Specific Non-essential Work Of Fracture Research Articles

Fracture toughness and fractographic investigation of polybutylene terephthalate/thermoplastic polyurethane binary blends reinforced by multi-walled carbon nanotubes using essential work of fracture approach

In this paper, fracture toughness evaluation of polybutylene terephthalate (PBT)/thermoplastic polyurethane (TPU) binary blends and PBT/TPU/carbon nanotubes (CNTs) ternary nanocomposites have been conducted using both Izod impact and quasi-static fracture tests. Essential work of fracture (EWF) approach is used to study the fracture properties in details. The results of EWF tests revealed an effective role of TPU and CNTs in toughening mechanism of binary blends and ternary nanocomposites. According to EWF results, both the crack resistance and plastic deformation energies promoted in all compounds as compared to neat PBT. Energy dissipation in the yielding and tearing stages determined by the energy partitioning method. The obtained results indicated that displacement up to the failure point increased by increasing the TPU content, while inclusion of CNTs reduced this quantity. The specific non-essential work of fracture [Formula: see text] , [Formula: see text], and [Formula: see text] increased with increasing the TPU contents which is confirmed by load-displacement curves. Whereas, addition of CNTs reduced [Formula: see text] and [Formula: see text] values as compared to reference binary blend, however, ternary nanocomposites still have higher values as compared to pure PBT. In contrast with EWF results, high strain rate of impact test prevents the activation of toughness improving mechanisms that readily occurs in quasi-static loading.

Microstructure and mechanical properties of PA6/NBR nanocomposites fabricated by friction stir processing

Thermoplastic elastomer (TPE) based on polyamid6 (PA6) / acrylonitrile-butadiene rubber (NBR) containing 5% wt nanoclay (Closite 30B) have been prepared via friction stir process (FSP). In this study, the essential work of fracture (EWF) approach was employed to investigate the fracture behavior of PA6/NBR nanocomposites. Also, the modulus strength of specimens was modeled by response surface methodology (RSM), considering three input variables including rotational speed (ω), traverse speed (S), and shoulder temperature (T). Thus, a quadratic mathematical model between input variables (ω, S and T) and response (modulus strength) of PA6/NBR/clay nanocomposites was achieved. Moreover, the morphology of the PA6/NBR blends containing 5% wt was investigated by x-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The results show that a sample of PA6/NBR thermoplastic elastomer (TPE) containing 5% wt nanoclay at maximum tensile strength exhibited the maximum specific essential work of fracture (we) and specific non-essential work of fracture (wp). Also, the results of the RSM method demonstrate that the optimum condition of the process was found to be at including rotational speed (ω), traverse speed (S), and shoulder temperature (T) of 1200 rpm, 25mm/min, and 146 ℃, respectively. Thus, under the condition optimum, maximum modulus strength of 658 MPa was obtained.

Clay-Based Polymer Nanocomposites: Essential Work of Fracture.

This work details the general structure of the clays used as a reinforcement phase in polymer nanocomposites. Clays are formed by the molecular arrangement of atomic planes described through diagrams to improve their visualization. The molecular knowledge of clays can facilitate the selection of the polymer matrix and achieve a suitable process to obtain clay-based polymer nanocomposite systems. This work highlights the development of polymer nanocomposites using the melt intercalation method. The essential work of fracture (EWF) technique has been used to characterize the fracture behavior of materials that show ductility and where complete yielding of the ligament region occurs before the crack propagation. In this sense, the EWF technique characterizes the post-yielding fracture mechanics, determining two parameters: the specific essential work of fracture (we), related to the surface where the actual fracture process occurs, and the specific non-essential work of fracture (wp), related to the plastic work carried out in the outer zone of the fracture zone. The EWF technique has been used successfully in nano-reinforced polymers to study the influence of different variables on fracture behavior. In this work, the fundamentals of the EWF technique are described, and some examples of its application are compiled, presenting a summary of the most relevant contributions in recent years.

