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This study experimentally and numerically investigated the crack propagation behavior of porous polymer membranes in order to identify the criterion for crack propagation. A notch was introduced into the membrane as an initial crack (pre-crack), and a uniaxial loading was applied to produce stable crack propagation. During the test, crack propagation was observed using a CCD camera and the digital image correlation (DIC) method. The strain around the pre-crack tip at the onset of crack propagation was measured experimentally using the DIC method. We found that large-scale yielding developed before crack propagation. Stable crack propagation was observed for all tensile tests. In parallel, a homogeneous model that mimicked the porous polymer membrane was created using the finite element method (FEM) to investigate the stress/strain distribution around the crack tip. This study adopted the yield criterion proposed by Deshpande and Fleck. The computed strain distribution was compared with the experimental results, and the distributions were found to be similar. The strain distribution obtained by the DIC method and FEM computation yielded a J-integral value, which could be used to investigate the criterion for crack propagation. Regardless of the initial crack length, the J-integral value at the onset of crack propagation was a constant value for all tests. We concluded that we successfully determined the criterion for crack propagation in the porous polymer membrane. Our comprehensive study using DIC experiments and FEM computations is useful for identifying the crack propagation behavior of a porous polymer membrane and for determining the criterion for crack propagation.

Abstract The effects of initial crack length on the mode I fracture properties of crosslinked elastomers were investigated. A J -integral approach was implemented using single-specimen test procedures. Quasi-static fracture tests were carried out on filled and unfilled acrylonitrile-butadiene rubbers with various pre-cut (initial) crack lengths, a 0 , at a fixed rate of extension, using single edge notch rectangular bar specimens. Data from these experiments were analyzed and crack resistance curves (R curves) were obtained. A detailed analysis of the single-specimen method was carried out to establish correlation with the fracture properties derived from the more involved multi-specimen method. The weak dependence of geometry factor on rubber composition and displacement (in the neighborhood of crack initiation displacement) was verified. The crack initiation resistance and tearing modulus of the materials were calculated based on the R curve for each initial crack length. Fracture properties of lightly cracked specimens ( a 0 / W < 0.4 , where W is the specimen width), including crack initiation resistance, strain at crack initiation, tearing modulus and maximum load and extension before fracture, were found to show significant variations with a 0 . These variations are characterized and discussed for the filled and unfilled rubber materials. Highlights • Fracture analysis of unfilled and filled nitrile-butadiene rubbers was performed. • Geometry factor for SENT specimen was evaluated for different CTODs. • Geometry factor was almost material independent and only weakly dependent on CTOD. • Specimen elongation (strain) at crack initiation was found material independent. • Critical strain, J-integral and tearing resistance varied with initial crack length. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

To evaluate the performance of pyrolytic carbon black (pCB), we filled styrene-butadiene rubber (SBR) with pCB and N330 industrial carbon black (CB). We used two ratios of pCB and N330: 1/9 and 1/1. N330 was selected because its specific surface area was close to that of pCB. The overall CB content in the mixes was 0, 30, 45 and 60 part per hundred rubber (phr). We studied the effects of types and amounts of CB on the dispersion, cure behavior, dynamic mechanical thermal behavior, tensile mechanical and fracture mechanical properties of the filled rubbers. Dispersion of pCB was poorer than that of N330 CB. With respect to tensile mechanical properties – except tear strength – N330 outperformed pCB. The tear strength and fracture mechanics characteristics (J-integral at crack tip opening, and trouser tear strength) of SBR were higher with pCB than with N330. This can be attributed to the broader dispersion of pCB than N330. The combined use of N330 and pCB resulted in intermediate values, reflecting the actual N330/pCB ratio for all measured parameters. We wanted to correlate the mechanical performance with the apparent molecular weight between crosslinks (M c ), and found reasonable correlations for the Payne effect, tensile strength and critical J-integral. On the other hand, we only found a tendency for tear characteristics; this was ascribed to additional effects of (p)CB dispersion. [ABSTRACT FROM AUTHOR]

