Maximum Shear Deformation Research Articles

Локальное изменение напряженного состояния в образцах горных пород перед разрушением по данным коэффициента Лоде–Надаи

In this paper, the relationship of the Lode–Nadai coefficient, which determines the shape of the stress ellipsoid, with the nature of brittle fracture in sandstone, pyrophyllite and dolomite samples for a rigid loading machine is investigated. The measurement of the inhomogeneous deformation field in the samples and the observation of the internal fracture process were performed using strain gauges and acoustic sensors. It is shown that the formation of the main crack is preceded by the evolution of local deformations in the sample, recorded by the strain gauge method. Special processing of strain gauge data, taking into account the free lateral surface of the samples, made it possible to calculate the principle deformations and three invariants of the strain tensor: maximum shear deformation, volume change deformation and the Lode–Nadai coefficient. It has been established that at the final stage of deformation, when a main crack is formed in local sections of the sample, the axes of the principal deformations are reindexed, which is expressed in the achievement of the maximum values of +1 and -1 by the Lode–Nadai coefficient. A comparison with field observations was made.

Investigation on the seismic performance of the masonry infill wall with damping layer joint

Aimed at improving the seismic performance of the traditional masonry infill wall (MIW), an innovative configuration called Damped Masonry Infill Wall (DMIW) is developed through subdividing the MIW horizontally and introducing damping layer joint (DLJ) into the wall. In order to verify the feasibility and the seismic performance of DMIW, the optimized material used as DLJ was determined among four types of materials via the shear-hysteretic test firstly. Then, a quasi-static test was performed to investigate the seismic performance of 1:2 scaled RC frame specimens with DMIW and traditional MIW, in terms of damage pattern, seismic parameters, shear deformation characteristics of DLJ. The results show that the modified asphalt waterproof (MAW) product, APF-500 (also labelled No.1 MAW in this study), is the optimized material used for DLJ among other three tested material. The expected working mechanism of DMIW that the shear deformation of the wall concentrates in the DLJs is able to be realized by using the optimized DLJ material. Also, it proves that DMIW is capable of presenting a prominent reduction of damage level and significant decrease of the lateral force and stiffness. It is anticipated that the detrimental effect of traditional MIW on the seismic performance of the frame structure can be avoided by adopting DMIW. Furthermore, a fitted equation of the relationship between the maximum shear deformation demand of DLJ and the lateral deformation of the RC frame is developed for determining the minimum thickness of DLJ in the case where DMIW has three masonry units.

Strain Field Evolution and Constitutive Model of Coal considering the Effect of Beddings

Abstract In order to study the bedding effect of coal and rock deformation, the surface deformation fields of coal and rock at different bedding angles were obtained by means of digital image correlation (DIC). By optimizing the statistical index describing the nonuniformity of strain field, the initiation and evolution characteristics of deformation localization were analyzed quantitatively. The concepts of equivalent cohesive force and equivalent tensile strength were put forward, and a transverse isotropic constitutive model of coal and rock was established. The results show that the maximum shear deformation field of uniaxial compressed coal and rock in parallel bedding is more likely to show the three-stage characteristics of uniform stage, localization stage, and failure stage. In the vertical and parallel bedding directions, the modified statistical index curve of coal and rock in the process of uniaxial compression shows typical two-stage characteristics. When loading perpendicular to bedding, the starting stress of deformation localization of coal and rock is closer to the peak strength, and when loading parallel to bedding, coal and rock are easier to show localization characteristics.

Comparative study on overall and local static performance of steel open‐web girders

SummaryTo quantify the mechanical properties of five types of steel open‐web girders that have been tested or applied in practical engineering, a systematic study of the overall and local mechanical properties of steel open‐web girders based on the same dimensions and material conditions was presented. An overall study of the quasi‐intersection beam method for shear deformation was introduced for 8 × 8 grid open‐web girders to derive the determinants of the load distribution factor. Based on the load distribution factors, the essence and formula of any shear key node domain (SKND) were derived theoretically. The reliability of the numerical model was verified by tests on the H‐type unidirectional SKNDs, which led to a comparative load–displacement study of unidirectional and bidirectional SKNDs. Quantitative results of the overall flexural capacity and SKND load capacity of the H‐type, TH‐type, TS‐type, T‐type, and DT‐type open‐web girders were obtained. The maximum shear deformation in the elastic phase of the five open‐web girders accounted for 39.04% to 54.76% of the overall deformation. In this study, the adjustment factors of the modeling analysis based on the current practical design of equivalent dense‐ribbed solid beams (DRSBs) were revised. A method of SKND's design load capacity under the action of bidirectional forces was put forward for the first time.

