Essential Work Of Fracture Tests Research Articles

The Use of Various Measurement Methods for Estimating the Fracture Energy of PLA (Polylactic Acid).

The essential work of fracture (EWF) and Izod/Charpy impact tests have been used to investigate the fracture toughness in the plane stress of brittle polymers. In this paper, we had three goals: first, we aimed to employ how to estimate PLA toughness in different geometries; then, we proposed to compare Izod and Charpy Impact toughness in the same geometry; finally, we intended to determine the difference between EWF toughness and dynamic toughness. The results showed that the EWF method could be applied to evaluate PLA fracture behavior with small ligaments (2-4 mm), while the dynamic test could be employed with larger ligaments (5-7 mm). A comparison of the two impact test results obtained the following conclusions: Charpy impact toughness was higher than Izod impact toughness in the same geometry, and the impact toughness under a notch angle of 90° was larger than that of an angle of 45°. Both EWF and dynamic tests can be used to explore PLA toughness with small ligaments. The fracture energy decreases with ligament size in the EWF test, but it increases in the dynamic test.

Evaluation of different specimen geometries and testing configurations for the assessment of the degree of gelation of unplasticized poly(vinyl chloride) pipes using the essential work of fracture approach

An unplasticized (U-PVC) pipe sample (ABNT NBR 5647-2, nominal diameter DN 100, outside diameter 110 mm) is studied using essential work of fracture (EWF). This pipe sample is also tested for the quality of processing (degree of gelation) via differential scanning calorimetry (DSC) and tensile strength. The comparative evaluation of different specimen configurations – flat (SENB) and curved (CTPB) specimens in three-point bending, using different support spans, and C-shaped (SNRB) and full rings in tension (SNRT), shows significant differences in their suitability for EWF testing. While SENB- and CTPB-type specimens, independently of the support span ratio S/W adopted, confirm previous findings that both specimen configurations are very suitable for EWF testing of pipe samples, SNRB- and SNRT-type specimens, by their turn, do not show suitability for the purposes of this study, at least using the testing configurations here adopted. When comparing results from this study with previous publications from the authors, it is shown that EWF seems to be an interesting alternative approach for gelation assessment, since it is evident from the comparative results that there is some high degree of correlation between EWF parameters and the DSC degree of gelation.

The essential work of fracture method for the characterisation of fusion bonding in 3D printed short carbon-fibre reinforced polyamide 6 thin films

The fusion bonding between individual filaments of 3D printed short carbon-fibre reinforced polyamide 6 (SCF/PA6) in thin films manufactured using the fused filament fabrication (FFF) process has been studied. The thin films were deposited by an ‘in-plane’ mode or an ‘interlayer’ mode. The main characterisation technique employed was the essential work of fracture (EWF) method. Undertaking EWF tests on such thin films is shown to be a feasible and efficient way to evaluate the extent and quality of fusion bonding between individual filaments of the 3D printed SCF/PA6 composites. For example, firstly, for the 3D printed SCF/PA6 thin films it was readily evident that the extent of fusion bonding, i.e. the adhesion via molecular inter-diffusion, often termed the autohesion, between the filaments is the weakest, and the most variable, in the 3D printed SCF/PA6 thin films deposited via the interlayer mode. This was indicated by the lowest measured values of both the specific essential work of fracture, we, and the coefficient of determination, R2, of 19.6 kJ/m2 and 0.05, respectively, for the interlayer printed SCF/PA6 thin films. Secondly, the quality of the 3D printed SCF/PA6 thin films deposited via the in-plane mode was significantly enhanced by the use of further compression moulding process, since the value of R2 increased from 0.77 to 0.92. The results clearly suggest the need to improve the extent and quality of fusion bonding between individual filaments printed using the FFF process when 3D printed components are made for practical applications.

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.

Fracture toughness examination of dual‐phase and interstitial free steel using essential work of fracture method

AbstractFracture toughness of automotive‐grade dual‐phase steel (DP450) and interstitial free (IF) steel is determined using essential work of fracture (EWF) methodology. Geometrical constraints of standard fracture toughness tests made the EWF method an alternative for thin sheets. Double edge notched tension (DENT) specimens are used for the EWF tests. The two steels have different mechanical and microstructural properties, which helps test the applicability of the EWF methodology to different materials. The effect of notch‐tip radius on the EWF test results is analyzed for both the steels. The sensitivity of fracture toughness to notch‐tip radius is not the same for both steels. During the EWF test, the digital image correlation (DIC) technique is used to determine the local strain variation of DENT specimens. The hole expansion ratio is determined for the two steels to compare against the EWF test results. The IF steel, despite lower strength, has better fracture toughness and hole expansion capability against the DP450 steel.

