Point Bending Configuration Research Articles

Fracture of notched samples of chocolate

The present work is focused on the development of a numerical model based on the inverse methodology and an optimization process for the determination of the fracture behavior of chocolate using notched samples. Two notched geometries were analysed and the fracture tests were carried out using the three point bending configuration at two span lengths. The experimental program was completed with tensile tests. The optimum values of Young’s modulus and maximum stress of the softening function obtained from the model were similar to those measured from tensile tests. Moreover the fracture energy of chocolate was also extracted. obtained as the area under softening function of the optimum solution.

Mixed modes crack paths in SCB specimens obtained via SLS

The paper presents experimental results of the crack path in Semi-Circular Bend (SCB) specimens obtained through additive manufacturing using Selective Laser Sintering (SLS) process. Determination of fracture parameters for components obtained via Additive manufacturing is a challenging topic, due to the influence of manufacturing parameters on the mechanical properties. Several researches provided the fracture toughness of SLS components, however there are not yet available results regarding the crack paths in such materials. The SCB specimens were designed with different crack orientations (0°, 15°, 30°, 45°, and 54°) and manufactured using EOS Formiga – SLS equipment (energy density 0.066 J/mm2, chamber temperature 169.5 °C, layer thickness 0.1 mm) using PA2200 material. The specimens were tested in symmetric three point bending configuration, creating 6 mode mixity from mode I (0° – crack orientation) to pure mode II (54° – crack orientation). Tests were performed at room temperature using 2 mm/min loading speed in a Zwick ProLine Z005 testing machine. For each crack orientation five specimens were tested. Crack initiation angle and crack propagation were measured by image digitization after the mechanical testing and presented in accordance to the initial orientation of the crack. Also, numerical simulation of crack path was conducted in the same way like the experiment and results were compared to the measured one.

Multifunctional Cement Mortars Enhanced with Graphene Nanoplatelets and Carbon Nanotubes.

Recent findings have brought forward the potential of carbon nano-species, especially nanotubes and graphene, to impart exceptional multifunctional potential to cement, offering simultaneous enhancement of mechanical, fracture mechanical and electrical properties. While available knowledge on the topic is still limited, there is a complete absence of direct comparisons of the potential of the nano-species to improve strength and toughness and provide multifunctionality to the mortars. The study offers a comprehensive overview of these potentials, for mortars modified with pure graphene nanoplatelets and carbon nanotubes at consistent, directly comparable, concentrations up to 1.2 wt.%. Testing included flexure under pure bending moments, axial compression, electrical resistivity measurements and fracture tests under three point bending configuration; the latter were also independently assessed by acoustic emission. Differences in documented properties and optimal concentrations associated with improved mechanical performance were directly compared and rationalized in terms of nanospecies morphology. Dramatic, statistically consistent improvements in fracture behavior, up to 10-fold of control values, were documented for specific nanofiller concentrations, indicating an excellent potential of the material system for contemporary smart construction applications. An exceptionally favorable comparison of acoustic emission and fracture energy data confirmed that the non-destructive technique can independently assess the fracture performance of mortars with exceptional precision.

The Influence of Reclaimed Asphalt Pavement on the Mechanical Performance of Bituminous Mixtures. An Analysis at the Mortar Scale