A method is presented to characterize the fracture resistance and interlayer adhesion of fused deposition modeling (FDM) 3D printed materials. Double cantilever beam (DCB) specimens of acrylonitrile butadiene styrene (ABS) were designed and printed with a precrack at the layers' interface. The DCBs were loaded in an opening mode and the load-displacement curves were synchronized with the optical visualization of the crack tip to detect the critical load at the crack initiation. A finite element model, coupled with J -integral method and fracture surface analysis was then developed to obtain the apparent fracture resistance ( J cr,a ) and the interlayer fracture resistance ( J cr,i ), as a measure of the interlayer adhesion. The maximum J cr,i was measured to be 4017 J/m 2 , a value close to the fracture resistance of bulk ABS. Both J cr,a and J cr,i increased with the printing temperature. This method can find a great importance in the structural applications of printed materials. [ABSTRACT FROM AUTHOR]

Microfibrillar composites (MFC) are polymer-polymer composites with many advantages, including good dispersion and bonding of in-situ generated fibrils. Recently, it has been shown that their performance can be enhanced by suitable addition of organophilized montmorillonite (oMMT) provided the numerous oMMT-induced effects are harmonized. This work deals with evaluation of resistance against unstable crack propagation (J-integral) in combination with Charpy and tensile impact strength methods, and SEM observation of fibrils shape and size and fracture surfaces. The results indicate that addition of PA6 inclusions and oMMT to relatively ductile HDPE reduces toughness evaluated using Charpy and J-integral. The fact that tensile impact strength is not reduced by oMMT indicates the importance of the impact testing mode for MFC. Of importance is the fact that formation of PA6 fibres reinforced with oMMT practically does not reduce toughness. Hence, the drawn oMMT-modified system with significantly higher stiffness and practically unchanged fracture resistance can be obtained. Combination of the complex effect of oMMT and in-situ fibrils reinforcement present a tool to attain polymer systems with enhanced well-balanced properties. [ABSTRACT FROM AUTHOR]

A unique set of double-edge notched tension specimens of a Polyethylene Terephthalate Glycol-modified film was tested in mode I, plane stress. The load was registered on a universal testing machine. The displacements, ligament lengths, and video frames were recorded by a Digital Image Correlation system. With these registered data, the essential work of fracture, J-integral, and crack tip opening displacement (CTOD) fracture concepts have been applied. The onset of crack initiation was through a complete yielded ligament. The analysis showed that the intrinsic specific work of fracture, w e , is the specific energy just up to crack initiation, which is an initiation value. w e has both a coincident value and the same conceptual meaning as J o , the J-integral at the onset of crack initiation. The relationship between J o and CTOD is also determined. The influence on the notch quality when the specimens were sharpened by two different procedures, femtosecond laser ablation and razor blade sliding, was analysed in detail. [ABSTRACT FROM AUTHOR]

Round robin tests carried out under the direction of the Technical Committee 4 of the European Structural Integrity Society (ESIS TC4) have shown that, for determining the fracture resistance of ductile polymers at low loading rates, the multi-specimen methodology based on the construction of the material crack growth resistance curve often does not provide reliable data due to the uncertainties associated with the measurement of crack advancement (Δa). With the aim of strengthening this multi-specimen methodology, the ESIS TC4 attention has been recently focused on the analysis of a testing scheme based on the load separation criterion, which does not require the measurement of Δa. The present work gives the results of a multi-laboratory round-robin testing exercise carried out by ESIS TC4 in order to assess the degree of reproducibility of the fracture parameters obtainable with the application of this load separation criterion based testing scheme. Encouraging results have been obtained. [ABSTRACT FROM AUTHOR]

