in the microstructure, which also reduces the typical flaw size in the composite. The same technique could also be used to make ceramic or intermetallic matrix continuous fiber precursors.

The new technique is based on a system for manufacture of continuous fiber polymer matrix prepreg that was developed at the Composite Materials and Structures Center at Michigan State University. In this process for making polymer matrix prepreg (Fig. 1), fiber tows are spread out (a 3k carbon fiber tow becomes about 75 mm wide), and intoduced into a chamber with an aerosol of electrostatically charged polymer powder particles that are attracted to the fiber surface. The aerosol is suspended over a fluidized bed of polymer particles that are on the order of the fiber diameter at the bottom of the chamber. Next, the fibers pass through a heater, where softening and surface tension causes the polymer particles to stick to, or coat the fibers. The resulting prepreg is then cooled and rolled onto a take-up drum for future use as lay-ups for structures. In the pilot scale composite process, fibers are adequately coated at a rate of 30 cm/min. When consolidated, this technique causes small diameter fibers to be evenly distributed throughout the matrix, without fiber-fiber contact, and fiber fractions near the maximum possible volume fraction can be obtained.

The process shown in Figure 1 can be modified for metal matrix composites by adding a similar impregnation chamber of metal powder following the heater. This chamber has a similar aerosol of fine metal powders, which stick to the fibers, since the warm, tacky polymer coating acts as a binder. However, the explosion hazard with suspended metal powders precludes adding such a chamber to the existing system, so we have done some demonstration experiments with an aerosol of aluminum powder suspended above a fluidized bed of the same powder in argon gas. We have used a fine (5.5 u avg.) pure aluminum powder from Valimet. We have suspended heated prepreg made by the process shown in Fig. 1 in the argon chamber to coat the prepreg. The resulting precursor tape had an even layer of powder, and it survived the handling needed to prepare SEM specimens for observation. Many layers of the precursors were then laid up and vacuum hot pressed to consolidate the sample. The polymer was removed from the composite by the vacuum prior to hot pressing.

In our first attempt, the polymer prepreg had many fiber bundles due to the furnace residence time and temperature that caused the polymer to become liquid-like and draw many fibers together. This caused many fibers to be hidden from the aerosol of aluminum powder, and consequently no matrix was around these fibers after consolidation.

In our second attempt, we made a batch of prepreg using a lower furnace temperature for the polymer prepreg adhesion process. The resulting consolidated CFMMC had significant reduction in the number of fibers in a bundle (from 90% to 40%) in the fiber distribution in the metal matrix. The matrix was higher than in the first attempt, so the pickup rate was also improved. We know that this batch was an over correction, so we know that we can make a significant further improvement with our existing apparatus. Also, three point bending experiments have shown that the matrix powders were successfully consolidated.

Compared to other techniques for making continuous fiber metal matrix composites such as melt infiltration, plasma spraying, and fiber/foil lay-up processes, the proposed technique has the potential to eliminate many common problems, as well as having cost effective scale-up potential for mass production. Very fine fiber diameters are used, since the fiber spreader makes each surface equally accessible to the aerosol of powder particles. At any given elevation above the fluidized bed, the particle size range is bounded, so that the powder coating the fibers is nominally the same size, even though the 5.5 u (avg.) powder we use has a size range from 1 - 10 u. The powder particles are evenly distributed around the fibers. Large powder particles ar agglomerates are broken up, or remain at the bottom of the fluidized bed, below the aerosol. The volume fraction of the matrix powder applied can be controlled by length of time of exposure in the aerosol. This technique is partially automated, though there is potential for immediate consolidation (if a polymer binder is not used) of multiple layers to make sheet or surface coatings of this composite possible. The even powder distribution, without voids or big lumps, reduces the consolidation temperature, time, and pressure, and consequently reduces the interface reactions and fiber damage.

Since this process must be done in an inert gas environment, we have made thermodynamic computations and determined safe methods to prevent an explosion hazard. One helpful fact is that a powder kept in an Argon environment has a layer of Ar atoms absorbed on the surface that lasts for a few hours, so that an inadvertant exposure to oxygen for a short time will not present an immediate explosion hazard (PICKENS, J.R. J. Mat. Sci. 16, (1981) 1437-57.)

Our recent results demonstrate that all of the qualities described above can be obtained (we have filed patent disclosure forms). We have not obtained them all at once with our simple experimental apparatus. Our biggest challange is the minimization of fiber-fiber contact. We think that we can control the amount of fiber-fiber contact, but we cannot address this problem with our existing apparatus. We can explore this particular issue, as well as general producibility, only by making a continuous process aparatus similar to Figure 1, but it needs to be contained in an inert environment whenever heat or powder suspensions are present, to prevent an explosion hazard.

