Shear Test Data Research Articles

In vitro fatigue testing of a dental bonding system on enamel.

The aim of this study was to investigate the in vitro fatigue behavior of a dental bonding system [ScotchBond Multi Purpose (SBMP)] by using a cyclic shear loading test. Cylinders of a light-cured hybrid composite resin (Z100) were formed on, and bonded with SBMP to, the flattened, acid-etched enamel surface of human teeth. Thirty-two samples (eight per group) were used to determine the 1-h, 1-day, 7-day, and 30-day shear bond strengths. For the shear fatigue test, the stress was cycled, at a rate of 1 Hz, between 0 and a present value in the 12-28 MPa range (from -3 SD to +1 SD around the 24-MPa mean bond strength of the 1-h specimens). The applied stress and the number of cycles to failure were recorded for each of the 75 samples tested (15 samples per set-stress). Three stress versus number of cycles curves (low, median, and high S-N curves) were obtained and an approximate endurance limit of 10 MPa was identified for the SBMP bonding system. The data obtained explain, in part, the discrepancy between in vitro and in vivo results and underline the difficulty of predicting the in vivo behavior based on results of in vitro bond strength tests alone. Shear fatigue test data, however, could provide a better insight into the long-term in vivo behavior of a dental bonding system.

The Multidirectional Direct Simple Shear Apparatus

AbstractThe paper describes a new simple shear testing device, the multidirectional direct simple shear (MDSS) apparatus, for testing soil specimens under conditions that simulate, at the element level, the state of stress acting within the foundation soil of an offshore Arctic gravity structure. The MDSS uses a circular specimen that is consolidated under both a vertical effective stress (σ′vc) and a horizontal shear stress (τ1). The specimen is subsequently sheared undrained by applying a second independent horizontal shear stress (τ2) at an angle ϑ relative to the horizontal consolidation shear stress τ1. Evaluation of the MDSS first compares conventional K0-consolidated undrained direct simple shear (CK0UDSS) test data (τ1 = 0) on normally consolidated Boston blue clay (BBC) with results obtained in the Geonor DSS device. The MDSS gives lower secant Young's modulus values and on average 8% lower strengths, but produces remarkably less scatter in the test results than the Geonor DSS. Kinematic proof tests with an elastic material (rubber) confirm that the setup procedure, application of forces, and strain measurement systems in the MDSS work properly and produce repeatable results.Results from a MDSS test program on BBC wherein specimens were first normally consolidated with σ′vc and τ1 = 0.2σ′vc and then sheared undrained at ϑ varing in 30° increments from zero (shear in same direction) to 150° show dramatic differences in the response of the soil as a function of θ. The peak undrained strength varies almost twofold from θ = 0 to 120°, while the deformation behavior varies from very brittle at low θ angles to becoming ductile at higher angles. The experimental results indicate that dramatic changes in foundation response at different θ angles will be an important design issue.

Endochronic Modeling for Cyclic Behavior of Overconsolidated Clays

ABSTRACT The constitutive relations based on the endochronic theory have been presented to describe the behavior of overconsolidated clay subjected to cyclic loading. The proposed constitutive law is capable of describing (a) strain softening and hardening, including a softening steady state which is eventually reached as the number of cycles increases; (b) densification and dilatancy; (c) effect of effective confining pressure; (d) effect of overconsolidation ratio OCR. The model is applied to describe the strain-controlled cyclic undrained triaxial test data on Shanghai clay carried out by the second author and strain-controlled undrained simple shear test data on Drammen clay (Andersen et al., 1980). The comparison between the theoretical prediction and the test data shows that the presently proposed model provides a reasonable description for the clay under consideration.

On The Concept of Characteristic States of Cohesionless Soil and Constitutive Modeling

The concepts of two characteristic states and their representation as characteristic state lines in the stress space are introduced to describe volumetric behavior of cohesionless soil during shearing. The first characteristic state line represents the state of cohesionless soil at failure, while the second characteristic line represents the state at which the rate of volumetric strain momentarily vanishes as the soil passes from the compressive mode of deformation to the dilative mode of deformation during shearing. Explicit forms of the two characteristic state lines in the stress space are proposed and used to develop a constitutive model based on the framework of plasticity theory. The general forms of the characteristic state lines are verified using drained shear test data for a fine sand. Stress-strain and volumetric-axial strain responses are predicted using the proposed model and good correlations are observed with experimental data.