J-integral theory and fatigue testing were adopted to investigate the fracture and fatigue properties of silica/carbon black (CB)/natural rubber composites with total filler content of 50 phr. Critical J-value JIC and tearing modulus TR, were obtained. JIC, as an indicator of crack initiation resistance, was dependent on the pre-cut length. TR was related to the crack propagation of the composite. With increasing the silica/CB ratio, both JIC and TR were enhanced, indicating that the resistance to crack initiation and propagation were improved. The strain energy density at a fixed strain decreased with an increase in the silica/CB ratio. Fatigue testing under constant tensile strain conditions demonstrated that the composite with higher silica/CB ratio exhibited lower cyclic crack growth rate and longer fatigue life. This was in accordance with the results of TR, JIC and strain energy density of the composite, hence TR, JIC and strain energy density of the composite can be used to predict its fatigue properties. [ABSTRACT FROM AUTHOR]

Abstract: The application of an experimental approach based on the load separation criterion for the determination of the point of fracture initiation in a fracture test on a ductile polymer was critically examined. To this aim, the fracture process outlined by the application of this method was related to that described by the visual analysis of the fracture surfaces obtained in fracture tests on nominally identical specimens, in which different levels of crack extension were produced. The material examined was an acrylonitrile-butadiene-styrene (ABS) resin, and the fracture tests were performed at low loading rate on single-edge notched in bending specimens. The results demonstrated that this load separation criterion based methodology is a promising approach for the determination of the point of fracture initiation, and for material fracture resistance, JIc, evaluation. The method also has experimental simplicity and a high degree of repeatability. [Copyright &y& Elsevier]

Abstract: The applicability of the essential work of fracture (EWF) in SENB geometry as an alternative to the J-integral methodology has been assessed. An amorphous poly(lactic acid) (PLA) with ductile behaviour promoted by a de-ageing heat treatment has been used. The results demonstrate that the EWF technique can be used as a simple alternative methodology to determine the J0.2 value in plane strain conditions, using the ESIS-2000 protocol and ASTME813-87 standard. As a validation of the range of ligament length to be used in the EWF analysis, the SENB solution of the Slip Line Field theory could be employed. [ABSTRACT FROM AUTHOR]

Abstract: The characterization of the fracture behaviour of polypropylenes following standard procedures is a complex task due to the difficulties encountered in the experimental measurement of the crack length. The load separation parameter S pb method is capable of determining J–R curves by testing a single pre-cracked specimen and a single blunt notched specimen. This work examines several aspects of the method, such as load separation property, its sensitivity to the initiation criterion, the influence of the blunt notched specimen used as reference and the calibration procedure. A polypropylene homopolymer and an ethylene–polypropylene block copolymer (REPSOL YPF) were analyzed. The results have shown that load separation property can be applied to both materials. Also, the initiation crack growth energy, J IC, is very sensitive to the point chosen as crack growth onset. For that reason, a criterion is proposed. Finally J–R curves are modified depending on the number of calibration points used. [Copyright &y& Elsevier]

Abstract: Polyamide 6/montmorillonite nanocomposite (NC) containing fine ethylene-co-methyl acrylate inclusions represents a system with significant toughness enhancement accompanied by only slight decrease in stiffness. Evaluation of NC behavior using a fracture mechanics concept (J-integral) has shown that the synergistic influence of fine rubber particles and clay affects fracture behavior at low clay content. [Copyright &y& Elsevier]

This study is focused on numerical investigation on fracture behaviors of carbon black (CB) and silica filled elastomeric composites. Finite element analysis (FEA) in compliance with multi-specimen method is used to calculate J-integral and geometry factor of the rubber composites up to a displacement of 20 mm for single edge notch in tension (SENT) and double edge notch in tension (DENT) specimens. An empirical relationship between crack tip opening displacement (CTOD) and crack advancement is established depending on notch to width ratio (NWR). The stress contours across the notches for SENT and DENT specimens is discussed briefly. It is found that fracture propagation resistance of CB filled elastomer is 125% more than that of silica filled elastomer. Although, Silica filled elastomer have good tensile strength and crosslink density but it fails to replace carbon black in terms of fracture properties. The critical J-integral for CB filled elastomer is 18.7% and 32.2% more than silica filled elastomer for SENT and DENT specimens respectively. The effect of specimen type on various fracture properties is also explored. The factor of safety is found to be significantly more in case of CB filled elastomers making them less vulnerable to crack propagation and catastrophic failure. Image 1 • Non-linear fracture analysis of SENT and DENT geometries is performed. • Factor of safety based mechanical characterization is performed. • Stress contours across notches is presented. • Reinforcing efficacy of CB filled hybrid elastomeric systems is discussed. • FEA is used to characterize fracture of elastomeric composites. [ABSTRACT FROM AUTHOR]

