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Mechanical properties and deformation mechanisms of polyurethane materials

Kau, Chia-Chiun James
http://rave.ohiolink.edu/etdc/view?acc_num=case1055883413

Abstract Details

1991, Doctor of Philosophy, Case Western Reserve University, Macromolecular Science.
In this work, the relationships among structure, mechanical properties and deformation mechanisms of polyurethane materials were studied. The emphasis was placed upon the characterization of the deformation behavior during straining. Chapter one examines the microdeformation and damage mechanisms in glass fiber reinforced injection molded (RRIM) polyurethane composites. Two surface conditions represented the extremes in good and poor fiber-matrix adhesion. Deformation mechanisms observed directly by an SEM technique with the specimen deformed in three-point bend were correlated with the number and amplitude distribution of acoustic emission (AE) events detected during tensile testing. Yielding of the unreinforced resin was accompanied by microcracking initiated at holes that produce AE with a peak at 43 db. A similar AE pattern observed in the untreated fiber composite was also identified with microcracking at holes in the resin and at rod-shape holes produced by debonded fibers. The amine-treated fiber composite exhibited considerably more AE activity in the yield and post-yield regions with additional peaks in the amplitude distribution at 59 db and 65 db. These were identified with microcracking at the well-bonded interface and fiber fracture respectively. In the second chapter, m icrocrazing in the struts of flexible polyurethane foams was discovered during compressive deformation and observed directly in the scanning electron microscope. Attributed to this phenomena was the decrease in stress at maximum compression and the intensity of acoustic emission during compressive cycling. Higher content of SAN copolymer in these foams resulted in higher modulus, more severe microcrazing, an increase in acoustic emission activity and a decrease in the stress at maximum compression as cycling progressed. In the third chapter, hard elastic behavior which is characterized by high porosity, high recoverability from large strain and initial Hookean elasticity was discovered in polyurethane foams containing styrene acrylonitrile SAN copolymer particles. The presence of SAN particles introduces a heterogeneous morphology and when the foam was strained in the SEM, it was observed that the struts became highly porous with profuse voiding nucleated by the SAN particles. It was found that these flexible polyurethane foams had a similar morphological structure in the strained struts as the typical hard elastic materials. The phenomenon of stress depression, when foam specimens under stress were subjected to nonswelling liquids, was utilized to probe the role of surface stress in these hard elastic foams. An analytic methodology established for other highly porous hard elastic materials based on stress depression was utilized to obtain the average distance between voids in the struts. The calculated values were in good agreement with direct scanning electron microscopy observations confirming that voiding initiated at the boundaries of SAN particles.
Anne Hiltner (Advisor)
162 p.
Plastics Technology
mechanical properties deformation mechanisms polyurethane materials

Recommended Citations

Citations

  • Kau, C.-C. J. (1991). Mechanical properties and deformation mechanisms of polyurethane materials [Doctoral dissertation, Case Western Reserve University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=case1055883413

    APA Style (7th edition)

  • Kau, Chia-Chiun. Mechanical properties and deformation mechanisms of polyurethane materials. 1991. Case Western Reserve University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=case1055883413.

    MLA Style (8th edition)

  • Kau, Chia-Chiun. "Mechanical properties and deformation mechanisms of polyurethane materials." Doctoral dissertation, Case Western Reserve University, 1991. http://rave.ohiolink.edu/etdc/view?acc_num=case1055883413

    Chicago Manual of Style (17th edition)

case1055883413
805
© 1991, all rights reserved.
This open access ETD is published by Case Western Reserve University School of Graduate Studies and OhioLINK.