An Endochronic Constitutive Law for Static Shear Behavior of Overconsolidated Clays

Based on the endochronic theory, constitutive relations for overconsolidated clay subjected to static loading have been obtained. The constitutive relations expressed in a closed form can generally describe both deviatoric shear responses and pore pressure responses including negative responses induced by dilatancy. The model further can account for the effect of effective confining pressure on the responses, strain hardening and softening behaviors, dilatancy behaviors, and the effect of overconsolidated ratio, OCR, on the responses. The model is applied to describe the undrained simple shear test data on Boston Blue clay (Ladd and Foott, 1974) and undrained triaxial compression tests on Shanghai clay as well as South Sea clay carried out by the second author. It is shown in this paper that the model yields a reasonable description for the mechanical behaviors of overconsolidated clays subjected to static loading.

Empirical tests of a model for thin plate perforation

This work presents a series of mechanical and ballistic tests designed to the test the material assumptions used in, and the performance of, a model for the perforation of thin metallic plates by blunt cylindrical missiles. Tensile, bend and shear test data show reasonable concurrence with the simplified forms assumed for the model. Quasi-static punching and dishing test data demonstrate the importance of dishing as an energy absorbing mechanism, and provide simplified perforation data for comparison with ballistic limit velocity. Predictions of ballistic limit velocities at two scales are good, provided yaw of the projectile is negligible. Large amounts of projectile yaw can lead to a low energy failure by a mechanism of cutting, shearing and bending of the plate. In addition an unusual hinging failure mechanism is observed, particularly for thin plates, and attributed to modification of the stress fieldby unloading around the crack during the progress of propagation of the failure itself.

Borehole shear test and slope stability : Handy, R L In: Use of In Situ Tests in Geotechnical Engineering (papers to the Conference, Blacksburg, 23–25 June 1986)P161–175. Publ New York: ASCE, 1986 (ASCE Geotechnical Special Publication No 6)

Three Iowa landslides analyzed on the basis of Borehole Shear Test (BST) data are reported. The soils included CL and ML loess and glacial till, and CH clay shale. Backcalculations from BST friction angles measured in the shear zones consistently indicated that cohesion after sliding is near zero, suggesting that after-slip equilibrium must derive mainly from internal friction in the shear zone. A unique advantage of the BST is that it can measure Ф that is in effect at the time of sliding. Stage BST's were performed on a 28-ft high lagoon embankment of compacted CH soil over random fill, to determine if the lagoon could be safely put into service. 14 BST shear envelopes were obtained in 2 days and gave sufficient data for probabilistic determinations of the failure risk based both on the range in individual strengths and the range in predicted means. The stage BST separately measures c and Ф means and variabilities, not possible when tests are performed on individual samples that may or may not share a common shear envelope.

Friction bond, dynamic models of plane strain in powder systems

Theoretical models have been developed to describe plastic failure in plane shear in powder systems. The models are based upon the concept of friction bonds acting across the shear plane. These bonds support normal stress and resist shear strain. In plastic failure, they are in a dynamic state. Models have been developed from theoretical arguments which provide rate equations of bond formation and rupture at plastic failure. These equations have been combined with bond initiation mechanisms to provide an overall description of the shear process. The models agree qualitatively with experimental shear test data.

Reliability assessment of test embankments on soft Bangkok clay by variance reduction and nearest-neighbor methods

This paper presents the application of probabilistic slope stability model based on variance reduction method on the Nong Ngoo Hao (NNH) test embankment and the probabilistic settlement evaluation of AIT test embankment using the nearest-neighbor method. The NNH embankment was constructed to failure. Sample autocorrelations were obtained from corrected vane shear test data as well as from the Dutch cone test data in both horizontal and vertical directions. The results showed that using a design criteria of probability of failure of 10 −3, a design safety factor of 1.12 is recommended for 3-D analysis. In 2-D analysis, the variance reduction method yielded lower probabilities of failure compared to an earlier work based on Monte Carlo method. For the AIT test embankment, the statistical data for the occurrence of fine sand and silt lenses in the soft Bangkok clay were obtained and the inclusions were probabilistic settlement prediction in conjunction with the method of Skempton and Bjerrum and Lacasse's approximation showed reasonable agreement with the observed values.

