Evaluation of the Effect of Raster Angle on the Fracture Properties of 3D Printed Polycarbonate Using the Essential Work of Fracture Method

Characterisation of injected EPBC plaques using the essential work of fracture (EWF) method

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

The potential of a fracture mechanics approach (Essential Work of Fracture or EWF method) to determine the toughness of PE/PEgMAH/PA multilayer films has been investigated. The films had been modified either by blending EVA in the PE and PEgMAH layers or by inserting clay nanoparticles in the PA layer. The method was first calibrated on PE and PA single layer films. An analysis of the sensitivity of the toughness, assessed by the EWF method, to both sample geometry and test conditions has been carried out, so as to optimise the testing procedure for these materials. Then these optimal test conditions have been used to characterise PE- and PA-based multilayer films. The results show that the Essential Work of Fracture method is relevant for this type of structure, and may be more sensitive to the film composition variations than standard tensile mechanical tests, especially when the composition modification affects the layer of lowest rigidity and tensile strength.

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

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.

The present work investigates the relationships between the microstructural state and fracture properties in commercial polypropylene‐based materials. In this case an isopolypropylene homopolymer and three ethylene propylene block copolymers (EPBC) with different ethylene content (EC) have been studied. A variety of morphologies were obtained by a combination of several processing methods (injection molding, injection molding‐annealing, and compression molding) and thickness. Fracture behavior of deeply double‐edged notched specimens was evaluated by scanning electron microscopy (SEM) and by the essential work of fracture (EWF) method, analyzing the influence of processing, thickness (t), EC, and orientation respect to melt flow direction (MD and TD). The testing direction and EC are the most relevant variables that affect the ability of the crack tip to deform plastically during the crack propagation, determining the final fracture behavior. The fracture parameters obtained with the EWF method, specific EWF, we, and plastic item, βwp, have proved to be very sensitive to the processing induced morphology, finding interesting relationships between such morphologies (characterized by crystallinity index, orientation level, and skin/core ratio) and the fracture parameters of the plaques. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 2714–2724, 2006

Effect of POSS and chain extender on tensile and fracture properties of neat and short glass fiber reinforced polyamide 6 composites

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

Ethylene–(vinyl alcohol) (EVOH)/organo‐modified montmorillonite clay (OMMT) composites were prepared using commercial OMMTs with two different organo‐modifiers. The first one has polar groups, which interact with EVOH chains, whereas the second one is non‐polar. Composites with a high weight percentage of OMMT were prepared by melt‐extrusion in a twin‐screw extruder. Films were prepared in a cast‐film line in order to evaluate the tensile and fracture parameters. The morphology of the EVOH/OMMT composites was characterized using wide‐angle X‐ray scattering and transmission electron microscopy, complemented by image analysis. The mechanical properties were evaluated using uniaxial tensile tests; the fracture behaviour was analysed using the essential work of fracture (EWF) method. Results show differences in composite morphologies and crystalline fraction, depending on the content and the nature of the organo‐modifier. The mechanical and fracture behaviours are strongly influenced by those parameters, which act in opposite senses. The EWF method is shown to be a useful tool for the analysis of the structure–properties relationships of these composites. Copyright © 2010 Society of Chemical Industry

The essential work of fracture (EWF) method is widely used in the experimental characterization of fracture toughness of thin polymer films. However, the underlying physics of this method and the EWF parameters are not completely understood. In the present work, we investigated the correlations between the EWF parameters and the molecular structures of amorphous and ductile polymers. Based on our experimental observations, a physical model describing the EWF method on the molecular level was built. With this model, the variations of the EWF parameters with extrinsic and intrinsic factors under a plane stress condition were explained successfully; the theoretical values estimated with some assumptions and approximations of the EWF parameters agree satisfactorily with the experimental ones. This is the first theoretical model in the development history of the EWF method, which gives reliable physical meanings of the EWF parameters. The precise description of the molecular structure and fracture toughness relationships given by this model can also provide guidelines to molecular design of new polymers with high toughness.

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.

High-density polyethylene resins have increasingly been used in the production of pipes for water- and gas-pressurized distribution systems and are expected to remain in service for several years, but they eventually fail prematurely by creep fracture. Usual standard methods used to rank resins in terms of their resistance to fracture are expensive and non-practical for quality control purposes, justifying the search for alternative methods. Essential work of fracture (EWF) method provides a relatively simple procedure to characterize the fracture behavior of ductile polymers, such as polyethylene resins. In the present work, six resins were analyzed using the EWF methodology. The results show that the plastic work dissipation factor, βwp, is the most reliable parameter to evaluate the performance. Attention must be given to specimen preparation that might result in excessive dispersion in the results, especially for the essential work of fracture we.

The addition of the low-cost mineral filler kaolin to high-density polyethylene (HDPE) creates a composite with both improved stiffness and toughness properties. This study focuses on two aspects of the toughness of these composites: the fracture toughness increment produced by work at the fracture surface and the directionality induced by the injection molding fabrication process. The Essential Work of Fracture (EWF) method gives results which show that a higher volume fraction of kaolin produces more surface work, consistent with earlier work using Compact Tension (CT) tests. The EWF method also demonstrates that a lower volume fraction can produce a higher overall plastic work and apparent toughness. A heat treatment which removes the orientation of the matrix but not that of the particles was applied to study the effect of matrix crystallinity. The results indicate that the matrix supramolecular structure (crystallinity and skin-core effect) is responsible for the directionality of toughness, and that a heat treatment can be used to produce high toughness behavior in both major directions.

The addition of the low-cost mineral filler kaolin to high-density polyethylene (HDPE) creates a composite with both improved stiffness and toughness properties. This study focuses on two aspects of the toughness of these composites: the fracture toughness increment produced by work at the fracture surface and the directionality induced by the injection molding fabrication process. The Essential Work of Fracture (EWF) method gives results which show that a higher volume fraction of kaolin produces more surface work, consistent with earlier work using Compact Tension (CT) tests. The EWF method also demonstrates that a lower volume fraction can produce a higher overall plastic work and apparent toughness. A heat treatment that removes the orientation of the matrix but not that of the particles was applied to study the effect of matrix crystallinity. The results indicate that the matrix supramolecular structure (crystallinity and skin-core effect) is responsible for the directionality of toughness, and that a heat treatment can be used to produce high toughness behavior in both major directions.

Effect of water content on the fracture behaviour of hydroxypropyl cellulose films studied by the essential work of fracture method