Conventional Bending Tests Research Articles

Microscopic mechanical properties of silicon nitride ceramics corroded in sulfuric acid solution

The microscopic mechanical properties including the bending strength and Young’s modulus for Si3N4 ceramics doped with Y2O3 and Al2O3 which was immersed in 5 wt% sulfuric acid solution using microcantilever beam specimens was investigated in comparison with the macroscopic results obtained in conventional three-point bending tests. Both the properties sharply dropped in very short periods of the corrosion in the microcantilever tests, resulting from the dissolutions of yttrium and aluminum ions of grain boundary glass networks, followed by the hydration. After the drops at the beginning of the corrosion, they showed little degradation afterwards. The degradation behaviors of the mechanical properties are basically the same as those in conventional macroscopic approaches; however, they changes appear in very short periods of the corrosion in the microcantilever bending tests. This study also verified that a small difference of a ratio of sintering additives results in different grain boundary strengths of Si3N4 ceramics.

A Novel Model of Ultrasonic Fatigue Test in Pure Bending.

The very high cycle fatigue (VHCF) failure of in-service components is mainly caused by the vibration of thin-wall elements at a high frequency. In this work, a novel model of ultrasonic fatigue test was developed to test thin-wall material in bending up to VHCF with an accelerated frequency. The theoretical principle and finite element analysis were introduced for designing a sample that resonated at the frequency of 20 kHz in flexural vibration. In the advantage of the second-order flexural vibration, the gauge section of the sample was in the pure bending condition which prevented the intricate stress condition for thin-wall material as in the root of cantilever or the contact point of three points bending. Moreover, combining the constraint and the loading contact in one small section significantly reduced heating that originated from the friction at an ultrasonic frequency. Both strain gauge and deflection angle methods were applied to verify the controlling of stress amplitude. The fractography observation on Ti6Al4V samples indicated that the characterized fracture obtained from the novel model was the same as that from the conventional bending test.

Hybrid Finite-Discrete Element Modelling of Various Rock Fracture Modes during Three Conventional Bending Tests

The numerical techniques for modelling the rock fracture have been briefly reviewed. A hybrid finite-discrete element method (HFDEM) is proposed to simulate various fracture types of rock. A fracture model is implemented in the HFDEM for simulation of the three main fracture types. In addition, the influence of the strain rate is considered during the HFDEM modelling rock behavior. Then, two typical rock mechanism tests are employed to calibrate the HFDEM. The proposed method has well modelled the rock fracture processes and can obtain reasonable stress distribution and force–displacement curves. After that, the HFDEM is used to model three convention bending tests. The obtained rock fracture processes indicates that the HFDEM can simulate various fracture types. The obtained rock strengths and fracture toughness indicate that the HFDEM can reflect the influence of the strain rate. It is concluded that the HFDEM can model the entire and complete rock fracture process during the three convention bending tests, and it also can capture the rock’s behavior on the strain rate.

Proposal of a pure bending test method for advanced composite materials

This paper proposes a simple and precise pure bending test method for composite materials. With CFRP as the subject, we compare conventional bending test methods and extract issues for each of them. Based on the results, we propose a test method that can solve the complexities of the conventional pure bending test method and can also accurately measure the characteristics of the pure bending property. The proposed test method is simpler than the conventional ones and agrees well with the theoretical values.

Strengthening mechanism of fracture properties by nano materials for cementitious materials subject to early-age frost attack

With the increasing interest and utilization of nano materials to cementitious materials, the mechanical properties of the nano materials-modified cementitious materials under the severe environmental conditions is critical for their successful application. This study investigates the fracture toughness of nano materials-strengthened cement paste by nano silica particles and carbon nanotubes at the micro and macro scales by using nano-scratch technique and the conventional three-point bending test, respectively. The aim is to better understand the strengthening mechanism of these two nano materials on the fracture properties of cementitious materials subject to early-age frost attack. The paste sample is designed subject to freeze-thaw cycles at the age of 1, 3, and 7 days, and then sealed cured after the 7 days’ freeze-thaw period until the age of 28 days. The micro fracture toughness of the unreacted clinker, the hydrates, and the interfacial transition zone (ITZ) between the unreacted clinker and the surrounding hydrates is measured as well as the thickness of ITZ. The effect of nano silica and carbon nanotubes on the fracture properties are discussed and compared, and the different strengthening mechanism of these two nano materials are recognized. The results of this study are beneficial for designing mixtures to achieve better early age frost resistance that satisfies the engineering applications.

Mechanical Characterisation of Single-Walled Carbon Nanotube Heterojunctions: Numerical Simulation Study.

