Double Edge Notch Research Articles

RETRACTED ARTICLE: Influence of crumb rubber particle sizes on rutting, low temperature cracking, fracture, and bond strength properties of asphalt binder

The present study aimed at evaluating the effect of Crumb Rubber (CR) particle size on rutting, low temperature cracking, fracture, and bond strength properties of asphalt binder. Three different CR particle sizes (#10–20, #30–40, and #60–80) were considered in this research work. Rutting performance was evaluated using Multiple Stress Creep Recovery (MSCR) tests. Although the addition of CR was found to improve the rutting performance, asphalt binder combination with higher CR particle size exhibited better performance compared to asphalt binder combination with lower CR particle size. Similarly, low temperature cracking properties were evaluated using Bending Beam Rheometer (BBR). It was found that the addition of CR has positive impact on the low-temperature performance of asphalt binder. Fracture property was evaluated using Double Edge Notch Tension (DENT) test and found to be improving with the increase in CR particle size. Finally, the effect of CR particle size on moisture damage resistivity potential was evaluated using the recently developed Bitumen bond strength (BBS) test. Although the addition of CR was found to have deteriorating impact on bond strength behavior, the degree of impact was found to be lower for asphalt binder containing the lowest considered CR particle size.

Photoelastic evaluation of stress fields and coefficients of multi-parameter asymptotic expansion of the crack-tip stress field

In this work, digital photoelasticity method is appliedfor estimation of the crack tip fracture mechanics parameters for a plate with double edge notches and different crack configurations.The digital image processing tool for experimental data obtained from the photoelasticity experiments is developedand utilized. The digital image processing tool is based on the Ramesh approach but allows us to scan the image in any direction and to analyse the image after any number of logical operations. In the digital image processing fringe analysis, the optical data contained in the transmission photoelasticisochromatics were converted into text file and then the points of isochromatic fringes with minimum light intensity were used for evaluating fracture mechanics parameters. The multi-parameter stress field approximation is used. The mixed mode fracture parameters, especially stress intensity factors (SIF) are estimated for specimen configurations like double edge notches and inclined center crack using the proposed algorithm based on the classical over-deterministic method. The effects of higher-order terms in the Williams expansion were analysed for different cracked specimens. It is shown that the higher order terms are needed for accurate characterization of the stress field in the vicinity of the crack tip. The experimental SIF values estimated using the proposed method are compared with analytical/finite element analysis (FEA) results, and are found to be in good agreement.

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.

A finite element method based comparative fracture assessment of carbon black and silica filled elastomers: Reinforcing efficacy of carbonaceous fillers in flexible composites

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.

Compressive intralaminar fracture toughness and residual strength of 2D woven carbon fibre reinforced composites: New developments on using the size effect method

This paper presents new developments in the use of the size effect method for obtaining the compressive fracture toughness of 2D woven carbon fibre composites. A modification of the Double Edge Notch Compression (DENC) specimen geometry is proposed, to fit the Combined Loading Compression (CLC) standard fixture, and shown to reduce peak load dispersion. The notch tip diameter sensitivity on the peak load is also investigated, experimentally and numerically, and shown not to have a significant influence on fracture toughness. The use of the CLC fixture also allows for the residual compressive strength of the material to be calculated from post-peak crushing.

Is there a ply thickness effect on the mode I intralaminar fracture toughness of composite laminates?

The apparent crack resistance curves associated with longitudinal tensile failure of carbon fibre reinforced epoxy composite systems with ply thicknesses of 0.075 mm, 0.134 mm and 0.268 mm are determined experimentally from the size effect law of geometrically similar double edge notch tension cross-ply specimens. An increase in notched strength as a function of the ply thickness and a corresponding increase of the measured intralaminar fracture toughness is observed. This increase is shown to be a consequence of the appearance of split cracks in the thicker 0° plies in the vicinity of the notches. The numerical models developed demonstrate that if the notch blunting mechanisms are properly represented, the laminate strength is well predicted for a constant value of the ply intralaminar fracture toughness. This supports the hypothesis that these mechanisms are responsible for the higher strength of the thicker plies, and that the intralaminar fracture toughness of the 0° plies should not be scaled with the ply thickness.

