Polymers fracture toughness values

Composites provide an atPactive alternative to the various metal-, polymer- and ceramic-based biomaterials, which all have some mismatch with natural bone properties. A comparison of modulus and fracture toughness values for natural bone provide a basis for the approximate mechanical compatibility required for arUficial bone in an exact structural replacement, or to stabilize a bone-implant interface. A precise matching requires a comparison of all the elastic stiffness coefficients (see the generalized Hooke s Law in Section 5.4.3.1). From Table 5.15 it can be seen that a possible approach to the development of a mechanically compatible artificial bone material... 

The objectives of this paper are (1) to compare force based and dynamic tests methods and data reduction schemes for both bending and tensile type fracture specimens, (2) to define the requirements and limitations for the applicability of FBA and DKC methods, and (3) to determine fracture toughness values of several engineering polymers over a wide range of loading rates (up to 7 decades). 

LEFM methods are applicable to characterize the rate dependent fracture behavior of engineering polymers in the regime of quasi-brittle failure, yielding material specific fracture toughness values independent of specimen configuration. 

In the regime of quasi-brittle failure, there is a clear tendency for a decrease in fracture toughness with increasing impact rate for all materials investigated. However, the ra e sensitivity of fracture toughness values strongly depends on the specific polymer type. 

The load-displacement curves for C(T) tests of the neat EpoxyH were almost linear until the final unstable fracture. The fracture toughness value in 77K-LNj was 210 J/m and that in RT-air was 120 J/m. Thus the toughness increased by 1.8 times by changing the test environment from RT-air to 77K-LN. Brown and co-workers have found that amorphous polymers crazed in 77K-LNj, but not in a helium or vacuum at about 78K [20-22]. They have also reported that the stress-strain behavior of all polymers, amorphous and crystalline, is affected by at low temperatures [22]. Kneifel has reported that the fracture toughness of epoxy in 77K-LNj is higher than that in RT-air and 5K, and that the reason for this is the reduced notch effect by plastic deformation [23]. Then, the increase of the fracture toughness of the neat EpoxyH in this study is probably caused by the similar effect. 

Presented in this manner, is considered a material property and is referred to as the fracture toughness. Values for the factor Y have been derived for many test specimen geometries and can be found in an excellent book on fracture mechanics of polymers by Williams. ... 

The polymer matrices and their fibre-reinforced versions can be ranked based on their fracture toughness value into three main groups, i.e. polymers and composites with K ... 

As mentioned previously, epoxy polymers possess low flaw tolerance. Typically the fracture toughness values are below 1 MPa m or, in terms of fracture energy, below 200 J/m. These values are extremely low when one compares them with a ductile thermoplastic polymer such as polycarbonate, which has a Kic = 2.4 MPa m and a Gjc = 2400J/m. However, there are organic based materials that can be added to epoxy polymers that increase their fracture toughness such that it even exceeds the fracture toughness of common thermoplastic resins ... 

These effects have been found by Creton et al. [79] who laminated sheets of incompatible polymers, PMMA and PPO, and studied the adhesion using a double cantilever beam test to evaluate fracture toughness Fc. For the original laminate Fc was only 2 J/m, but when interface reinforced with increasing amounts of a symmetrical P.M.M.A.-P.S. diblock copolymer of high degree of polymerisation (A > A e), the fracture toughness increased to around 170 J/m, and then fell to a steady value of 70 J/m (Fig. 9). 

As can be seen from the results, the composite formed from monomer/-polymer 114a with Celion G30-500 8HS fabric exhibited excellent mechanical properties [28], To a first approximation it would appear that the inherent fracture toughness of the matrix resin has been carried over to the composite panels. The CAI (compressive strength after impact) and OHC (open hole compression) tests are a direct measurements of the toughness of the composite part, the value of 332 MPa for the CAI compares very favorably to the value of 300 MPa typical for the thermoplastic composites. The OHC values under hot-wet test conditions would seem to indicate that the composite has very good retention of its mechanical properties at both 177°C and 203 °C. 

The values of the fracture toughness Kjc depend on the structural and morphological characteristics of the polymer sample such as molecular mass, degree of cross-linking, and degree of crystallinity, but they also... 

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