Notched Bending Tests Research Articles

Effect of neutron irradiation on fracture resistance of advanced SiC/SiC composites

In order to identify the neutron irradiation effects on fracture resistance of advanced SiC/SiC composites, unloading–reloading single edge notched bend tests were conducted and an analytical model based on non-linear fracture mechanics was applied. As a result of the analysis, energy release rate contributed by macro-crack initiation of 3.1kJ/m2 for both unirradiated and irradiated advanced SiC/SiC composites (Hi-Nicalon Type-S (0°/90° plain woven)/multilayer/chemically vapor infiltration) is estimated. This result indicates no significant degradation in fracture resistance after neutron irradiation to 5.9×1025n/m2 at 800°C.

Thermal Properties, Fracture Toughness and Water Absorption of Epoxy-Palm Oil Blends

Epoxidized palm oil (EPO) was blended with cycloaliphatic epoxide, epoxy novolac and diglycidyl ethers of bisphenol-A. The fracture toughness and thermal properties of epoxy/EPO blends were characterized using single-edge notched bending tests and differential scanning calorimetry. Increased EPO loading improved the fracture toughness (K IC ) of the epoxy blends. The epoxy blends with higher EPO loading exhibited higher degree of conversion. The glass transition temperature (T g ) of the epoxy blends shifted to higher temperature as the increasing of DSC heating rate. Water absorption caused T g reduction of epoxy blends but it was determined that the water molecules absorbed were totally reversible.

Effect of Bimodal Grain Size Distribution on Scatter in Toughness

Blunt-notch tests were performed at −160 °C to investigate the effect of a bimodal ferrite grain size distribution in steel on cleavage fracture toughness, by comparing local fracture stress values for heat-treated microstructures with uniformly fine, uniformly coarse, and bimodal grain structures. An analysis of fracture stress values indicates that bimodality can have a significant effect on toughness by generating high scatter in the fracture test results. Local cleavage fracture values were related to grain size distributions and it was shown that the largest grains in the microstructure, with an area percent greater than approximately 4 pct, gave rise to cleavage initiation. In the case of the bimodal grain size distribution, the large grains from both the “fine grain” and “coarse grain” population initiate cleavage; this spread in grain size values resulted in higher scatter in the fracture stress than in the unimodal distributions. The notch-bend test results have been used to explain the difference in scatter in the Charpy energies for the unimodal and bimodal ferrite grain size distributions of thermomechanically controlled rolled (TMCR) steel, in which the bimodal distribution showed higher scatter in the Charpy impact transition (IT) region.

Effect of phosphate group addition on the properties of denture base resins

Acrylic resins are prone to microbial adherence, especially by Candida albicans. Surface-charged resins alter the ionic interaction between the denture resin and Candida hyphae, and these resins are being developed as a means to reduce microbial colonization on the denture surface. The purpose of this study was to investigate the physical and mechanical properties of phosphate-containing polymethyl methacrylate resins for their suitability as a denture material. Using PMMA with cross-linker (Lucitone 199) as a control, 4 experimental groups containing various levels of phosphate with and without cross-linker were generated. The properties examined were impact strength, fracture toughness, wettability (contact angle), and resin bonding ability to denture teeth. Impact strength was tested in the Izod configuration (n=16), and fracture toughness (n=13) was measured using the single-edge notched bend test. Wettability was determined by calculating the contact angle of water on the material surface (n=12), while ISO 1567 was used for bonding ability (n=12). The data were analyzed by 1- and 2-way ANOVA (alpha=.05). A trend of increased hydrophilicity, as indicated by lower contact angle, was observed with increased concentrations of phosphate. With regard to the other properties, no significant differences were found when compared with the control acrylic resin. No adverse physical effect due to the addition of a phosphate-containing monomer was found in the acrylic denture resins. Additional mechanical and physical properties, biocompatibility, and clinical efficacy studies are needed to confirm the in vivo anti-Candida activity of these novel resins.

