Uniaxial Bending Tests Research Articles

High-temperature fracture behaviour of layered alumina ceramics with textured microstructure

Mimicking the damage tolerance of biological materials such as nacre has been realised in textured layered alumina ceramics, showing improved reliability as well as fracture resistance at room temperature. In this work, the fracture behaviour of alumina ceramics with textured microstructure and laminates with embedded textured layers are investigated under uniaxial bending tests at elevated temperatures (up to 1200°C). At temperatures higher than 800°C monolithic textured alumina favours crack deflection along the basal grain boundaries, corresponding to the transition from brittle to more ductile behaviour. In the case of laminates, the loss of compressive residual stresses is counterbalanced by the textured microstructure, effective up to 1200°C. This study demonstrates the potential of tailoring microstructure and architecture in ceramics to enhance damage tolerance within a wide range of temperatures.

Development and investigation of an innovative, light-weight, two-way spanning timber-concrete composite slab

Timber-concrete composite (TCC) slabs play an essential role in modern timber construction. Consisting of a timber member in the tension zone, a concrete layer in the compression zone and a shear connection between the two parts, TCC slabs feature a number of advantages that make them ideally suitable for use in both office and residential buildings. However, currently used TCC slab systems carry loads only in one direction. In the frame of a large research project in cooperation with the industry, an innovative, light-weight, two-way spanning timber-concrete composite slab using beech laminated veneer lumber with steel tubes as connectors was developed. This paper presents the main results of the research project. First, the structural behaviour of the connection is characterised and discussed based on extensive experimental and analytical analysis. Second, the load-bearing behaviour of the TCC slab investigated in uniaxial bending tests is presented. The uniaxial bending tests showed a remarkably ductile global load-bearing behaviour due to the ductile failure mode in the connectors. A developed analytical model can describe the observed load-bearing behaviour of the tested TCC members accurately. Finally, the biaxial load-bearing behaviour of the TCC slab is characterised and discussed based on a large-scale experiment that allowed to perform static and dynamic tests on the same specimen in different support conditions. A substantial increase in stiffness and fundamental frequency in biaxial versus uniaxial support conditions was observed and accurately modelled, showing the great potential of the novel TCC slab.

Probability of failure and weibull size-scaling parameters for thin glass subjected to two-point bending

The two-point bending test is a valuable test for estimating the strength of the thin and flexible glass/ceramic parts that are increasingly used in next-generation flexible electronics devices. We present closed-form expressions for determining Weibull material scale parameters and probability of failure for the two-point bending test. The presented solution, tested on Corning® Willow® glass samples, eliminates the need for iterative and often time-consuming approaches (e.g., Finite Element Analysis) for estimating scale parameters. Considering the strength-controlling flaw distribution on a surface or inside a volume, the solution assumes that the Weibull modulus (m) and scaling modulus (mAor mV) are distinct quantities to ensure the scale parameter is independent of the applied load. This condition reveals a special relationship between the moduli that is unique to two-point bending given its highly non-uniform state of stress, which contrasts with other uniaxial bending tests (such as three and four-point bending) in which both moduli have the same numerical value.

The Effect of Low-Processing Temperature on the Physicochemical and Mechanical Properties of Bovine Hydroxyapatite Bone Substitutes.

Bovine bone grafts (BBX) require protein removal as part of the manufacturing process to reduce antigenicity and, in consequence, to be safely used in humans. Deproteinisation may have direct effects on the characteristics of the bone material and on in vivo material performance. This research aimed to comprehensively study the physicochemical and mechanical properties of BBX processed at low deproteinisation processing temperatures. Cubes of bovine bone (8 mm3) were treated with temperatures between 100 °C and 220 °C at 30 °C intervals and with pressures ranging from 1.01 to 24.58 Bar. The samples were characterised topographically and mechanically using scanning electron microscopy (SEM), atomic force microscopy (AFM), and uniaxial bending tests. The organic content and the chemical composition were determined using thermogravimetric analysis (TGA) and Fourier-transform infrared spectroscopy (FTIR). X-ray diffraction (XRD) and FTIR were also used to quantitatively determine the specimen crystallinity. Increasing temperature/pressure was associated with decreasing protein levels and compressive strength and increasing surface irregularities and crystallinity. The findings suggest that low-temperature processed bone is likely to exhibit a rapid in vivo degradation rate. The deproteinisation temperature can be adjusted to tailor the graft properties for specific applications.