Consequently we wish to obtain support from other sources, since design and fabrication of such a chamber is no possible on the basis of the minimal funding we have through an internally reviewed source of funding from the State of Michigan. The internal/State of Michigan funding has priority for matching funds on projects that can attract outside funding, so approximately 1/3 of the funding needed to continue to develop this process can come from this existing source.

Most Errors in Science Result from Self-Delusion

K.M. Reese, taken from November 8, 1993 C&EN

Denis Rousseau at Bell Labs, Murray Hill, N.J., believes that most errors in science result from self-delusion and the associated sloppiness (Lab Notes, AT&T Bell Laboratories, Fall 1993). The late Irving Langmuir, Nobel Laureate, generated a formal model of the syndrome, which he called pathological science. Rousseau's experience led him to study and refine Langmuir's ideas. He sees three major characteristics of pathological science:

Rousseau grew interested in pathological science because of his early work at Bell Labs, which he joined in 1969. At the time, scientists everywhere where worked up about the Soviet discovery of polywater, in which water molecules were proposed to be linked in groups of six, a previously unknown structure. Among other properties, polywater boiled at much higher temperatures than ordinary water and froze at much lower temperatures.

When Rousseau joined Bell Labs, he says, "Dielectric losses were increasing in some of the trans-Atlantic telephone cables, prompting chemists to wonder if polywater had seeped into the cables and changed their properties." Rousseau was assigned to the problem. He and his colleagues, on analyzing samples of polywater, found impurities that did not occur in regular water. Polywater pushers argued that Rousseau's samples were contaminated, whereas theirs were not.

Anyway, Rousseau returned to the lab from a handball game one day and wrung the sweat from his shirt into a flask. He found on analysis that the sweat looked just like the polywater. He concluded that polywater was water contaminated with bioorganic matter that condensed on the surfaces of the tiny glass tubes containing the samples. His publication of the results, he says, stopped nearly all research on polywater.

As a recent example of the genre, Rousseau cites cold fusion. Some scientists are still exploring the phenomenon, he says, but most believe that it's pathological science.

In any event, Rousseau says, "Self-delusion in scientific research was recognized centuries ago, is evident today, and will no doubt continue into the future."

SEM Correction

It has come to our attention that a typographical error occurred in an article of the October, 1993 issue of the CMSCourier. Mistakenly included in the title of "SEM Elects New President" was the logo for SME, the Society of Manufacturing Engineers. We apologize for any confusion this error may have caused.

MSU Awarded a Technology Reinvestment Project

Michigan State University and the University of Deleware were jointly awarded a Manufacturing Education & Training Technology Reinvestment Project (TRP) in December, 1993, under the direction of Dr. Martin Hawley, MSU. The title of the project is "Education & Training Program in Composite Materials for the Department of Defense and Durable Goods Industries". The estimated total funding of this three-year project is almost ten million dollars.

The objective of the program is to improve the effectiveness of the educational programs and technology transfer activities of the two participating universities and to integrate the latest developments in low-cost manufacturing into the undergraduate engineering and continuing education programs. Industrial consortia representing the two sectors are already in place in the NSF-funded State/Industry/University Cooperative Research Center for Low-Cost, High-Speed Polymer Processing at Michigan State University (MSU) and in the ARO/URI Center of Excellence for the Manufacturing Science of Polymeric Composites at the University of Deleware Center for Composite Materials (UD-CCM). In addition, both centers have cooperative research agreements with the U.S. Army--the Tank Automotive Research, Development and Engineering Center (TARDEC) in Michigan and the Army Research Laboratory in Maryland.

The program will proceed by developing high-technology courseware such as videotapes, computer based tutorials with interactive process simulations and manufacturing design software that emphasize the connection among characterization, processing, performance and design for manufacturing in the context of composite materials. In the area of design for manufacturing, a synthesis of the knowledge-based systems software developed at MSU and UD-CCM will lead to a unique and effective training tool. Two primary mechanisms will be employed in this program. University faculty will develop and teach courses to students enrolled in degree programs and to industrial personnel; industrial leaders with practical expertise will collaborate in teaching courses at the universities to new students, continuing students, and transfer students. Workshops will address fundamental issues in process design for composites fabrication as well as design for manufacturing. Resident internships will be provided at various sites to facilitate more intense learning. The new courses will also be broadcast over the satellite network of the National Technological University. Thus the program will enhance the education of engineers across the country in technical areas with dual use potential.