The elastic properties of single-walled carbon nanotube heterojunctions were investigated using conventional tensile, bending and torsion tests. A three-dimensional finite element model was built in order to describe the elastic behaviour of cone heterojunctions (armchair–armchair and zigzag–zigzag). This comprehensive systematic study, to evaluate the tensile, bending and torsional rigidities of heterojunctions, enabled the formulation analytical methods for easy assessment of the elastic properties of heterojunctions using a wide range of their geometrical parameters.

A new perspective on mechanical characterisation of Arabidopsis stems through vibration tests

The mechanical properties of plants are important for understanding plant biomechanics and for breeding new plants that can survive in challenging environments. Thus, accurate and reliable methods are required for the determination of mechanical properties such as stiffness and Young's modulus of elasticity. Much attention has been paid to the application of static methods to plants, while dynamic methods have received considerably less attention. In the present study, a dynamic forced vibration method for mechanical characterisation of Arabidopsis inflorescence stems was developed and validated against the conventional three-point bending test. Compared to dynamic tests based on free vibration, the current method allows to determine simultaneously more than one natural frequency, thus increasing the overall accuracy of the results. In addition, this method can be applied to the top parts of the stems that are more flexible, and where application of the three-point bending test is often limited. To demonstrate one of the potential applications of this method, it was applied to evaluate the influence of turgor pressure on the mechanical properties of Arabidopsis stems. Overall, the new dynamic testing approach has been shown to provide reliable data for the local mechanical properties along the Arabidopsis inflorescence stem.

Low-cost bending test laboratory kit

The big dimension and higher price of conventional bending test machine is making the school and start-up company hard to fulfilled. This study aims to demonstrate a new design of a low-cost and portable laboratory kit that is prospective for bending test. The kit is using hydraulic pressure tools with maximal capacity is about 6 tons. Economic analysis and smaller dimension of this kit (length x width x height of 700x100x750 mm) Showed that this kit is a low-cost and adaptable to classroom and easy to assemble for school. The different between another modification before bending test kit is on the pedestal and the suppressor of the kit is the which is allowing the machine to test materials with Thicker dimensions. The test result Obtained by calculating the maximum compressive force, moment of cross section innersia, flexural strength and elastic modulus of speciment. The result Also Compared with another test material from bending test machine with the American society of testing and materials (ASTM) standard and Showed that there is not much different in the test result for both. Further development of this kit is Potentially implemented an as an experimental tool for the student.

Measurement of tensile strength of brittle rocks using a half ring shaped specimen

A tensile test using a half ring (HR) shaped specimen is attempted for the determination of the tensile strength of rock materials. The HR test is a 3-point bend test similar to the semicircular bend (SCB) test. However, the HR specimen is a curved prismatic bar. The theoretical tensile strength of this special bar can be obtained by an analytical formula derived from a basic theory of strength of materials. Owing to the eccentricity of the HR specimen, the possibility for a single tensile fracture to begin at the intended location can increase. This may give results that are more accurate than the conventional bending tests. In this paper, after the concept and formula of the HR test are introduced, its applicability to brittle rocks is investigated by FEM simulations and laboratory tests. In the processes, the theories of the Brazilian test and a special SCB test, which is an alternative to the Brazilian test, are used to examine the accuracy of the HR test.

The IC in the Flexible Hybrid Electronics Technology: Flexibility and Bend Testing

Abstract Flexible Hybrid Electronics (FHE) can be described as thinned, flexible silicon chips packaged on flexible circuit board (FCB) with printed conductors and passives. The flexibility of ICs can be achieved only if the thickness of the silicon is reduced to 50μm or less. The bend testing of the ultra-thin dies is a critical issue in the FHE technology as it allows to establish the fundamental relationships between the die flexural strength, die geometry, and the methods for thinning and dicing the silicon. The conventional bend tests are not adequate for testing ultra-thin dies. Presented is a semi-empirical test method, which allows for the estimation of the flexural strength of the highly compliant ultra-thin dies. The limiting Radius of Curvature (RoC) is an important parameter for the FHE device since it accounts for the bending characteristics of the entire FHE device, not only the IC. Presented is a simple analytical approach that allows to estimate the minimum RoC for an FHE assembly.

Quantitative evaluation of bending reliability for a flexible near-field communication tag

Flexible electronic devices under repetitive use inevitably entail damage accumulation that can cause failures in the components and interconnects. The main aim of this study involves proposing test procedures and corresponding testers that can be used to systematically evaluate the bending reliability of flexible electronic devices. In contrast to conventional bending test techniques based on a collapsing radius method, in the present study, the flexible devices were wrapped onto a roller to ensure a constant strain. An example of a near-field communication tag for smart phones was examined to verify the proposed test methods and testers. The results indicated that the critical curvature for cyclic failure was significantly lower than the static critical curvature. Curvature-life diagrams as evaluated by the proposed test method revealed that bending radius and alignment methods significantly affected the reliability of the tags. Thus, the curvature-life diagrams can be used to design a roller radius based on a predefined product life.

