Theoretical Shear Research Articles

Parameter Estimation and Application of Anisotropic Yield Criteria for Cylindrical Aluminum Extrusions: Theoretical Developments and StereoDIC Measurements

Theoretical and experimental studies are presented to characterize the anisotropic plastic response under torsion loading of two nominally identical aluminum Al6061-T6 extruded round bars. Theoretical models are developed using isotropic (Von Mises 1913) and anisotropic (Barlat 1991) yield criteria, along with isotropic strain hardening formulae, to model post-yield behavior under simple torsion loading. For the case of simple shear loading, incremental plasticity theory is used to determine the theoretical elastic, plastic, and total shear strains. A set of experiments are performed to calibrate Barlat’s 1991 yield function. Several specimens are extracted at different orientations to the longitudinal direction of each round Al6061-T6 bar and tested under uniaxial tension and simple torsion to optimally determine all anisotropic (Barlat 1991) yield function parameters. During loading, Stereo Digital Image Correlation (DIC) is used to quantify surface deformations for the torsion experiments and a baseline tension specimen to identify and correct measurement anomalies. Results show the isotropic yield model either underestimates or overestimates the experimental shear strains for both extrusions. Conversely, results using the Barlat 1991 anisotropic yield criteria are in excellent agreement with experimental measurements for both extrusions. The presence of significant differences in the anisotropic parameters for nominally similar extrusions confirms that plastic anisotropy is essential for the accurate prediction of mechanical behavior in longitudinally extruded Al6061-T6 bars.

Diaphragm shear and diagonal compression testing of cross-laminated timber

To learn the characteristics of a cross-laminated timber (CLT) panel, it is crucial to perform experimental tests. This study presents two experimental test methods to measure the in-plane shear modulus of CLT panels. This characteristic can be measured by multiple methods such as the picture frame test, the diagonal compression test, and the diaphragm shear test. In this study, the same CLT panels are tested and evaluated in the diaphragm shear test and the diagonal compression test to see if more reliable results can be achieved from the diaphragm shear test. This evaluation is done by experimental tests and finite element simulations. The theoretical pure shear simulation is used as a reference case. Finite element simulations are made for both edge glued and non-edge glued CLT panels. Nine CLT panels are tested in the diaphragm shear test and the diagonal compression test. During ideal conditions (uniform material properties and contact conditions), all three simulated methods result in an almost equal shear modulus. During the experimental testing, the diagonal compression test gives more coherent results with the expected shear modulus based on finite element simulations. Based on the diaphragm shear test results, the CLT panels behave like edge glued, but this situation is dismissed. However, during ideal conditions, the diaphragm shear test is seen as a more reliable method due to the higher proportion of shear in the measured area.Article HighlightsComparing the two experimental methods: the diaphragm shear test and the diagonal compression test.Using the theoretical pure shear simulations to verify the experimental methods.Experimental testing and finite element analysis of the same cross-laminated timber panel.

Deployment of SMP Miura-ori sheet and its application: Aerodynamic drag and RCS reduction

Origami, such as Miura-ori, is the art of folding two-dimensional materials into complex, elaborate, and multifunctional three-dimensional objects. In this paper, SMP MO sheet are prepared, and the accuracy of deployable process is verified by experiments. The folding and deployable process of SMP MO sheet is divided into 4 stages, and each stage is described in detail. The stiffness of smart deployable stage is characterized by an exponential decline at the beginning and a gradual decrease to 0, and this is similar to the theoretical shear equivalent modulus in the Y direction. The effects of various parameters on strain and stress are also explored. The purpose of studying these mechanical characteristics is to provide driving force reference in application; In terms of application, the flow field and electromagnetic characteristics of MO sheet in different directions are studied. The aerodynamic drag and RCS reduction of MO unit cell and graded MO sheet during the deployable process are evaluated. When the dihedral fold angle is about 45°, the RCS reduction and drag reduction characteristics of MO sheet are relatively optimal, which is most beneficial to morphing aircraft.