The breakdown of the Weibull behavior in dental zirconias

AbstractHere we attend to the controversy of the use of Weibull statistics for describing the strength distribution of dental brittle materials. Our approach is purely experimental by means of testing for the strength size effect, a requirement for Weibull materials. Zirconia materials of five important dental manufacturers were selected, each represented by two compositions, being one a 3 mol% Y2O3‐stabilized zirconia, and the other being a “translucent” zirconia with 4 or 5 mol% stabilizer content. Specimens of increasing sizes were fractured, whether by using a biaxial flexure test in plates or a uniaxial bending test in beams, thereby sampling different ranges of effective surfaces and volumes. A systematic deviation from the Weibull behavior over the range of 1–40 mm2 effective surface was demonstrated, regardless of manufacturer and Y2O3 content in the powder. Extensive testing using a wider range of specimen sizes narrowed down the threshold for the breakdown of the defect size distribution from the parent population to be located between 10 and 20 mm2 effective surface. A comparable behavior was confirmed for the partly sintered white‐bodies, with similar defect morphology to the fully sintered analogs, indicating a defect size distribution stemming from the pressing steps of manufacture. The defect shape related to open particle aggregate junctions, pointing to an association of their size distribution to that of the distribution of aggregate sizes in the source powders.

Derivation of a fatigue damage law for an adhesive from in-situ bending tests

The adhesives used for the attachment of electronic components to space boards should withstand harsh vibrations of the space launch, which requires their characterization in fatigue. The present study investigates Ablestik 8-2 epoxy adhesive within this context. Novel adhesive test assemblies were devised, which consist of a rigid ceramic component bonded to a resonant flexible epoxy-fibreglass (E-glass) support. Cantilever and square E-glass supports produced uniaxial and biaxial bending, respectively. The in-situ fatigue tests, conducted on batches of uniaxial/biaxial bending adhesive assemblies, led to distinct data sets of maximum support deflection versus the number of cycles to crack initiation/total failure. The derivation of an intrinsic fatigue damage law of the adhesive relied on the substitution of deflection by the maximum principal strain of each adhesive point while keeping the Basquin’s form. In so doing, the adhesive strain was computed from finite element models of test assemblies built and simulated under Abaqus. The adhesive layer was meshed by cohesive elements created through a Fortran user-element subroutine coupled to Abaqus. The subroutine incorporated an already validated static damage together with the strain-based fatigue damage law sought. The retained Basquin’s fatigue damage law has undergone calibration against uniaxial bending test data and validation by biaxial bending test data.

The physical properties and strength characteristics of kenaf plants

This article reports some physical properties and strength characteristics of two kenaf (Hibiscus cannabinus) varieties in Nigeria at critical stages of harvest with a view of understanding the plant material reaction to the load and deformation. The kenaf samples were subjected to a uniaxial compression test between two parallel plates at a loading rate of 20 mm·min<sup>–1</sup> and a uniaxial bending test between two supports on each end at a loading rate of 50 mm·min<sup>–1 </sup>using a Universal Instron Testing Machine (Instron, USA). The results of the parameters studied revealed that Tianung 1 gave the higher stem height, stem diameter, compressive stress, bending stress, rupture load, rupture energy, Young’s modulus, and toughness, which were 293.10 cm, 18.45 mm, 8.70 MPa, 44.86 MPa, 191.51 N, 3.43 J·mm<sup>–2</sup>, 350.81 MPa, and 6.85 N·mm<sup>–1</sup>, respectively, at four months after planting. The parameters studied significantly increased with maturity for the two kenaf varieties. However, the moisture content significantly reduced with maturity.

Fractography of zirconia-specimens made using additive manufacturing (LCM) technology

A relatively new method to manufacture complex ceramic prototypes and components is additive manufacturing (AM). With the LCM (Lithography-based Ceramic Manufacturing)-technology the green body is manufactured layer-by-layer using selective curing of light-sensitive ceramic slurry by a mask exposure process. After curing by blue light the component is removed from the building platform and the green body is sintered to a ceramic component.The aim of this work is to investigate the influence of processing and layer architecture on the mechanical properties of an Yttria-stabilized zirconia ceramic. Strength tests were performed by uniaxial bending tests and by biaxial Ball-on-three Balls (B3B) tests. To identify typical fracture initiating flaws a systematic fractographic investigation was performed on different batches of Ball-on-three Balls-test and bending test specimens, respectively.Through additional investigations it was found that hardness and fracture toughness were independent on the layer architecture. But an extensive fractographic analysis showed that the strength was limited by flaws, which were introduced by processing and handling. If these flaws can be avoided by optimisation of the process the strength should be equal to that of conventional processed ceramics.

