Single Edge Notch Bend Research Articles

Notch Effect in Acrylonitrile Styrene Acrylate (ASA) Single-Edge-Notch Bending Specimens Manufactured by Fused Filament Fabrication.

This paper analyses the notch effect in the fracture behaviour of acrylonitrile-styrene-acrylate (ASA) material manufactured by fused filament fabrication (FFF). The research is performed on 72 single-edge-notch bending (SENB) specimens containing U-notches with nominal notch radii varying from 0 mm (crack-like defects) up to 2.0 mm, and fabricated with three different raster orientations (0/90, 45/-45, 30/-60). Apparent fracture toughness values are obtained for the different conditions and the resulting notch effect is analysed through the Theory of Critical Distances. A fractographic analysis is also performed using Scanning Electron Microscopy (SEM) in order to justify the fracture (macroscopic) behaviour from the observed fracture micromechanisms. The notch effect observed in the three ASA raster orientations is very similar, and lower than that observed in other FFF polymeric alternatives (ABS, PLA).

Toughening Immiscible Polymer Blends: The Role of Interface-Crystallization-Induced Compatibilization Explored Through Nanoscale Visualization.

This study explores the novel approach of interface-crystallization-induced compatibilization (ICIC) via stereocomplexation as a promising method to improve the interfacial strength in thermodynamically immiscible polymers. Herein, two distinct reactive interfacial compatibilizers, poly(styrene-co-glycidyl methacrylate)-graft-poly(l-lactic acid) (SAL) and poly(styrene-co-glycidyl methacrylate)-graft-poly(d-lactic acid) (SAD) are synthesized via reactive melt blending in an integrated grafting and blending process. This approach is demonstrated to enhance the interfacial strength of immiscible polyvinylidene fluoride/poly l-lactic acid (PVDF/PLLA) 50/50 blends via ICIC. IR nanoimaging indicates a cocontinuous morphology in the blends. The blend compatibilized with SAD exhibits a higher storage modulus, as unveiled by small amplitude oscillatory shear (SAOS) in the melt state at a temperature below the melting temperature of the stereocomplex (SC) crystals and by DMTA measurements in the solid state. This increase is attributed to the formation of a 200-300 nm thick rigid interfacial SC crystalline layer that is directly visible using AFM imaging and chemically characterized via IR nanospectroscopy. This ICIC also results in a significant toughening of the blend, with the elongation at break increasing more than 20-fold. Moreover, the fracture toughness factor obtained from single edge-notch bending (SENB) tests is doubled with ICIC as compared to the uncompatibilized blend, indicating the strong crack-resistance capability as a result of ICIC. This improvement is also evident in SEM images, where thinner and longer fibrillation is observed on the fractured surface in the presence of ICIC.

Effect of different parameters on mode I fracture toughness of resin samples manufactured by DLP

Abstract Additive manufacturing is spreading rapidly in almost all industries, from household to advanced engineering. Components produced by Digital Light Processing (DLP) are not comprehensively characterized, but exceed the capabilities of many AM processes. Its advantages include the ability to produce highly complex designs, superior precision, fast printing and lower operating costs. The present paper investigates the mode I fracture toughness (KIC) of UV-sensitive resin specimens obtained through DLP process. Single edge notch bending (SENB) specimen were 3D printed and tested according to the ASTM D5045 standard. The influence of printing orientation-PO (0°, 45° and 90°), resin color-RC (white, black and transparent) and corrosive environment-CE (air, water and saline solution) was studied. It was observed that all the studied parameters have some effect on the fracture properties. The highest KIC values were obtained for 45°-PO, white-RC (1.88 MPa•m0.5) and saline solution-CE (2.24 MPa•m0.5). However, the greatest influence is highlighted by RC (∼92%), while CE (∼32%) shows a minimal effect. The fracture surface of the investigated samples is influenced by the printing parameters.

