Essential Work Of Fracture Parameters Research Articles

Effect of thermal and hygrothermal aging on the plane stress fracture toughness of poly(ethylene terephthalate) sheets

The in-plane (plane stress) fracture toughness of two polyester (PET, PETG) sheets were assessed using the essential work of fracture (EWF) method after thermal and hygrothermal aging performed just below glass temperature. This ensured that physical aging takes place. On the aged sheets the yield stress (σy), enthalpy relaxation (ΔH) and EWF parameters were determined. It was observed that the essential work of fracture component related to the specific yielding (we,y) is suitable for assessing physical aging - independently of the humidity content. A good linear correlations exists between we,y, σy and ΔH.

Structures and properties of blown moulding LLDPE films

The crystalline structures, mechanical properties, transparence and fracture behaviours of linear low density polyethylene blown moulding films with nucleating agents incorporated in were investigated. The results indicated that with the nucleating agents used, the melting temperature Tm, crystalline structures, general profile of the stress–strain curves, tensile yield strength σy and essential work of fracture parameters before yield of the films, were almost unchanged, while the strain hardening phenomenon, tensile fracture strength σb, elongation at break &epsib, transparence and fracture parameters we and βwp were enhanced greatly. As the loading content of nucleating agent increasing, the crystallinity first decreased and then increased rapidly; the strain hardening phenomenon ϵb and σb increased to a maximum and then decrease to a stable value, while the Tm and σy were also unchanged; the haze decreased first and then reached a stable value; the we and we,y decreased remarkably first and then rapidly increased, even enormously exceeding the we of pure linear low density polyethylene, while βwp and βywp,y increased to a quite high value first and then dropped to a lower level.

Mechanical behavior and fracture toughness evaluation of K resin grafted with maleic anhydride compatibilized polycarbonate/K resin blends

The mechanical behavior and fracture toughness evaluation of polycarbonate (PC)/K resin (K) blends, with and without maleic anhydride grafted K resin (K-g-MAH) incorporated, have been studied. The effect of K-g-MAH on the mechanical performance of the PC/K blends was investigated. The results showed that both the tensile strength, elongation at break and impact strength of PC/K blends were improved considerably with incorporating K-g-MAH. This resulted from the melioration of compatibility between the PC and K resin phases. The essential work of fracture (EWF) method was employed to determine the fracture toughness of PC/K blends with and without K-g-MAH incorporated. The effect of composition on the EWF parameters of the blends was particularly investigated. The results showed that a significant improvement in w e of PC/K blends appeared when the K-g-MAH was incorporated, but it hardly influenced the plastic deformation during the fracture process.

In-plane and Out-of-plane Fracture Toughness of Physically Aged Polyesters as Assessed by the Essential Work of Fracture (EWF) Method

The in-plane (mode I) and out-of-plane (mode III) fracture behavior of amorphous (co)polyester sheets are studied as a function of physical aging using the essential work of fracture (EWF) concept. Physical aging was followed by measuring the yield stress and enthalpy relaxation of the (co)polyesters. The specific essential work of fracture term did not reflect the physical aging either in mode I or III loading. On the other hand, the corresponding values were closely matched indicating the mode III type loading turns into mode I for thin films. Aging was best manifested in the mode I – related EWF parameters, viz. specific yielding-related essential work and non-essential necking/tearing related work.

Essential work of fracture (EWF) analysis for polypropylene grafted with maleic anhydride modified polypropylene/calcium carbonate composites

The essential work of fracture (EWF) method was employed to determine the fracture behavior of calcium carbonate (CaCO 3) filled polypropylene (PP) composites with and without polypropylene grafted with maleic anhydride (PP- g-MA) incorporated. The effect of composition on the EWF parameters of the composites was particularly investigated. It was found that the plane-stress EWF approach worked well for the pure PP, PP/CaCO 3 and PP/CaCO 3/PP- g-MA composites. The specific essential work of fracture, w e, of PP/CaCO 3 composites was appreciably lower than that of pure PP, while the specific plastic work item, βw p, decreased markedly with increasing CaCO 3 content. For the composites modified with PP- g-MA in which the mass ratio of PP to CaCO 3 was fixed, w e increased considerably at first and then decreased with increasing amount of PP- g-MA. It was noted that the w e value of PP/CaCO 3/PP- g-MA at a mass ratio of 80/20/3 was about 4 KJ/m 2 higher than that of PP/CaCO 3, and even higher than that of pure PP. However, all βw p values for the hybrid composites with different content of PP- g-MA were lower than that of the PP/CaCO 3 composites. In addition, the specific work of fracture for yielding ( w e,y and β′ w p,y) and that for necking and subsequent fracture ( w e,n and β″ w p,n) obtained based on the partition of the specific work were also analyzed. It was found that the dominant factors which affected w e and βw p for the studied systems were the necking terms, as a majority of fracture energy was dissipated in the necking and fracture process.