The effect of rubber functionality on the phase morphology, mechanical performance and toughening mechanisms of highly toughened PP/PA6/EPDM ternary blends

Abstract The main purpose of the present work was to study the phase morphology, mechanical properties and fracture behavior of PP/PA6/(EPDM:EPDM-g-MA) (70/15/15) ternary blends with various rations of EPDM:EPDM-g-MA. The mechanical properties of the blends were examined technique tensile and impact tests. The fracture properties were characterized in detail by the essential work of fracture (EWF) approach. The test results the essential work of fracture for ternary blends with different weight rations indicated that the full ligament yielding took place before the onset and crack propagation for all blends with different weight ratio of EPDM:EPDM-g-MA. The energy partitioning method was also employed to determine energy dissipation in the stage of yielding, necking and tearing. The results revealed that with increasing of the EPDM-g-MA displacement to the point of failure in a constant ligament reduced. The specific non-essential work of fracture β W p and β n t . W p , n t decreased with increasing of EPDM-g-MA content that such an increase is confirmed according to the force-displacement curves. Whereas, the specific non-essential work of fracture β y . W p , y increased with increasing of EPDM-g-MA content. As well as the yielding component of W e and W e , n decreased with increasing of EPDM-g-MA content. While the yielding component of W e , y increased with increasing of EPDM-g-MA content.

Notch effect on the fracture of a polymeric film

The fracture behavior of a bio-based thermoplastic copolyester film has been studied by combining the essential work of fracture, the J-integral, and the crack tip opening displacement characterization methods on double edge notched tension specimens, in an attempt to provide a better understanding of the details that play an important role in the repeatability and the reproducibility of the essential work of fracture test, with particular attention to the effect of the quality of the notches generated by two different notch sharpening techniques. Specifically, the femtosecond pulsed laser ablation and the classic razor blade sliding techniques have been applied. The equivalence, reported and discussed in the literature, between the specific essential work of fracture and the J value at crack initiation, as well as their relationship with the crack tip opening displacement, have been confirmed. It is also identified the parabolic shape of the stress-displacement curves, which modeled relates the specific non-essential work of fracture with the stress at initiation and the extension ratio during the crack growth.

Refined fixture design for effective essential work of fracture toughness characterization of m-LLDPE thin films

Characterization of Mode-I fracture toughness of ductile polymeric thin films is nontrivial. Proper specimen preparation and experimental procedures are required to ensure in-plane tensile loading. In this study, a custom-built double-edge notched tensile test fixture was employed to characterize the Mode-I essential work of fracture (EWF) toughness of metallocene linear low-density polyethylene (m-LLDPE) films. Effects of specimen geometry, strain rate and film orientation on the specific essential work of fracture, we, and the specific non-essential work of fracture, wp, were investigated. Results indicate both EWF parameters are independent of the crosshead speed, gauge length (distance between upper and lower clamps) and specimen width within the ranges tested. we is significantly higher for thinner films and for crack propagation perpendicular to the blown film machine direction (MD). The usefulness of EWF for evaluating m-LLDPE fracture toughness is discussed.

Micro-Structure and Fracture Behavior of High-Melt-Strength PPs Prepared by Reactive Extrusion

In this study, high-melt-strength polypropylenes (PPs) were prepared by reactive extrusion of PP and varied amount of divinylbenzene in the presence of dicumyl peroxide and an antioxidant, and the dynamic rheological behavior, crystalline morphology, and fracture behavior of the resultant materials were investigated. It was found that at relatively low frequency, with the cross-linking and branching structures increasing, the complex viscosity of the melt of the modified PP increased significantly and then leveled off. The modulus of the melt, particularly the storage modulus, increased. The storage moduli of the melts with higher content of cross-linking and branching structures were higher than the loss modulus in the whole range of testing frequency, indicative of a completely elastic behavior. The crystallinity and the size of spherulites of the modified PP decreased, while the number of spherulites increased. The specific essential work of fracture and the specific non-essential work of fracture of the modified PP were found to be reduced compared with pure PP, but the specific essential work of fracture showed an increasing trend with the cross-linking and branching structures increasing.