Interpretation of the data of soil shear tests

1. It was shown experimentally that the shear planes in a soil sample in a shear box in the general case do not coincide with the plane of contact between the shear rings (design shear plane). 2. The shear strength of noncohesive soils (dense and loose) increases monotonically with an increase of displacement of the shear rings and has an ultimate value determined by the value of the angle of internal friction. The value of the angle of internal friction is determined by the soil composition and does not depend on its density. The orientation of the shear planes depends on the soil density. 3. Peak and residual shear strength are characteristic for soils with sensitivity. The residual strength in this case is determined only by the forces of internal friction at a constant value of the angle of internal friction and cohesion equal to zero. 4. The values of the angle of internal friction according to the results of its determination in triaxial apparatus and a shear box are equal among themselves. When determining the angle of internal friction in a shear box an additional cheek of the coincidence of the shear planes with the design shear plane is necessary.

Additional Comparisons of Interlocked Fabric and Laminated Fabric Kevlar 49/Epoxy Composites

Compression, gas gun planar impact, and post-impact short beam shear test results are presented for a novel interlocked fabric reinforced Kevlar 49/epoxy composite. This material has roughly 4% fiber volume fraction in the through-the-thickness direction. For the purpose of comparison, similar results are also presented for a laminated Kevlar 49/epoxy composite. Both materials have a compressive stress-strain curve that can be approximated as bilinear with a secondary modulus of on the order of 10% of the initial modulus. Although the materials have comparable yield strengths (∼ 10% difference), their respective initial and secondary moduli are not in as close agreement (up to 50% difference). Gas gun planar impact spall test data indicate that relatively low levels of impact stress (∼1 kbar, ∼100 MPa) generate matrix cracking in both materials. The interlocked fabric's binder yarns, however, show no visible sign of damage even at an impact stress level of 5.1 kbar (510 MPa). Post-impact short beam shear test data for both materials show that once a threshold impact level is exceeded (∼1 kbar, ∼100MPa), specimen stiffness and load carrying capacity decrease as the impact level is increased. This is presumably because of mid-plane matrix cracks of increasing size and density. Even though the properties of the interlocked fabric reinforced composite are substantially reduced by impact at the 5.1-kbar (510-MPa) level, the binder yarns give the material a degree of integrity that would not otherwise exist. The interlocked fabric reinforced Kevlar 49/epoxy composite has a higher residual load carrying capacity than the laminated Kevlar 49/epoxy at all impact levels.

Vertical and lateral variability of vane shear test data for a clayey soil : Can J soil sci V65, N2, May 1985, P371–374

Vertical and lateral variability of vane shear test data for a clayey soil : Can J soil sci V65, N2, May 1985, P371–374

Vertical and lateral variability of vane shear test data for a clayey soil : Can J soil sci V65, N2, May 1985, P371–374

Vertical and lateral variability of vane shear test data for a clayey soil : Can J soil sci V65, N2, May 1985, P371–374

Data processing methodology in the characterization of the mechanical properties of terrain

The methodology for processing load-sinkage and shear test data obtained using the bevameter is examined. A weigthed least squares technique is proposed for deriving terrain values from experimental data. To streamline data processing time, a portable automatic data processing unit for the bevameter has been developed. The basic features and functions of the unit are described. The automatic data processing unit, together with associated bevameter, has undergone extensive field trials. They have been employed to measure the properties of various types of natural terrain. The results indicate that this new system can provide a basis for the development of a reliable, convenient and standardized technique for identifying terrain properties in relation to off-road mobility.