The Influence of the Rolling Direction on the Mechanical Properties of the Al-Alloy EN AW-5454-D

A complementary characterisation of the Al-alloy EN AW-5454 was carried out, intended for obtaining the laser hybrid welding parameters of subassemblies in the automotive industry. The investigation included a microstructural examination and the determination of the alloy’s properties using several analytical methods (HV5 hardness measurement, tensile test, Charpy impact toughness, fracture mechanics analysis). Samples were prepared in the longitudinal and transverse directions of a cold-rolled sheet of EN AW-5454 with thicknesses of 3.5 mm and 4 mm. The measured hardness on the thinner sheet was 5% higher than on the thicker sheet. The tensile and yield strength were nominal, while the elongations were smaller by 2.2–3.2% for the longitudinal samples and by 2.7–13.7% for the transverse samples. The smaller deviations from the nominal values are for the thinner sheet metal. A precise topographical analysis showed the brittle fractures of the samples. The Charpy impact toughness results on the thicker plate showed a 20% greater work needed to break it in the longitudinal direction than in the transverse direction. With the thinner sheet metal, 40% greater work was needed. SEM (scanning electron microscope) analysis has shown that the intermetallic Al6(Mn,Fe) particles in the longitudinal samples were mostly intact, with evidence of tough areas on the upper part of the fracture, indicating a better toughness than the specimens in the transverse direction. More crushed intermetallic particles were observed at the fractures of the transverse samples, and their distribution appeared to be more oriented in the direction of rolling. Fracture mechanics SENB (single edge notch bending) tests and their analysis showed that the resistance of the material to crack propagation in the longitudinal sample was about 50% greater than that in the transverse sample. SEM analysis of the fractures showed that the state of the intermetallic particles in the fracture mechanics testing and the fracture mechanism differed from the one in the Charpy fractures.

Investigation of the fracture characteristics of mixed-mode I/III crack by using two kinds of sandstone specimens

This study aims to identify specimens that are more suitable for examining the failure properties of I/III mixed-mode cracks under static loads. We employed single-edge notched bending (SENB) and edge-notched disc bending (ENDB) specimens, and used ABAQUS finite element method software to calculate the stress intensity factors for modes I and III at various crack inclination angles θ. Fracture toughness was tested using three-point bending experiments on two types of sandstone specimens. The evolution of mixed-mode I/III fracture morphology and failure patterns was investigated with a monocular microscope. Additionally, the evolution of the strain field and crack tip opening displacement was analyzed using the digital image correlation method. Our findings indicate that the fracture toughness of the ENDB specimens surpassed that of the SENB specimens. The effective fracture toughness of both SENB and ENDB specimens initially increased with crack inclination angle θ but then decreased. The fracture mode correlated with energy release; the energy release rate of the ENDB specimens exceeded that of the SENB specimens, making the former more brittle. For SENB specimens, crack initiation was primarily intergranular, while ENDB specimens exhibited predominantly transgranular fractures. The crack initiation moments for both specimen types increased with higher crack inclination angles. Furthermore, at the same crack inclination angle, ENDB specimens cracked earlier than SENB specimens.

The effect of semi-curing on neat resin mode I fracture properties

The sensitivity of fracture toughness to the cure path of a high-performance hot infusion epoxy resin (EP2410) is assessed in this study through single-edge notch bend testing of neat resin specimens. The specimens were prepared using a two-stage semi-curing process. In the initial stage, the partial degree of cure and the semi-cure temperature were varied. In the second stage, samples were heated to 180 °C for a secondary post-cure. These samples were compared to two baseline samples produced using the manufacturer's recommended cure cycle of 180 °C, and a modified isothermal cure at a lower cure temperature of 140 °C. The results show that the semi-curing path has no statistically significant influence on the mode I fracture toughness of the material studied here. Sample similarity was confirmed through SEM examination of the fracture surface, which showed minimal variation in surface topography. These findings open new possibilities to use this type of material for novel manufacturing processes involving semi-curing steps.

Influence of processing parameters on the fracture behaviour of 316L SS printed by laser powder bed fusion

This study explored the relationship between process parameters and fracture behavior in 316L stainless steel printed by laser powder bed fusion. Fracture testing was conducted according to ASTM E1820 for single edge notch bending, and elastic mechanical properties were determined using ultrasonic surface wave analysis. Five test sets were considered in a vertical building configuration using five different volumetric energies belonging to conduction mode. The critical fracture toughness was calculated and discussed along with the plastic deformations at the crack tip. The study found that local plastic deformation for single edge notch bending was influenced by powder bed fusion process parameters. A correlation was observed between energy density, fracture toughness, and the dimensions of the fracture process zone. The R-curves showed different fracture behaviors depending on the energy density. The energy required to grow a crack was associated with larger plastic zones, resulting in fracture toughness values ranging from 43 (43 J mm−3) to 427 kJ/m2 (68 J mm−3). Results are discussed in terms of porosity and strain hardening capacity depending on the manufacturing conditions.

