properties of polymers and composites

... exceeds that of metals, but is of the same order of magnitude Young’s modulus of most polymers ismuch smaller.5 This should be expected, for the stiffness is determined bythe strength of the atomic ... betweenthe chains Fig 1.24 Schematic sketch of the cross-linking of different polymers As explained above, linear chains are the constituting units of polymers.However, it is possible to covalently ... independent of the geometry and dimension of the components so that they can be determined in experiments using standardised specimens.This can be achieved by normalising the load and the deformation

Ngày tải lên: 11/08/2014, 15:20

... standards for the size and diameter of the ball Commonlyused values are D = 10 mm and a force of 29.43 kN = 3000 kp The choice ofparameters depends on the tested material and the thickness of ... the size of the indentation and the yield strength ofthe material can be derived The material displaced by the indenter movesand causes a bulge, with a volume that is the same as that of the displacedmaterial ... because of the constant volume In reality, the volume of the bulge geome-is usually smaller than that of the indentation, showing that the assumption Trang 3110 3 Plasticity and failureof a rigid

Ngày tải lên: 11/08/2014, 15:20

... multitude of ways to influence material properties 6. 4 Strengthening mechanisms 211 Fig 6. 43 Calculation of the average spacing of randomly distributed particles within... area (2a)2 of the ... Cutting of a screw dislocation A jog forms in the cutting dislocation Fig 6. 32 Cutting of dislocations of various types and orientations (after [40]) The type and orientation of the ... a rectangular one with the appropriate height and width. The width d ∗ of the rectangle is then a measure of the width of the obstacle. A stress of τ m has to b e exerted to move the dislocation

Ngày tải lên: 11/08/2014, 15:20

... measure thesize and position of every single defect within a component and thus to predictits strength exactly (deterministically), the statistics of the defect distribution is considered, and, using ... number of experiments are formed on identical specimens, measuring the failure stress σi or failure time per-ti of each In both cases, the determination of the parameters (σ0 and m or t0and m∗, ... weincrease the stress σ by ∆σ, a fraction of Pf(σ + ∆σ) − Pf(σ) of all specimens Trang 16Fig 7.15 Plot of the accumulated number of specimensPij=0nj failed until theend of the current stress interval The

Ngày tải lên: 11/08/2014, 15:20

... gland because this is required to alignthe molecules Silks cannot be pressed or squirted out of the gland.The silk of the silk moth has been technically used for thousands of years Because of ... density and Young’s modulus of different types of polymers(cf section 1.4.2)type of material cross-linking density E/GPa As in the previous section, we start by discussing amorphous tics and afterwards ... They have a thickness of about 1µm to 10 µm and a diameter of about 10 µm to 1000 µm and arebridged by fibrils The fibrils comprise several chain molecules and have adiameter of approximately 10

Ngày tải lên: 11/08/2014, 15:20

... toughness and a glass temperature of about 150℃.Composite properties It was already stressed that the properties of fibre and matrix have to becarefully adjusted to obtain optimal properties of the ... but all of them are of limited appli-cability [29, 72, 122] 9.4 Examples of composites 9.4.1 Polymer matrix composites Polymers are well-suited as matrix materials due to their low density and theirlow ... fracture toughness of the matrix and the properties of the interface If thematrix is brittle and the fracture toughness of the interface is large, the stressconcentration in front of the crack tip

Ngày tải lên: 11/08/2014, 15:20

... Fig 10. 24 S-N curves for fully reversed bending of several polymers at a temperature of 20℃ and a loading frequency of 10. .. phase of the grain boundaries (see section 7.5.2), resulting ... ceramics S-N curves of polymers We already saw in section 10. 4 that the fatigue behaviour of polymers strongly depends on the load frequency because of their viscoelastic properties If ... cubic metals and hardened steels do not have a true fatigue limit (S-N curve of type II, figure 10.19(b)). At a number of cycles beyond 10 7 , the slope of the S-N curve is rather small and a limiting