Crack tip opening angle (CTOA) and δ5 measurements on SENT and DENT specimens of a thin interstitial-free steel sheet

The present study addresses characterizing ductile tearing resistance of a 1 mm thick sheet of an interstitial free steel sheet using crack tip opening angle (φ), and δ5 concepts. The transferability of the φ- crack growth (Δa) data between two geometry, namely single edge notch tensile (SENT) and double edge notch tensile (DENT), was verified. For a specified thickness the δ5-Δa data can also be used as a material parameter. Cohesive zone modeling (CZM) successfully reproduced the experimentally determined φ-Δa and δ5-Δa plots for pre-cracked specimens, and confirmed transferability of the CZM parameters between the two geometries.

Experimental creep behavior and life prediction through observation and numerical analysis for AISI 310

The present study conducted for the first time a life prediction based on numerical analysis of creep deformation and fracture behavior results of special notched specimens of AISI 310 steel. For this purpose, flat creep specimens with double edge notch were tested under stress is of 225, 160 and 100 MPa at temperatures of 700, 675 and 650 °C. Then it was analyzed the creep behavior of the material through observational and numerical analysis. Furthermore, the Q* parameter was used to establish a novel life predication equation for 310 steel. The creep curves were characteristic of the experiment, with a strong influence of the stress in the creep stage II. Using the Q* parameter, a good agreement was observed between the experimental and the calculated data. The characteristic of fracture surfaces was dependent on both stress and temperature with a transition from ductile fracture, with formation of dimples, to brittle intergranular fractures, evidenced by cavities in the grain boundaries. Coalescence and growth of microcracks on the specimen surface were also observed in a region at 45° from the notch tip, characteristic of the damage propagation caused by the creep test.

Effect of material orthotropy on the notch stress intensity factors of sharp V-notched plates under tension

In this paper, an analytical and numerical study is carried out on the role played by the elastic properties of orthotropic materials on the Notch Stress Intensity Factors (NSIFs) of pointed V-notches on plates under tension.In the first part of the work, new analytical solutions are presented to approximate the NSIFs of shallow and deep symmetric notches in Double Edge Notched plates under Tension (DENT).Subsequently, a comprehensive numerical study is carried out on finite size notches considering different orthotropic materials, with the aim to make explicit the effect of material orthotropy on the NSIFs. Eventually, based on a best fitting procedure of the numerical results, accurate expressions for the NSIFs are provided, and their degree of accuracy is discussed against data from the literature and results from ad hoc numerical analyses.

Effect of recycled asphalt binder on high and intermediate temperature performance of polymer modified asphalt binder

The present study aimed at investigating the effect of Recycled Asphalt Pavement (RAP) binder on high and intermediate temperature performance of Polymer Modified Binders (PMB) through advance laboratory characterization techniques. Different RAP binder proportions (0%, 15%, 25% and 40% by the weight of PMB) were initially blended with PMB. Different characterization techniques such as Superpave rutting parameter (G*/Sinδ), Shenoy parameter, Multiple Stress Creep Recovery (MSCR) and Zero Shear Viscosity (ZSV) tests were used for evaluating high temperature performance. Based on the different rheological parameters, improvement in rutting performance was observed with the addition of RAP binder. Likewise, intermediate temperature performance was evaluated using Linear Amplitude Sweep (LAS), Double Edge Notch Tension (DENT) and Elastic Recovery (ER) test. The improvement in high temperature performance and degradation in intermediate temperature performance shows that care must be taken while selecting the appropriate amount of RAP based on prevalent failure type in the field.

Notch effect on strength and fatigue life of woven composite laminates

This paper presents an experimental and numerical study of the notch effect on strength and fatigue life of double edge notched (DEN) composite laminates made of woven glass fibre lamina 3238A/EW250F and woven carbon fibre lamina 3238A/CF3052. Experimental results show that the notch effect is dependent on fibre type, notch depth, load type and load sequence. A s-n-R-d-r residual strength model was proposed to account for the effects of the notch and the stress ratio, and a progressive damage algorithm was developed to predict damage propagation and residual life of composites under spectrum fatigue load. Good agreement between the experimental results and the numerical predictions has been achieved.