Direct shear behavior of precast panel connections with cast-in-place shear keys using steel fiber-reinforced cementitious mortar (SFRCM)

In the present study, an experimental study was performed to investigate the direct shear behavior of precast panel connections using steel fiber-reinforced cementitious mortar shear keys. The main experimental parameters included the volume fraction of steel fibers adopted for the connections and the details and configurations of the cast-in-place shear keys. The volume fractions of steel fibers were in the range of 0.75–1.5%. In total, four series with 22 push-off test specimens were fabricated and tested with various shear key configurations. The experimental results obtained were analyzed and discussed in detail to examine the effects of various parameters on the shear behavior of the panel connections. On the basis of the experimental results and theoretical shear transfer mechanism, an analytical model to predict the shear strength of the panel connections with shear keys was proposed, and its predictions showed a good correlation with the experimental results.

High pressure lattice dynamics and stress-strain responses of LaIn3 and LaTl3

A detailed study of the ground state structure, non-zero elastic constants, high pressure lattice dynamics as well as theoretical tensile and shear strengths of the cubic intermetallic compounds LaIn3 and LaTl3 with AuCu3 (L12)-type has been made through first-principles. The optimized equilibrium crystal constants, cell volumes, bulk modulus and its pressure derivative, and single-crystalline elastic constants are in fair agreement with available experimental data and other calculations. More importantly, high pressure phonon spectrum, total and partial phonon densities of states in LaIn3 and LaTl3 up to 10 GPa are reported by employing Density Functional Perturbation Theory (DFPT), and the present results have demonstrated that both systems are dynamically stability up to 10 GPa. The differences between the dynamical properties of LaIn3 and LaTl3 have also been discussed systematically. Additionally, the tensile and shear stress-strain responses and the theoretical strengths of LaIn3 and LaTl3 are further calculated, we have found that LaIn3 exhibits larger tensile and shear strengths than LaTl3. These investigations are expected to provide beneficial references for further exploring the physical properties of rare earth compounds.

Estimate of theoretical shear strength of C60 single crystal by nanoindentation

The onset of plasticity in a single crystal C60 fullerite was investigated by nanoindentation on the (111) crystallographic plane. The transition from elastic to plastic deformation in a contact was observed as pop-in events on loading curves. The respective resolved shear stresses were computed for the octahedral slip systems langle{01}overline{1}rangleleft{ {{111}} right}, supposing that their activation resulted in the onset of plasticity. A finite element analysis was applied, which reproduced the elastic loading until the first pop-in, using a realistic geometry of the Berkovich indenter blunt tip. The obtained estimate of the C60 theoretical shear strength was about {1}/{11} of the shear modulus on {111} planes.Graphical abstract

A unified thermal vibration and transient analysis for quasi-3D shear deformation composite laminated beams with general boundary conditions

A unified procedure is proposed in this study to analyze the free and transient vibration behaviors of a composite laminated beam subjected to general boundary conditions under thermal scenario. A general theoretical quasi-3D shear deformation beam model incorporating both the shear deformation and thickness stretching effects is derived using the Hamilton's principle. The coupling of axial–shear–flexural–stretching with the thermal stress and the Poisson's ratio effect is taken into account. The natural frequencies, mode shapes and transient responses of composite laminated beams are evaluated analytically by the method of reverberation ray matrix (MRRM). The inhomogeneous term and the artificial spring boundary technique are introduced in MRRM to acclimatize itself to the general boundary conditions and the impulse loads of arbitrary distributions. The validity, reliability and efficiency of the proposed analytical solutions are verified by comparing with the results obtained from the published studies and finite element simulation. A considerable number of parametrical studies for the composite laminated beams with different elastic restraint parameters, lamination schemes, geometry parameters, material properties as well as various temperature rises are also analyzed and discussed. The present procedure is powerful in terms of its applicability for different high-order shape functions including polynomial and non-polynomial, as well as thin and thick beams subjected to arbitrary boundary conditions in practical engineering.