A Small-Scale, Contactless, Pure Bending Device for In-situ Testing

The introduction of flexible electronics calls for new ways of measuring the mechanical limits and failure mechanisms resulting from (large) bending loads during manufacturing and application. Therefore, an autonomous, miniaturized, pure bending test apparatus was developed to investigate material systems at the microscopic level. Improvements to conventional bending test methods are: (1) well-defined pure moment application without friction or local pressure contacts, through active feedback control of parasitic axial and transverse forces at the specimen edges, (2) continuous reversibility of the loading direction within an angular range of −114∘≤𝜃≤114∘ (minimum radius of 2 mm), (3) no view-obstruction from both the thickness and in-plane perspective, enabling in-situ optical and scanning electron microscopic studies of failure mechanisms under constant field-of-view. The pure bending test setup was validated by moment-curvature measurements of monocrystalline silicon. The setup’s continuous load-reversibility and strain determination were validated by cyclic tests and in-situ digital image correlation, respectively, on polyethylene napthalate specimens. Furthermore, in-situ microscopic failure analysis was demonstrated on multilayered flexible electronics, revealing fracture, delamination and buckling.

Evaluation of gas permeability and mechanical behaviour of soil barriers of landfill cap covers through laboratory tests

The soil barrier is one of the commonly used impervious barriers which are required to sustain deformation and prevent the migration of biogas to the atmosphere. In the present study, a simple custom designed gas permeability–bending test setup was developed and used to evaluate the deformation behaviour of the soil barrier material in-relation with gas permeability measurements. A series of conventional beam bending tests, unconfined compression tests and gas permeability–bending tests was performed to evaluate the influence of loading pattern, compaction characteristics and fibre reinforcement on the deformation behaviour of the soil barrier material. The experimental results reveal that loading pattern was not found to have any significant influence on the flexural tensile strength of the soil; however, a considerable influence on the displacement corresponding to gas breakthrough was noticed mainly due to the variation in the cracking pattern. An increase in the moulding moisture content of the soil leads to a significant delay in crack initiation and gas breakthrough with a slight reduction in the flexural tensile strength. The percentage increase in the flexural tensile strength of the soil beam compacted with 2% and 4% wet of optimum, upon inclusion of fibres was found to be 33% and 92% respectively. Similarly, the percentage increase in the limiting displacement of the soil moist-compacted at 2% and 4% wet of optimum, upon inclusion of fibres was found to be 30% and 25% respectively, which implies that soil reinforced with fibres can sustain its integrity in-terms of gas intactness up to relatively larger distortion than an un-reinforced soil barrier material. The performance of the deformation behaviour of the soil barrier material has significantly improved in-terms of flexural tensile strength and gas intactness upon inclusion of discrete fibre inclusions within the soil.

The effect of boot stiffness on field and laboratory flexural behavior of alpine ski boots

The aim of this work was to study the effect of boot stiffness on the field and laboratory flexural behavior of alpine ski boots. Ski boots have a direct influence on performance, safety, and comfort of alpine skiers. Despite their technological evolution during a number of years, the parameters used in the evaluation of boot stiffness are not yet standardized and still require a shared engineering approach to achieve common quantitative definitions to be used either in boot classification or in boot selection for the different users. This work reports the boot flexion angles between shell and cuff and between cuff and tibia, collected during slalom tests on three boots with different nominal Flex Index. The laboratory data collected on the same boots under conventional cyclic bending tests are reported and compared with the field data for the development of a new test method more representative of the field behavior. As a result, clear definitions of Flex Index and of boot stiffness are introduced: boot stiffness had a clear effect on both the field and the laboratory flexural behavior of boots.

3点曲げ試験によるCFRTPの縦弾性率および面外せん断弾性率に関する評価

Novel CFRTPs (carbon fiber reinforced thermoplastics) for mass production automobile have been developed in Japanese METI-NEDO project (2008-2012 fy). These CFRTPs have not only high mechanical properties, but also high cycle moldability and high recyclability. To perform reliable structural design for the CFRTP, we discussed if the use of conventional test method is applicable or not. Because shear modulus of the matrix of CFRTP is sometimes low, out-of-plane shear modulus of CFRTP would be lower than that of CFRTS (carbon fiber reinforced thermosetting resin), so conventional bending test standard may not be applicable to CFRTP. Hence this paper proposes a simple method to estimate accurate Young’s modulus and out-of-plane shear modulus by three point bending tests with small specimen. Three point bending tests are performed with changing the span length for the same specimen, the results of apparent flexural modulus are plotted, y-intercept and gradient are calculated by least squares method, and Young’s modulus and out-of-plane shear modulus are calculated based on a theory. It was found that Young’s modulus of CF/PP was accurately estimated by the method proposed in this study and underestimated by JIS standard. In addition, out-of-plane shear modulus was also able to be estimated by this method.