Use of Synergistic Effects in High Power Laser-GMA Hybrid Welding for Manufacturing of Thick Walled Structural Pipes

In the manufacturing thick structural pipes recently a new process has been developed. This Paper describes this newly discovered process called Laser Hybrid welding. In laser hybrid welding two processes i.e. laser welding and Gas Metal Arc (GMA) welding are combined together to create synergistic effects. In laser GMA hybrid welding of plates with thicknesses of up to 20 mm, the problem of pore formation and of centre rib defects occurs frequently which have, up to now, not yet been subject to detailed scientific analysis. It was the objective of this research work to reduce these weld defects by weld parameter investigations (of a geometrical and also metallurgical nature) or to even avoid them completely. It was investigated to determine the extent to which shielding gas composition, (root) gap width and misalignment of the joining partners affect the techno-mechanical properties. For this purpose, the welds were subjected to non-destructive test methods (viz. visual inspections and X-ray examinations) and also to destructive test methods (viz. transverse sections hardness measurements, tensile tests and notch bending tests). The synergistic effects have been discussed in the light of the mechanical and metallurgical characterisations of the weldments. Optimum process parameters have been evolved which could tolerate up to 0.4mm root gap and 0.8mm of misalignment without causing any centreline cracking. Combinations of helium and argon gas shielding have been found to produce porous free welds. It has been concluded that it is possible to replace submerged arc welds by laser GMA hybrid welds in the manufacturing of longitudinally welded pipes.

Self-healing epoxy composites – Preparation and effect of the healant consisting of microencapsulated epoxy and latent curing agent

To provide epoxy based composites with self-healing ability, two-component healing system consisting of urea–formaldehyde microcapsules containing epoxy (30–70 μm in diameter) and CuBr 2(2-MeIm) 4 (the complex of CuBr 2 and 2-methylimidazole) latent hardener was synthesized. When cracks were initiated or propagated in the composites, the neighbor microencapsulated epoxy healing agent would be damaged and released. As the latent hardener is soluble in epoxy, it can be well dispersed in epoxy composites during composites manufacturing, and hence activate the released epoxy wherever it is. As a result, repair of the cracked sites is completed through curing of the released epoxy. The present paper studied the preparation of epoxy microcapsules by amino resins, and the influencing factors as well. On the basis of this work, mechanical properties of the epoxy filled with the healing system were evaluated. It was found that incorporation of the two-component healing system nearly did not change the fracture toughness of the neat epoxy, as indicated by the single-edge notched bending test. In the case of 10 wt% microcapsules and 2 wt% latent hardener, the self-healing epoxy exhibited a 111% recovery of its original fracture toughness. Besides, the preliminary result of double-cantilever beam testing showed that the plain weave glass fabric laminates using the above self-healing epoxy as the matrix received a healing efficiency of 68%.

Instrumental measurement of apple texture: A comparison of the single-edge notched bend test and the penetrometer

The single-edge notched bend (SENB) test is a technique for measuring fundamental properties of materials. This technique is an easily applied measure of fruit texture that is related to sensory characteristics such as ‘crunchiness’ [Vincent, J.F.V., Saunders, D.E.J., Beyts, P., 2002. The use of critical stress intensity factor to quantify “hardness” and “crunchiness” objectively. J. Texture Stud. 33, 149–159]. The present study focuses on the relationship between SENB and the penetrometer test routinely used for fruit quality assessment. Fruit from cultivars Cox's Orange Pippin, Sciros, Sciearly and Scifresh were removed from cold storage at regular intervals, and texture was assessed after 1 and 7 days at 20 °C. Texture was measured using a conventional puncture test with an Effegi probe and a SENB test. During the SENB test, a notched beam of apple tissue was subjected to three-point bending until it broke. Fracture toughness ( K c) and fracture energy ( G c) were calculated, and Low-Temperature Scanning Electron Microscopy (LTSEM) was used to examine the fracture surface following beam failure. Both K c and G c were correlated with puncture force, but the relationship was different for Sciros and Sciearly (two siblings from a Gala × Splendour cross) compared to the other cultivars. Sciros and Sciearly apples had higher K c and G c values than would be anticipated from measurements of puncture force. This supports the suggestion that these apples are crisper when eaten than might be expected from puncture (penetrometer) values. Comparison of the texture of shrivelled and non-shrivelled Sciros apples indicated that puncture measurements are unreliable when fruit are dehydrated. Puncture measurements suggested shrivelled apples were ‘crisper’ than non-shrivelled fruit, while SENB parameters indicated the reverse.