Order in polycrystalline plasticity deformation fields: Short-range intermittency and long-range persistency

Cylindrical indentation into polycrystalline copper is studied experimentally using a split-specimen configuration that induces plane strain deformation to a very good approximation. The displacement field is determined by comparing a 5μm pitch grid in the deformed and reference configurations. The deformation gradient tensor is calculated along with the following deformation measures: Jacobian, Lagrange strain, right stretch tensor and associated rotation matrix, principal stretch ratios, principal directions of deformation, and the directions of maximum shear deformation. Trajectories of the principal directions of deformation adopt semi-circular and radial configurations. Trajectories of directions of maximum shear deformation adopt logarithmic spiral configurations. These configurations are consistent with a well-known analogy between wedge or cylindrical indentation and the growth of a cylindrical void in an elastic–plastic material. However, the analogy is not complete because the measured invariant deformation quantities are not axisymmetric. Another well-known analogy between indentation and fracture provides insight into the rapid spatial variations in deformation across the contact point singularities. Finally, logarithmic spiral shear patterns are characteristic of isotropic, homogeneous materials yet they appear in an anisotropic, heterogeneous material. There are many instances of strong shear localization confined to one or a few grains presumably of a preferable orientation, which are then interrupted by neighboring grains of less favorable orientation. Remarkably, though, preferably oriented grains further away again exhibit strong shear localizations along the same logarithmic spiral. Thus the polycrystalline material can be described as being isotropic and homogeneous based upon the persistent long-range order that develops even though the short-range order is intermittent. Detailed computer simulations treating individual grains as single crystals exhibit the same behavior. These results can give insight into the homogenization of an anisotropic and heterogeneous polycrystalline metal into an isotropic and homogeneous effective medium.

Elastic and Damping Properties of a Magnetorheological Coupling for Rotating Shafts

The elastic and damping properties of a magnetorheological coupling used in the diesel-generator system of portable power sources are considered. The finite-element method is used to assess the maximum shear deformation of a rotor shaft in a tractional generator.

Experimental Study of the Shear Capacity of Steel Beam-to-L-CFST Column Connections

This paper aims to investigate the shear performance of a new and innovative type of vertical stiffener connection between steel beams and L-shaped columns composed of concrete-filled steel tubes connected by transverse and vertical steel plates (L-CFST columns) in high-rise residential buildings. Quasi-static cyclic loading tests were performed on five full-scale specimens to investigate the panel zone behaviours. Based on the experimental results, the hysteretic responses, skeleton curves of the shear force–deformation, ductility, stiffness degradation, energy dissipation and strain are discussed. The variables studied in these experiments include the joint type, axial compression ratio, cross-sectional area and width-to-thickness ratio of the vertical stiffener, and presence of concrete. The results indicate that the cross-sectional area of the vertical stiffeners plays a critical role in the performance of the panel zone. Two types of failure modes were observed outside the panel zone: fracturing of the vertical stiffeners and fracturing of the beam flange connecting plate. Shear deformation of the panel zone was obvious in the exterior joint specimens, and the corresponding maximum shear deformation reached 0.05 rad. Furthermore, the scopes of the panel zone in the corner and exterior joint specimens were determined by the strain distribution.

Condition assessment of steel shear walls with tapered links under various loadings

A steel shear wall with double-tapered links and in-plane reference was developed for assisting the assessment of the structural condition of a building after an earthquake while maintaining the original role of the wall as a passive damper device. The double-tapered link subjected to in-plane shear deformation is designed to deform torsionally after the onset of local buckling and works as an indicator of the maximum shear deformation sustained by the shear wall during an earthquake. This paper first examines the effectiveness of double-tapered links in the assessment of the structural condition under various types of loading. A design procedure using a baseline incremental two-cycle loading protocol is verified numerically and experimentally. Meanwhile, in-plane reference links are introduced to double-tapered links and greatly enhance objectivity in the inspection of notable torsional deformation with the naked eye. Finally, a double-layer system, which consists of a layer with double-tapered links and a layer with rectangular links made of low-yield-point steel, is tested to demonstrate the feasibility of realizing both structural condition assessment and enhanced energy dissipation.