Influence of using two types of recycled aggregates on shear behavior of concrete beams

This paper investigates experimentally and theoretically the shear behavior of thirteen reinforced concrete (RC) beams made of Recycled Asphalt Pavement (RAP) and Recycled Coarse Aggregate (RCA). The span length of the beams was 2240 mm, and the width and depth of the beams were 200 and 400 mm, respectively. Three groups of beams were used in this study: The first group was five beams made of RAP and natural aggregate (NA), where the NA was substituted by RAP with replacement levels of 20%, 40%, 60%, 80%, and 100% by the total weight of NA. The second group was four beams made entirely of RAP and RCA. The third group was four RC beams made of RCA and NA, where NA was replaced by RCA with replacement levels of 20%, 40%, 60%, and 80%. The beams were tested under four-point loading setup. The maximum shear forces, deflections, and cracking patterns were studied. The experimental results were compared with theoretical results determined from the equations of selected international codes and fracture mechanics approaches available in the literature. The results showed that the experimental shear capacity increased as the RAP and RCA replacement levels decreased for the beams in group one and three, and decreased for group two beams when the RCA replacement levels increased. The theoretical shear strength capacities were more conservative when compared to the experimental results. Therefore, the theoretical shear equations can be applicable to the beams constructed with recycled aggregates. In general, using RAP and RCA in RC beams can be considered as an effective approach.

Strain compatibility model to optimise CFRP laminate for shear strengthening of RC beam

ABSTRACT Optimisation of CFRP shear strip in presence of connectors/anchors is the current interest to reduce retrofitting cost of structures. The main aim of this research was to propose design guideline considering strain compatibility nature between shear reinforcement and externally bonded CFRP laminate to optimise the dimension of CFRP laminate for shear strengthening of RC beam in presence of embedded connectors. The guideline had been experimentally verified through the structural investigations on five reinforced concrete beams. Results showed that the proposed guideline with connectors reduced the dimension of CFRP laminate significantly. The optimal strengthened beams had shown the highest flexural capacities, maximum ductility and cost effective structural performances. Shear reinforcement and externally bonded CFRP laminate had shown identical nature of strains until shear crack and micro debonding of laminate. The optimal strengthened beams with connector did not fail by shear or debonding of laminates prior to theoretical design shear capacities of beams. The design shear capacities of optimal strengthened beams (182 kN) were very close to those of flexural failure loads (181 kN and 184 kN). Overall experimental results satisfactorily verified the proposed design guideline.

PERILAKU GESER BALOK BETON BERTULANG MUTU TINGGI DENGAN VARIASI FLY ASH BATU BARA, PASIR POZZOLAN DAN BONGKAHAN CANGKANG SAWIT

The utilization of high strength concrete particularly on construction is an option in structural elements. High Strength Concrete (BMT) is a compressive strength exceeding 6000 psi or 41 MPa. High quality concrete can be obtained by mixing superplasticizers (high range water reducers) and cementitious mineral additives in the form of fly ash, pozzofume (super fly ash), and microscopy (silicafume). In this study, it will used the substitution of cement material using coal fly ash, fly ash pozzolan sand and palm shell ash fly ash, fine aggregates using pozzolan sand, coarse aggregates palm shell. The aim of this study is to compare the shear behavior of normal high quality reinforced concrete beams and beams with the addition of material substitution. The high quality reinforced concrete beam specimens were designed to experience shear failure by strengthening the bending area. Reinforced concrete beam specimens of beam size 150 mm x 300 mm x 2200 mm with shear reinforcement diameter 6 mm (fy) 423.46 MPa, compressive reinforcement 16 mm (fy) 412.39 MPa and tensile reinforcement 19 mm (fy) 462, 24 MPa. The beam specimen is pure flexural tensile strength with a size of 150 mm x 150 mm x 600 mm and a cylindrical specimen with a diameter of 150 mm x 300 mm in height. The magnitude of the flexural tensile strength for BMT-N with f cc = 44.4 MPa is 4.5, and for BMT-FBPP with f cc = 51.04 MPa which is 5.35 with FAS 0.3. The results of the two beams experienced shear failure, with a comparison of laboratory and theoretical shear capacity of 2,292 BMT-N with a maximum load of 27,200 MPa, BMT-FBPP 1,720 with a maximum load of 21,410 MPa. The values of deflection and ductility tend to decrease in BMT-FBPP beams which are equal to 19.780% and 6%.