The main characteristics of bituminous mixtures manufactured with a considerable amount of reclaimed asphalt pavement (RAP), compared to conventional mixtures, are a reduction in workability, an increase in stiffness, and a loss of ductility, due to the presence of the aged bitumen contained in the RAP particles. To minimize these impacts, softer binders or rejuvenators are commonly used in the design of these mixtures in order to restore part of the ductility lost and to reduce the stiffness. In spite of previous investigations demonstrating that the mortar plays an essential role in the workability, long-term performance, and durability of bituminous mixtures (where cracking, cohesion, and adhesion problems all start at this scale), not many studies have assessed the impacts caused by the presence of RAP. In response to this, the present paper analyzes the workability, fatigue performance, and water sensitivity of bituminous mortars containing different amounts of RAP (from 0% to 100%) and rejuvenators. Mortar specimens were compacted using a gyratory compactor and studied via dynamic mechanical analysis under three point bending configuration. The results demonstrated that the presence of RAP reduces the workability and ductility of asphalt mortars. However, it also causes an increase in their stiffness, which induces a more elastic response and causes an increase in their resistance to fatigue, which could compensate for the loss of ductility. This aspect, together with the low water sensitivity shown, when using Portland cement as an active filler, would make it possible to produce asphalt materials with high RAP contents with a similar long-term mechanical performance as traditional ones. In addition, the use of rejuvenators was demonstrated to effectively correct the negative workability and ductility impacts caused by using RAP, without affecting the fatigue resistance and material adhesion/cohesion.

Microstructure and Mechanical Properties of BCC-FCC Eutectics in Ternary, Quaternary and Quinary Alloys From the Al-Co-Cr-Fe-Ni System

This study aimed at understanding the structure and properties of dual-phase eutectics in ternary, quaternary and quinary alloys of the Al-Co-Cr-Fe-Ni system. The alloys at case were (i) Ni48Fe34Al18, (ii) Ni44Fe20Cr20Al16 and (iii) Ni34.4Fe16.4Co16.4Cr16.4Al16.4. Samples in form of cylindrical bars, dia. 10 mm x 150 mm, were produced by arc melting and suction casting from pure elements (> 99.9 wt%). Bridgman solidification at low growth velocity was used to produce additional samples with large eutectic spacing and lamellae thickness of the two phases BCC-B2 and FCC in order to facilitate phase characterization by energy dispersive x-ray analysis (SEM / EDS) and nano-indentation. In agreement with thermodynamic calculations, each of the phases was found to be multi-component and contain all alloying elements in distinct amounts. The mechanical properties of the individual phases were analyzed in relation to their composition using nano-indentation experiments. These measurements revealed some insights into “high-entropy effects” and their contribution to the elastoplastic response to indentation loading. Further analysis focused on as-cast as well as heat-treated samples comprising phase fraction measurements, micro-indentation and miniature testing in three point bending configuration. For optimum heat treatment conditions, a good balance of strength and ductility was obtained for each of the investigated alloys. Further work is necessary in order to assess their capability as structural materials.

Flexural Performance Evaluation of Fiber-Reinforced Concrete Incorporating Multiple Macro-Synthetic Fibers

Fiber-reinforced concrete (FRC) is a promising construction material mainly because of the crack-controlling mechanisms that discrete fibers can impart to inherently brittle concrete. Macrofibers, in particular, have been proven effective for providing post-crack ductility and toughness, while synthetic fibers are a promising solution to avoid corrosion-related durability issues. To assess the performance enhancement provided by macro-synthetic concrete fibers, this study performs flexural tests on FRC beams containing three different types of macro-synthetic fibers. The selected fibers include polypropylene (PP), polyvinyl alcohol (PVA), and alkali-resistant glass (ARG) macrofibers mixed at volume fractions of 0.5%, 1.0%, and 1.5%. Static and dynamic fresh properties are monitored using the vibrating Kelly ball (VKelly) test. Beam specimens are then placed under a third point bending configuration, as per ASTM C1609 Standard, to measure load versus mid-span deflection. Strength and toughness parameters are derived from the load–deflection data to assess the flexural performance of the FRC composite systems under consideration. The parameters of interest include first peak strength (pre-crack flexural strength) and post-crack residual strength and toughness provided by fiber addition. Of the mixtures tested, ARG fiber mixtures show the highest residual strength and toughness values, followed by PP and PVA fiber mixtures. ARG fibers produce the most workable mixtures at all fiber volumes, while PVA fibers show a tendency to encounter dispersion issues at higher volume doses. The outcome of this study is expected to facilitate the selection of fibers by giving insight into their relative contribution to fresh and hardened flexural properties of FRC.