Fatigue endurance design of plates with two semicircular edge notches and one quarter-elliptical corner crack or through-the-thickness crack

This paper presents an investigation on the failure of plates with double-edge notches and fatigue damage. The main aim is to develop a computational model for estimating the behaviour of a quarter-elliptical corner crack or a through-the-thickness crack located at semicircular edge notch. In such an analytical/numerical analysis, driving forces are evaluated by means of an analytical model and the finite element method, whereas the fatigue life is assessed employing a stress ratio-dependent crack growth law and the stress intensity factor.

Mode I intralaminar fracture toughness of 2D woven carbon fibre reinforced composites: A comparison of stable and unstable crack propagation techniques

This paper presents an experimental and numerical comparison of stable and unstable crack propagation techniques used to measure the mode I intralaminar fracture toughness of 2D woven carbon fibre composites. Compact Tension (CT) and Double Edge Notch Tension (DENT) specimens are used for the stable and unstable experimental tests, respectively. The precrack tip radius sensitivity of the scaled DENT specimens is investigated, concluding that the tested tip radii do not substantially affect the measured fracture toughness. The fracture toughness data obtained from the DENT and CT specimens are found to be in good agreement for both tested materials.

Prediction models of creep crack initiation for different specimen geometry

In this article, the prediction models of the creep crack initiation for the specimen geometry was quantified by six different types of cracked specimens [including C-ring in tension CS(T), compact tension C(T), single notch tension SEN(T), single notch bend SEN(B), middle tension M(T), and double edge notch bend tension DEN(T)]. Load-independence constraint parameter Q* was introduced to quantify the in-plane constraint. The specimen order of Q* and the creep damage accumulation rate of the different specimen geometries from high to low was C(T), CS(T), SEN(B), SEN(T), DEN(T), and M(T), which generally represented the distinctions of in-plane constraint level in these specimens. For a specific load level, C(T) and CS(T) specimens showed the highest crack damage accumulation rate or the shortest creep crack initiation time, whereas the lowest rates or the longest CCI time existed in M(T). Moreover, the relationship between the CCI times and specimen thickness and crack depths was obtained, and a series of empirical equations were fitted. Finally, the power law relation between the CCI times and constraint parameter Q* was extrapolated.

Evaluation of intermediate temperature cracking performance of warm mix additive modified asphalt binders

In the present study, intermediate temperature cracking performance of different types of asphalt binders containing warm mix asphalt (WMA) additives was evaluated using three test methods namely, Superpave fatigue parameter, linear amplitude sweep (LAS) and double edge notch test (DENT). The Superpave fatigue, LAS, and DENT tests are based on dissipated energy, viscoelastic continuum damage (VECD) and work of fracture approaches, respectively, and thus each of the tests may result into different performance ranking of asphalt binders. The outcome of the Superpave fatigue, LAS and DENT tests are G∗sinδ, number of cycles to fatigue failure (Nf), and critical tip opening displacement (CTOD) based on which cracking potential of asphalt binder can be assessed. An asphalt binder having a low Superpave parameter, high Nf and high CTOD values are expected to have better intermediate temperatures cracking performance. The present study selected three control binders namely virgin (AC), styrene-butadienestyrene (SBS) and crumb rubber modified (CRM) binders were modified using three WMA additives namely Fischer-tropsch (FT) wax based, chemical surfactant (CS) based and water based (WB). Control binders were modified with 2%, 6% and 2% (by weight of asphalt binder) of FT, WB and CS, respectively, using a mixer. The results showed that, based on G∗sinδ and CTOD parameters, CS modification reduced stiffness (reduced G∗sinδ) and improved ductile performance (increased CTOD) of control binders. However, WB and FT modification increased stiffness and degraded the ductile performance of control binders, except for SBS with 6%WB binder which showed higher CTOD than control SBS binder. On the other hand, considering performance based on Nf parameter, WMA additive modification improved fatigue life of control binders, except for SBS with 2%CS binder which showed lower Nf as compared to control SBS binder. Control binders with and without WMA additives were ranked based on G∗sinδ, Nf and CTOD parameters. AC and CRM binder with and without WMA additives followed similar performance ranking based on G∗sinδ and CTOD parameters. It is difficult to conclude over the best suitability of intermediate temperature performance parameter as mentioned tests involve different loading conditions and analysis approaches. Hence, further investigation on asphalt mixes is necessary to identify the best suited intermediate temperature performance parameter of asphalt binders, and its possible correlation with mix performance.