Effect of Particle Size on Fracture Toughness of Spherical-Silica Particle Filled Epoxy Composites

We investigated the particle size effects on the fracture toughness of epoxy resin composites reinforced with spherical-silica particles. The silica particles had different mean particle diameters of between 1.56 and 0.24µm and were filled with bisphenol A-type epoxy resin under different mixture ratios of small and large particles and a constant volume fraction for all particles of 0.30. As the content with the added smaller particle increased, the viscosity of each composite before curing remarkably increased. We conducted the single edge notched bending test (SENB) to measure the mode I fracture toughness of each composite. The fracture surface with the small particle content exhibited more rough areas than the surface with larger particles. The fracture toughness increased below the small particle content of 0.8 and saturated above it. Therefore, near the small particle content of 0.8, the composite had a relatively low viscosity and a high fracture toughness.

Fracture properties of a fiber-metal laminates based on magnesium alloy

Fiber-metal laminates (FMLs) are high performance laminated structures based on stacked arrangements of composite material and aluminum alloy. Currently, a glass fiber reinforced epoxy/aluminum alloy FML (GLARE) is being considered for use in the manufacture of the upper fuselage of the A380 Airbus aircraft [1]. Previous work on FMLs has shown that they combine the excellent durability and machinability common to many metals with the superior fatigue and fracture properties offered by many fiber-reinforced composites [2–4]. Krishnakumar [2] tested a Kevlar fiber FML (ARALL) and showed that its ultimate tensile strength is considerably greater than that of a conventional aluminum alloy. Vogelsang [3] conducted tension-tension fatigue tests on a number of FML systems as well as a plain aluminum alloy and showed that crack growth rates in the former were significantly less than those in the plain aluminum alloy. Several workers have investigated the impact response of aerospace-grade fiber-metal laminates [5, 6]. Vlot et al. [5] conducted low and high velocity impact tests on a GLARE system, a plain aluminum alloy and a carbon fiber reinforced thermoplastic. Their results showed that the FML offered the highest damage threshold energy of all the systems considered. The aim of the present work is to investigate the fracture properties of a novel fiber-metal laminate based on a lightweight magnesium alloy and a carbon fiber reinforced plastic. Magnesium alloys offer a number of advantages over many metals including their low density (thirty percent lower than an aluminum alloy), their superior corrosion resistance and their excellent electromagnetic shielding ability. Currently, magnesium alloys are being used in the automotive industry in the manufacture of transmission casings and in the aerospace industry for the manufacture of gearboxes and other lightweight components. The fiber-metal laminates examined in this study were based on 0.5 mm thick magnesium alloy sheets (AZ31 alloy from Advance Metals International Ltd.) and a woven carbon fiber reinforced toughened epoxy (Stesapreg EP121-C15-53 from Stesalit Ltd, Switzerland). The composite and metal plies were placed in a picture frame mold with dimensions 240 × 200 mm and cured for 4 h at 125 ◦C. All of the laminates tested in this research project were based on a 2/1 configuration (two magnesium alloy skins either side of a carbon fiber reinforced epoxy core). Table I summarizes the stacking configurations investigated in this study. The composite volume fraction within the FMLs was varied by increasing the number of composite plies between the two outermost magnesium alloy skins from two to eight. The tensile properties of the FMLs and the magnesium alloy were evaluated using 20 mm wide rectangular samples at a crosshead displacement rate of 2 mm/min. The initial strain history in each sample was recorded using a clip-on extensometer fixed to the specimen edge. The extensometer was incapable of measuring large strains. In such cases, the crosshead displacement was normalized by the length of the working section to yield a nominal strain (this was only undertaken when a complete stress-strain curve was required). The energy-absorbing properties of the fiber-metal laminates were evaluated through a series of single edge notch bend (SENB) tests on specimens with dimensions 100 × 18 mm × thickness. Prior to testing, a 9 mm long pre-crack was introduced at the mid-span. The precrack was sharpened by swiping a sharp razor blade along the tip of the stress concentration. The SENB specimens were positioned on two simple supports positioned 72 mm apart and loaded at a crosshead displacement rate of 5 mm/min. The work of fracture was then determined by dividing the area (energy) under the load-displacement curve by the cross-sectional area of the fractured ligament. Fig. 1 shows typical stress-strain (nominal) curves for the three FMLs and the plain magnesium alloy. The stress-strain curve for the plain magnesium alloy indicates that although its tensile strength is below that of the FMLs, it does exhibit quite a high degree of ductilty beyond the elastic limit. The stress-strain curves for all of the FMLs exhibited an almost linear response up to maximum stress at which point the composite layers fractured in a brittle manner. An examination