The Effect of Chopped Carbon Fibers on the Mechanical Properties and Fracture Toughness of 3D-Printed PLA Parts: An Experimental and Simulation Study

The incorporation of fiber reinforcements into polymer matrices has emerged as an effective strategy to enhance the mechanical properties of composites. This study investigated the tensile and fracture behavior of 3D-printed polylactic acid (PLA) composites reinforced with chopped carbon fibers (CCFs) through experimental characterization and finite element analysis (FEA). Composite samples with varying CCF orientations (0°, 0°/90°, +45°/−45°, and 0°/+45°/−45°/90°) were fabricated via fused filament fabrication (FFF) and subjected to tensile and single-edge notched bend (SENB) tests. The experimental results revealed a significant improvement in tensile strength, elastic modulus, and fracture toughness compared to unreinforced PLA. The 0°/+45°/90° orientation exhibited a 3.6% increase in tensile strength, while the +45°/−45° orientation displayed a 29.9% enhancement in elastic modulus and a 29.9% improvement in fracture toughness (259.12 MPa) relative to neat PLA (199.34 MPa√m). An inverse correlation between tensile strength and fracture toughness was observed, attributed to mechanisms such as crack deflection, fiber bridging, and fiber pull-out facilitated by multi-directional fiber orientations. FEA simulations incorporating a transversely isotropic material model and the J-integral approach were conducted using Abaqus, accurately predicting fracture toughness trends with a maximum discrepancy of 8% compared to experimental data. Fractographic analysis elucidated the strengthening mechanisms, highlighting the potential of tailoring CCF orientation to optimize mechanical performance for structural applications.

Comparison of Mode I fracture toughness of an elastic and an elastoplastic methyl methacrylate polymer as measured by SENB and DCDC tests

An elastic and an elastoplastic methyl methacrylate polymer, both in the glassy state, have been submitted to mode I fracture characterization with two different tests, the single edge notch bending (SENB) and the double cleavage drilled compression (DCDC) tests. The elastic material toughness was simply assessed by the linear elastic fracture mechanics analysis. For the elastoplastic material, the J-integral was computed when the strain fields were available. Moreover, numerical analyses were carried out using finite element simulations with a phase-field damage approach, providing comparison when the J-integral had been calculated and estimate otherwise, of the critical energy release rate. For each material, as well as for each test, the values of the critical energy release rate that have been estimated here, are in good agreement with the literature. More interestingly, for the same material, both tests provide with very different estimates of this material parameter, leaving engineers uncertain on which test to choose to assess the material toughness in crack opening mode.

Fracture Behavior and Mechanism of Nb-Si-Based Alloys with Heterogeneous Layered Structure.

Novel Nb-Si-based alloys with heterogeneous layers that have the same composition (Nb-16 at.%Si) but different phase morphologies were designed in this work. Heterogeneous layered structure (HLS) was successfully fabricated in Nb-16Si alloys by layering composite powders after various degrees of mechanical alloying (6 h, 12 h, 18 h, and 24 h) alternately and subsequent spark plasma sintering (SPS). The influence of HLS on the fracture behavior at both room and elevated temperature was investigated via single-edge notched bending (SENB) and high-temperature compression, respectively. The results show that the diversified HLS is obtained by combining hard layers containing fine equiaxed crystals and/or soft ones with coarse lamellar niobium solid solution (Nbss). By affecting the crack propagation in SENB, HLS is favorable for improving the fracture toughness and exhibits a significant increase compared with the corresponding homogenous microstructure. Moreover, for the same HLS, a more excellent performance is achieved when the initial crack is located in the soft layer and extended across the interface to the hard one through crack bridging, crack deflection, crack branching, and shielding effect. Fracture starts in the soft layer (from powders of ball-milled for 12 h) of a 12-24 alloy, and a maximum KQ value (14.89 MPa·mm1/2) is consequently obtained, which is 33.8% higher than that of the homogeneous Nb-16Si alloy. Furthermore, the heterogeneous layered alloys display superior high-temperature compression strength, which is attributable to the dislocation multiplication and fine-grained structure. The proposed strategy in this study offers a promising route for fabricating Nb-Si-based alloys with optimized and improved mechanical properties to meet practical applications.