The Technical Committee 4, "Polymers, Polymer Composites and Adhesives", of the European Structural Integrity Society (ESIS TC4) developed a draft protocol based on the load separation criterion to determine two fracture parameters (an initiation parameter, J I,lim , and a crack growth parameter, m s) without the need to measure the crack growth (Δa). This is especially beneficial, since the measurement of Δa is prone to errors. The developed testing scheme displays promising results, as shown in a round-robin testing exercise. To further push this testing scheme, it is necessary to verify the specimen size scaling possibility. Hence, in this work, single edge notched in bending (SE(B)) specimens with different sizes, but geometrically similar, were manufactured. ESIS TC4 testing scheme was successfully applied to specimens with the different sizes, and data of J I,lim and m s were obtained. The observed effect of the specimen size on the aforementioned fracture parameters is presented and discussed. • parameter m s , produced in the plastic region, showed a size dependent behaviour. • J I,lim displayed high amounts of scattering and an increase with increasing specimen size. • Calculated values of J I,lim were confirmed via optical measurements of the plastic zone radius. • J-R curves were constructed following the ESIS TC4 multi-specimen approach. [ABSTRACT FROM AUTHOR]

This work provides a direct comparison of several experimental approaches used in the literature to measure fracture toughness of rubber of rubber using single edge notched in tension (SENT) specimens, with the final aim to provide guidelines for an optimal testing procedure. Digital image correlation measurements were used to get new insights into the fracture process. SENT is experimentally advantageous because of the simple preparation from laboratory plates and the small amount of material required. The most common experimental approaches to measure fracture toughness of rubber rely on the energy release rate, measured by the tearing energy or the J-integral parameters. This work points out the importance of experimental conditions and test procedures: long specimens and short notches are preferred, identification of fracture initiation from the front view is necessary, strain energy density should not be evaluated from un-notched specimens at the critical stretch level, rather alternative strategies are shown in this work. • A standard procedure for fracture toughness testing of rubber still does not exist. • A comparison among different experimental approaches is shown here. • A simple specimen geometry, single edge notched in tension, SENT, is tested. • Digital image correlation measurements were used to get reference values. • From this work, optimal testing conditions are identified. [ABSTRACT FROM AUTHOR]

Bonded repairs using composite patches over metallic structures have been evaluated as a cost effective method to increase the life of damaged structures. The J-integral is a widely applied fracture mechanics parameter relating to the energy release associated with crack growth and is a measure of the deformation intensity at the crack tip. In practice, the calculated J-integral can be compared with a critical value for the material under consideration to predict fracture. This study aimed at providing an overview of the behavior of a cracked plate of AA7075-T6 alloy repaired with a boron-epoxy patch bonded with FM73 Adhesive layer. The Finite Element Method (FEM) using Abaqus Software 6.14 predicted the performance. The results show a considerable decrease in the value of the J-integral. This is due to the beneficial effect of the patch on the stress state at the crack tip. The best results were obtained from a uni-directional composite fibres orientation of 0°, where the fibers oriented parallel to the direction of load. A parametric analysis has been carried out to evaluate the effect of lay-up, load variation and crack mouth opening on the J-integral. It was found that the crack mouth opening displacement (CMOD) was reduced by 90–97%. • This study provided an overview of the performance and behavior of a repaired plate. • AA7075-T6 alloy repaired with a boron-epoxy patch bonded with FM73 Adhesive layer. • The results in a considerable decrease in the value of the J-integral. • The best results obtained from composite with the fibers collinear with load. • The crack mouth opening displacement (CMOD) could be reduced by 90–97%. [ABSTRACT FROM AUTHOR]