Chairside CAD/CAM materials. Part 2: Flexural strength testing

ObjectiveStrength is one of the preferred parameters used in dentistry for determining clinical indication of dental restoratives. However, small dimensions of CAD/CAM blocks limit reliable measurements with standardized uniaxial bending tests. The objective of this study was to introduce the ball-on-three-ball (B3B) biaxial strength test for dental for small CAD/CAM block in the context of the size effect on strength predicted by the Weibull theory. MethodsEight representative chairside CAD/CAM materials ranging from polycrystalline zirconia (e.max ZirCAD, Ivoclar-Vivadent), reinforced glasses (Vitablocs Mark II, VITA; Empress CAD, Ivoclar-Vivadent) and glass-ceramics (e.max CAD, Ivoclar-Vivadent; Suprinity, VITA; Celtra Duo, Dentsply) to hybrid materials (Enamic, VITA; Lava Ultimate, 3M ESPE) have been selected. Specimens were prepared with highly polished surfaces in rectangular plate (12×12×1.2mm3) or round disc (Ø=12mm, thickness=1.2mm) geometries. Specimens were tested using the B3B assembly and the biaxial strength was determined using calculations derived from finite element analyses of the respective stress fields. Size effects on strength were determined based on results from 4-point-bending specimens. ResultsA good agreement was found between the biaxial strength results for the different geometries (plates vs. discs) using the B3B test. Strength values ranged from 110.9MPa (Vitablocs Mark II) to 1303.21MPa (e.max ZirCAD). The strength dependency on specimen size was demonstrated through the calculated effective volume/surface. SignificanceThe B3B test has shown to be a reliable and simple method for determining the biaxial strength restorative materials supplied as small CAD/CAM blocks. A flexible solution was made available for the B3B test in the rectangular plate geometry.

Fracture strength and Weibull analysis of Ba0.5Sr0.5Co0.8Fe0.2O3−δ oxygen transport membranes evaluated by biaxial and uniaxial bending tests

The present study evaluates the fracture strengths and the Weibull modulus of Ba0.5Sr0.5Co0.8Fe0.2O3−δ (BSCF) oxygen transport membranes by means of biaxial and uniaxial bending tests at both room temperature (RT) and 800°C. The fracture strengths obtained from the biaxial bending tests are much lower than those obtained from the uniaxial bending tests while Weibull moduli (m) are similar. By utilising Weibull statistics the uniaxial strengths can be predicted from the biaxial values at both RT and 800°C. Fracture surfaces at both RT and 800°C show only a transgranular fracture mode. Failure origins are also determined by scanning electron microscope (SEM) based on the fractographic principles. Most defects determining the fracture strength of this particular material are found to be pores with a relatively large size.

Fracture Behaviors and Ferroelastic Deformation in W/Cr Co‐Doped Bi4Ti3O12 Ceramics

In this paper, the influence of Cr2O3 additive (y = 0~0.4 wt%) on fracture behaviors, ferroelastic deformation, and mechanical strengths of Bi4Ti2.95W0.05O12.05 (BTW) Aurivillius ceramics was investigated. For these W/Cr co‐doped Bi4Ti3O12 ceramics (BTW–yC), SEM analysis on their fractured surfaces demonstrate that the transgranular fracture is the main fracture mechanism, however, the intergranular fracture also exists in the sample at y = 0.3. Impedance analyses based electrical resonance show that their Poisson's ratio and Young's modulus vary with y in a similar trend, while the frequency constant and elastic compliance exhibit a contrary varying trend with y. On the other hand, under the Vickers indentation, the crack propagation in BTW–yC ceramics takes the form of the long‐straight extension, small‐angle deflection, and short‐distance branching at y = 0, 0.2, and 0.4, respectively. In the uniaxial compression tests, the stress–strain behavior of ceramics consist of three stages, i.e., linear elastic deformation, ferroelastic domain switching, and microcrack propagation. The ferroelastic domain switching tends to form the resistance for the microcrack propagation. Furthermore, uniaxial bending tests prove that the fracture strength is dependent on the grain size and fracture toughness, Overall, the sample at y = 0.1 gains a better mechanical strength among BTW–yC ceramics.

Structural behaviour of steel–concrete–steel sandwich composite wall subjected to compression and end moment

Steel–concrete–steel (SCS) sandwich wall infilled with ultra-lightweight cement composite has been developed and proposed for applications in offshore and building constructions. A new form of J-hook connector is introduced to connect the external plates to improve the composite action between the steel face plates and cement composite core to form an integrated unit which is capable of resisting extreme loads. This research experimentally investigates the structural behaviour of SCS sandwich composite wall based on a series of combined compression and uniaxial bending tests on short SCS sandwich composite wall with interlocking J-hook connectors. From the tests, it is found that the SCS sandwich wall exhibits good ductility behaviour with a bending failure mode. Nonlinear finite element (FE) model is also developed to simulate the mechanical behaviour of sandwich wall in terms of ultimate strength and load-deflection curves. Analytical studies show that the N–M interaction model based on Eurocode 4 may over-predict the combined resistance of the SCS sandwich walls subjected to eccentric compression. Therefore, a new approach is proposed to evaluate the resistance of sandwich wall. The axial force versus moment capacity interaction diagrams of sandwich wall are calculated. The validation against the test and FE results shows a reasonable and conservative estimation on the combined resistance of SCS sandwich wall.

