Essential Work Of Fracture Method 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.

Effect of Tensile Pre-strain and Specimen Orientation on Tearing Resistance Parameters of DP 780 Steel Sheet Determined Using Essential Work of Fracture Method

Effect of Tensile Pre-strain and Specimen Orientation on Tearing Resistance Parameters of DP 780 Steel Sheet Determined Using Essential Work of Fracture Method

Fracture behavior, microstructure, and mechanical properties of PA6/NBR nanocomposites

AbstractPolyamide 6/Acrylonitrile butadiene rubber/Perlite nanocomposites with different percentages of NBR phase and perlite nanoparticle were prepared using the melt mixing process. The fracture behavior of PA6/NBR/Perlite nanocomposites was studied by the essential work of fracture method (EWF). Furthermore, response surface methodology (RSM) was employed to evaluate the effect of input variables, namely NBR and perlite content, on fracture behavior and Young's modulus of these nanocomposites. Scanning electron microscopy was used as a method for studying the morphology of the thermoplastic elastomer matrix containing different percentages of NBR elastomer and perlite nanoparticles. The results confirmed that, with controlling input variables, the optimum conditions of the system could be obtained, which leads to an improvement in fracture behavior and modulus strength of PA6/NBR/Perlite nanocomposites. RSM results illustrated that Young's modulus is increased from 2539 to 2862 MPa with an increase in perlite content from 3 to 7 wt%, when NBR content is 20 wt%. Moreover, Elongation at break is increased from 59.8% for 20 wt% NBR elastomer up to 102.8% for 40 wt%. The results of the EWF test illustrated that the samples with 30 and 10 wt%. NBR and 5 wt% perlite, have the maximum values of essential work of fracture (283.8 N/mm) and nonessential work of fracture (22.2 N/mm2), respectively.

From polymeric waste to potential industrial product: Modification of recycled polycarbonate

The aim of this study is to investigate the effects of simultaneous addition of chain extender and impact strength modifier on tribological, mechanical, thermomechanical and morphological properties of recycled polycarbonate (r-PC). Mechanical properties of the samples were evaluated by using essential work of fracture method and tensile tests. Tribological properties were investigated by means of adhesive wear test. Thermomechanical properties were investigated by using dynamic mechanical analysis. As a result of the study, different types of samples were obtained, which simultaneously contained chain extender and impact strength modifier and exhibit improved fracture toughness, adhesive wear performance, storage modulus and not deteriorated tensile strength compared to neat r-PC. Thus, in this study, a solution alternative for both the expanding of the usage area of r-PC and waste management of it has been presented.

Optimization of the essential work of fracture method for characterization of the fracture resistance of metallic sheets

The essential work of fracture (EWF) method is a powerful approach to characterize the fracture resistance of thin ductile sheets based on a principle of separation of energy contributions. A major drawback of the method is an extensive use of material, requiring a series of double-edge notched tensile (DENT) specimens with several ligament lengths to extract the EWF. This can be a serious limitation when the material is difficult to process and/or expensive. Here, we propose an improved methodology to reduce the amount of material as much as possible while keeping the same statistical level of accuracy for the estimated EWF. We show that the width and height of the DENT specimens can be adapted as a function of the ligament length. A statistical model has been developed to determine the distribution of ligament lengths minimizing the total amount of material. This new approach is validated both numerically with Monte Carlo simulations and experimentally. In the experiments, the strain fields in the ligament were quantified by digital image correlation to ensure that the validity criteria were met for each specimen, as well as to provide an in-depth analysis of the plastic zone development. From these results, guidelines are provided to optimally rationalize EWF experimental data.

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 test to accelerate the prediction of polymer embrittlement during aging – Case of PET hydrolysis

Depending on the nature of a given polymer and the environment, the rate of degradation can vary significantly, from a few hours up to tens of decades. In the polymer aging community, it is therefore a true challenge to obtain an understanding of the loss in properties of a given polymer within a reasonable time frame. The present work presents a novel approach to decrease that time. Within this study the decrease in mechanical properties of the polyethylene terephthalate under hydrolysis process has been followed via the Essential Work of Fracture method (EWF-m) and compared to the more classical tensile test. The degradation has been accelerated by increasing temperature, (from 60 °C up to 110 °C). Results show a rapid decrease in the non-essential work of fracture compared to the maximal stress at break obtained by tensile test. It appears that fracture properties can be used for both time/temperature superposition as well as the determination of the critical molar mass. Moreover, as fracture properties are very sensitive to degradation, it appears that it is possible to decrease aging time/temperature using EWF.

