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J Kolarík

Publications and source records attributed to J Kolarík.

54 records · Page 3Linked to original sources
PubMed1984

Preparation and strength of poly(ethylene terephthalate) fiber bundles for model synthetic tendons.

Poly(ethylene terephthalate) fibers suited for model synthetic tendons were prepared on a pilot-plant scale by additional drawing (postdrawing) of commercial textile fibers texturized by false twist. The modified fibers have a tensile modulus of 7-9 GPa, a one-minute creep modulus of 5-6 GPa, tensile strength 0.55-0.63 GPa, and strain at break of 16-19%. It is essential for their application in synthetic tendons that plastic deformation was reduced to about 0.5%, which could be completely eliminated by subsequent mechanical conditioning of fibers. Since the strength of model tendons consisting of 20 vol % of fibers and of a hydrogel matrix is primarily determined by the strength of the fibers, some aspects of the theory of strength of fiber bundles are briefly recapitulated. The prediction is compared with earlier experimental results obtained for the synthetic tendons. Such an approach, taking into account the fiber-strength distribution in the bundle, predicts a strength of model tendons lower by 20-40% than does the rule of mixtures.

Polyethylene Terephthalates↗
PubMed1983

Mechanical properties of hydrophilic copolymers of 2-hydroxyethyl methacrylate with ethyl acrylate, n-butyl acrylate, and dodecyl methacrylate.

Copolymers were prepared of 2-hydroxyethyl methacrylate, which is strongly hydrophilic, with hydrophobic comonomers having a low glass transition temperature, i.e., ethyl acrylate, n-butyl acrylate, and dodecyl methacrylate. The glass transition temperature, T alpha (1 Hz), of polymers in the dry state (xerogels) was determined by means of dynamic mechanical measurements. The dependence of T alpha on composition in all the three series of copolymers was described in terms of a one-parameter equation. The equilibrium swelling of copolymers in water decreases more steeply than the weight fraction of 2-hydroxyethyl methacrylate. When swollen in water to equilibrium, all copolymers with ethyl acrylate or n-butyl acrylate are in the rubberlike state; their tensile modulus E assumes values in the range 0.17-0.50 MPa. While poly(2-hydroxyethyl methacrylate) has the modulus E = 0.39 MPa, the tensile strength sigma u = 0.32 MPa, and the strain-at-break epsilon u = 1.81, for the weight fraction of the comonomer in the range 0.36 less than or equal to omega 2 less than or equal to 0.56 it is possible to achieve sigma u and epsilon u lying in the respective ranges 0.7-0.9 MPa and 5-7. Copolymers with the dodecyl methacrylate content omega 2 less than 0.2 or omega 2 greater than 0.8 are rubberlike, and at 0.30 less than or equal to omega 2 less than or equal to 0.62 they become leathery; the latter have the modulus E and strength sigma u within the ranges 12-32 and 3-4 MPa, respectively. The stress-strain curves of these copolymers evidence yielding and orientation hardening which have been tentatively explained by the nonhomogeneous composition and structure of the copolymers.

Acrylates↗
PubMed1981

Mechanical properties of model synthetic tendons.

Model synthetic tendons consisting of 20 vol % of texturized poly(ethylene terephthalate) fibers and of the water-swollen poly(2-hydroxyethyl methacrylate) matrix have the tensile modulus E = 1.5 +/- 0.1 GPa, strength and strain-at-break sigma b = 85 +/- 10 MPa and epsilon b = 0.08 +/- 0.02. The force required for breaking tendons with the diameters 2, 3, 4 mm is, respectively, 300, 500, and 960 N. By these properties model synthetic tendons closely imitate the properties of natural tendons. Long-term (100 min) and repeated short-term (30 times 1 min) creep shows that on loading model tendons lose some 10% of their stiffness, but that the whole deformation is reversible. The shape of the compliance vs. time dependence of synthetic tendons closely resembles the dependence determined for the parent fiber. The stiffness and strength of a tendon are given by those of the fiber bundle used; by varying fiber volume fraction, it is possible to adjust the required mechanical properties of tendons.

Animals↗