Work of fracture of polystyrene/high density polyethylene blends compatibilized by triblock copolymer

The fracture toughening behavior of polystyrene/high density polyethylene blends compatibilized by 10 wt % of a styrene‐ethylene‐butylene‐styrene triblock copolymer (SEBS) was assessed using single‐edge notched tension (SENT) and double‐edge notched tension (DENT) specimens of various gauge lengths over a wide range of tensile rates. The fracture of DENT and SENT specimens was completely ductile under the plane‐stress condition. A linear relationship was observed between the specific total work of fracture and the ligament length (L) for a given L range. The results showed that the essential work (w_e) was independent of the tensile rate (R) range of 1–30 mm/min, and it then decreased considerably when R was increased to 50 mm/min and above. However, the nonessential work exhibited a rate independent trend behavior. In addition, w_e and the specific nonessential work of fracture (βw_P) were basically independent of the gauge length (G), provided that G was greater than the width of the sample. Finally, it was also shown that the w_e and βw_P values for SENT specimens are obviously greater than those for DENT specimens. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 2074–2081, 2000     

Work of fracture of PBT/PC blend: Effect of specimen size,geometry, and rate of testing

Fracture behavior of PBT/PC blend was studied at room temperature using two specimen geometries (SENT and DENT) and a wide range of specimen sizes and crosshead speeds. It was found that the fracture of all SENT and DENT specimens is completely ductile and stable. A linear relationship was obtained between the specific total work of fracture, w_f, and the ligament length, L. Extrapolation of this linear relationship to zero ligament length gave the specific essential work of fracture, w_e, which for PBT/PC blend was 35 ± 5 kJ/m² and was almost insensitive to geometry and the dimensions of test specimens as well as testing rate.     

Determination of the fracture toughness of polybutylene terephthalate (PBT) film by the essential work method: Effect of specimen size and geometry

The fracture behavior of PBT films of thicknesses 0.125, 0.175, 0.275, 0.375 and 0.5 mm was investigated according to Essential Work of Fracture (EWF) method. Single edge and double edge notched specimens of varying ligament lengths were tested in tension producing load‐displacement traces that were typical of ductile failure. A linear relationship was obtained between the total specific work of fracture (W_f) and ligament length (L). This linearity was maintained as ligament length exceeded the plastic zone size or one third of sample width. It was found that while the specific essential work of fracture (W_e) was independent of thickness, the specific non‐essential work of fracture (βW_p) decreased with increasing thickness. It was found also, that work of fracture parameters were independent of the specimen width for the range of thicknesses used in the present study. Nevertheless, for a sample width of 20 mm, a lower w_e and a higher βw_p value was obtained. Good agreement was found between values of W_e obtained from SENT and those obtained from DENT specimens; the value of βw_p was consistently higher for SENT specimens.     

Fracture behaviour of polyethylene naphthalate (PEN)

Fracture toughness of a semi-crystalline polyethylene naphthalate (PEN) film of thicknesses 0.050, 0.075 and 0.125 mm was measured as a function of temperature and loading rate using both double edge notched tension (DENT) and single edge notched tension (SENT) specimens. The specific essential work of fracture (EWF) and the multi-specimen J-integral methods were used to evaluate fracture toughness. The variation of the specific total work of fracture (w_f) with ligament length (L) was linear for ligament lengths between 5 and 15 mm. Within this range, w_f versus L was independent of thickness at all temperatures but was dependent on both temperature and loading rate. The specific EWF (w_e) was found to be independent of thickness and loading rate but showed three regions of varying temperature dependence. Between 23 and 80°C (region I) w_e was essentially independent of temperature but increased with temperature between 80 and 120°C (region II) and decreased with temperature thereafter (region III). At glass transition temperature (i.e. 120°C), w_e reached a maximum value of 75 kJ/m². The specific non-EWF (βw_p) increased with both loading rate and temperature. The greatest change in βw_p value with respect to temperature was obtained in region II.The plot of J-integral versus crack extension (Δa) was independent of thickness but was dependent upon temperature. w_e was found to be equivalent to both J_0.2 and J₀.     