The utility of low-cost photogrammetry for stiffness analysis and finite-element validation of wood with knots in bending

This article presents the capabilities of low-cost photogrammetry as a tool for stiffness analysis and finite-element (FE) validation in conventional bending tests of structural timber that contains knots. The accuracy offered by three consumer-grade digital cameras with a resolution of 10 megapixels was 1/6200, which did not allow for the evaluation of the stresses or strains in a multiaxial stress field, but provided a thorough contrast of the 3D nodal displacements, showing the distortion of knots in the modulus of elasticity (MOE), so that the heterogeneous stiffness of this natural material could be measured and accounted for. This allowed a more precise determination of the wood stiffness in bending, and a novel procedure for the estimation of a Clear MOE related to the defect-free areas, an MOE in Knots related to the distorted regions, and a Global MOE which encompasses both was developed. The proposed method can be applied to conventional mechanical tests. In addition, other interesting possibilities for FE validation and monitoring were obtained. The case study demonstrates how, with a very small investment, an FE model that simulates the influence of knots in bending could be accurately validated with many fewer specimens, and how the predictions of displacements could be improved by up to 49% using the Clear MOE measured by means of the photogrammetry rather than the conventional MOE without shearing strain. ► Low-cost photogrammetry used to determine mechanical properties of timber pieces. ► Novel procedure for obtaining more precise wood stiffness measurement is proposed. ► Predicted stiffness using proposed numerical simulations improved by up to 49%

Should screening for scoliosis be conducted?

This review provides an overview of the new evidence on the use of school screening for adolescent idiopathic scoliosis (AIS), in response to the concerns of the United States Preventive Services Task Force.School scoliosis screening, if carefully designed and planned, can effectively detect AIS patients with significant curvature. A tandem use of screening methods in addition to the conventional forward bending test may improve screening effectiveness. School scoliosis screening continues to be an effective platform for early conservative treatment of AIS.

Influence of Surface Quality on the Biaxial Strength of Silicon Nitride Specimens

Abstract Details of surface finish affect significantly the surface quality of ceramic specimens (e.g. surface roughness, residual stress). To analyse the influence of surface quality on strength five samples of silicon nitride specimens were machined applying different surface finishing procedures. Then they were strength tested using the biaxial Ball-on-three Balls (B3B) test. The test results were compared to those of conventional bending tests. A fractographic analysis was performed on selected specimens to identify the fracture origins. It could be shown that a better surface quality leads to an increased strength but increases the scatter of strength data too.

Simple method of dynamic Young’s modulus determination in lime and cement mortars

The present work explains a simple method to determine the dynamic Young module (MOE) by inducing a set of small mechanical perturbation to samples of lime and cement mortars and correlating the results obtained with results determined using other techniques and methods. The procedure described herein follows the instructions stated in the UNE-EN ISO 12680-1 standard for refractory products although in this study the instructions are applied to standardized RILEM 4x4x16 cm test samples made of lime and cement mortars. In addition, MOE determinations are obtained by using ultrasonic impulse velocity while static Young's modulus determinations are obtained by performing conventional bending tests. The ability of this procedure to correlate with results from other techniques, along with its simplicity, suggests that it can be widely adapted to determine the deformability of mortars under load using standardized samples.

Effects of Impurity Elements on Green Strength of Powder Compacts

The green strength of a powder compact results from the mechanical interlocking of the irregularities on the particle surfaces. During compaction, particle rearrangement, plastic deformation and particularly surface deformation of powders occur. Titanium powder is susceptible to interstitial element contamination, which may lead to solid solution strengthening of the particles and/or the formation of non-metallic compounds on the surface. However, the influence of these various impurities, namely oxygen and nitrogen, on the green strength has not been investigated. This work investigates and quantitatively evaluates the factors influencing the green strength of the powder compacts. The indirect tensile test was applied for the determination of the green strength of the powder compacts, and test results were compared to that of a more conventional 3-point bending test. The substantial dependence of green strength on both the amount of impurity element in the core of the powder particles and the compaction pressure is demonstrated. The effect of the surface condition of the powder particles on green strength is also reported.