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1997 TMS Annual Meeting: Wednesday Session

COMPOSITES: Mechanical Properties & Processing
(General Abstract Session)

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Room: 240D

Session Chairperson: M.A. Self, Mechanical Engineering Dept., Tuskegee University, Tuskegee, AL 36088

8:30 am

DOUBLE CANTILEVER BEAM TEST APPLIED TO MODE I COMPOSITE DELAMINATON: A COMPARISON OF ANALYSIS METHODS FOR FIBER BRIDGING MATERIALS: W. Richards Thissell, Anna K. Zurek, Los Alamos National Laboratory (LANL), MST-5, G755, Los Alamos, NM 87545; Frank Addessio, Todd O. Williams, T-3, B-216, Los Alamos, NM 87545

The double cantilever beam (DCB) test is widely used to characterize the mode I delamination and bridging behavior of laminated continuous fiber composite materials. Many composite systems exhibit significant large scale fiber bridging that is not included in the derivation of the analysis methods. The bridging contribution to fracture energy is statistical in nature. A comparison is made of several analysis methods for applicability to systems exhibiting significant fiber bridging. A general DCB analysis method is described that takes into account loading pin effects, material orthotropy, crack root inelasticity, and large scale deformation behind the crack faces. Some material system specific characteristics that lead to enhanced fiber bridging are described.

8:50 am

HYGRO-MECHANICAL BEHAVIOR OF A CLASS OF SWELLING-TYPE THREE-DIMENSIONALLY BRAIDED COMPOSITES: Surya R. Kalidindi, Abdel Abusaifeh, Materials Engineering Department Drexel University, Philadelphia, PA 19104

A new class of swelling-type composite materials using three-dimensionally braided graphite or Kevlar fibers have been designed and processed for potential applications in bone implants. These composites derive their swelling from the hydrophillic nature of the matrix material used in their production. A combined experimental and modeling study was undertaken to study the hygro-mechanical behavior of this class of materials. The properties of interest included the swelling strains, elastic properties, yield strengths, and impact strengths. Note that these properties for the braided composites are highly anisotropic. Furthermore, the mechanical properties are strongly affected by the amount of absorbed water. Cylindrical samples of braided composites were produced with varying fiber volume fractions, braid angles, fiber type (graphite and Kevlar), matrix cross-linking (to control the degree of swelling in the composite), and fiber architecture (uniaxial, rectangular braided, and circular braided). Swelling strains at saturation were measured in these samples. Simple compression tests were performed on these samples in at least two principal material directions in both dry and saturated conditions. Elastic moduli and yield strengths were extracted from these tests. Cylindrical samples of the matrix material (without fibers) were also produced and utilized to fully characterize the hygro-mechanical behavior of the matrix material. Constitutive models have been proposed to predict the various hygro-mechanical properties of the 3-D braided composites in both dry and saturated states as a function of the fiber and matrix properties, fiber volume fraction, and fiber orientations. A weighted average of the currently employed isostrain and isostress models in literature for this class of materials was found to consistently yield better predictions for the anisotropic elastic moduli, when compared to the predictions of either of these models. The weighting factor was found to be dependent primarily on the fiber and matrix materials (i.e. independent of the type of loading, fiber volume fraction, and fiber orientation) and has been interpreted as an interaction parameter between the various fiber and matrix systems. These models were then extended to predict the swelling behavior and yield strengths of the 3-D braided composites. The accuracies of the proposed models were evaluated by comparisons against experimental measurements described above as well as the predictions from a finite element simulation of the response of a representative unit-cell of the braided composite. These comparisons revealed that the proposed models are reasonably accurate in their predictions.

9:10 am

RF MAGNETRON SPUTTERING OF MoSi2 + X SiC COMPOSITE TO FIIMS: S. Gonodaryan1, J.J. Moore1, T.R. Ohno2, 1Advanced Coatings and Surface Engineering Laboratory, Dept. of Met. and Materials Eng., Colorado School of Mines; 2 Dept. of Physics, Colorado School of Mines, Golden, CO 80401-1887

A critical component of a prototype coating system being developed to protect molybdenum against high temperature oxidation (i.e. at 1600°C for 500 hours) is a functionally graded layer based on MoSi2 + x SiC (where x is the variable mole fraction of SiC in the film). Different approaches for synthesizing composite films include sputtering from elemental or compound targets, reactive sputtering, and direct sputtering of composite targets. This paper will explore the feasibility of synthesizing composite films by RF magnetron sputtering of a composite target. Results of compositional depth profiling using Auger Electron Spectroscopy, microstructural evaluation and X-Ray diffraction analyses of the films will be presented. In particular, the diffusion of silicon and carbon in to the substrate will be characterized using a "ball-cratering" technique followed by auger electron spectroscopy (AES). This technique will help to overcome the disadvantages associated with ion-beam sputtering during depth profiling (e.g. different sputter yields for the constituent elements, interface broadening effects, etc.).