Fracture of polybutylene terephthalate (PBT) film

Combined effects of thickness and temperature on essential work of fracture (EWF) of polybutylene terephthalate (PBT) film were studied using single edge notched tension (SENT) and double edge notched tension specimens. It is found that specific essential work of fracture (w_e) for PBT is independent of temperature below T_g (≈80 °C), but decreases above T_g. Between temperatures 25 and 100 °C, w_e was independent of film thickness in the range 0.125-0.375 mm. The specific non-essential work of fracture (βw_p) was temperature and thickness dependent, being greater for the SENT type specimens. Specimen orientation had no influence on w_e but strongly affected βw_p. It was found that βw_p is greater for cracks propagating normal to the extrusion direction as compared to the parallel direction.     

Combined effect of temperature and thickness on work of fracture parameters of unplasticized PVC film

The combined effect of temperature and thickness on the essential work of fracture (EWF) parameters for an unplasticized poly(vinyl chloride) (uPVC) film was investigated using double edge notched tension specimens. It was found that for the range of temperatures (23°C to 60°C) and thicknesses (0.15 mm to 0.40 mm) studied here, specific essential work of fracture (w_e) was independent of temperature at each thickness but increased with thickness at each temperature. It was found that at each temperature, w_e and its yielding (w_e,y) and necking/tearing components (w_e,nt), all increased linearly with increasing thickness. However, whilet w_e showed no significant variation with respect to temperature, its yielding component (w_e,y) decreased and its necking/tearing component increased (w_e,nt) with increasing temperature. It was found that estimated values of w_e and its components w_e,y and w_e,nt via crack opening displacement values were by and large unsatisfactory, being either much higher or lower than the directly measured values.     

The essential work of plane stress ductile fracture of linear polyethylenes

The specific essential works of plane stress ductile tearing of several high- and ultrahigh-molecular-weight polyethylenes were obtained from deeply edge-notched tension specimens, with either single or double notches, by extrapolating the straight line relationship between the total specific fracture work and ligament length to zero ligament. Provided the fracture morphologies of the torn ligament are not widely different, the specific essential work (w_e) is a material property dependent on thickness but independent of specimen geometry. The specific essential fracture work also can be identified with J_c the critical value of the J-integral along a contour immediately bordering the fracture process zone at the crack tip. There is good agreement between the experimental we values and theoretical J_c estimates for these polyethylene materials.     

Essential work of fracture analysis of short glass fiber and/or calcite reinforced ABS/PA6 composites

The effect of reinforcing agent type and composition on the fracture behavior of short glass fiber (SGF), CaCO₃ particle, and glass fiber/CaCO₃ hybrid reinforced ABS/PA6 blend based composites have been studied by using the essential work of fracture (EWF) method. Two millimeter thick rectangular shaped samples were first processed in twin‐screw extruder and they were subsequently injection molded. Double edge notched tensile (DENT) specimens with various ligament lengths were subjected to tensile tests at 2 mm/min constant deformation rate at room temperature in order to determine EWF parameters. For the neat matrix and 10 wt% calcite reinforced materials fractured in ductile manner, that is, the ligament fully yielded and the crack stably propagated unlike the other compositions. For the neat matrix, both the specific EWF, w_e, and the nonessential work of fracture, βw_p, values dramatically decreased with increasing reinforcement weight ratio regardless of the agent type. The analyzing of yielding and necking/tearing components of essential and nonessential parameters showed that for the samples reinforced with SGF w_e,nt > w_e,y and β_ntw_p,nt > β_yw_p,y, indicating that a majority of fracture energy was dissipated in the necking and tearing stages of fracture process. POLYM. ENG. SCI., 54:540–550, 2014. © 2013 Society of Plastics Engineers     

Deformation rate dependence of work of fracture parameters in polybutylene terephthalate (PBT)

Essential work of fracture (EWF) analysis was used to study the effect of loading rate (v = 2, 5, 25 and 50 mm/min) on fracture toughness of PBT film of thicknesses 0.175, 0.275, 0.375 and 0.5 mm. Using single edge notched tension (SENT) specimens, it was found that the specific essential work of fracture, w_e, increases slightly with increasing loading rate but Within the specified range of loading rate, it showed no significant variation with respect to thickness. The specific non-essential work of fracture, βw_p, decreased with increasing rate and increasing thickness.     