Comments on “Essential work of fracture analysis for surface modified carbon fiber/polypropylene composites with different interfacial adhesion” [Polymer Composites 41 (9) (2020): 3541–3551

AbstractIn this paper, some comments on the study “Essential work of fracture analysis for surface modified carbon fiber/polypropylene composites with different interfacial adhesion” Polymer Composites 41 (9) (2020): 3541–3551, have been discussed. The comments are mostly concentrated on the technique utilized for the assessment of the parameters of fracture toughness. The essential work of fracture (EWF) approach was employed for all the samples to characterize the fracture manner, while it appears that some of the samples did not meet the prerequisites of the EWF method. These prerequisites are as follows: the ligament length must be completely yielded before the onset of crack propagation, self‐similarity between load–displacement curves is a requirement, and fracture must occur under plane stress conditions. Therefore, the information, data, and results obtained by the authors are questionable.

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.

Investigation on fracture toughness of polytetrafluoroethylene with impact essential work of fracture method

Polytetrafluoroethylene (PTFE) polymer has a wide range of applications in various industries. Therefore, for designers it is essential to know the strength properties of the material under dynamic loads. In this study, pure-PTFE, bronze and carbon filled-PTFE are tested under dynamic load. In addition, pure and carbon filled specimens were used to determine the temperature effect of PTFE. All tests were carried out in the Charpy impact device according to impact essential work of fracture method. At 23°C, pure-PTFE showed the highest impact strengths, bronze filled-PTFE and carbon filled-PTFE showed lower respectively and it has been found that the carbon filler increases the fracture toughness approximately two times at high temperature (150°C). On fracture surfaces phase transitions effects of PTFE and behavior of fillers used were investigated with Scanning Electron Microscope.

Outstanding cracking resistance of fibrous dual phase steels

Dual phase (DP) steels are widely used for their excellent combination of strength-ductility-cost performance. However, several forming and/or structural applications are affected by cracking resistance issues. We show here that DP steels with a ‘Thomas-fibers’ type platelet martensite morphology exhibit significantly larger cracking resistance compared to corresponding equiaxed microstructures. The superior cracking resistance is demonstrated both for thin and thick specimens processed with different martensite volume fractions and thicknesses. The cracking of thin sheets involves complex intermingling of work spent for crack tip necking and for material fracture as quantified using the essential work of fracture method, complemented with fractography and microstructure characterization. The better cracking resistance is shown to originate from a remarkable resistance to damage nucleation related to the alignment of the platelets upon deformation and from their small size. This finding offers a new path to optimize the fracture toughness of DP steels without compromising the strength and/or changing the chemical composition.

Uticaj orijentacije vlakana na žilavost loma kod Z/HDPE kompozita ojačanih svilenim vlaknima

The aim of this work is to investigate the fracture toughness and deformation of silk fiber (SF)-reinforced zeolite (Z)/high density polyathylene (HDPE) composites. The chopped SFs are arranged in the thickness middle of the dry mixture of Z/HDPE powder that has been prepared in a mold. Composites were produced by the compression molding to produce double-edge notch tensile (DENT). The fracture toughness characterization was carried out based on essential work of fracture method. The results show that the presence of SF increased the essential fracture work even though the non-essential fracture work for Z/HDPE was higher than S-Z/HDPE. The evolution of plastic zone growth coincides with the growth of the fracture process zone (FPZ) whose height has no effect on energy consumption.

Characterisation of fusion bonding between filaments of thin 3D printed polyamide 6 using an essential work of fracture method

The extent and quality, i.e. consistency, of the fusion bonding between filaments that occurs during the fused filament fabrication (FFF) process play an important role in determining the mechanical performance of 3D printed polymeric parts. This present research is designed to quantify these parameters of the fusion bonding between individual filaments deposited during the 3D printing process. Polyamide 6 (PA6) specimens were prepared from both 3D printed single-layer and single-filament films. Also, to provide a benchmark material, 3D printed PA6 films prepared by the FFF process were further processed by using compression moulding (CM) to investigate whether the fusion bonding could be enhanced. An essential work of fracture method was employed to evaluate the fusion bonding between the filaments by determining the value of the specific essential work of fracture, we, and the associated experimental reproducibility. The higher value of we, and the relatively low degree of scatter determined for the benchmark material revealed that the extent and quality of fusion bonding attained when using only the FFF process clearly needed to be improved when parts are fabricated for practical applications. To study the effect of temperature on the fusion bonding, the structural detail and fracture surfaces of thin polymer films were studied, with the thermal history of the deposited filaments also being measured using a thermal camera.

Morphologies, interfacial interaction and mechanical performance of super-tough nanostructured PK/PA6 blends

Nanostructured polyketone (PK)/polyamide 6 (PA6) blends can be readily prepared via melt blending technologies and exhibit ultra-high toughness when PA6 is present as the nanoscale phase domains. When PA6 content is 30 vol%, the impact strength of the blends increases from 21.4 kJ/m2 of pure PK to 103.2 kJ/m2. The impact strength of the PK/PA6 blends with a 5:5 composition ratio reaches as high as 113 kJ/m2. The strong intermolecular force between PK and PA6 molecular chains enables the PA6 nanophase to cavitate to dissipate a significant amount of impact energy and effectively prevents the crack propagation or even terminates the cracks. The fracture mechanism of the PK/PA6 blends was further examined by the essential work of fracture method which proves that PK/PA6 blends show improved ability to prevent crack propagation. This work may deepen the understanding of polymer blend systems with strong hydrogen bonding interaction.