Short sisal fiber reinforced recycled concrete block for one-way precast concrete slabs

This work is dedicated to the assessment of the structural performance of a new lightweight block for one-way precast concrete slabs made of short sisal fiber reinforced concrete (SSFRC) containing natural and recycled aggregate. The influence of the sisal fibers and recycled aggregate on the physical and mechanical properties was assessed experimentally, with clear benefits of fiber reinforcement on the post-cracking flexural capacity, while the higher water absorption of recycled aggregates had favorable impact on the compressive strength mainly in the FRC. Flexural tests were carried out on SSFRC blocks, as well as on ceramic and expanded polystyrene (EPS) blocks used commercially. The SSFRC blocks presented higher load and deflection capacity with much more ductile behavior, and with a geometry favorable for the passage of infrastructures. Slab panels including SSFRC, ceramic and EPS blocks were tested under four point bending configuration to assess the benefits of the new SSFRC block in quasi-real slab conditions. The results of these tests demonstrated the best structural performance of the SSFRC blocks over the other considered commercial solutions, not only in terms of initial stiffness, but also for the load at serviceability limit deflection conditions (average increase of 23%) and yield initiation (average increase of 38%); The observed continuous crack pattern crossing the SSFRC blocks and the main precast RC beams demonstrated the potentialities of these blocks to contribute for the structural performance of this type of slabs. Material nonlinear finite element simulations were carried out to derive, by inverse analysis, the values of the fracture mode I parameters of SSFRC. This multidirectional smeared crack model was also used to simulate the behavior of the composite materials and the SSFRC blocks, and the obtained level of accuracy has demonstrated the adequacy of the adopted inverse analysis strategy. A Finally, a parametric study was carried out to preview the potentialities of these new SSFRC blocks for this structural application, having been verified that a SSFRC block of 12 mm thickness and 250 mm height, of about 10 kg, is capable of accomplishing the standard recommendations, constituting a competitive and efficient solution for this market segment.

Influence of the Bone Cements Processing on the Mechanical Properties in Cranioplasty

The aim of this study is to observe the time of mixing influence on the properties of commercially available PMMA bone cement, widely used in cranioplasty. The studied bone cement is provided in the form of a solid powder (the copolymer) and a liquid monomer. The increase of the mixing phase duration and the use of two mixing methods (manual and mechanical) effect on surface and mechanical characteristics were studied. The samples were prepared as if in the operation room. Surface characteristics were studied by means of contact angle measurements, morphology by scanning electron microscopy (SEM) and mechanical characteristics determined by flexural tests in a three point bending configuration. The conclusion of this study is that by using a mechanical mixing method and increasing mixing time higher flexural strength can be achieved by reducing pore content within bone cement.

Modeling post-fire behavior of aluminum structural components using a maximum temperature approach

Aluminum alloys exhibit permanent degradation of material strength subsequent to reaching temperatures above 200°C. While modeling of aluminum structural components during fire is becoming more heavily researched, modeling response of aluminum structures following fire events has still not been explored. Previous research suggests that the post-fire strength of AA6061 is heavily correlated to the maximum temperature reached during the fire. This research uses the maximum exposure temperature as an input to finite element simulations of a small scale aluminum beam to predict the post-fire behavior of the beam. Results of the simulations were compared to a set of post-fire thermo-mechanical experiments. Samples were heated using a radiative source, water quenched, and then loaded to failure in a four point bending configuration. The simulated thermal response of the aluminum was within 10% of measured values across the entire side of the beam. Prediction of the unexposed mechanical response was within 5% of experimentally measured response. The post-fire peak bending load from simulations generally over-predicted the experimentally measured value while predictions of the flexural stiffness were within 15% of experimental results.