Effect of the Temperature and of the Drawing Conditions on the Fracture Behaviour of Thermoplastic Starch Films for Packaging Applications

In this work the effects of testing temperature and drawing orientation on the fracture behaviour of biobased and biodegradable thermoplastic starch based films, currently applied in the food packaging field, were investigated. At this aim, the Essential Work of Fracture (EWF) approach was applied on samples tested at 0 °C, 25 °C and 50 °C both in machine (MD) and in cross (CD) directions. The specific essential work of fracture (we) values strongly decreased with the testing temperature, and we values of CD samples were systematically higher than those of the corresponding MD samples. Considering that photograms of the CD samples taken during the EWF tests highlighted that the yielding zone became progressively opaque as an effect of the strain induced crystallization, it was hypothesized that in CD specimens part of the tensile energy applied during the straining process was utilized for the orientation of the macromolecules along the strain direction, rather than for the propagation of the crack in the ligament zone. Tensile tests under quasi-static conditions on dumbbell specimens highlighted that, regardless to the drawing direction, the stiffness and the resistance at yield and at break decreased with the temperature, while the strain at break was considerably enhanced. Moreover, because of the strong anisotropy induced by the molecular orientation in the drawing direction, MD tested samples had higher elastic modulus, yield resistance, and stress at break compared to CD samples.

Identification of fracture toughness parameters to understand the fracture resistance of advanced high strength sheet steels

The fracture toughness of four advanced high strength steel (AHSS) thin sheets is evaluated through different characterization methodologies, with the aim of identifying the most relevant toughness parameters to describe their fracture resistance. The investigated steels are: a Complex Phase steel, a Dual Phase steel, a Trip-Aided Bainitic Ferritic steel and a Quenching and Partitioning steel. Their crack initiation and propagation resistance is assessed by means of J-integral measurements, essential work of fracture tests and Kahn-type tear tests. The results obtained from the different methodologies are compared and discussed, and the influence of different parameters such as specimen geometry or notch radius is investigated. Crack initiation resistance parameters are shown to be independent of the specimen geometry and the testing method. However, significant differences are found in the crack propagation resistance values. The results show that, when there is a significant energetic contribution from necking during crack propagation, the specific essential work of fracture (we) better describes the overall fracture resistance of thin AHSS sheets than JC. In contrast, energy values obtained from tear tests overestimate the crack propagation resistance and provide a poor estimation of AHSS fracture performance. we is concluded to be the most suitable parameter to describe the global fracture behaviour of AHSS sheets and it is presented as a key property for new material design and optimization.

Preparation of PBT/POE‐g‐GMA/PP ternary blends with good rigidity–toughness balance by core–shell particles

ABSTRACTCompared with poly(butylene terephthalate)/glycidyl methacrylate grafted poly(ethylene–octene) (PBT/POE‐g‐GMA) binary blends, supertough PBT‐based ternary blends with little rigidity loss were successfully obtained by adding rigid polypropylene (PP) into PBT/POE‐g‐GMA blends to construct core–shell particles during melt blending. The effects of PP content and type on the phase morphology and mechanical properties of the blends were systematically investigated. Theoretical predictions and scanning electron microscopy observation showed that a core–shell structure was formed in PBT matrix with PP as the core and POE‐g‐GMA as the shell. The mechanical property tests showed that POE‐g‐GMA and PP had significant synergistic toughening effect. When PP with high melt flow index (H‐PP) was used, PBT/POE‐g‐GMA/H‐PP (70/15/15) blends possessed the highest Izod notched impact strength, which was 1.9‐fold compared with PBT/POE‐g‐GMA (70/30) binary blends, while the tensile performance loss was little. The essential work of fracture tests was performed to evaluate the fracture resistance of different samples. The results demonstrated that PBT/POE‐g‐GMA/PP ternary blends possessed much better resistance to crack propagation than PBT/POE‐g‐GMA binary blends. The decrease of interparticle distance and the fibrillation of core–shell particles activated intense matrix shear yielding, which was the reason for the high crack resistance of ternary blends. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020, 137, 48872.

Study on the fracture toughness and deformation micro-mechanisms of PP/EPDM/SiO2ternary blend-nanocomposites

A detailed fracture analysis of polypropylene/ethylene–propylene–diene monomer rubber/nano-silica (PP/EPDM/SiO2) ternary blend-nanocomposites was conducted through using both Izod impact and quasi-static fracture tests. The phase morphology and the fractured surfaces were evaluated using scanning electron microscopy. Morphological observations revealed that the SiO2nanoparticles were mainly located either around the EPDM particles or at the PP/EPDM interface. A synergistic effect was observed between the soft EPDM rubber particles and rigid SiO2filler on activation of different toughening micro-mechanisms, so that the impact strength of the ternary systems was significantly higher than that of corresponding binary blends. This effect was much more significant for percolated morphologies. The concept of the essential work of fracture (EWF) was used to analyze the fracture behavior and toughening/deformation mechanisms of the samples. The percolated structure of the EPDM particles and the SiO2nanoparticles exhibited superior fracture resistance under EWF fracture tests. Formation of multiple void-fibrillar structures dissipated further energy and significantly improved fracture resistance under EWF tests. It was demonstrated that the toughness and stiffness could successfully be balanced via controlling the microstructure of the ternary systems.