COMPOSITES MANUFACTURING EDUCATION

Tools and Delivery Mechanisms

MSU-NSF Center, U-D CCM, DOD, Industry Consortium

Research Activities

Process Research and Development

Process Models and Software

Manufacturing Knowledge and Design Protocols

Tools For Education

Teaching Laboratory

Videotaped Modules

Interactive Computer Simulation

Knowledge Based System Software

Delivery

Classroom Instruction

Graduate Student Training and Interns from DOD and Industry

Short Courses and Workshops for DOD and Other Industries

SPE Design Contest Demonstrates Excellence in Polymer/Polymer Composite Education

This year saw the second annual Society of Plastics Engineers Paper Contest. The contest is open to al undergraduate students at Michigan State University but has seen most of it's participation from the Department of Chemical Engineering. The student chapter of SPE has existed at MSU for a number of years and consists of members from the Departments of Chemcical Engineering, Packaging, and Chemistry. Each year the society invites professionals from the plastics industry, and related academic fields, to come and speak to the membership on campus.

This year's contest goal was to design a car door panel made from a polymer or polymer composite. Each design engineering team was asked to perform a design analysis for the production of 100,000 door panels per annum by injection molding and an economic analysis based on material costs, production rates, operating costs and machinery costs. Teams were required to outline the emerging trends in materials and processes that are used in the making of exterior body panels of passenger cars. Each team selected or tailor designed a material from the list of materials available that would be ideal for this application, taking into account mechanical performance, weight of the final part, processing conditions and other issues which may be deemed important for a door panel.

The student chapter of SPE would like to thank Dr. M.C. Hawley, Dr. L.T. Drzal, and Dr. K. Jayaraman for their assistance in formulating the problem and judging the entries. Thanks to the following members that contributed much of their valuable time composing the contest problem as well as participating in the selection of best paper: Murty Vyakarnam, John Knight, and Ajay Gupta.

A number of excellent design reports were submitted which made choosing a winner difficult. After much deliberation the following design teams were selected as best among those designs presented:

1st Prize - $100

Brian Debbaudt and Jennifer Jewett

2nd Prize - $75

Max Wettlaufer and Rich Wordelman

3rd Prize - $50

Paul Blowers and Edwin Childs

Honorable Mention and SPE T-shirts were awarded to the teams of Barb Pilmore/Jeff Potoff, and Mike Filary/Tony Grai/Bob Stauffer. The winning paper will be presented at the Annual AIChE Symposium Day in March of 1993.

For information regarding SPE please contact Rick Delgado @ (517)353-9947 or Murty Vyakarnam @ (517)353-4708.

University of Deleware to Host ASC Ninth Technical Conference

The theme of this joint conference is "Composite Science and Technology for the 21st Century." Research papers addressing challenges and opportunities in composite materials in the following areas are sought for presentation, at the conference and publication in the conference proceedings:

Processing, Science & Manufacturing

innovative processing techniques; preforming technology; process modeling; low-cost, high-volume manufacturing methods

Materials Science

interfaces/interphases; material development for polymer-, ceramic, metal- and intermetallic-based composites; experimental characterization techniques

Joining Mechanics

constitutive modeling; damage mechanics; life prediction; high-strain-rate effects

Durability

failure mechanisms, damage tolerance; nondestructive evaluation techniques; environmental degradation; creep; fatigue

Design and Applications

design methodologies; microstructure property relationships in automotive, aerospace, aircraft, marine, transportation, and civil infrastructure applications

All types of composites including PMC's, MMC's, CMC's, and intermetallic comsites and their application - automotive, aerospace, aircraft, marine, transportation, power generation, and civil infrastructure, are of interest. Plenary sessions are also planned.

Abstracts of 300 words should be sent to Dr. Tsu-Wei Chou (CCM, University of Deleware, Newark, DE, 19716-3144) by Jan. 10, 1994. Notifications of acceptance will be mailed to authors by Feb. 15, 1994. Mats and instructions will be mailed to authors by Mar. 1, 1994, and final papers (10 pages) must be received no later than May 16, 1994. For more information, call Dr. Chou at (302)831-2904.

Upcoming Conferences and Seminars

In order to increase communications between the Composite Materials and Structures Center and its various members, we would like to inform you of upcoming conferences and seminars pertaining to your research areas. Here is a list of some events which might be of interest. Brochures on these conferences are available at the Composite Center. Please contact Margie Gray at (517)353-5466 for any requests.

