Tensile yield stress

In summary, tensile yield stress depends on filler particle size, concentration and on the interaction between the matrix and the filler. There are various means of improving tensile yield stress through the proper selection of filler for a particular polymers and through the surface modification of filler. 

---

Figure 11.3. Variation of tensile yield stress with melt flow index (10 kg load at 190 C) and isotactic index. (After Crespi and Ranalli )...

If the extruder is to be used to process polymer melts with a maximum melt viscosity of 500 Ns/m, calculate a suitable wall thickness for the extruder barrel based on the von Mises yield criterion. The tensile yield stress for the barrel metal is 925 MN/m and a factor of safety of 2.5 should be used. 

The von Mises criterion relates the tensile yield stress of a material to a state of multi-axial stress in a component made from the material. In a cylinder (the... 

Material Type and condition Typical standard for implant application Ultimate tensile strength M Pa min 0.2% tensile yield stress M Pa Young s modulus X lO M Pa Elongation at fracture % min Compressive strength M Pa Vickers hardness Fatigue strength (10 cycles) M Pa... 

Fig.1. Effect of matrix properties on the tensile yield stress of particulate filled composites. Symbols (O) PVC, (A) LDPE filler CaC03,r=1.8 pm... 

Fig. 16. Effect of treatment on the tensile yield stress of PP/CaC03 composites. Treatment (A) stearic acid, (O) no treatment, (+) aminosilane...

Fig. 15. Relation between KIc/Klcs, true tensile yield stress and type of crack growth...

Figure 12.13 Fracture energy (G c or J C) at 25°C versus tensile yield stress for different epoxy networks. (Reprinted with permission of SPE from Crawford and Lesser, 1999.)...

Table 1 Typical physical and (room temperature) mechanical properties (melting point Tm, glass transition temperature Tg) Young s modulus E, Izod toughness, tensile yield stress av elongation at break b) and applications of commodity polyolefins...

Fig. 10.64 The temperature dependent tensile yield stress for LLDPE (Dow, Dowlex 2045) obtained at Instron crosshead speed of 20 in/min. [Reprinted by permission from H. Jung and J. L White, Investigation of Melting Phenomena in Modular Co-TSEs, Int. Polym. Process., 18, 127 (2003).]...

Thermal conductivity Mass density Isochoric specific heat Tensile yield stress Mean stress First stress invariant Principal stresses... 

The tensile yield stress variation as a function of W for a material which has a von Mises-type yield locus is illustrated schematically in Figure 5. This variation is caused by the fact that as the width of the specimen increases, the biaxiality also increases toward the asymptotic value at plane strain. If the material obeys the von Mises yield criterion exactly, the plane strain yield stress should be 15% higher than it would be for simple tension. On the other hand, if the material obeys the Tresca yield criterion, the plane strain yield stress should be identical... 

Since spallation is controlled by the response to tensile stress pulses, the measurements of yield behavior were performed in uniaxial tension rather than in shear, and a tensile yield stress criterion was required. Bouwens-Crowet et ah (6) rearranged Equation 1 to give an expression for the uniaxial-tension yield stress [Pg.201]

DMS Dimethylsiloxane block. c E = Tensile modulus. d (jy — Tensile yield stress. 

O-, semi-brittle failure, tensile yield stress. 

Kinetics of Yielding. Tensile yield stresses were measured at several Instron rates for block polymer B. These results and those of Bauwens-Crowet et ah (9) for BPA polycarbonate were analyzed in the framework of the Rhee-Eyring stress bias activation theory for comparison purposes. Yield stress of the block polymer is roughly half that of the homopolymer at a given temperature. The apparent activation volume for the block polymer is double that of the homopolymer at each temperature. Activation energies at zero stress are essentially the same (60 kcal/mole for the block polymer vs. 70 kcal/mole for BPA polycarbonate above —50°C). 

Tensile Yield Stresses of Cast Films. At room temperature all of the BPFC-DMS polymers investigated (with one exception) reached their yield stresses before fracturing. BPF polycarbonate on the other hand is brittle, breaking at about 11,000 psi. Traces of residual chloroform make the homopolymer ductile however the yield stress decreased linearly with chloroform content. Extrapolation of these results to a dry polymer gives a yield stress of 14,000 psi. 

---