Evaluation of ductile tearing resistance of dual-phase DP 780 grade automotive steel sheet from essential work of fracture (EWF) tests

The Essential Work of Fracture (EWF) method is adopted to study the ductile tearing resistance of Dual-Phase steel (DP 780) sheet of 1 mm nominal thickness. All the three characterizing parameters, namely EWF, estimate of crack tip opening displacement (CTOD) for crack initiation and crack tip opening angle (CTOA), that can be determined by the EWF testing paradigm have been examined. It is concluded that, of these three parameters, the CTOA estimated by this easy and rapid procedure is the best choice both in terms of statistical robustness and for potential application in integrity assessment.

Fracture toughness evaluation of interstitial free steel sheet using Essential Work of Fracture (EWF) method

Essential Work of Fracture (EWF) method has been used to evaluate ductile tearing resistance of interstitial-free (IF) steel sheet of 1 mm thickness. Experiments have been done on double edge notched tensile (DENT) specimens with and without fatigue precracking at three different quasi-static ramp rates. The fracture in all cases was flat with maximum specimen necking of 36% of thickness. The estimated crack tip opening angle (CTOA, ψe) was found to be essentially independent of ρ, and also of deformation rate. The critical CTOA (φe) was optically estimated using a precracked DENT specimen. Also, the tearing resistance parameters obtained from EWF tests have been compared with that determined using 3-dimentional Finite Element Modeling (FEM). Results of FEM, along with a chosen traction-separation law, were used in a 3-dimentional Cohesive Zone Model (CZM) for flat fracture to simulate crack growth behavior in the DENT specimens.

Fracture toughness characterization of polymers-based composites using essential work of fracture method

Fracture toughness of polymer-based composites in plane stress condition has been successfully evaluated using latest method namely essential work of fracture (EWF). This method has been extensively performed in order to assess the performance of two parameters in fracture, i.e. essential work of fracture (we) and non-essential work (βwp) ones. The use of EWF method is widespread due to the preparation of uncomplicated specimens, easy examination and easy data processing procedures but accurate in data analysis. This review is focused on the EWF application for the characterization of fracture toughness of polymer-based composites in which the fracture occurs in plane stress state. The EWF testing procedure is in accordance with the recommendations of the ESIS protocol TC-4. Literature reviewed includes all the major areas of testing and simplification of associated data for both quasi-static and dynamic condition. The latter is an EWF application classified by the type of load applied.

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.

Ductile Tearing Resistance Indexing of Automotive Grade DP 590 Steel Sheets: EWF Testing Using DENT Specimens

The essential work of fracture (EWF) method has been explored for indexing the ductile tearing resistance of DP 590 automotive grade dual-phase steel sheet both in longitudinal (L-T) and transverse (T-L) orientations. The simplest possible test and analysis procedures have been adopted. The EWF method is found to be eminently suitable for routine quality control and product development purposes for such materials. Areas for further research for improving the experimental strategy are highlighted. For the investigated steel sheet, the estimated tearing resistance is found to be distinctly higher for the L-T orientation compared to the T-L orientation; the reason thereof merits further investigation.

Essential Work of Fracture and Size Effect in Copper/Glass-Reinforced Epoxy Laminate Composites Used as MEMS Devices

Microelectromechanical systems (MEMS) are made of components in the range of 1 to 100 micrometers. These systems have a large application in electrical and electronic devices. The manufacturing of MEMS categorized under semiconductor device branch fabrication. The performance of such precision material very strongly depended on the mechanical and fracture properties of the composite material they get fabricated from. A MEMS thin strips are manufactured by bonding a thin copper film on a substrate of glass-reinforced laminated fabric with an epoxy resin binder. Generally, the tested samples are glass fiber laminates with a 1.5mm thickness having 35-micron copper layer. Two sets of samples were cut; first ones are in the form of a flat specimen with a small hole at the center for size effect tests whereas, the second ones are double edge notch (DENT) specimens for essential work of fracture tests. The fracture toughness of such material is measured using essential work of fracture tests. These types of material are considered a quasi-brittle material which mainly anisotropic material, therefore, the size effect is tested over this material. The results showed that the essential work of fracture for this MEMS material is measured as 72.883 kj/m2 and is subject to size effect which make a reduction in nominal strength namely 15%.