Experimental Behavior of Nonconforming RC Columns with Plain Bars under Constant Axial Load and Biaxial Bending

Available capacity models for the assessment of seismic capacity of RC columns are mainly based on experimental tests under axial load and uniaxial bending. Furthermore, experimental tests have been mainly performed on columns representative of new constructions. To analyze the effects of biaxial bending on the seismic performances of existing RC columns with design characteristics nonconforming to present day seismic codes and practices, this paper presents the results of a first stage of tests on RC columns under both axial load and biaxial bending, which effectively simulate the seismic actions. In particular, this paper presents results of four tests on full-scale square columns reinforced with plain bars subjected to constant axial load and biaxial cyclic actions. Two different cyclic displacement paths were investigated: horizontal displacements with an inclination angle of 45 or 30°, with respect to the cross-section principal axes. The influence of biaxial bending actions on the global behavior of existing RC columns in terms of stiffness, strength, deformation capacity, and the effects of different horizontal displacements orientation on their performances are herein investigated and discussed; the comparison with experimental outcomes provided by uniaxial bending tests on companion specimens are also presented. Experimental findings showed that biaxial bending actions affect columns rotational capacity more than strength. The rotational capacity reduction because of biaxial bending actions, even if more significant than the flexural capacity reduction, is not currently taken into account in the available seismic guidelines related to existing RC buildings.

Characterization of Statical Properties of Rat's Whisker System

This contribution describes mechanical properties of the whisker system of rats. The motivation for the work was to achieve a better understanding of the functionality of this remarkable sense organ by defining structure-function-correlations. Special features of the different types of whisker are interpreted in terms of their morphological background, e.g., object recognition and texture discrimination. The whiskers are found to be conical in shape. Theoretical considerations of rod types reveal certain advantages of conically shaped rods over cylindrical rods. There is a difference in deformation, with the higher values applying to conical rods. Whiskers have a very flexible tip which is sensitive to very small forces. Uniaxial bending tests using actual whiskers were performed to characterize the static parameters. From experimental data obtained, the spring constant, the Young's modulus and the flexural stiffness are calculated. Young's modulus is one standard parameter for the characterization of materials. It was found that this can be regarded as constant along the whiskers with an average value of 7.36 GPa. Flexural stiffness was found to depend on the hair diameter and decrease from base to tip. The short vibrissae exhibit the lowest flexural stiffness, which means they are sensitive to very small forces. The experimental results obtained might well be used as a basis for the optimization or the construction of bioinspired technical sensor systems.

Behavior of Hollow, Rectangular Reinforced Concrete Piers Subjected to Biaxial Loading

The authors establish a slenderness limit for design by using previous experimental investigations and current experiments of hollow, rectangular reinforced concrete piers subjected to a combined axial load and uniaxial bending test. The goals of this investigation was to study the behavior of thin-walled concrete compression members subjected to biaxial bending, and to determine if local buckling of the walls limited the capacity of the cross section. Fiber models were used to evaluate the responses of the specimens, and the results were compared to the current design provisions in the American Association of State Highway and Transportation Officials Load and Resistance Factor Design Bridge Specifications to determine possible applications of the slenderness limits.

Weakest-link failure predictions for ceramics using finite element post-processing

Weakest-link failure prediction models according to Weibull, Stanley and Lamon have been implemented in a post-processing program supplementing a finite element modelling code. Failure predictions for equibiaxial loading from uniaxial bending test data reveal significant differences between the various formulations. The choice of a particular failure model for a particular material therefore has to be validated by additional information, e.g. by fractography or micrography.

Biaxial Fracture Studies of a Glass‐Ceramic

Uniaxial and equibiaxial tensile strengths are reported for glass‐ceramic specimens exhibiting strength isotropy. Uniaxial strengths were determined in both 3‐ and 4‐point bend tests. Stressing rate was a controlled variable and the tests were conducted in both dry N2 and water environments, to provide data for different conditions of slow crack growth. There was little or no difference between strengths in the 3‐ and 4‐point bend tests, indicating the absence of a size effect. In comparable tests, the strength under equibiaxial tension was greater than under uniaxial tension. The biaxial strengthening became less pronounced with increased slow crack growth during testing. A maximum observed biaxial‐to‐uniaxial strength ratio of 1.21 resulted from ball‐on‐ring and uniaxial bend tests in dry N2. These results are attributed to differences in flaw severity between biaxial and uniaxial stressing. The decreasing strength ratios can be explained by a change in configuration of critical flaws due to slow crack growth. Numerical calculations, using a simplified two‐dimensional model of the strength‐controlling flaw, supported this hypothesis. The calculations also indicate that the slow crack growth exponent is smaller for the biaxial tension mode of stressing than for the uniaxial mode.