Fracture Toughness Analysis of Automotive-Grade Dual-Phase Steel Using Essential Work of Fracture (EWF) Method

Fracture toughness determination of dual-phase DP450 steel using the essential work of fracture (EWF) methodology is the major focus of this research work. The EWF method is used for the determination of fracture toughness of thin sheets in a plane stress dominant condition. The EWF method is discussed in detail with the help of DP450 steel experimental results. Double edge notched tension (DENT) specimens with fatigue pre-crack and without fatigue crack (notched) have been used for testing. Specific essential work of fracture (we), crack tip opening displacement (δce) and crack tip opening angle (ψe) parameters were used for the comparative analysis. High-intensity laser beam cutting technology was used for the preparation of notches. Fracture toughness values of fatigue pre-cracked and notched samples were compared. The effect of notch tip radius and fatigue crack on the fracture toughness values were analysed. Digital image correlation (DIC) technology was used for the identification of local strain distribution and validation of the methodology. Fractured surfaces were examined by a scanning electron microscope (SEM) to analyse the fracture morphology and stress state.

Essential work of fracture analysis for surface modified carbon fiber/polypropylene composites with different interfacial adhesion

AbstractThe fracture behavior of polypropylene/carbon fiber composites with different interfacial adhesion was evaluated using the essential work of fracture method. All samples exhibited ductile fracture characteristics, while the specific essential fracture work, we, was obviously decreased by carbon fiber incorporation, indicating the impaired ductility and toughness for polypropylene. The cracks were easily formed and expanded at the fiber‐matrix interface under external force for polypropylene/original carbon fiber composites, since the weak interfacial adhesion between the fiber and matrix could not prevent the generation of new crack. Introduction of compatibilizer as well as surface modification of fibers effectively improved the interfacial adhesion between the fiber and matrix, so that the value of we increased and the elastic deformation of the composites became more prominent. Therefore, the improvement of interfacial adhesion between the fiber and matrix influenced both elastic and plastic deformation of the composites.

Investigation of damage mechanisms of polyethylene film during stable crack growth

In this research the fracture behavior of medium density polyethylene (MDPE) films has been evaluated using the essential work of fracture method. Also damage mechanisms of MDPE have been investigated by scanning electron microscopy and transmission optical microscopy. The results show that the EWF approach could provide a reliable toughness assessment for MDPE. Some birefringence was observed when the crack tip deformation zone was examined under cross-polarized light indicating that extensive shear yielding has occurred in front of the crack tip. It is found that shear yielding is the most effective energy absorbing mechanism in MDPE films. Microscopic evaluations also demonstrated the formation of shear bands and craze-like deformation bands in the crack tip damage zone.

Bio-inspired design for enhanced damage tolerance of self-reinforced polypropylene/carbon fibre polypropylene hybrid composites

In this work, we investigate the toughness of an inter-layer Self-Reinforced Polypropylene/Carbon Fibre Polypropylene (SRPP/CFPP) cross-ply hybrid composite and devise strategies to improve two aspects of its damage tolerance: (i) increasing the energy dissipation capability and (ii) enhancing the impact damage tolerance. To this end, we introduced discontinuities in the form of laser-cuts across the fibres of the CFPP plies, tailoring two patterns of laser-cuts to meet each specific damage tolerance requirement. We conducted penetration impact and Double Edge Notched Tensile (DEN-T) tests. The DEN-T tests, analysed via the Essential Work of Fracture method, show that engineering the microstructure successfully diffused damage. This resulted in a great increase in energy dissipation capability — 90% higher than a reference non-engineered structure. Engineering the microstructure of impact samples has led to enhanced impact damage tolerance with increased energy dissipation at a sub-critical level and delayed critical failure.

Numerical modeling of essential work of fracture on ductile polymeric films

Essential work of fracture method has been successfully used to characterize the fracture behavior of ductile polymeric films. The observed essential and non-essential fracture process zones are related to the toughness of the films. Three-dimensional finite element method (FEM) modeling has been carried out in this study to elucidate the film fracture process based on the essential work of fracture concept. Experimental observation on a model linear low-density polyethylene (LLDPE) blown film was used to validate the FEM model. The numerical model facilitates an in-depth understanding of the development of stress and strain fields and the fracture process zones at different loading steps. The FEM findings show that film thickness and ligament length have significant influence on the development of stress and strain fields at and around the ligament area. Furthermore, the numerical analysis reveals how various material properties, such as yield stress and strain hardening slope, can influence the development of fracture process zones. Usefulness of FEM modeling for developing tough polymeric films is discussed.

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.