Ngày tải lên: 11/08/2014, 15:20

... loading the band with a force FB= const The cross section of both rubber bands is identical (A) Assume thatboth rubber bands are linear-elastic Young’s modulus of the rubber band of booth B is ... movement and causesthe high strength of these alloys The dislocations can cut the particles only at rather high stresses Thus, stresses of 100 MPa can be applied at tures of 1000℃ and service times of ... of aluminiumand tungsten at a grain size of 32µm Although both maps have the sameoverall structure as the schematic map from figure 11.9, they neverthelessdiffer in the size and exact shape of

Ngày tải lên: 11/08/2014, 15:20

... position of thecrack tip Solution 14: We start by adding the elastic line and the 95% line to the diagram (figure 13.5).Reading off the forces yields F5= 13.5 kN, Fmax= 14.5 kN F5is to the left of ... placement of one crack surface which is half of the crack opening corre-b) The equilibrium position at x = a/2 is unstable because the atoms of one layerare situated between those of the other ... throughout the crystaland thus have a length of 10 mm The resulting dislocation density is thus% =aN a3 = N a2 = 7 × 109m−2.Not all of the dislocations can contribute because of their orientation

Ngày tải lên: 11/08/2014, 15:20

... E.Mechanical properties of polymers and composites / Lawrence E. Nielsen Robert F Landel — 2nd ed., rev and expanded. p cm — (Mechanical engineering ; 90) Includes bibliographical references and index. ... Moduli of l-ther-Filled Composites 463 III Strength of Fiber-Filled Composites 471 A Uniaxialty oriented fibers :i 472 B Strength of randomly oriented fiber composites and laminates 479 IV Other Properties ... dependence on temperature and time of the properties of polymers compared to those of other materials such as metals This strong dependence of properties on temperature and on how fast the ma terial

Ngày tải lên: 12/08/2014, 03:20

... of mechanical tests and testing instru-ments Most of these tests are very specialized and have not been officially recognized as standardized tests Some of these tests, however, have been standardized ... variety of units are used in reporting values of mechanical tests Stresses, moduli of elasticity, and other properties are given in such units as MK.S (SI), cgs, and English units A table of conversion ... been standardized, it must be recognized that a standardized test may be no better than one that is not considered a standard One objective of a standardized test is to bring about simplicity and

Ngày tải lên: 12/08/2014, 03:20

... effect of any change in £ ()jr Copolymers and plasticized materials often show another effect—a broadening of the transition region with a decrease in the slope of the modulus curve in the region of ... plateau. Plasticizers and Copolymerization also shift the glass transition responses of the amorphous phase of crystalline polymers. In addition, the degree of Crystallinity and melting point are ... detail in later chapters. E. Block and Graft Polymers and Polyblends In a few cases mixtures of two polymers are soluble in one another, where there is a close match of the solubility parameters or

Ngày tải lên: 12/08/2014, 03:20

... 1Creep and Stress Relaxation I INTRODUCTION Creep and stress-relaxation tests measure the dimensional stability of a material, and because the tests can be of long duration, such tests are of great ... the creep of rigid materials, the difficulty arises from the ne-cessity to measure accurately very small deformations and deformation rates In the case of the stress relaxation of rigid polymers, ... is used When the stresses and strains become large and the stress-strain curve becomes nonlinear, simple descriptions of the response and interconversions between creep and relaxation become increasingly

Ngày tải lên: 12/08/2014, 03:20

... state and the steady-state compliance, but the star polymers also decrease the rate of stress relaxation (and creep) compared to a linear polymer (169). The decrease in creep and relaxation rate of ... entanglements because of the many long branches, or the effect can be due to the suppression of reptation of the branches. Linear polymers can reptate, but the bulky center of the star and the different ... polymer, and is the volume fraction of polymer. Creep and Stress Relaxation 101 3. Mixing a high-viscosity liquid with one of low viscosity reduces the viscosity just because of the dilution of the