Temperature dependence of essential and non-essential work of fracture parameters for polycarbonate film

Abstract

Single edge and double edge notched polycarbonate specimens of thickness 0·;375 mm have been pulled to complete fracture at temperatures between 25 and 120°C. Within this temperature range specimens underwent full ligament yielding prior to final fracture, producing load–displacement curves at various ligament lengths that were geometrically similar to one another for a specific geometry. On the basis of these, the method of the essential work of fracture was used to study the effect of temperature on fracture toughness of polycarbonate film. Results showed that a linear relationship exists between specific total work of fracture w_t and ligament length L over the entire temperature range under consideration. The slope of the line, which is referred to as the specific non-essential total work of fracture βw_p , increased with increasing temperature. However, the interception at L = 0, which is referred to as the specific essential total work of fracture w_e , showed little variation with respect to temperature. Change of geometry affected both values, although the change in βw_p was more significant than that of w_e , for which change of no more than 10%was attained. Based on the maximum load on the load–displacement curve, w_t for double edge notched specimens was partitioned into the specific work of fracture for yielding w_y and the specific work of fracture for yielding necking/tearing w_nt . Linear relationships were found for both terms as a function of ligament length from which the essential (w_e,y , w_e,nt ) and non-essential (β_y w_p,y , β_{nt w p, nt} ) related work terms were attained. Results showed that the yielding related work terms for polycarbonate decrease, while the necking/tearing related work terms increase, with increasing temperature.     

Influence of temperature on plane stress ductile fracture of poly(ethylene terephthalate) film

Abstract

Double edge notched poly(ethylene terephthalate) (PET) specimens of varying ligament lengths and 0·125 mm thickness have been pulled to complete fracture between 23 and 160°C. Within this temperature range, propagation of the crack was always stable, producing load–displacement curves at various ligament lengths that were geometrically similar to one another. Essential work of fracture (EWF) analysis was used to study the effect of temperature on fracture toughness. A linear relationship was obtained between specific total work of fracture W _f and ligament length over the entire temperature range under consideration. The slope of the line, which is termed specific non-essential work of fracture βw _p , showed a maximum near the glass transition temperature of the material (T _g ≈ 93°C). Beyond this point, βw _p decreased sharply with increasing temperature. The intercept of the line at zero ligament length, which is referred to as specific essential work of fracture w _e , showed three types of variation with respect to temperature. Below T _g , w _e was found to be more or less independent of temperature; above T _g it increased with temperature and reached a maximum value at the end of the leathery region (～120°C); beyond which it decreased steadily.     

Effects of 2-ethyl-4-methylimidazole and tetraethylammonium bromide on the fracture properties of epoxidized soybean oil based thermoset

In this paper, we aim to report the effects of catalyst (types and concentrations) on the fracture mechanics of epoxidized soybean oil (ESO) based thermosets. ESO resin was thermally cured using methylhexahydrophthalic anhydride curing agent in the presence of two types of catalysts, i.e., tetraethylammonium bromide and 2-ethyl-4-methylimidazole (EMI). The loading of the catalysts varied from 0.3 to 0.8?phr. The fracture behaviour of ESO thermoset was examined on the basis of the principle of linear elastic fracture mechanics (LEFM) and essential work of fracture (EWF). LEFM measurements were performed using single-edge notched tensile and double-edge notched tensile (DENT) tests, while, EWF measurements were carried out using DENT tests. The fracture morphologies of the ESO thermosets were characterized via field emission scanning electron microscopy. It was determined that the plane-strain fracture toughness (K _IC), the specific EWF (w _e), and the specific plastic fracture work (??w _p) of ESO thermosets were significantly influenced by the types and loading of catalysts. In addition, the fracture toughness properties were associated with the crosslink density of the ESO thermosets. In addition, it was found that the brittle?Cductile transition of EMI-catalyzed ESO thermosets can be assessed by the combination of LEFM and EWF in the fracture toughness measurement.     