Fracture properties of interfacially doped Nb-A1 2O 3 bicrystals: I, fracture characteristics

The influence of orientation and impurities on the fracture behavior of Nb–sapphire interfaces was studied using notched bending tests. Single crystals were diffusion bonded in UHV for different interface orientations. The bicrystals were doped to produce prescribed fractional interfacial coverages of Ag. The interfacial impurity content was measured after fracture with Auger spectroscopy. The tougher bicrystals exhibit significant nonlinearity in loading. A J-integral analysis was used to account for the large plastic zones. For undoped bicrystals bonded at 1400°C, the interfacial fracture energy ranged from J c of 77 to 2100 J/m 2 depending on the interface planes of the Nb and sapphire. Greater toughnesses were derived from bonding at 1300°C, owing to less oxygen contamination of the Nb. Interfacial doping by Ag atoms leads to a strong reduction of J c at coverages of only 0.2 to 0.5 of a monolayer. Higher fracture energy is caused by greater plastic deformation in the Nb as observed by slip lines on the metal fracture surface. Evaluation of the loading and fracture characteristics revealed that sharp precursor cracks developed initially in the ceramic. Extensive crack blunting also occurs, especially for the tougher bicrystals, but is often followed by erratic or unstable extension during which far less plasticity occurs, apparently owing to the rate sensitivity for Nb deformation.

Influence of hot pressing sintering temperature and time on microstructure and mechanical properties of TiB2 ceramics

Abstract In this paper, a titanium diboride ceramic was produced by the hot pressing sintering method. The effects of hot pressing parameters on the TiB 2 ceramic microstructure and mechanical properties were studied. The bending strength and fracture toughness were measured by three point bending testing and single edge notched bending tests (SENB), respectively. The microstructure features of the TiB 2 sintered material were revealed by means of SEM and TEM. The results show that the TiB 2 grain size increases quickly with the increasing temperature and time during hot pressing sintering. The density and the TiB 2 grain size have a great influence on the mechanical properties. The bending strength decreases with increasing TiB 2 grain size, whilst the fracture toughness increases.

Acoustic Emission Monitoring of Foam Core Sandwich Composites

An acoustic emission based investigation was conducted of damage initiation and progression in cellular foam core sandwich composites. Acoustic characteristics of Mode I and Mode II fracture of PVC foam were determined in Single Edge Notch Bend and End Notch Flexure tests. Core shear fracture initiation and growth were successfully detected in four point bending fatigue tests. Analysis of the acoustic emission signals confirmed that the majority of the damage growth occurs at the peak load levels and the increase in emission signals can be correlated with the reduction in stiffness due to the progression of the fatigue damage.

