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Digitale Medien

Impact strength of polymers 2: The effect of cold working and residual stress in polycarbonates (1980)

Thakkar, B. S. ; Broutman, L. J. ; Kalpakjian, S.

Stamford, Conn. [u.a.] : Wiley-Blackwell

Polymer Engineering and Science 20 (1980), S. 756-762

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ISSN: 0032-3888

Schlagwort(e): Chemistry ; Chemical Engineering

Quelle: Wiley InterScience Backfile Collection 1832-2000

Thema: Chemie und Pharmazie , Maschinenbau , Physik

Notizen: The influence of cold working on the toughness improvement in glassy amorphous polycarbonates was studied. Cold working processes, namely rolling and. Steckel rolling were used to produce thickness reductions up to 40 percent in flat-strip specimens. The notched Izod impact strength and tensile properties were measured as a function of strip thickness reduction. It was shown that the toughness enhancement in polycarbonates cold worked to low thickness reductions was due to the residual stress state present as opposed to molecular orientation which becomes significant at higher degrees of cold work. Residual stress measurements were made by using the layer removal technique. Residual tensile stresses as high as 2100 psi were present in 1/4-in. cold-rolled polycarbonate at the surface. The maximum stress in the center of the specimen was 1100 psi in compression. The residual stresses at the surface decreased with increasing thickness reduction. The residual stress state for Steckel rolled. 1/2-in. polycarbonate was also measured and found to be more complex than for the thinner samples, The results demonstrated that surface tensile stresses and interior compressive stresses can produce large values of impact strength if the notch is to be machined after cold working. Thus, the values of impact strength measured from the notch Izod specimen are sensitive to the residual stress state in the polymer. This behavior is in contrast to earlier studies on thermally quenched material in which the material was quenched after notching. The thermal quenching produced surface compressive stresses which were also present at the notch tip. The presence of compressive residual stresses at the center of the notch suppressed the formation of a craze leading to toughness enhancement in cold worked polycarbonate strips. It is shown that by control of residual stresses in polycarbonate, strips at least 1/2 in. in thickness can be made to exhibit ductile failure in the notched Izod impact test.

Zusätzliches Material: 14 Ill.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1002/pen.760201110

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Digitale Medien

The influence of residual stresses and orientation on the properties of amorphous polymers (1980)

Thakkar, B. S. ; Broutman, L. J.

Stamford, Conn. [u.a.] : Wiley-Blackwell

Polymer Engineering and Science 20 (1980), S. 1214-1219

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ISSN: 0032-3888

Schlagwort(e): Chemistry ; Chemical Engineering

Quelle: Wiley InterScience Backfile Collection 1832-2000

Thema: Chemie und Pharmazie , Maschinenbau , Physik

Notizen: The effect of cold rolling on impact strength of poly(vinyl chloride) (PVC) acrylonitrile-butadiene-styrene (ABS), and an alloy of ABS and polycarbonate (Cycoloy) was studied. The results were presented in terms of Izod impact strength and present oil thickness reduction. The residual stresses molecule orientation and modification of mechanical properties due cold rolling were measured. It was shown that the mechanism of toughness enhancement in PVC, ABS, and Cycoloy different than the one observed in rolled polycarbonates. In the case of a highly localized failure initiation event (a single eraxe), which appears to be present in polycarbonate, the influence of residual stresses, is great, whereas in rubber modified polymers having multiple erasing over a large volume, orientation is more important than residual stress. Hot rolling of poly(methyl methaerylate) holds promise for a continuous process to achieve orientation and toughness enhancement.

Zusätzliches Material: 13 Ill.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1002/pen.760201807

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Digitale Medien

Impact strength of polymers. 3: The effect of annealing on cold worked polycarbonatesBased upon the Doctoral Thesis of B. S. Thakkar submitted to the Illinois Institute of Technology. (1981)

Thakkar, B. S. ; Broutman, L. J.

Stamford, Conn. [u.a.] : Wiley-Blackwell

Polymer Engineering and Science 21 (1981), S. 155-162

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ISSN: 0032-3888

Schlagwort(e): Chemistry ; Chemical Engineering

Quelle: Wiley InterScience Backfile Collection 1832-2000

Thema: Chemie und Pharmazie , Maschinenbau , Physik

Notizen: Cold working (rolling) of polycarbonates introduces residual stresses and molecular orientation both of which can improve, the notched Izod impact value. Annealing relieves both residual stresses and orientation. Annealing for various time periods established the critical level of residual stress necessary for the ductile failure mode of polycarbonate in the Izod impact test. The relaxation of both residual stress and molecular orientation was measured as a function of annealing temperature, for annealing times of 2 hs, and the relative changes have thus been determined. It is shown that residual stresses cannot be entirely removed without significantly influencing orientation for 2 h annealing times.

Zusätzliches Material: 13 Ill.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1002/pen.760210308

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