Demand on Stiffened Steel Shear Panel Dampers in a Rigid-Framed Bridge Pier under Repeated Seismic Ground Motions

Destructive earthquakes in recent years show that strong aftershocks are prone to occur frequently, which accelerate the destruction of structures after the main shocks. However, it is difficult to evaluate the intensity of the seismic ground motion by the aftershock. To account for this effect, it is assumed in this study that the structures would sustain three times of severe earthquakes during the service life, and for simplicity the input ground motions are repeated by three times with the same amplitude. Performance requirements on Shear Panel Dampers (SPDs) installed in framed bridge piers under repeated strong earthquakes are examined by dynamic analyses, and the sensitivity of two quantities of the SPD's capacity (maximum shear deformation and cumulative inelastic deformation) is studied. The SPDs are designed to vary on different dimensional and mechanical parameters to be applied in a steel rigid-framed bridge pier, and three kinds of design earthquake motions are used. By comparing the results of three times of earthquakes with that of one time, the performance requirements are concluded and corresponding safety margin of the capacity is discussed for practical seismic design.

Surface damping effect of anchored constrained viscoelastic layers on the flexural response of simply supported structures

Viscoelastic (VE) materials are commonly used to control vibration-induced fatigue in airframes and to suppress general vibration in various structures. This study investigates the effects of anchored constrained VE layers on the flexural response of simply supported Euler beams or plate strips under base excitations. Emphasis is placed on the development of two surface damping treatments: one VE layer anchored at one end, and two VE layers anchored at their different ends. Each anchorage is realized with a thin stiff layer in tension, such as a fiber reinforced polymer sheet, bonded to the surface of a VE layer and anchored to one end of the beam for maximum shear deformation in the constrained VE layer. Non-uniform shear deformation in VE layers is taken into account in the new solution formulation. Sensitivity analyses are performed to understand and quantify the effects of various parameters on flexural responses of the structures. The minimum thickness of VE layers is mainly bounded by the relative stiffness between the VE layers and the constraining face layer. The performances of various configurations are compared and the two-end anchored configuration is found most effective in vibration suppression.

Measurement of geometric deformation of lumbar intervertebral discs under in-vivo weightbearing condition

Quantitative data of spinal intervertebral disc deformation is instrumental for investigation of spinal disc pathology. In this study, we employed a combined dual fluoroscopic imaging system and the MR imaging technique to determine the lumbar disc deformation in living human subjects. Discs at L2-3, L3-4 and L4-5 levels were investigated in 8 normal subjects. The geometric deformation of the discs under full body weight loading condition (upright standing) was determined using the supine, non-weightbearing condition as a reference. The average maximum tensile deformation was −21% in compression and 24% in tension, and maximum shear deformation on the disc surface reached 26%. The data indicated that different portions of the disc are under different tensile and shear deformation. Further, discs of L2-3, L3-4 and L4-5 have different deformation behavior under the physiological weightbearing condition. In general, the higher level discs have higher deformation values. The technique used in this study can be used to investigate the deformation behaviors of diseased discs as well as the efficacy of different surgical modalities at restoring normal disc deformation patterns.

The Effect of Orthodontic Retention on the Mechanical Properties of the Periodontal Ligament in the Rat Maxillary First Molar

The load-deformation curves obtained by extraction of the rat maxillary first molar from its socket in the dissected jaw were analyzed so that the effect of orthodontic retention on the mechanical properties of the periodontal ligament could be examined. An elastic band was inserted between the rat maxillary first and second molars for four days, and then the interdental space was filled with resin for four or eight days. The average interdental spaces between the teeth ranged from 315 to 398 microns during the experimental period. The maximum shear load, elastic stiffness, and failure energy in shear decreased markedly following application of an orthodontic force, but they increased gradually and reached control levels on the 8th day after the retention. Maximum shear deformation at maximum load was not significantly different between the experimental and control teeth during the experimental period. It is suggested that, following orthodontic tooth movement, occlusal function was restored after a relatively short retention period, as was the impaired mechanical strength of the periodontal ligament.