Experimental evaluation of the short and long fatigue crack growth rate of S355 structural steel offshore monopile weldments in air and synthetic seawater

Welded steel structures used in the offshore wind industry are exposed to harsh marine environments, which can result in corrosion-induced fatigue damage. Of particular concern is the heat affected zone (HAZ) of welded joints, a region known for its altered microstructure and mechanical properties, which can significantly influence the initiation and propagation of fatigue cracks. This study investigates the short and long fatigue crack growth rates, and the effect of seawater exposure, for the HAZ in S355 steel weldments. Single-edge notch bend (SENB) specimens are used, with a shallow notch in the HAZ. A series of specimens is immersed in synthetic seawater that is continuously circulated at a controlled temperature to assess the synergistic effects of corrosion and fatigue. The experimental method integrates a novel application of front face strain compliance for monitoring short cracks, alongside an extended back-face strain compliance approach for monitoring long crack propagation. It is concluded that the short fatigue crack growth rate of the HAZ is 2.7 to 3.5 times higher in seawater as compared to air. As the crack propagates and enters into the long crack regime, the ratio decreases to 2.2 times at the transition point of the two-stage crack growth curve and further decreases to 1.5 times when the notch advances towards fracture. The findings indicate that the fatigue crack growth rates documented in standards tend to be on the conservative side. This study significantly enriches the fatigue crack growth data available in literature, which will contribute to a more accurate lifetime assessment offshore wind turbine structures.

Quantification of crack tip constraint effect based on the critical distance

AbstractThe effect of crack tip constraint on the fracture properties of flawed components is a critical consideration in the safety assessment of engineering structures. In this work, an approximate expression of three‐dimensional von Mises stress fields ahead of the crack tip has been derived by referring to the classic Hutchinson‐Rice‐Rosengren (HRR) solution. The critical distance rc is chosen as the constraint parameter to quantify the level of the crack tip constraint. A theoretical relationship between the parameter rc and fracture toughness JQ has been proposed. The critical constraint parameter rc can be experimentally determined by using the critical fracture toughness JQ. The experimental results of compact tension (CT) and single edge‐notched bending (SENB) specimens with different crack tip constraint levels for SA‐508 and Q345B steels successfully validate the relationship between the critical fracture toughness JQ and the constraint parameter rc. According to the test results, the critical distance rc is feasible to quantify the crack tip constraint of CT and SENB specimens with different crack tip constraint levels.

Enhanced fracture toughness and tensile strength of 3D printed recycled ABS composites reinforced with continuous metallic fiber for load-bearing application

PurposeThis study aims to present an experimental approach to develop a high-strength 3D-printed recycled polymer composite reinforced with continuous metal fiber.Design/methodology/approachThe continuous metal fiber composite was 3D printed using recycled and virgin acrylonitrile butadiene styrene-blended filament (RABS-B) in the ratio of 60:40 and postused continuous brass wire (CBW). The 3D printing was done using an in-nozzle impregnation technique using an FFF printer installed with a self-modified nozzle. The tensile and single-edge notch bend (SENB) test samples are fabricated to evaluate the tensile and fracture toughness properties compared with VABS and RABS-B samples.FindingsThe tensile and SENB tests revealed that RABS-B/CBW composite 3D printed with 0.7 mm layer spacing exhibited a notable improvement in Young’s modulus, ultimate tensile strength, elongation at maximum load and fracture toughness by 51.47%, 18.67% and 107.3% and 22.75% compared to VABS, respectively.Social implicationsThis novel approach of integrating CBW with recycled thermoplastic represents a significant leap forward in material science, delivering superior strength and unlocking the potential for advanced, sustainable composites in demanding engineering fields.Originality/valueLimited research has been conducted on the in-nozzle impregnation technique for 3D printing metal fiber-reinforced recycled thermoplastic composites. Adopting this method holds the potential to create durable and high-strength sustainable composites suitable for engineering applications, thereby diminishing dependence on virgin materials.