Essential work of fracture: application for polymers showing ductile-to-brittle transition during fracture

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. Received: 1 February 1999/Revised version: 25 March 1999/Accepted: 31 March 1999     

Effects of injection molding–induced morphology on the work of fracture parameters in rubber-toughened polypropylenes

The effects of the injection-molding induced skin-core morphology on the fracture behavior of rubber-toughened polypropylene (RTPP) systems were studied by employing the essential work of fracture (EWF) method. RTPP with 31 wt% ethylene/propylene rubber (EPR) showed no skin-core structure after molding and the EWF approach worked well in this case. In contrast, RTPP with 10 wt% EPR exhibited a pronounced skin-core morphology: EPR deplection and enrichment was observed in the skin and core region, respectively. This morphology caused necking instead of crack growth in deeply double edge-notched (DDENT) specimens under tensile loading along the filling direction (MFD). The necking process not only was accompanied by a large scatter but also yielded highly unrealistic specific essential work of fracture (w_e) values. This skin-core structure was also the reason for an anistropic EWF response of this system observed by loading the specimens both in longitudinal (L) and transverse (T) directions to the MFD. The failure sequence and its characteristics were studied by light microscopy (LM) and infared thermography (IT). It was concluded that the EWF approach cannot be applied for RTPP with a prominent skin-core structure. Since yielding preceded the limited crack growth prior to necking in the loading directin for the DDEN-T specimen of RTPP with 10 wt% EPR, the yielding-related specific essential work (w_e,y) was used for toughness comparison. In case of RTPP with 31 wt% EPR, where yielding was less pronounced prior to the crack growth, the work of fracture until the maximum load was assigned to the yielding-related work of fracture (w_f,y) used for computing w_e,y. The latter value seems to be closely matched to the plane-strain essential work of fracture value.     

Impact specific essential work of fracture of compatibilized polyamide‐6 (PA6)/poly(phenylene ether) (PPE) blends

The essential work of fracture (EWF) method has aroused great interest and has been used to characterize the fracture toughness for a range of ductile metals, polymers and composites. In the plastics industry, for purposes of practical design and ranking of candidate materials, it is important to evaluate the impact essential work of fracture at high‐rate testing of polymers and polymer blends. In this paper, the EWF method has been utilized to determine the high‐rate specific essential fracture work, w_e, for elastomer‐modified PA6/PPE/SMA (50/50/5) blends by notched Charpy tests. It is found that w_e increases with testing temperature and elastomer content for a given specimen thickness. Morphologically, there are two failure mechanisms: shear yielding and pullout of second phase dispersed particles. Shear yielding is dominant in ductile fracture, whereas particle pullout is predominant in brittle fracture.     

Studies on fracture behavior of tough PA6/PP blends

Fracture toughness of injection-molded PA6/PP blends compatibilized with SEBS-g-MA was studied using deeply double-edge notched tension (DDENT) specimens according to the essential work of fracture procedure. The fracture mechanical studies also included tensile impact tests on the DDENT specimens and characterization of the fracture surfaces by electron microscopy. The results were compared with those of traditional tensile tests and Izod impact tests on single-edge notched samples, and the sensibility of the methods was evaluated. Effects of sample position, ligament length, testing direction, and test speed were studied as well. It was found that the essential work of fracture concept, earlier applied to thin sheets, can also be applied to injection-molded tough blends. High deformation of the skin may, however, interfere with the measurements and cause a “tail” in the load-deformation curves. The plastic work of fracture (w_p) was found to correlate with the impact strength, and thus, it described the toughness. The highest values for work of fracture were recorded for the compatibilized blend with a PA6/PP ratio of 80/20. The essential work of fracture (w_e) in turn increased with increasing PA6 content and behaved like tensile strength. The test speed was found to affect the fracture behavior substantially: differences between the materials were more pronounced in high-speed tensile impact tests, which revealed signs of cavitation in addition to large-scale plastic deformation for the tough PA6-rich blend compositions. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 2209–2220, 1997     

Influences of hot stretch ratio on essential work of fracture of in‐situ microfibrillar poly(ethylene terephthalate)/polyethylene blends