Effect of service temperature on the flexural creep of vacuum infused GFRP laminates used in sandwich floor panels

This paper presents an experimental and analytical study about the effect of temperature on the flexural creep of GFRP laminates produced by vacuum infusion. Such laminates are considered for use in the faces of sandwich panels for building floor application. Flexural creep tests were carried out in a three point bending configuration for stress levels of 15%, 25% and 35% of the laminate's flexural strength, and temperatures of 20 °C, 24 °C and 28 °C (a range likely to be found in the envisaged application), with durations between 1000 h and 2215 h. The creep response was observed to increase both with temperature and stress level. Findley's power law was used to model the experimental results, and extended to include an Arrhenius equation for temperature dependence of the creep response. The proposed model provided a good fit to the experimental creep curves, and was used to derive a set of practical design equations for the time-temperature dependent (i) flexural modulus, (ii) creep coefficient, and (iii) flexural modulus reduction factor. Finally, the time-temperature-stress superposition principle (TTSSP) and the time-stress superposition principle (TSSP) were used to obtain “master curves” that compared well with the proposed model's predictions.

Experimental and Numerical Study on the Cracked Chevron Notched Semi-Circular Bend Method for Characterizing the Mode I Fracture Toughness of Rocks

The cracked chevron notched semi-circular bending (CCNSCB) method for measuring the mode I fracture toughness of rocks combines the merits (e.g., avoidance of tedious pre-cracking of notch tips, ease of sample preparation and loading accommodation) of both methods suggested by the International Society for Rock Mechanics, which are the cracked chevron notched Brazilian disc (CCNBD) method and the notched semi-circular bend (NSCB) method. However, the limited availability of the critical dimensionless stress intensity factor (SIF) values severely hinders the widespread usage of the CCNSCB method. In this study, the critical SIFs are determined for a wide range of CCNSCB specimen geometries via three-dimensional finite element analysis. A relatively large support span in the three point bending configuration was considered because the fracture of the CCNSCB specimen in that situation is finely restricted in the notch ligament, which has been commonly assumed for mode I fracture toughness measurements using chevron notched rock specimens. Both CCNSCB and NSCB tests were conducted to measure the fracture toughness of two different rock types; for each rock type, the two methods produce similar toughness values. Given the reported experimental results, the CCNSCB method can be reliable for characterizing the mode I fracture toughness of rocks.

EFFECT OF NANOCLAY CONTENT ON FLEXURAL PROPERTIES OF GLASS FIBER REINFORCED POLYMER (GFRP) COMPOSITES

This paper presents a study on the flexural properties of glass fiber reinforced polymer composites. The epoxy-nanoclay resin was milled using a three roll mill machine to produce exfoliated structure nanocomposites. The fiber laminates specimens were manufactured by vacuum bagging system. These specimens were tested in the three point bend configuration following the ASTM D7264. The flexural modulus, flexural strength and strain to failure were then determined based on the flexural test results. The results showed that flexural modulus and flexural strength increases when a certain amount of nanoclay was included in the resin system. A maximum of 80% and 37% improvement of flexural strength and flexural modulus, respectively, were found at 5 wt% nanoclay content when compared to the neat GFRP composite. The improved properties of GFRP composites were achieved mostly due to an increase on the interfacial surface areas as well as a well-dispersion of nanoclay in the GFRP composite system. The fracture surfaces of specimens after flexural test were observed under FESEM. The results showed that the compressive failure region in the fiber was a dominant failure mechanism of the specimens due to a large compressive area on the fracture surface.

Bending test for capturing the vivid behavior of giant reeds, returned through a proper fractional visco-elastic model

This paper presents results of experimental investigations made to evaluate the vivid behavior of giant reed Arundo donax. In particular, attention was paid to the relationship between visco-elastic properties and moisture content, which is widely recognized as one of the key factor that influences the mechanical properties of all wood-based materials. To this aim, after a controlled drying treatment on samples of reed, stress relaxation tests in three point bending configuration were performed to evaluate the effects of moisture content on visco-elastic behavior of the giant reed. Further, the novel aspect of this paper is that of using an Euler–Bernoulli model embedded with an advanced visco-elastic constitutive law to fit experimental data of bending tests. Such a model of continuum beam takes into account different constitutive laws of viscoelasticity, being natural materials visco-elastic.