FATIGUE OF MONOLITHIC NIOBIUM AND BNIOBIUM-BASED "IN-SITU" COMPOSITES: William A. Zinsser, Jr. and John J. Lewandowski, Department of Materials Science and Engineering, Case Western University, Cleveland, OH 44106

9:30 am

EFFECT OF COMBINED LOADING ON CRACK-TIP DEFORMATION IN GRAPHITE/EPOXY COMPOSITES: M.A. Seif, C.M. Hargrove, Mechanical Engineering Dept., Tuskegee University, Tuskegee, AL 36088

An experimental investigation of the crack displacement and failure modes of graphite/epoxy plates [0/±45/90]2s under tensile loading with central cracks at various angles (15°, 30°, 60°, 75°, and 90°) was carried out. A mixed mode state of stresses developed at the center of the crack as a result of the crack orientation. Laser Speckle technique, a high sensitive noncontact technique, was employed to measure Crack Opening Displacement (COD) and Crack Shearing Displacement (CSD) of the crack emanating from the normal and tangential stresses at the crack center. Damage zones of the material at different crack orientation were examined and evaluated. The critical stress intensity factors for mode I and mode II were obtained from COD and CSD at failure. Detail studies were performed to investigate the behavior of the material during loading application and the effect of the angles on the stress distribution. The data obtained were compared with the Linear Elastic Fracture Mechanics (LEFM) solutions. The comparisons suggested a correlation within ±8 percent deviation. It was concluded from this investigation that the theoretical analysis could be applied to obtain the fracture properties of graphite/epoxy composites.

9:50 am

INCREASING THE OFF-AXIS AND MONOLITHIC STRENGTHS IN CONTINUOUS FIBER REINFORCED ALUMINUM MATRIX COMPOSITES: Colin McCullough, Paul R. Nisson*, Steven R. Pittman Bill E. Birkholz, MMC Program, 3M Company, St. Paul, MN 55144-1000; *3M/MMC Production Plant, Middleway, WV 25430

Tremendous progress has been made in the properties of aluminum alloys reinforced with 60-70 vol. % of continuous alumina fibers, with tensile strengths routinely averaging 250 ksi (1.7 GPa) in the longitudinal direction. The choice of matrix and its resulting microstructure is critical in obtaining such strengths and the matrices used at 3M to date are a pure Al and an Al-2%Cu alloy. This leads to design considerations in composite performance (transverse and shear strengths) and in any unreinforced areas. To date, the pure Al and Al-2%Cu matrix composites have transverse strengths of 25 ksi (170 MPa) and 40 ksi (275 MPa) respectively. While these values have applications, higher strengths may be desirable. Also unreinforced areas could benefit greatly from higher yield strengths. Use of traditional higher strength alloys is seriously restricted due to both the reactivity with the fiber and their segregation behavior which dramatically reduces longitudinal strength. How ever a new aluminum alloy matrix composition promises to combine all the desired features of the matrix. Data will be presented showing retention of high longitudinal strengths while also achieving much higher transverse and monolithic strengths. The specifics of this system will be discussed as well as directions for optimization.

10:10 am BREAK

10:20 am

STRUCTURE AND PROPERTIES OF ALUMINUM BASED PARTICULATE COMPOSITES SYNTHESIZED BY MECHANICAL ALLOYING: J.M. Molnar, T.H. Courtney, Department of Metallurgical and Materials Engineering, Michigan Technological University, Houghton, MI 49931

Aluminum-based particulate composites have potential application in services requiring high strength combined with low density. We have used mechanical alloying followed by hot isostatic pressing (HIPing) to fabricate a series of Al-Si-C particulate composites. Pure Al or Al-Si eutectic powder was mixed with graphite and SPEX milled for varying times. Consolidation of the mechanically alloyed powders was done by HIPing at 180MPa (26 ksi) which resulted in a fully dense composite. Aluminum carbide (Al4C3) is formed during consolidation. Formation of SiC is a possibility as well. Maximum hardnesses following HIPing correspond to an approximate yield strength of 990 MPa (144 ksi). Properties as they depend upon processing conditions and the resulting microstructure are discussed. This work was supported by the Army Research Office.