A model for modifying the S‐N curve considering the effect of boundary conditions on the fatigue crack growth of welded components

AbstractThe present study proposes a novel model to modify master S‐N curves of components according to their load redistribution capability reflected in different boundary conditions (BCs) based on the fracture mechanics analysis. To that end, a comprehensive numerical study was conducted on a Single Edge Notch Bend (SENB) specimen constrained with different kinematic BCs using discrete fatigue crack growth (FCG) simulation. It was observed that BCs indeed can have a significant effect on the crack growth behavior and consequently on the resulting fatigue life under the same nominal loading conditions. The proposed model was applied to the S‐N curve of a T‐welded joint, and the predicted fatigue life was validated against 3D FCG simulations. Finally, FCG tests were conducted on SENB specimens to experimentally corroborate the effect of BCs on the FCG rate.

Modelling of crack propagation in miniaturized and normal SENB specimens based on local failure criterion

The use of miniaturized specimen testing methods is a promising way to solve the problem of limited materials in RPV monitoring programs. The use of miniature specimens allows the evaluation of fracture toughness from other specimen materials used. In particular, the small-size compact tensile test specimen (0.16T CT) is promising for the determination of fracture toughness, as it can be produced from the standard size Charpy specimen that has already been tested. However, if we have only 0.16T CT test, we cannot investigate the dimensional response and also have only one restricted deformation state, which may pose problems in verifying geometry independence and determining local parameters for state-of-the-art analyses. It is therefore recommended to prepare at least two tests with two different restricted deformation specimens. Therefore, the testing of mini single edge notched bending (SENB) is also required and can be worked out from the Charpy specimens. The paper presents the determination of fracture toughness for these miniaturized specimens by modifying the virtual crack closure technique (VCCT) simulation method using GTN parameters instead of energy release as the driving force. This allows the calculation of the J-integral to proceed in parallel with the crack propagation.

Investigating the constraint role in J-CTOD relationship for compact tension (CT) specimen

The Crack Tip Opening Displacement (CTOD or δ) estimation from J-integral (J) defined by ASTM 1820 considers the CTOD dependency on material properties, and the constraint factor (m). The m in Compact Tension (CT) specimen is based on yield to tensile strength ratio (σys/σut) without taking into account of in-plane dimensions as in Single Edge Notch Bending (SENB). Hence, an attempt is made to understand the effect of crack length to specimen width (a/W), specimen thickness to specimen width (B/W) for different σys/σut on CTOD using CT specimen. A new method of estimating the CTOD from FE analysis is demonstrated and validated with 450-intercept method. It has been found that the ASTM 1820 based CTOD (δASTM) assessed values under-estimate the actual CTOD present in the CT specimen. The variation in a/W and B/W doesn’t affect the J-CTOD relationship as stated by ASTM 1820. However, the CTOD measured by FE analysis (δFE) are consistently higher than the δASTM. Therefore, an effort is made to correct the constraint factor, m based on present FE analysis by considering the effect of σys/σut. The proposed corrected constraint factor, mFE, can be employed in fracture applications that generally need both the J-integral and the CTOD.

Experimental Study of the Physical and Mechanical Properties of Cement‐Based Composite Reinforced With Macro‐/Microfibers: Case of Rhecktophyllum camerunense and Triumfetta pentandra

Plant fibers have the ability to bridge crack propagation on a microscopic scale for microfibers and on a macroscopic scale for macrofibers. Therefore, the use of two or more fiber types in an appropriate combination can potentially improve the overall properties of the cement composite as well as promote green construction. The hybrid composite was cast using random orientation with two fibers: Rhecktophyllum camerunense as macrofiber and Triumfetta pentandra as microfiber. Cement mortar matrices were reinforced with a constant microfiber length of 1 mm and three different macrofiber lengths of 1.5, 3, and 6 mm at varying fiber contents of 1%, 1.5%, and 2.5% wt. The physical characteristics of the composite were assessed by porosity, density, and water absorption. Mechanically, three‐point bending tests and single‐edge notch bending (SENB) tests were performed after 7 and 14 days of curing. Mode I fracture behavior (KIC) and modulus of rupture (MOR) were calculated as per formulation. Physical experimental results reveal that there is a correlation between the rate of water absorption, porosity, density, and that of the fiber loading and length in the composite. Mechanically, the developed material presented a multiple cracking behavior under bending. There was a decrease in MOR and fracture toughness values with a decrease in macrofiber content in the hybrid composite. They both presented an increase in value with an increase in fiber content and fiber length. The composites reinforced with both fibers presented higher values of MOR than the unreinforced due to the powerful interfacial bond between the fibers and the cement matrix. The unreinforced composites had the least MOR and fracture toughness values of 0.442 MPa and 694,000 N.m1.5, respectively, showing that they are very reactive to faults at low stress levels.