Effect of composition on fracture behavior of polypropylene–wollastonite–polyolefin elastomer system

The fracture behavior of polypropylene (PP)–wollastonite–polyolefin elastomer (POE) in the mixed mode region was studied using the essential work of fracture (EWF) method. The relationship between the microstructure and the fracture parameters was analyzed. The effect of wollastonite content on the essential work of fracture and the work of plastic deformation was discussed. The energy dissipation during a double-edge-notched tension (DENT) test was calculated with the EWF method. It was found in the mixed mode region that σn increases with shortening of the ligament length region as plastic constraint effect rises and variation of the specific total work of fracture with ligament length was still reasonably linear within the mixed mode region. With increasing wollastonite content, w e (specific essential work of fracture) increases, while the βw p (specific non-essential work of fracture) decreases. The measurements of energy dissipation show that improvement in the fracture toughness of PP–wollastonite–POE is mainly due to the increase in crack propagation resistance during the necking and tearing processes after yielding, while the plastic deformation capability of the material depends mainly on the properties of fracture behavior before yielding. It is also found that the impact strength of the material decreases with increasing wollastonite content. However, the composition with high impact strength has lower specific essential energy of fracture and lower long-term fracture resistance, indicating that EWF is a better indicator of long-term fracture properties than the impact strength. DSC results show that the presence of wollastonite hinders crystallization of the PP.

Essential Work of Fracture Parameters of Injection-Molded Polypropylene/Polyolefin Elastomer Blends

The influence of polyolefin elastomer (POE) content on the fracture behavior of injection-molded polypropylene (PP)/POE blends was evaluated by means of the essential work of fracture (EWF) method. The results indicated that the EWF approach worked well for the PP/POE blends when POE content was 0∼7.5 wt% of the blends. The specific essential work of fracture (w e) increased with increasing POE content, and the dominant factor that affected w e was the necking and subsequent fracture process. The specific nonessential work of fracture (βw p) slightly decreased with increasing POE content, while the specific plastic work (w p) showed an increasing trend with the decrease of the shape factor (β) of the specimen. Finally, it was shown that w e could be predicted reasonably well via the COD values.

Essential Work of Fracture Evaluation of Compression-Molded Polypropylene/Ethylene and 1-Octene Copolymer Blends

The influence of ethylene and 1-octene copolymer content on the fracture behavior of compression-molded polypropylene/copolymer of ethylene and 1-octene blends was evaluated by means of the essential work of fracture method. The results indicated that the approach worked well for the polypropylene/copolymer of ethylene and 1-octene blends when copolymer of ethylene and 1-octene content was 0∼7.5 wt%. The specific essential work of fracture (we) of the blends increased with increasing copolymer of ethylene and 1-octene content and the dominant factor which affected we was the necking and subsequent fracture term (we,n). The specific non-essential work of fracture (βwp) slightly increased with increasing copolymer of ethylene and 1-octene content, while the term wp showed a decreasing trend with increasing shape factor (β). The trend of w e values obtained from crack-opening displacement was similar to that of essential work of fracture tests.

On the essential work of fracture of linear low-density-polyethylene. I. Precision of the testing method

The precision (i.e. the repeatability) of the essential work of fracture (EWF) method in determining the fracture parameters of a highly extendible linear low-density-polyethylene film is investigated. In order to minimize any interference from external variables, a random data collection procedure is adopted to extract, from a large data set, various EWF samples with sizes ranging from 11 to 150 data points. Two different notching procedures have been considered, involving different tools (scalpel or razor blade) and cutting methodologies. The notching procedure has only a marginal influence in terms of the correlation coefficient of the linear regression and standard error on the specific essential work of fracture ( w e). However, the mean of w e values is markedly affected by the notching procedure, being its influence on the specific non-essential work of fracture ( βw p) parameter relatively lower. The dispersion of the w e and βw p data around their mean values decreases as the sample size increases, with a trend clearly affected by the notching procedure.

The Essential Work of Fracture (EWF) method – Analyzing the Post-Yielding Fracture Mechanics of polymers

The Post-Yielding Fracture Mechanics describe the fracture behaviour of pre-cracked films and thin sheets that show yielding phenomenon at the crack tip during fracture. The Essential Work of Fracture method (EWF) has been used for this type of fracture characterization, determining two parameters: the specific work of fracture, w e related with the real fracture process area, and the specific non-essential work of fracture, w p that corresponds with the work done in the outer region of the crack tip. The EWF technique has been successfully employed especially with polymers, allowing the study of the influence of many variables in fracture properties, unavailable using other techniques such us K IC or J IC determination. In this work, the fundamentals of the technique and examples of application are reviewed, presenting a brief summary of the most relevant contributions of our group to the EWF method.