An in‐situ microfibrillar blend based on poly(ethylene terephthalate) (PET) and polyethylene (PE) was fabricated through slit die extrusion, hot stretching, and quenching. The morphological characteristics of the PET phase, such as diameter and its distribution, which were observed after the matrix was etched away, appear to be dependent on the hot stretch ratio at a fixed blend composition. The increase of the hot stretching ratio makes the PET particles change from spheres and ellipsoids to rodlike particles, and finally to well‐defined microfibers. The fracture toughness of the in‐situ microfibrillar blend was evaluated using deeply double‐edge notched tension (DDENT) specimens according to the essential work of fracture procedure. Initially, the increase of hot stretch ratio makes the specific essential work of fracture (w_e) rise. A maximum we appears at 25.4. Further increase of hot stretch ratio causes a slightdecrease of w_e. On the other hand, it shows that lower hot stretch ratios make the specific non‐essential work of fracture (w_p) rise slightly. As it exceeds 6.4, w_p decreases substantially. It was believed that the characteristics of the PET domains were responsible for the fracture behaviors of the in‐situ microfibrillar blend. Polym. Eng. Sci. 44:2165–2173, 2004. © 2004 Society of Plastics Engineers.     

Relationships between molecular and plane-stress essential work of fracture parameters in amorphous copolyesters

The plane-stress fracture toughness of amorphous copolyester (aCOP) sheets of different intrinsic viscosity (IV) was determined by the essential work of fracture (EWF) concept using tensile-loaded deeply double-edge notched (DDEN-T) specimens. It was found that the specific essential work of fracture (w_e) is a composite parameter: its constituents are relied on yielding (w_e, y) and necking (w_e, n), respectively. The w_e values, and especially w_e, y did not change as a function of IV. This finding along with the fact that the mean entanglement length of the aCOP series was constant, suggest that w_e, y (which is related to the critical plane-strain toughness value) is likely dependent on the entanglement network. This assumption was reasoned by the observation that the plastic zone was completely recovered after annealing the specimen beyond the glass transition temperature (T_g). Recall that the shape recovery in case of cold-drawing (i.e. deformation below T_g) is controlled by the initial entanglement network structure in amorphous polymers. Received: 6 May 1997/Revised: 14 August 1997/Accepted: 15 August 1997     

Fractographic analysis of the crack resistance of styrene–acrylonitrile/polybutadiene‐g‐styrene–acrylonitrile blends as evaluated by the essential work of fracture method

The fracture surfaces and deformation micromechanisms of styrene‐co‐acrylonitrile (SAN)/polybutadiene‐g‐styrene‐co‐acrylonitrile (PB‐g‐SAN) blends with the compositions ranging from 65/35 to 0/100 were studied with a scanning electron microscopy technique. The results were compared to the essential work of fracture parameters obtained in a previous study conducted on double‐edge notched tension specimens. Different plastic damage mechanisms were observed, and they depended on the blend composition. For blends of 65/35 and 45/55, a high degree of rubber particle cavitation and multiple cracking followed by the massive shear yielding of the matrix were found to be the main source of energy dissipation during crack growth. Within this compositional range, more intense plastic damage in a larger volume of material, especially at the notched region, was observed as the concentration of the rubbery phase increased. For the 25/75 blend, the prevailing mechanism was pure shear yielding without any sign of cavitation inside the particles, and the fracture surface became relatively flat and was covered with aligned small microcracks. This sample showed the highest specific essential work (w_e) value among the blends examined in the previous study. For the samples containing concentrations of dispersed phase higher than 75%, the shear yielding process gradually became less important with the progressive importance of multiple crazing so that high‐magnification micrographs revealed extensive microcracking/crazing both inside and between the rubber particles, as the only active deformation micromechanism for neat PB‐g‐SAN. The variation w_e and specific plastic work of fracture with the PB‐g‐SAN phase content were successfully explained in terms of prevalent deformation mechanisms. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40072.     

Effects of rubber content and temperature on dynamic fracture toughness of ABS materials

The effects of rubber content and temperature on dynamic fracture toughness of ABS materials have been investigated based on the J‐integral and crack opening displacement (COD, δ) concepts by an instrumented Charpy impact test. A multiple specimens R‐curve method and stop block technique are used. It is shown that the materials exhibit a different toughness behavior, depending on rubber content and temperature. The resistance against stable crack initiation (J_0.2 or δ_0.2) increases with increasing rubber content. However, J_0.2 first increased with increasing temperature until reaching the maximum value; after that, it decreases with further increasing the temperature. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 1605–1614, 2000