Evaluation of fracture toughness of ABS polymers via the essential work of fracture (EWF) method (original) (raw)
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Polymer Bulletin, 1999
The essential work of fracture (EWF) fails for the toughness determination of polymers showing a decrease of the specific work of fracture, as a function of the specimen ligament. This type of behaviour was observed for poly(butylene terephthalate) (PBT) and its core/shell rubber modified blend (PBT/CS). It was found that this peculiar behaviour is due to a ductile-to-brittle transition (DBT) in the crack propagation phase. Experimental data were corrected by considering only the ductile-fractured specimen area. When a non linear function of the type y=a+bx -1 was applied for the corrected specific work of fracture and ligament data, the specific essential work of fracture (w e ) could be deduced. The latter being an inherent material toughness parameter was compared with the critical J-integral (J c ) values and a good correlation was found between them.
Polymer Engineering & Science, 2000
The plane strain fracture toughness of two ductile polymers, ultra high molecular weight polyethylene (UHMWPE) and acrylonitrile-butadiene-styrene (ABS), was measured by using the essential work of fracture approach. Truly plane strain fracture toughness (Wre) was measured for ABS at quasi-static and impact rates of loading. For UHMWPE, the measured values were only "near" plane strain values (Wre*). It was confirmed both w,~* and wIe were independent of specimen type but dependent on strain rate. For UHMWPE, there was a negative strain rate effect, i.e., wIe* decreased with increasing loading rate. At low quasi-static loading rate (v 5 10 mm/min), wr,* was constant at 55 kJ/m2. It then decreased to 15 W/m2 when the loading rate was increased to 100 mm/min, and remained at that value even up to impact rate of loading (u = 3.7 m/s). For ABS, a mild positive strain rate effect was observed. w,, increased from 13 kJ/m2 at u = 10 mm/min to 17 kJ/m2 at u = 3.7 m/s.
Rubber Chemistry and Technology, 2014
Material anisotropy induced by strain in filled vulcanized rubbers strongly affects fracture toughness. The influence of carbon black content on fracture phenomenology and fracture toughness was investigated by performing video-recorded tests adopting a suitable grooved notched pure shear test specimen. In such a way, it was possible to analyze the so-called ''knotty tearing'' deformation mechanism occurring at the crack tip: sideways cracks perpendicular to the notch plane develop before the onset and propagation of a forward crack parallel to the notch plane. The J-integral fracture mechanics approach was adopted and digital image correlation analysis was performed to measure the strain at the crack tip. The presence of carbon black modifies the maximum chain extensibility and strain-induced crystallizability of the rubber matrix in the compound. The formation of sideways cracks occurred in all filled compounds and resulted in a link to the maximum chain extensibility. Nevertheless, toughness enhancement was observed only when strain-induced crystallization took place at the crack tip before the onset of the forward crack.
Fracture behaviour of rubber-toughened polymer blends
Journal of Materials Science, 1992
The fracture toughness of a core-shell rubber modified polycarbonate-copolyester blend was determined by using the J-integral approach. Single-edge notch bend specimens were tested at room temperature using a crosshead speed of lmm mint. The resistance curve for the blend was not affected by specimen width, direction of crack growth with respect to mouldflow direction, and sidegrooving. Fractographic analysis suggested that the matrix debonded from the rubber particles thus relieving the triaxial stresses and enabling the matrix to yield more easily. The initiation of crack growth in the J-tests was observed to occur shortly after the onset of non-linearity in the load-deflection curve. Consequently, an attempt was made to describe fracture in this blend by using linear elastic fracture mechanics.
Fracture toughness determination of ABS polymers using the J-method
Polymer Testing, 1992
The suitability of J-R curve fitting methods proposed by ASTM E 813-81 and E 813-87 metal standards in fitting ABS J-R curves is discussed. Tests were carried out at room temperature on one commercial grade ABS resin in three-point bending. Specimens were precracked with a razor blade and tests were performed over a X20 range of crosshead rate in the quasistatic regime. Specimens of different geometric relationships (B/W, a/W, smooth specimens of different thickness, and side-grooved specimens) were assayed. The two ASTM fitting procedures were also checked against data reported by other authors for other ABS type resins. Model appropriateness was checked by statistical analysis. Results appeared to be geometrically independent for deeply notched specimens. No significant variation in the J-R curve was found for changes in the displacement rate. Both J-R curve fittings appeared to be adequate. The ASTM E 813-87 procedure led to less conservative critical initiation J1c values.
2014
The purpose of this thesis work was to study the effect of sulfur (S) content, carbon black (CB) type and carbon black content on the ultimate properties of three different rubber compounds, based on natural rubber, polybutadiene and their 50/50 blend. First, swelling test, dynamic mechanical analysis and tensile test were carried out to obtain information on physical characteristics of the compounds: crosslink density, filler-filler and filler-rubber interactions and the maximum chain extensibility. Then, ultimate stress and strain from uniaxial tensile tests and the fracture toughness, using notched pure shear specimens and adopting J-integral fracture mechanics approach, were evaluated. Finally, a correlation between the ultimate mechanical properties and the physical characteristics of the compounds was attempted. The main results obtained are: high fracture toughness is achieved when “sideways” cracks, perpendicular to the notch plane, develop before the onset and propagation...
Polymer Testing, 2019
The effects of initial crack length on the mode I fracture properties of crosslinked elastomers were investigated. A J-integral approach was implemented using single-specimen test procedures. Quasi-static fracture tests were carried out on filled and unfilled acrylonitrilebutadiene rubbers with various pre-cut (initial) crack lengths, , at a fixed rate of extension, using single edge notch rectangular bar specimens. Data from these experiments were analyzed and crack resistance curves (R curves) were obtained. A detailed analysis of the single-specimen method was carried out to establish correlation with the fracture properties derived from the more involved multi-specimen method. The weak dependence of geometry factor on rubber composition and displacement (in the neighborhood of crack initiation displacement) was verified. The crack initiation resistance and tearing modulus of the materials were calculated based on the R curve for each initial crack length. Fracture properties of lightly cracked specimens (/ < 0.4, where is the specimen width), including crack initiation resistance, strain at crack initiation, tearing modulus and maximum load and extension before fracture, were found to show significant variations with. These variations are characterized and discussed for the filled and unfilled rubber materials.
ESSENTIAL WORK OF FRACTURE CONCEPT IN POLYMERS
Plane-stress fracture toughness of amorphous copolyester (COP) sheets of different composition and molecular mass characteristics was determined by the essential work of fracture (EWF) concept using tensile-loaded deeply double-edge notched (DDEN-T) specimens. It was determined that these COPs meet the basic requirement of the EWF concept since their yielding along the full ligament preceded crack growth. A drop in load in the corresponding load-displacement (F − x) curves indicated yielding and allowed us to split both the specific essential and non-essential work of fracture (w e and w p , respectively) into their contributing terms based on yielding (w y ) and necking including fracture (w n ). Development and size of the plastic zone were studied by light microscopy (LM) and infrared thermography (IT).