Effect of α- and β-nucleating agents on the fracture behavior of polypropylene-co-ethylene

The effect of α- and β-nucleating agents (NA) of various amounts on the fracture behavior of polypropylene-co-ethylene (CPP) was evaluated using the essential work of fracture (EWF) method. The specific EWF values of CPPs incorporated with α-NA of different amount were all lower than that of pure CPP, while the specific nonessential work of fracture was the highest at relative low α-NA loading (0.1 wt %), and then decreased with further increasing amount of α-NA. Similar trend of variation was observed with increasing amount of β-NA in CPP, and it was found that the variation of Kβ for β-NA nucleated CPP versus NA content accorded well with the EWF versus NA content, which indicated that the addition of β-NA could lead to effectively increased β-crystal content and consequently improved fracture resistance of CPP. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Influences of molecular weight and crystalline structure on fracture behavior of controlled-rheology-polypropylene prepared by reactive extrusion

The molecular weight of ethylene- block- co-polypropylene (co-PP) was adjusted by reactive extrusion with the incorporation of dicumyl peroxide (DCP), and the effect of molecular weight on the crystallization behavior, crystal morphology, and fracture behavior was investigated. It was found that, with increasing DCP content, the molecular weight (MW) decreased and the polydispersity ( M w/ M n) slightly decreased. After modification, the number of spherulites with obscure boundaries increased, and the size of the spherulites was more even due to increasing amount of grafting and micro-cross-linking structures, generated in co-PP degradation, which were acting as nucleating agents. Evaluated by essential work of fracture method, the specific essential work of fracture, w e, was found to be strongly dependent on the molecular weight, especially, on the number average molecular weight ( M n) linearly, while the specific non-essential work of fracture, βw p, was enhanced with decreasing z-average molecular weight ( M z), probably owing to the reduction of ultra-high molecular weight component in degraded co-PP.

Evaluation of Silica Content on Fracture Toughness of PI/SiO<sub>2</sub> Hybrid Films

The effect of silica content on plane-stress fracture toughness of Polyimide/silica (PI/SiO2) composite films was studied using the specific essential work of fracture (EWF) method. The specific essential and non-essential work of fracture for PI/SiO2 hybrid thin films with different silica doping levels was tested by experiment. The shape factor of the plastic region and specific non-essential work of fracture per unit volume were received by finite element (FE) calculation. It demonstrated that the plastic zone for specimens studied here was much different from the traditional result given through optical microscopic observation.

Thermal effects on fracture of biaxial-oriented poly(ethylene terephthalate) (BOPET) film

The effect of temperature on the fracture behaviour of biaxial-oriented poly(ethylene terephthalate) (BOPET) film was studied using the Essential Work of Fracture (EWF) approach. Fracture tests were performed over the temperature range +25 to +160 °C at the speed of 5 mm/min using double edge notched tension (DENT) specimens. The length of the specimens was either along the machine direction (MD) (0°), transverse direction (TD) (90°) or at 45° to either MD or TD. Ductile tearing of the ligament region was noted over the entire temperature range in all three directions. A linear relationship was found between the specific total work of fracture and the ligament length at all test temperatures. Values of the specific essential work of fracture (w e) in the MD and TD were similar and smaller than in the 45° direction. Within temperature range 25–140 °C, w e showed little variation if any with respect to temperature. As expected, the Specific Non-Essential Work of Fracture (βw p) was temperature dependent. This parameter increased with increasing temperature and reached a maximum around the glass transition temperature of BOPET (T g ≈ 80 °C). The values of the maxima are respectively 16.15, 20.38 and 17.8 MJm−3 for the 0°, 45° and 90°.

Essential and Non-essential Work of Fracture of PI/SiO2 Hybrid Thin Films

Essential work of fracture (EWF) analysis is used to study the effect of the silica doping level on fracture toughness of polyimide/silica (PI/SiO2) hybrid films. By using double-edge-notched-tension (DENT) specimens with different ligament lengths, it seems that the introduction of silica additive can improve the specific essential work of fracture (w e ) of PI thin films, but the specific non-essential work of fracture (βw p ) will decease significantly as the silica doping level increasing from 1 to 5 wt.%, and even lower than that of neat PI. The failure process of the fracture is investigated with online scanning electron microscope (SEM) observation and the parameters of non-essential work of fracture, β and w p , are calculated based on finite element (FE) method.

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.