Performance evaluation of reinforced concrete beams with corroded web reinforcement: Experimental and theoretical study

This study investigated the effect of corroded web reinforcement on the shear behavior of reinforced concrete (RC) beams. In this study, nine shear-critical RC beams were cast and tested. Six of these beams were corroded stirrups, while the remaining three beams were uncorroded stirrups serving as control samples. An accelerated corrosion technique was employed to corrode the stirrups in the beams. After the accelerated corrosion process, the beams were tested in three-point bending over a simply supported span. The shear span-to-depth ratio was kept constant at 3 for all beam specimens. The effects of the corrosion level, the type of steel stirrups (smooth or deformed), and the stirrup diameter were considered in the tests. The corrosion damage could easily be observed in the form of rust stains and corrosion cracks, which developed parallel to the stirrups. The beams with higher corrosion levels showed a reduction in their shear capacities. This reduction was more apparent in the beams with deformed steel stirrups. The shear capacities of the test beams were analyzed using a theoretical model that considers the effects of corrosion of the stirrups. The results of the analysis showed a good correlation between the experimental and theoretical shear strengths of the beam specimens.

An experimental approach for strengthening of RC deep beams with web openings using GFRP fabrics and gas actuated fasteners

In this paper, the influences of externally bonded (EB) glass fibre reinforced polymer (GFRP) fabrics and gas actuated fasteners (GAF) on the strengthening of reinforced concrete (RC) deep beams with circular/square web openings of different sizes are investigated experimentally with respect to shear strength, failure mode, load-deflection and stiffness. A total of 19 deep beams having 120 × 420 × 1000 mm size are prepared and tested under two-point loading. One solid deep beam is left un-strengthened, which is considered as the control beam. Out of 18 beams with web openings, six beams, i.e. one beam for each opening size are kept un-strengthened. Other six counterpart beams are strengthened with U-wrapped EB-GFRP fabrics throughout the beam length. In order to improve the bond strength between GFRP fabric sheets and concrete surface, the remaining six counterpart beams are strengthened using both EB-GFRP fabrics and GAF at shear spans only. Test results demonstrate that the presence of web openings in deep beams significantly reduces the shear strength of the beams up to 72% with respect to the solid beam. The beams with web openings strengthened using both the EB-GFRP fabric and GAF are seen to be effective in enhancing the shear strength up to 64% with respect to the counterpart un-strengthened deep beams. Finally, the theoretical shear strength results obtained from the theoretical models available in the previous works are compared with the experimental results for the verification of their accuracy.

High-performance titanium-based composite strengthened with in-situ network-distributed 3D reinforcements

Ti-based composite with in-situ 3D nano-reinforcements consisted of boron nitride nanosheets (BNNSs), titanium boride (TiB) nanowires and titanium diboride (TiB2) nanoparticles was prepared in a facile way—blending spherical Ti powder and BNNSs via low-energy ball milling and then consolidating the composite powder by spark plasma sintering. It has an excellent combination of strength and ductility: the composite with 0.5 vol% BNNSs exhibits high tensile strength of around 715.1 MPa and excellent toughness of 115.2 MJ/m3, which is 73.4% higher and 16.6% lower than those of pure Ti, respectively. The strength enhancement is mainly attributed to the interlocking structure formed by TiB2 nanoparticles and BNNSs, which increases the dislocation density and doubles the theoretical interfacial shear strength limit. The considerable ductility arises from the crack blocking brought by the 3D network.