Effects of compatibilization on the essential work of fracture parameters of in situ microfiber reinforced poly(ethylene terephtahalate)/polyethylene blend

A novel in situ microfiber reinforced blend (MRB) based on poly(ethylene terephthalate) (PET) and polyethylene (PE) was prepared by extrusion-hot stretching-quenching process, and was compatibilized with ethylene vinyl acetate copolymer (EVA) in the presence of the transesterification reaction catalyst, dibutyltin oxide (DBTO). The effects of compatibilization on the essential work of fracture parameters in PET/PE MRB were examined. It is found that the specific essential work of fracture ( w e) and the specific non-essential work of fracture ( w p) were significantly increased, when adding 1 and 2.5 phr of EVA to PET/PE MRB and it was further increased with the addition of 0.5 phr of DBTO as the catalyst of the transesterification reaction. The fracture surfaces study by scanning electron microscope (SEM) further proved that EVA is a successful compatibilizer for PET/PP blend. The morphology study of the blends shows that the well-defined fibers with the diameter of several microns were generated in situ during melt extrusion-hot stretch-quenching processing.

Effect of temperature on work of fracture parameters in poly(ether-ether ketone) (PEEK) film

The effect of temperature on plane-stress ductile fracture of an amorphous poly(ether-ether ketone) (PEEK) film of thickness 0.125 mm was studied between 23 and 140 °C using double edge notched tension (DENT) specimens. Within this temperature range, DENT specimens underwent full-ligament yielding prior to final fracture, producing load–displacement curves at various ligament lengths that were geometrically similar to one another at a given temperature. On the basis of these, “essential work of fracture (EWF)” methodology was used to determine the temperature dependence of the fracture toughness of PEEK film. Results showed that specific total work of fracture ( w f) is a linear function of ligament length ( L) over the entire temperature range under consideration. The value of w f at L=0 which is referred to as the “specific essential work of fracture, w e” decreased with increasing temperature. However, below the glass transition temperature, T g (≈140 °C), the amount w e decreased but was less than 10%. The slope of the line w f versus L which is referred to as the “specific non-essential work of fracture, βw p” increased with increasing temperature and showed a significant drop in value at T g. It is shown that w e and βw p are both composite terms, each consisting of a yielding ( w ey, β y w py) and necking/tearing ( w ent, β nt w pnt) components. It is found that w ent≫ w ey and β nt w pnt≫ β y w py, at all temperatures thus indicating that plastic deformation zone is linked mostly to necking/tearing component of the fracture process. Finally, it is shown that temperature dependence of the specific essential work of fracture parameters ( w e, w ey, w ent) can be predicted via crack opening displacement values.

Effect of temperature on fracture toughness of an amorphous poly(ether-ether ketone) film using essential work of fracture analysis

The effect of temperature on plane-stress ductile fracture of an amorphous poly(ether-ether ketone) (PEEK) film of thickness 0.125 mm was studied between 23 and 140 °C using double edge notched tension (DENT) specimens. Within this temperature range, DENT specimens underwent full-ligament yielding prior to final fracture, producing load–displacement curves at various ligament lengths that were geometrically similar to one another at a given temperature. The ‘essential work of fracture’ methodology was used to determine the temperature dependence of the fracture toughness of PEEK film. Results showed that specific total work of fracture ( w f) is a linear function of ligament length ( L) over the entire temperature range under consideration. The value of w f at L=0 which is referred to as the ‘specific essential work of fracture’, w e decreased with increasing temperature. However, below the glass transition temperature, T g (≈140 °C), the decrease in w e was not more than 10%. The slope of the line w f versus L, which is referred to as the ‘specific non-essential work of fracture’, βw p increased with increasing temperature and showed a significant drop in value at T g. It is shown that w e and βw p are both composite terms, each consisting of yielding ( w ey, β y w py) and necking/tearing ( w ent, β nt w pnt) components. It is found that w ent⪢ w ey and β nt w pnt⪢ β y w py, at all temperatures, thus indicating that plastic deformation zone is linked mostly to the necking/tearing component of the fracture process. Finally, it is shown that temperature dependence of the specific essential work of fracture parameters ( w e, w ey, w ent) can be predicted via crack opening displacement values.