Effect of stacking direction and raster angle on the fracture properties of Onyx 3D printed components: A mesoscale analysis

3D printing is a technology that has gained increasing importance both in academia and industry for the possibilities offered. Among the many, one of the most appealing is the possibility to choose different printing configurations, tailoring stacking direction, and raster angle. The choice of such parameters deeply influences the structural response, as already shown in the literature. This study aims at providing a deep understanding of the phenomena taking place at the mesoscale level which justify such differences in the fracture behavior. An experimental campaign is carried out with a Single Edge Notch Bending (SENB) specimen printed in Onyx using four different combinations of raster angles and stacking directions. The results are compared in terms of mechanical response, fracture toughness and surface roughness to identify the main driving mechanisms during the fracture process. The same bending test is replicated numerically, aiming at comparing the fracture toughness values obtained experimentally with the ones used in the simulation to match the experimental curves. The study shows that the stacking direction and the raster angle deeply influence the fracture behavior and the mechanical properties of the specimen, along with the fracture toughness and surface roughness. In particular, it is highlighted how improved mechanical behavior can be achieved by printing the specimen in the vertical direction and with a raster angle of 45°/−45°. Moreover, useful fracture toughness values are identified for different combinations of printing parameters by means of a Cohesive Zone Model formulation, providing useful input values for numerical simulations.

Experimental and Numerical Analysis of Fracture Mechanics Behavior of Heterogeneous Zones in S690QL1 Grade High Strength Steel (HSS) Welded Joint.

The heterogeneity of welded joints' microstructure affects their mechanical properties, which can vary significantly in relation to specific weld zones. Given the dimensional limitations of the available test volumes of such material zones, the determination of mechanical properties presents a certain challenge. The paper investigates X welded joint of S690QL1 grade high strength steel (HSS), welded with slightly overmatching filler metal. The experimental work is focused on tensile testing to obtain stress-strain properties, as well as fracture mechanics testing. Considering the aforementioned limitations of the material test volume, tensile testing is carried out with mini tensile specimens (MTS), determining stress-strain curves for each characteristic weld zone. Fracture mechanical testing is carried out to determine the fracture toughness using the characteristic parameters. The experimental investigation is carried out using the single edge notch bend (SENB) specimens located in several characteristic welded joint zones: base metal (BM), heat affected zone (HAZ), and weld metal (WM). Fractographic analysis provides deeper insight into crack behavior in relation to specific weld zones. The numerical simulations are carried out in order to describe the fracture behavior of SENB specimens. Damage initiation and evolution is simulated using the ductile damage material behavior. This paper demonstrates the possibility of experimental and numerical determination of fracture mechanics behavior of characteristic heterogeneous welded joint zones and their influence on crack path growth.

Experimental and Numerical Fracture Toughness Evaluation of Spiral Seam Weld of API X65 Steel

In this research fracture toughness of spiral seam weld of API X65 is measured through the ASTM E1820 standard recommendations. According to thin-wall pipe of API X65 in this research, specimen sizes could not satisfy the plain strain condition of ASTM E399 therefore, indirect method is accomplished by evaluating the crack tip opening displacement. According to the nature of welding procedure and inhomogeneous probable defects in the different regions of seam weld, δ-R curve with multi-specimen technique of single-edge notched bend (SENB) specimens is applied for test procedure in this research. The measured CTOD and K1C are 0.23 mm and 265 MPam3/2 respectively. Furthermore, Three-dimensional finite element method numerical evaluation of crack propagation with GTN model has been performed. Good agreement with the other researches was observed for CTOD and fracture toughness of tested material. The difference was about 10 percent.