Fatigue Life of GMAW and PAW Welding Joints of Boron Microalloyed Steels

Recently boron microalloyed steels have become an alternative in weight saving in structural elements in automotive industry, especially for parts like pillars and columns and reinforcements. These materials are used as quenched and tempered, reaching strength values between 1000 and 1500MPa. Welding is a relevant issue as a fabrication process in automotive industry, in particular for high strength steels. Furthermore, fatigue life of these welded joints plays a very important role for these applications. Gas metal arc welding (GMAW) is one of the more widely used welding processes in automotive industry. Indeed, different aspects of plasma arc welding (PAW) make it an interesting option for these applications. The objective of this work was to evaluate the fatigue life of GMAW and PAW welded joints of boron microalloyed steels, in a quenched and tempered condition. Samples of 100×100mm were butt welded by GMAW and PAW and microstructural and mechanically characterized. Fatigue curves were obtained for both processes in a four point bending configuration. It was observed that PAW welded samples had a higher fatigue life than those welded by GMAW. Weld bead toes of GMAW joints acted as geometric stress concentrators, being the main responsible for fatigue resistance reduction.

Dynamic Fracture Toughness of a Plain Weave Carbon-Epoxy Composite: Validation of Test Results with Finite Element Analyses

Abstract This document presents the Dynamic Fracture Toughness (KID) measurement for a plain weave carbon-epoxy composite material. An instrumented Hopkinson bar arrangement is used to perform the tests with pre-cracked specimens loaded on a three point bending configuration. The material behavior obtained by the experimental results is compared with Finite Element simulation of static and idealized Hopkinson bars events. A number of important aspects are approached. Among them, the Stress Intensity Factor (SIF) for fiber-epoxy composites considered as transversely isotropic media, the formulae to obtain this parameter compared with isotropic materials, and the precise follow of the SIF evolution during these events. The Finite Element Analyses (FEAs) suggest loss of contact phenomena not only in the transmitted but also with the incident bar, and according to this, a specimen FEA is used to verify the influence of this loss of contact in the SIF evolution and KID calculations. Accordingly, a novel approach using the incident pulse as input for a FEA of the complete arrangement including contact elements is proposed and implemented, so the new revealed phenomena are taken into account. The experimental results using this approach show that the dynamic fracture toughness varies from 15.45 to 25.6 MPa*m0.5 in the projectile speed range between 10 and 20 m/s.

Dynamic mechanical analysis of high pressure polymerized urethane dimethacrylate

ObjectivesThe aim of this study was to compare the viscoelastic properties of high pressure (HP) polymerized urethane dimethacrylate (UDMA) with those of control, ambient pressure thermo-polymerized and photo-polymerized, UDMA and to assess the effect of varying polymerization parameters (protocol, temperature, and initiator) on the viscoelastic properties of HP polymerized UDMA. MethodsThe viscoelastic properties of the two control polymers, polymerized under atmospheric pressure, and four experimental polymers, polymerized under HP, were determined via dynamic mechanical analysis (DMA), in three point bending configuration. Atomic force microscopy (AFM) was used to characterize fractured polymer surface morphologies. ResultsThe results showed that: HP-polymerization lead to a polymer with significantly higher Tg and E′rub, indicative of a higher crosslink density; modifying the polymerization protocol resulted in a significant increase in tanδ; increasing the polymerization temperature lead to a significant decrease in E′rub and Tg; and that the polymer with no initiator had the lowest E′, E″, Tg, and E′rub and the highest tanδ, suggesting that under this conditions a polymer with significantly reduced crosslink density had been obtained. A characteristic nodular appearance was seen for the two control polymers under AFM, while a modified surface morphology was present in the case of HP polymerized materials. SignificanceThe DMA results suggest that polymerization under HP resulted in polymers with an increased crosslink density and that the higher polymerization temperature or the lack of initiator was detrimental to the viscoelastic properties determined. Changes in polymer network morphology were identified by AFM characterization.