The fracture testing of ductile polymer films: Effect of the specimen notching

The fracture of a ductile polymer film, a heterophase ethylene-propylene block copolymer, has been studied, combining a range of characterisation methods in an attempt to provide a better understanding of the intricate details that play an important role in the repeatability and reproducibility of the essential work of fracture test. The experimental factors that have a strong influence on the resulting parameters are clearly explained, with particular attention to the effect of the quality of the notches, the non-collinearity of the two edge notches in double edge notched tension specimens, and the lack of alignment of the specimen with the load axis once it is mounted on the load train. Furthermore, the influence of these experimental factors on the registered stress-displacement curves is also studied, and a criterion and the method for separating non-valid specimens are established.

Effect of localization of carbon nanotubes on fracture behavior of un-vulcanized and dynamically vulcanized PP/EPDM/MWCNT blend-nanocomposites

Effect of localization of multiwall carbon nanotube (MWCNT) on the fracture toughness and deformation mechanisms of un-vulcanized and dynamically vulcanized polypropylene/ethylene-propylene terpolymer/multiwall carbon nanotube (PP/EPDM/MWCNT) blend-nanocomposites were investigated under both the Izod impact loading and the essential work of fracture (EWF) test as quasi-static loading conditions. The localization of MWCNT in the PP matrix led to increased impact fracture toughness via multiple crazing and crack deviation induced by MWCNT aggregates in the PP matrix, while it had negative effect on the fracture toughness under EWF test condition through hindrance effect on the yielding and necking processes. This contradiction was attributed to the different dominant deformation mechanisms in the PP matrix under high speed multiaxial Izod impact and low speed plane biaxial EWF fracture tests (crazing and shear yielding, respectively). Although the various toughening mechanisms such as nano-bridge mechanism were activated during the fracture processes, vulcanization induced interfacial adhesion improvement between the PP and EPDM particles played the main role in determining of the fracture toughness of the vulcanized blend-nanocomposites.

Essential work of fracture assessment for thin aluminium strips using finite element analysis

The fracture toughness of a commercial thin aluminium sheet (1.2mm) is measured by the essential work of fracture (EWF) method using a double-edge notch tension specimen. The EWF method is implemented at room temperature at a deformation speed of 2mm/min. The basics of the EWF method and its relation with J-integral are described in this paper. Ligament yielding is observed to occur at the peak of the load-displacement curve. Following this, necking and tearing occur in the softening region. The EWF for the thin aluminium sheet is measured as 51.5kJ/m2. However, the non-essential work of fracture is dissipated in the tearing process after yielding, causing expansion of the plastic region. In this work, two advanced finite element models, namely, non-linear and linear J-Integral finite element models, are implemented to simulate the essential work of fracture test. The results for the essential and non-essential fracture indicate good agreement with EWF fitting. The linear extended finite element (XFEM) model yields more accurate results than the J-integral method. Crack opening displacement is measured by the EWF method, and is compared with the results of the studied models.

Fracture investigation in starch-based foods.

The study of oral processing and specifically cutting of the food piece during mastication can lead towards optimization of products for humans or animals. Food materials are complex biocomposites with a highly nonlinear constitutive response. Their fracture properties have not been largely investigated, while the need for models capable of predicting food breakdown increases. In this study, the blade cutting and the essential work of fracture (EWF) methodologies assessed the fracture behaviour of starch-based pet food. Tensile tests revealed rate-dependent stiffness and stress softening effects, attributed to viscoplasticity and micro-cracking, respectively. Cutting data were collected for 5, 10 and 30 mm s(-1) sample feed rates, whereas the EWF tests were conducted at 1.7, 3.3 and 8.3 mm s(-1) crosshead speeds corresponding to average crack speeds of 4, 7 and 15 mm s(-1), respectively. A reasonable agreement was achieved between cutting and EWF, reporting 1.26, 1.78, 1.76 kJ m(-2) and 1.52, 1.37, 1.45 kJ m(-2) values, respectively, for the corresponding crack speeds. These toughness data were used in a novel numerical model simulating the 'first' bite mastication process. A viscoplastic material model is adopted for the food piece, combined with a damage law that enabled predicting fracture patterns in the product.

Effect of processing parameters on essential work of fracture toughness of LLDPE blown films

Blown film process is one of the most attractive processes for producing low-cost, high-performance polyolefin films. In this study, mode-I essential work of fracture (EWF) analysis and Elmendorf tear test were performed on m-LLDPE films to investigate how different processing conditions influence blown film EWF and tear properties. After the EWF test, the film was carefully characterized, especially within the necked zone. Effects of frost-line height, draw down ratio, blow-up ratio, and haze-zone region on the EWF parameters of the films were determined. Correlation between the EWF parameters and the films' Elmendorf tear properties was also made. The usefulness of the EWF test for investigating ductile polymeric blown films fracture performance is discussed. POLYM. COMPOS., 55:2403–2413, 2015. © 2015 Society of Plastics Engineers