Plasma sprayed hydroxyapatite coatings on titanium substrates Part 1: Mechanical properties and residual stress levels

Hydroxyapatite (HA) coatings have been sprayed on to substrates of Ti–6Al–4V, using a range of input power levels and plasma gas mixtures. Coatings have also been produced on substrates of mild steel and tungsten, in order to explore certain aspects of the mechanical behaviour of HA without the complication of yielding or creep in the substrate. Studies have been made of the phase constitution, porosity, degree of crystallinity, OH - ion content, microstructure and surface roughness of the HA coatings. The Young’s moduli in tension and in compression were evaluated by the cantilever beam bend test using a tungsten/HA composite beam. The flexural Young’s modulus was determined using a free-standing deposit under the same test. Adhesion was characterised using the single-edge notch-bend test; this is considered superior to the tensile bond strength test in common use. Measured interfacial fracture energies were of the order 1–10 J m -2. Stress levels were investigated using specimen curvature measurements in conjunction with a numerical process model. The quenching stress for HA was measured to be about 10–25 MPa and the residual stress level in HA coatings at room temperature are predicted to lie in the approximate range of 20–40 MPa (tensile). These residual stresses could be reduced in magnitude by maintaining the substrate at a low temperature (possibly below room temperature) during spraying and it may be worthwhile to explore this. Ideally, the HA coating should have low porosity, high cohesive strength, good adhesion to the substrate, a high degree of crystallinity and high chemical purity and phase stability. In practice, such combinations are rather difficult to achieve by just varying the spraying parameters.

Effects of Thermal Aging on the Mechanical Behavior of K3B Matrix Material

In this study, the timeand temperature-dependent behavior of unaged as well as aged samples of neat K3B (a thermoplastic polyimide made by Du Pont) has been characterized. The aging temperature was 1770C (350'F), and aging times are 5,000 hours and 10,000 hours. Testing temperatures were room temperature, 930C, 1350C, and 1770C (200'F, 2750F, and 350'F). A combination of monotonic tensile tests and stress relaxation provided the necessary information. Notch bend tests were conducted to determine fracture toughness. Neat K3B has been found to be very brittle and prone to defects. Aging for both 5,000 and 10,000 hours resulted in much lower failure strains, especially at elevated temperatures. The time dependence exhibited, especially after aging, may not be enough to affect correlations to composite behavior, and a time-dependent approach may not be necessary. FTIR data shows some slight changes in peak size, so a change in the structure of K3B cannot be ruled out. DSC data shows a very slight (negligible) change in the glass transition and no melting point (as expected). The polymer molecules are approaching equilibrium during aging (physical aging), but crosslinking has not been ruled out. The main goal of this study was to gather more information on the timeand temperaturedependent behavior of K3B. This has been accomplished by first characterizing the viscoplastic behavior of neat resin samples after aging for long periods of time at elevated temperatures. The data gathered was used to determine the effects of thermal aging on the mechanical behavior of K3B. The work being discussed presently focuses primarily on the neat matrix material.

A SIMPLE TEST METHOD FOR ENERGY DISSIPATION RATE, CTOA AND THE STUDY OF SIZE AND TRANSFERABILITY EFFECTS FOR LARGE AMOUNTS OF DUCTILE CRACK GROWTH

Abstract— Simple extensions to the standard deep notch bend test procedure are suggested to allow the collection of data relevant to the energy dissipation rate, D, crack opening angle, COA, and J, all for arbitrarily large amounts of growth in extensive plasticity. The methods of analysis are detailed for real elastic‐plastic behaviour of a high strength low‐hardening type metal with a view to encouraging use on a wider range of materials. A proposal is made, and equations given, that the particular version of J used for an R‐curve derived from the area under the loading diagram, should correspond to the value of the far‐field integral, Jff.The relationship between the global measure of COA that emerges from D and the local crack tip opening angle, CTOA, as used in computational studies, is established. Transferability of CTOA data is examined in the light of effects of size and configuration. An explicit rule of the form CTOA √G =f (material and configuration) is proposed for the modelling of ductile growth in finite element studies. It is applied to a set of data in the literature, for the variation of CTOA with size in the deep notch bend test and for the configurations, bending, double edge and centre cracked tension.