Numerical–experimental method to study the viscous behaviour of ceramic materials

The aim of the work deals with the development of a numerical–experimental method to study the viscous behaviour of ceramic materials and to estimate the viscosity evolution as a function of temperature. The current state of the art regarding the study of viscous behaviour of ceramic materials is carried out by using optical methods able to perform measurements without contact with the sample to be analyzed. The two point bending configuration is the conventional test currently used. Despite the use of the optical technology, the test specimen, because of its viscous behaviour, interferes with the measuring device. The experimental test results are inevitably compromised. The developed numerical–experimental method aims at overcoming the drawbacks of the conventional experimental test configuration and at determining the material viscosity. This method consists of an ad hoc developed experimental test configuration and of a numeric simulation of the experimental test.

Flexural Properties of Wheat Straw Reinforced Polyester Composites

A study on the flexural properties of wheat straw reinforced polyester composites is presented in this paper. The wheat straw/polyester composites were made as per the hand layup procedure and the instructions provided by the manufacturers. These specimens were then tested in the three point bend configuration in accordance with ASTM D790-07 at a span to depth ratio of 16. Four weight fractions of wheat straw 2%, 4%, 6% and 8% were chosen to be studied. The process-induced voids were studied and it is shown that voids play an important role in flexural properties. When voids exist, flexural modulus was calculated using a micromechanical model. It is shown from both the experimental results and calculation that flexural modulus decreases with the addition of wheat straw, and this reduction in flexural modulus is due to process-induced voids. Flexural strength of polyester resins does not increase with the addition of wheat straw as rein- forcement. This is due to poor interfacial adhesion and the existence of voids. In order to achieve reinforcement, treatment of straw fibers and better processing techniques to reduce voids are needed.

Flexural properties of macadamia nutshell particle reinforced polyester composites

A study on the flexural properties of macadamia nutshell particle reinforced polyester composites is presented in this paper. The macadamia nutshell/polyester composites were made as per the hand layup procedure and the instructions provided by the manufacturers. These specimens were then tested in the three point bend configuration in accordance with ASTM D790-07 at a span to depth ratio of 16. Four weight fractions of macadamia nutshell particles 10%, 20%, 30% and 40% were chosen to be studied. The process-induced voids were studied and it is shown that voids play an important role in flexural properties. When voids exist, flexural modulus was calculated using a micromechanical model. It is shown from both the experimental results and calculation that flexural modulus increases with the weigh fraction of macadamia nutshell particles, while decreases with increasing void content. Adding macadamia nutshell particles does not improve the flexural strength of polyester. It is shown flexural strength decreases with increasing void content.

Flexural properties of S‐2 glass and TR30S carbon fiber‐reinforced epoxy hybrid composites

AbstractA study on the flexural properties of hybrid composites reinforced by S‐2 glass and TR30S carbon fibers is presented in this article. Test specimens were made by the hand lay‐up process in an intraply configuration with varying numbers of glass/epoxy laminas substituted for carbon/epoxy laminas. These specimens were then tested in the three point bend configuration in accordance with ASTM D790‐07 at a span to depth ratio of 32. The failed specimens were examined under an optical microscope, and the results show that the dominant failure mode is at the compressive side. The flexural behavior was also simulated by finite element analysis (FEA). Based on the FEA results, the flexural modulus and flexural strength were calculated. Good agreement is found between the experiments and FEA. It is shown that flexural modulus decreases with increasing percentage of S‐2 glass fibers, positive hybrid effects exist by substituting carbon fibers for glass fibers, and applying a thin layer of S‐2 glass fiber‐reinforced polymer on the compressive surface yields the highest flexural strength. The modeling approach presented will pave a way to the effective design of hybrid composites. POLYM. COMPOS., © 2012 Society of Plastics Engineers