International Association of Science and Technology for Development (IASTED) - International Conference Modeling and Stimulation
Location: Pittsburgh, PA
Dates: 5/2-4/94

Society of Plastics Engineers - Annual Technical Conference of the Society of Plastics Engineers - The Forum on Plastics Engineering
Location: San Fransisco, CA
Dates: 5/1-5/94

CALL FOR PAPERS - Minnesota Chromatorgraphy Forum - HPLC '94 - 18th International Symposium on Column Liquid Chromatography
Location: Minneapolis, MN
Dates: 5/8-13/94
Papers Due: 5/8-13/94

Association for Unmanned Vehicle Systems (AUVS) - 2nd Annual International Ground Robotics Competition
Location: Rochester, MI
Dates: 5/20-22/94

AUVS - National Symposium; (focus on current and future cooperation and opportunities for integrated Research Development in vehicle intelligence, automation, navigation, etc.)
Location: Detroit, MI
Dates: 5/23-25/94

International Association of Science and Technology for Development (IASTED) and American Institute of Chemicals (AIChE) - Modeling, Simulation and Control International Conference. (Forum for interchange of information and experience between engineers, academics, etc. interested ion the modeling, simulation and control of industrial processes.)
Location: Ottawa, Canada
Dates: 5/25-27/94

CALL FOR PAPERS - ASEE Chemical Engineering Division 1994 Annual Conference (Papers in the Topics of: Innovative Methods in Chemical Engineering Education including Laboratory, Design and Problem Solving, Creativity in Chemical Engineering, Teaching Effectiveness, Tricks of the Trade)
Location: Edmonton, Alberta
Dates: 6/26-29/94

School of Chemical Engineering, Purdue University - International Symposium on Foundation of Computer Aided Process Design. (Separation System Synthesis and Design, Green Trends in Design, Methods Driven by Advanced Computing Environments, Integrating Design Criteria, Subsystems and Tools).
Location: Snowmass, CO
Dates: 7/10-15/94

CALL FOR PAPERS - Summer AIChE meeting. Design for the Environment - Incorporation pollution prevention into Chemcial Engineering curriculum
Location: Denver, CO
Dates: 8/14-17/94

CALL FOR PAPERS - AIChE Summer National Meeting - Application of Chemical Engineering Fundamentals to Environmental Problems (Environmental Issues of Energy Conversion Technology, Energy from Solid Waste)
Location: Denver, CO
Dates: 8/14-17/94

American Institute of Chemical Engineers - 1st International Particle Technology Forum (Exchange of Education, Research in the Field of Particle Technology)
Location: Denver, CO
Dates: 8/17-19/94

CALL FOR PAPERS - University of New Orleans - 1st International Conference on Composite Engineering (ICCE/1). (Conference goals: bridge gap between mechanics and materials science of composites, encourage interactions between basic and applied research groups composites; assess the state of the art in modeling and analysis of modern composites structures and materials relevant to the need of the commerical or defense industries.)
Location: New Orleans, LA
Dates: 8/28-31/94

CMSC April Calendar

American Institute of Chemical Engineers - Safety Analysis and Risk Assessment for Chemical Process Industry Practitioners - COURSE 1: Hazards Evaluation Qualitative Methods
Location: Atlanta, GA
Dates: 4/11-15/94

Society for the Advancement of Materials and Process Engineering (SAMPE) - 39th International SAMPE Symposium and Exhibition
Location: Anaheim, CA
Dates: 4/11-14/94

Composites Education Association, Inc. - 5th International Conference on Marine Applications of Composite Materials - (provide a forum for the exchange of state-of-the-art marine FRP technology)
Location: Melbourne, FL
Dates: 4/12-14/94

American Institute of Chemical Engineers - National Meeting - Application of Supercritical Fluids
Location: Atlanta, GA
Dates: 4/17-21/94

American Institute of Chemical Engineers - AIChE National Meeting - Phase Equilibria and Thermophysical Properties of Mixtures and Pure Fluids, I and II
Location: Atlanta, GA
Dates: 4/17-21/94

The National Science Foundation and The Defense Logistics Agency - Conference on Computer Integrated Manufacturing in the Process Industries.
Location: New Brunswick, NJ
Dates: 4/25-26/94

American Institute of Chemical Engineers - Safety Analysis and Risk Assessment for Chemical Process Industry Practitioners - COURSE 2: Hazards Evaluation: Quantitative Methods.
Location: Atlanta, GA
Dates: 4/25-29/94

Composite Materials and Structures Center
College of Engineering
Michigan State University
East Lansing, MI 48824-1326

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