10:40 am

THERMOMECHANICAL PROCESSING OF SUPERPLASTIC SICP/6061 ALUMINUM ALLOY COMPOSITE MADE BY A VORTEX METHOD: Tsunemichi Imai1 and Takeo Hikosaka2, 1National Industrial Research Institute of Nagoya, 1 Hirate-cho, Kita-ku, Nagoya 462, Japan; 2Industrial Research Institute, Aichi Prefectural Government, Nishishinwari Hitotsugi, Kariya City, Aichi 448, Japan

Thermomechanical processing to produce the HSRS for the SiC/6061 Al alloy composite fabricated by a vortex method before squeeze casting and extrusion was investigated. The SiC/6061 A1 composites hot-rolled in rolling strain per passes of 0.05~0.3 and at 573K indicate the m value of 0.4~0.6 and the total elongation of 200~300% in the strain rate of 0.08~1.3 s-1 and at 853K. The total elongations of the composite hot-rolled at 523 and 623K decrease to less than 150%. The flow stress of the composite heat treated by T6 after rolling increased and the total elongation decreased as compared with those of the composite without T6 due to reaction between SiC and matrix. The fracture surface of the composite has a partially liquid phase and filaments and it is thought that an interfacial sliding at the liquid phase contributes to the HSRS in addition to grain boundary sliding in the SiC/6061 Al composite fabricated by a vortex method.

11:00 am

COMPATIBILITY OF SEVERAL REINFORCEMENTS WITH Ti-Al AND DEVELOPMENT OF THE COMPOSITES: Chikura Fujiwara, Nagoya Aerospace Systems Works, Mitsubishi Heavy Industries, Ltd., 10, Oye-Cho, Minato-Ku, Nagoya, 455 Japan

Titanium aluminide matrix composites have received considerable attention due to their potential to have high specific strength and stiffness at high temperature. And SiC fibers are considered to be promising candidates for reinforcement of the composites. SiC/TiAl composites, however, are difficult to be fabricated in good state because of severe reactions at the interface being taken place during fabrication process. One of the most effective means to suppress the excessive reaction is to apply the diffusion barrier coating on the surface of SiC fiber. Another solution to fabricate a TiAl matrix composite is to apply the reinforcement which has good compatibility with matrix, TiAl. Several candidates for diffusion barrier coating between SiC fiber and TiAl were evaluated, then W and HfC showed excellent effects on suppress excessive interfacial reaction, while other candidates such as Al2O3, Zr, B2, Ce2O3 were not effective. Based on these results, a desirable interface model of organic polymer derived SiC reinforced TiAl composite is proposed. Other fibers were evaluated as reinforcements of TiAl matrix composites. Then it was found that W, W-Re, Re were good in compatibility with TiAl and consolidated with TiAl in good state. As a result, W-3%Re/TiAl showed 680 Mpa at 1373K.

11:00 am

THE EFFECT OF MATRIX MICROSTRUCTURE ON THE MECHANICAL PROPERTIES OF Ti3Al/TiB PARTICULATE COMPOSITES: Satoshi Emura, Masuo Hagiwara and Yoshikuni Kawabe*, National Research Institute for Metals, 1-2-1 Sengen Tsukuba Ibaraki 305 Japan; *Chiba Institute of Technology, 2-17-1 Tsudanuma Narashmo Chiba 275 Japan

Ceramic particulates reinforced composite is considered to be an effective way for improving the mechanical properties of Ti alloys and Ti-A1 intermetallics. In the present study, Ti-24Al-llNb(at%)/l0wt%TiB in-situ composites were prepared by the blended elemental powder metallurgy method. The tensile and high cycle fatigue properties of the composites were found to be much superior to those of the unreinforced matrix. Modification of the matrix microstructure was performed by annealing the composite at 1573K and air cooling, which resulted in a very fine 2+ microstructure. The mechanical properties, particularly the fatigue property, were further improved by this microstructural modification technique.

11:20 am

A STRUCTURE DESIGN OF CARBON FIBER REINFORCED ALUMINUM MATRIX COMPOSITE: Jiwen Wang ,Geyang Li, Tao Hong, Pengxing Li, Anjing Yang, Dept. of Mat. Sci., Shanghai Jiao Tong University, Shanghai, 200030, China

A process which combines fiber coating and particles hybridizing together has been utilized for the structural optimization of carbon fiber reinforced aluminum matrix composite. SiC coating was derived by Sol-gel method and SiC particle hybridizing was processed in Sol-gel solution simultaneously. Squeeze-cast process was used to get bulk composite materials. SEM analysis of the material showed a well fiber distribution in Al matrix by particles hybridizing. Mechanical properties of the composite were improved especially for the axial strength. HRTEM research indicated the coating to be an effective barrier of the interface reaction. C/Al interfacial reaction was also studied meantime which revealed that pan-based carbon fiber reacted heavily with aluminum matrix. The nucleation and growth of the reactants were discussed.

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