Advanced carbon fiber composite out-of-autoclave laminate manufacture via nanostructured out-of-oven conductive curing

Next-generation composite manufacturing processes are needed to overcome several limitations of conventional manufacturing processes (e.g., high energy consumption). Here we explore, via experiments and modeling, the characteristics of the newly developed out-of-oven (OoO) curing technique that cures a composite laminate via resistive heating of a carbon nanotube film. When compared to oven curing of an aerospace-grade out-of-autoclave (OoA) carbon fiber prepreg advanced composite laminate, the OoO curing reduces energy consumption by over two orders of magnitude (14 vs. 0.1 MJ). Thermophysical and mechanical tests including differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), short beam shear (SBS), and ex-situ and in-situ double-edge notch tension (DENT) indicate that the physical and mechanical properties of OoO-cured laminates are equivalent to those of oven-cured (baseline) laminates. In addition to energy savings, the OoO curing process has the potential to reduce part-to-part variations through improved spatiotemporal temperature control.

Influence of fibres on rheological properties and toughness of bituminous binder

Many studies have been made to examine different ways to modify bitumen and asphalt mixtures in response to increasing performance requirements. One of these is the use of additive materials and in this study, the potential of cellulose and glass fibres to modify the rheological properties of bitumen has been investigated. To achieve this, mixtures of bitumen with different contents of fibre were prepared and the properties of the bitumen and resulting modified binders were tested (penetration, softening point, viscosity and double edge notch tension test along with rheological testing in the dynamic shear rheometer). The experimental results demonstrated that adding fibres improves the rheological properties of bitumen across a range of loading frequencies and temperatures. Adding fibre reduced the penetration and increased the softening point and viscosity of bitumen implying improved rutting resistance of asphalt mixtures using these mastics. Finally this investigation established that adding fibre to bitumen improved its toughness, which could lead to improvement in asphalt fatigue performance. However, there are some limitations that are also discussed.

Toward Utilization of ground tire rubber and reclaimed pavement materials with asphalt Binder: Performance evaluation using essential work of fracture

Utilization of ground tire rubber (GTR) binder in combination with reclaimed asphalt pavements (RAP) binder can provide added benefits in terms of material, cost and environmental saving, and hence a promising step toward sustainable construction of pavements. The present study utilized essential work of fracture (EWF) principal to evaluate performance of a GTR binder blended with two different types of RAPs: RAP-A and RAP-S, having different rheological properties. The GTR binder was mixed with different percentages (0%, 15%, 25% and 40% by weight of virgin binder) of RAP-A and RAP-S. First, Superpave performance grade (PG) of different combinations of asphalt binders was determined in the laboratory. Thereafter, the EWF of binders was determined using a newly developed double edge notch tension (DENT) test. Further, the data obtained from the DENT test were used to estimate critical crack tip opening displacement (CTOD). The results showed that addition of RAP decreased fracture resistance of GTR binder. Addition of RAP-A resulted in a faster decrease in performance of GTR binder compared to RAP-S. It can be concluded that low percentage of RAP may be utilized with GTR binder. Further, analyses indicated that RAP sources and its quantity could have significant impact on performance of asphalt mixes.

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%.

Strain rate effects on the intralaminar fracture toughness of composite laminates subjected to compressive load

This paper presents an experimental and numerical study focused on the mode-I intralaminar toughness characterization of a woven carbon/epoxy composite loaded in compression and subjected to high strain rates. Simulations for non-standardized Single Edge Notch Bending (SENB) and Double Edge Notch (DEN) specimens were carried out using a continuum damage mechanics based failure model implemented as an user defined material model within ABAQUS software. A Finite Element Model was used in order to produce an optimal specimen for intralaminar fracture toughness tests. A new data reduction scheme based on the numerical evaluation of the strain energy release rate using the J-integral method is proposed to determine the stress intensity factor for composites. The proposed methodology accounts for finite geometry and material anisotropy effects. The dynamic tests were carried out at strain rates of 560s-1,690s-1,770s-1 using an adapted version of the Split Hopkinson Pressure Bar. A high-speed camera was used for monitoring the crack propagation. A Scanning Electron Microscope (SEM) was used to aid the fractographic analyses on the damaged surface of the tested samples searching for the possible failures mechanisms within the material. The experimental results indicated that the composite laminates studied herein are very sensitive to the strain rate effects.