Nanoindentation of pure and gas-saturated fullerite C60 crystals: Elastic-to-plastic transition, hardness, elastic modulus

Elastic-plastic transition at nanoindentation of (111) plane of pure C60 fullerite single crystals was studied. The onset of plastic deformation in the contact was noted due to the plateau formation in the initial part of loading curve. The estimated stress of plasticity beginning was found to be on the order of the theoretical shear stress required for homogeneous dislocation nucleation in the ideal crystal lattice of C60. The empirical values of elastic modulus E ∼ 13.5 GPa, hardness of the ideal crystal lattice H ∼ 1.4 GPa, and hardness at different indentation loads were obtained. The hardness vs load dependence was found consistent with the model of geometrically necessary dislocations. The loading diagrams shape and the dependencies of contact pressure vs indentation depth were strongly affected by gaseous interstitial impurities (hydrogen, oxygen, nitrogen) in C60 crystal; transition stress was essentially less and plateaus formation was observed at elevated indentation loads and depths as compared with pure fullerite crystal. For crystals, saturated with hydrogen, the enhanced value of elastic modulus (∼ 20.4 GPa) and hardness (∼ 1.1 GPa) were obtained. The results acquired at room temperature for C60 with face-centered cubic lattice are important for the description of the physical-mechanical properties of simple cubic lattice phase of C60 below 260 K (S. V. Lubenets, L. S. Fomenko, V. D. Natsik, and A. V. Rusakova, Fiz. Nizk. Temp. 45, 3 (2019) [Low Temp. Phys. 45, 1 (2019)]).

Development and application of interatomic potentials to study the stability and shear strength of Ti/TiN and Cu/TiN interfaces

A modified embedded atom method interatomic potential was developed to study semi-coherent metal/ceramic interfaces involving Cu, Ti and N. A genetic algorithm was used to fit the model parameters to the physical properties of the materials. To accurately describe interfacial interactions and shear, two-dimensional generalized stacking fault energy profiles for relevant slip systems were selected as one of the major parameterization targets for the models. The models were applied to study semi-coherent Ti(0001)/TiN(111) and Cu(111)/TiN(111) systems. Ti/TiN was stable with misfits accommodated away from the interface. Cu/TiN, in contrast, was more stable with misfits at the interface. A spiral pattern in the misfit dislocation networks was observed away from the Cu/TiN interface, similar to the metal/metal (111) semi-coherent interfaces. The theoretical shear strength calculated for Ti/TiN when the misfits were several layers away from the interface and for Cu/TiN with the misfit at the chemical interface, had reasonable agreement with experiment.

Plastic Forming of Metals at the Nanoscale: Interdiffusion-Induced Bending of Bimetallic Nanowhiskers.

Controlled plastic forming of nanoscale metallic objects by applying mechanical load is a challenge, since defect-free nanocrystals usually yield at near theoretical shear strength, followed by stochastic dislocation avalanches that lead to catastrophic failure or irregular, uncontrolled shapes. Herein, instead of mechanical load, we utilize chemical stress from imbalanced interdiffusion to manipulate the shape of nanowhiskers. Bimetallic Au–Fe nanowhiskers with an ultrahigh bending strength were synthesized employing the molecular beam epitaxy technique. The one-sided Fe coating on the defect-free, single-crystalline Au nanowhisker exhibited both single- and polycrystalline regions. Annealing the bimetallic nanowhiskers at elevated temperatures led to gradual change of curvature and irreversible bending. At low homological temperatures at which grain boundary diffusion is a dominant mode of mass transport this irreversible bending was attributed to the grain boundary Kirkendall effect during the diffusion of Au along the grain boundaries in the Fe layer. At higher temperatures and longer annealing times, the bending was dominated by intensive bulk diffusion of Fe into the Au nanowhisker, accompanied by a significant migration of the Au–Fe interphase boundary toward the Fe layers. The irreversible bending was caused by the concentration dependence of the lattice parameter of the Au(Fe) alloy and by the volume effect associated with the interphase boundary migration. The results of this study demonstrate a high potential of chemical interdiffusion in the controlled plastic forming of ultrastrong metal nanostructures. By design of the thickness, microstructure, and composition of the coating as well as the parameters of heat treatment, bimetallic nanowhiskers can be bent in a controlled manner.