Ngày tải lên: 12/08/2014, 03:20

... Library of Congress Cataloging-In-Publitation Date Nielsen Lawrence E Mechanical properties of polymers and composites / Lawrence E Nielsen Robert F Landel — 2nd ed., rev and expanded p cm ... MECHANICAL PROPERTIES OF POLYMERS AND COMPOSITES SECOND EDITION,REVISED AND EXPANDED LAWRENCE E.NIELSEN Monsanto Company St Louis Missouri F LANDEL Jet Propulsion Laboratory California institute of Technology ... Effect of MokcLil.ir Weight Effect of Cross-linking Effects of Crystallinity and Morphology Effects of Plasticizcrs and Copolymerization Effect of Molecular Orientation Effect of Strength of Intcrmolccular...

Ngày tải lên: 22/03/2014, 12:20

... Library of Congress Cataloging-In-Publitation Date Nielsen Lawrence E Mechanical properties of polymers and composites / Lawrence E Nielsen Robert F Landel — 2nd ed., rev and expanded p cm ... MECHANICAL PROPERTIES OF POLYMERS AND COMPOSITES SECOND EDITION,REVISED AND EXPANDED LAWRENCE E.NIELSEN Monsanto Company St Louis Missouri F LANDEL Jet Propulsion Laboratory California institute of Technology ... Effect of MokcLil.ir Weight Effect of Cross-linking Effects of Crystallinity and Morphology Effects of Plasticizcrs and Copolymerization Effect of Molecular Orientation Effect of Strength of Intcrmolccular...

Ngày tải lên: 13/08/2014, 16:21

... has a yield point and is typical of a material that cold-draws with necking down of the cross section in a limited area of the specimen Curves of the third graph (C) arc typical of elastomeric materials ... between the applied stress and strain is landa, and it is defined by a ratio called the loss tangent or dissipation factor: Tan landa, a damping term, is a measure of the ratio of energy dissipated ... tests have traditionally been the most popular and universally used of alt mechanical tests and are described by ASTM standard Vests such as D638, D882, and D412 These tests can be more difficult...

Ngày tải lên: 13/08/2014, 16:21

... moderate rates of deformation, the amorphous polymer is soft and flexible and is either an elastomer or a very viscous l i q u i d , Mechanical properties show profound changes in the region of the glass ... between 1.0 and 1.2; it is a function of the ratio of segmental mobilities of crosslinked to uncross-linked polymer units and the relative cohesive energy densities of cross-linked and uncross-linked ... by the pairs of polymers polypropylene ( T g = C) and polyisobutylene (Tg = -70 C), and poly(vinyi chloride) (Tg=87 C) and poly(vinylidene chloride) (Tg =- 19°C) The symmetrical polymers have...

Ngày tải lên: 13/08/2014, 16:21

... point to point and is a combination of uniaxial and biaxial orientation A second type of anisotropic system is the biaxially oriented or planar random anisotropic system This type of material is ... is applied, and Lo the unstretched length of the specimen Equation (6) also applies to and gives one of the moduli of anisotropic materials if the applied stress is parallel to one of the principal ... deflection V is measured and the Young's modulus E is calculated as follows: where C and D are the width and thickness of the specimen (11,12) This flexure test often gives values of the Young's modulus...

Ngày tải lên: 13/08/2014, 16:21

... weight and molecular weight distribution, degree of cross-linking, and of Plasticization For two-phase and multiphase systems such as semicrystalline polymers and polymer blends, morphology and ... comparisons of the responses of a set of polymers (7,16,54-56) These frequency/time response curves serve to delineate the effects of changes in backbone structure (i.e., the type of polymer or ... seldom made and there is no equivalent to the characteristic time of Figure 5A) In this section we summarize the effect of structural and compositional factors on the modulus of the simplest of amorphous...

Ngày tải lên: 13/08/2014, 16:21