The effect of amine/epoxy ratio on the fracture toughness of tetrafunctional epoxy resin

The effect of amine/epoxy ratio on the fracture toughness(KIc) of tetrafunctional epoxy resin was investigated. KIc value was measured by single-edge notch-bend test. The KIc value of the tetrafunctional epoxy resin increased with increasing the amount of amine curing agent. This result was explained with the structural viewpoint of the epoxy network. The network structure of the tetrafunctional epoxy was analyzed with dynamic thertnomechanical measurement and in-situ near IR technique.

THE BRITTLE FRACTURE OF 475°C EMBRITTLED CAST DUPLEX STAINLESS STEEL

Abstract— The fracture behaviour of cast duplex stainless steels, heat treated to different ferrite contents and hardness was investigated using tensile and notched bend tests. The purpose was to identify the microstructural features which controlled the ductile‐to‐brittle fracture transition of 475°C embrittled duplex stainless steel. The results indicate that twin nucleated cleavage has a tensile stress fracture criteria and the brittle‐to‐ductile transition temperature depends on ferrite microhardness, ferrite grain size and constraint.

Weld defects and evaluation of weld quality: Welding phenomena and process control in flash welding of steel sheets (1st report)

Summary This paper describes an investigation of the effects of the chemical composition of the base material on the quality of flash welds. Bending tests of welds were run for 43 types of steel sheets, including solution‐strengthened, precipitation‐strengthened, and complex structure‐strengthened (dual‐phase) high‐strength steels up to 590 MPa. A fractographic analysis showed cracks at the weld interface to be caused by oxide inclusions. Aluminium, silicon, and manganese are the major constituents of the inclusions, and the relative intensity of effect of these elements broadly has an Al:Si:Mn = 10:1:0.01 sequence. Carbon is also shown to affect interface cracking by reducing weld ductility. An equivalent formula is experimentally established to determine the effects of these elements on interface cracking. The ordinary bending test is shown to be a simple and reliable method for quantitative evaluation of the interface quality of flash welds, with the notch bending test being more effective for evaluation purposes.

The influence of cyclic fatigue damage on the fracture toughness of carboncarbon composites

The influence of cyclic loads on the fracture toughness of a tightly woven carboncarbon composite was investigated as a function of stress levels. Results of fracture toughness tests were correlated with microstructural examination using scanning electron microscopy (SEM). Values for the stress intensity factor, K Ic, were determined using the ASTM single-edge notched bend test. Results were discussed in terms of the effects of applied cyclic stress levels and the relationship of the load-displacement curves. The fracture toughness of the composite remained unaffected when the maximum tensile load in the fatigue cycle was up to 80% of the static tensile strength. However, a decrease in the fracture toughness was determined when it was exposed to cyclic loads above this threshold stress level. Changes in texture associated with cyclic fatigue were determined in the matrix of this composite.

Fully plastic ductile tearing of HY130 steel—an analysis by J, COD, energy rate and crack opening angle

The dependence of J-R curves on size of test piece is examined for fully plastic deep notch bend (DNB) tests on HY130 steel, taken to large amounts of ductile crack growth (60 per cent of the ligament) for a range of initial widths at 20 mm thick and one geometrically similar size, 50 mm thick. The object is to understand the cause of the widely different patterns of behaviour that have been reported in the literature, even within the DNB type of configuration. In the present tests, the proportion of shear lip is the same for the geometrically similar pair but the J-R curve for the 50 mm thick piece is much lower than for the similar piece, 20 mm thick. The rate of change of displacement, dq/da, is analysed using the factor. r∗, that defines the instantaneous centre of rotation at each step of growth, to give a measure of crack tip opening angle (CTOA), xg. After an initial transient regime of small growth, xg and r∗ remain constant. The normalized load. L, rises due to work hardening during crack growth by amounts that depend on size while xg and r∗ vary mildly with initial width to give an appreciable variation of the combined term Lxg/r∗, which is the factor that controls the behaviour of the JR curves. It is speculated that CTOA and its variation with configuration (as seen in the literature) may, for large growth, assume the role of the two parameters suggested in recent literature as controlling the variation of toughness with constraint.