Effect of hygrothermal aging on the essential work of fracture response of amorphous poly(ethylene terephthalate) sheets

The toughness of amorphous poly(ethylene terephthalate) (PET) sheets before and after hygrothermal aging was determined by the essential work of fracture (EWF) concept. Hygrothermal aging at 60 °C for 100 h of the specimens was performed in hot water and soft drink (Coca-Cola), respectively. The EWF parameters were determined using the energy partitioning method of Karger-Kocsis et al., at various testing temperatures ( T=−20 °C, +23 °C, +60 °C, respectively) at constant deformation rate ( v=2 mm/min). It was found that the specific essential work of fracture terms are more sensitive for the test conditions than the plastic ones. Changes in the former terms were assigned to an alteration in the viscoelasticity of PET owing to temperature and the plasticising effect of water.

Fracture behaviour of polypropylene films at different temperatures: fractography and deformation mechanisms studied by SEM

The fracture surfaces and the deformation micro-mechanisms of one polypropylene homopolymer and three ethylene–propylene block copolymers (EPBC) have been studied by scanning electron microscopy. The results are compared to the essential work of fracture parameters obtained in a previous study with deeply double-edge-notched-tension samples of films fractured between −40 and 70 °C. The homopolymer shows shear-yielding at T≥−20 °C, but at lower T, crazing prevails. The EPBC display shear-yielding for T>0 °C, while a combination of cavitation and shear-yielding occurs at lower T, which is responsible for stress-whitening. The variations of the specific essential fracture work and specific plastic work with T and with ethylene content have been successfully explained in terms of the prevalent deformation mechanisms.

Effect of glass fiber and maleated ethylene–propylene rubber content on the impact fracture parameters of nylon 6

The impact fracture parameters of blends of nylon 6 and maleated ethylene–propylene rubber (EPR-g-MA) reinforced with glass fibers as a function of glass fiber and EPR-g-MA content were examined. Both the linear elastic fracture mechanics (LEFM) model and a modified essential work of fracture (EWF) model were used to analyze the data. It was found that the addition of EPR-g-MA to unreinforced nylon 6 increased the EWF parameters uo and ud defined by U/A=uo+udℓ, where U/A is the total fracture energy per unit area and l is the ligament length. Beyond a critical rubber content, which coincided with the ductile-to-brittle transition, there was a large increase in ud. When glass fiber reinforcement was used without rubber toughening, the EWF model was unable to model the observed fracture response. On the other hand, the LEFM model adequately described the fracture behavior, and it was found that the critical strain energy release rate, GIC, increased with increasing glass fiber content. When both glass fiber reinforcement and rubber toughening were used, the uo increased with increasing EPR-g-MA or glass fiber content; whereas, ud increased with increasing ERR-g-MA content or decreasing glass fiber content.

Temperature dependence of the fracture behavior of nylon 6/ABS blends

Essential work of fracture and critical strain energy release rate analyses were used to investigate the effect of temperature (from 25 to −25°C) and specimen ligament length on the fracture energy, obtained from an instrumented drop tower test, of two compatibilized nylon 6/ABS blends (40 and 25wt% ABS) and the neat ABS. Three types of fracture were observed: ductile, mixed mode, and brittle. The essential work of fracture parameters were obtained by an analysis of the fracture energies for samples that failed in a ductile manner. The dissipative energy density, ud, was found to decrease with decreasing temperature for each of the three materials, while the specific limiting fracture energy, uo, was found to be nearly invariant with temperature for the two blends but to decrease with decreasing temperature for the ABS. The critical strain energy release rate, GIC, model gives an excellent description of the fracture energies of samples that failed in a brittle manner; GIC was found to decrease as temperature was reduced. The yield stress, σy, and the plane-strain critical stress intensity factor, KIC, were also determined. The yield stress was found to be invariant with temperature, while KIC decreases as the temperature is lowered.

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 (we) is a composite parameter: its constituents are relied on yielding (we,y) and necking (we)/ respectively. The we values, and especially we,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 we,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 (Tg). Recall that the shape recovery in case of cold-drawing (i.e. deformation below Tg) is controlled by the initial entanglement network structure in amorphous polymers.