Shear modulus analysis of cross-laminated timber using picture frame tests and finite element simulations

Determining the mechanical properties of cross-laminated timber (CLT) panels is an important issue. A property that is particularly important for CLT used as shear walls in buildings is the in-plane shear modulus. In this study, a method to determine the in-plane shear modulus of 3- and 5-layer CLT panels was developed based on picture frame tests and a correction factor evaluated from finite element simulations. The picture frame test is a biaxial test where a panel is simultaneously compressed and tensioned. Two different testing methods are simulated by finite elements: theoretical pure shear models as a reference cases and picture frame models to simulate the picture frame test setup. An equation for calculating the shear modulus from the measured shear stiffnesses in the picture frame tests is developed by comparisons between tests and finite element simulations of the CLT panels. The results show that pure shear conditions are achieved in the central region of the panels. No influence from the size of the tested panels is observed in the finite element simulations.

Electronic properties, anisotropic elasticity, theoretical strengths, and lattice vibrational mode of orthorhombic YSi

We investigated the crystal structure, electronic structure, elastic stiffness constants, responses to tensile and shear deformations, lattice vibrational modes as well as vibration heat capacity and vibration entropy of the orthorhombic YSi compound using ab initio approach. The relaxed ground-state lattice constants a, b and c of YSi exhibit fair agreement with the available experimental and theoretical data. Nine independent elastic stiffness constants have been computed by increasingly varying minute strains based on “energy-strain” approach, which confirm that the orthorhombic YSi is mechanically stable. Some polycrystalline moduli involving bulk modulus, Young's modulus and shear modulus, Poisson's ratio, brittle/ductile characteristic have also been systematically derived, and YSi can be classified as brittle compound. Both three-directional Young's modulus anisotropy and bulk modulus anisotropy are calculated in detail, and the calculations indicate that the orthorhombic YSi takes on significant elastic anisotropy. We further studied the theoretical tensile and shear strengths under different loads. Also, the phonon spectra, total and partial phonon densities of states are researched by employing Density Functional Perturbation Theory (DFPT) and the finite-displacement method, and the infrared-active and Raman active vibration modes at the center of Brillouin zone are classified using the group theory. Moreover, we predicted the constant volume heat capacity of YSi under high temperature relying on the calculated phonon densities of states as well as quasi-harmonic approximation (QHA) and Debye model.

Dynamic shear fracture behaviors and “pseudo-plastic” constitutive model of carbon/carbon composite pins

To understand the strain rate sensitivity of carbon/carbon (C/C) composite pins’ shear behaviors, quasi-static and dynamic experiments are conducted using an electric universal testing machine and a drop weight impact testing machine. A scanning electron microscope (SEM) is used to observe the shear fracture surfaces. The results show that the shear failure stress increases with increasing strain rate. Under quasi-static loading, the C/C composites damage with fibers fracture successively, and the shear stress-strain curve shows a “pseudo-plastic” characteristic, while brittle fracture features subjected to dynamic loading. In order to explain such differences, a viscoelastic constitutive model incorporated with a damage model based on the Weibull distribution function is proposed. Parameters of the constitutive model are estimated based on the experimental data. After that, the theoretical shear failure stresses are obtained by calculating the maximum shear stress of the constitutive model for different shear strain rates. The fitted model and theoretical failure stress match well with the experimental data.

Quantitative study on slip/twinning activity and theoretical critical shear strength of Mg alloy with Y addition

Slip/twinning activity and theoretical critical shear strengths (τmax) during room-temperature tensile deformation of as-extruded pure Mg and Mg-1wt.%Y sheets were investigated quantitatively via electron back-scattered diffraction (EBSD), scanning electron microscope (SEM) and first-principles calculation. Slip trace analysis results indicated the relative frequency of the active slip modes transformed from basal slip (100%) for pure Mg, to basal slip (84.8%), prismatic slip (9.7%) and pyramidal slip (5.5%) for the alloy. The proportion of grains containing twins reduced significantly from 20.5% to 5.92% with Y addition. To explain the mechanism for the enhancement of the non-basal slip activity in Mg–Y alloy, the critical resolved shear stress of basal slip and pyramidal II slip were assessed by calculating τmax. The calculated results showed that the τmax ratio of the pyramidal II slip to basal slip decreased from 13.7 to 7.5, which may be responsible for the observed enhanced activity of non-basal slip.