岩石の強度と弾性波速度の関係に関する確率論的研究

A theoretical model of rock was proposed to predict the strength of rock by longitudinal-wave-velocity measurement. Rock was assumed to be made of a homogeneous, isotropic, linearly elastic material containing a large number of penny-shaped cracks. The effective compliance of rock that contains cracks was evaluated following the way proposed by Amos Nur. The longitudinal-wave-velocity can be uniquely correlated with the effective compliance. The tensile strength of the rock was also evaluated with the aid of the stochastic process theory and linear fracture mechanics. From the theoretical considerations, the authors developed the foundamental equations by which field velocity data can be interpreted to the tensile strength. The experiments were carried out to measure ultrasonic velocity and tensile strength in laboratory. The theoretical result compared favorably with the experimental data of two kinds of shale.We also studied the compressive strength of rock based on the modified Griffith theory. The apparent coefficient of friction obtained from data of direct shear tests remains almost constant for the sample rock used. This result indicates that the linear correlation exists between compressive and tensile strengths, therefore the theoretical equations for tensile strength can be used to estimate compressive strength with little modification. The experimental result also showed fine coincidence with the theoretical results.

Advanced Beaded and Tubular Structural Panels

A program to develop lightweight beaded and tubular structural panels is described. Applications include external surfaces, where aerodynamically acceptable, and primary structure protected by heat shields. The design configurations were optimized and selected with a computer code which iterates geometric parameters to satisfy strength, stability, and weight constraints. Methods of fabricating these configurations are discussed. Nondestructive testing produced extensive combined compression, shear, and bending test data on local buckling specimens and large panels. The optimized design concepts offer 25 to 30% weight savings compared to conventional stiffened sheet construction.

The Inclination of Talus, Arctic Talus Terraces, and Other Slopes Composed of Granular Materials

Recent engineering research into the strength of rockfill suggests that the minimum angle of shearing resistance () of most materials composing talus slopes is likely to be about 39°-40°. The assumption that the typical 35° inclination of well-drained talus slopes reflects the shearing resistance of the talus material is therefore incorrect. The inclination of well-drained talus slopes will reflect the angle of shearing resistance only if (1) the slopes are being rapidly eroded, or (2) deposition rates are high compared with the degradation rates resulting from processes on the talus slope. In both instances, the slope angles will generally be 39° or steeper. This suggestion is supported by laboratory shear-test data from some Spitsbergen talus terraces which have eroded, and consequently relatively steep (up to 39°), outer slopes. Further support is provided by a number of observations reported in the literature. Shallow landslips sometimes occur on these and other "granular" slopes in Spitsbergen at angles considerably less steep than 39°-40°. This appears to be the result of impeded drainage due to the presence of permafrost at a shallow depth. A further observation suggests that average degradation rates over the past 10,000 years for the faces of two Spitsbergen talus terraces originally steepened by marine erosion are about 0.3° per 1,000 years.

A model study of rock-joint deformation

Existing techniques of rock-joint modelling are reviewed. It is concluded that no methods presently in use are acceptable as either realistic models of mating rock joints or as mass production methods for the development of large, highly jointed models of rock masses. A method is described for producing mating tension fractures in a weak, brittle model material using a large guillotine device. Parallel sets of model joints can be produced which are continuous, cross-jointed or offset (stepped) depending upon the chronological order of fracturing. The direct shear properties of these three types are compared and evaluated. The model results are used as a basis for predicting the full-scale (1: 500) displacements accompanying shear failure of a 96-ft long prototype tension joint. Recent numerical modelling of jointed rock masses has been based on assumed values of the shear and normal stiffness of the joints. These components are found to dominate the elastic deformation properties of the intact rock. The results of shear and normal stiffness tests on the model joints are used for a careful assessment of these quantities. The shear stiffness (peak shear stress per unit tangential displacement) is found to be both normal stress and size dependent, and this is confirmed by a survey of shear-test data for joints in rock. There appears to be an inverse proportionality between test dimension and shear stiffness, for a given normal stress. The normal stiffness (normal stress per unit closure) is found to be dependent on the preconsolidation or virgin normal stress level. The problems of simulating the behaviour of jointed rock masses by the finite-element method are reviewed. Two particular drawbacks seem to be the conservation of energy demanded during computation, and the computer storage problems involved in modelling dilatent joints. Both these features are of fundamental importance to rock-mass deformation. A move towards realistic physical modelling is considered essential to an understanding of real processes.

Computer analysis of powder flow characteristics

In order to devise a satisfactory method of analysing shear test data using computer techniques, it is first necessary to determine experimentally at least one of the unknowns, the index n, or tension T, in the suggested equation of the yield locus ( τ C ) n = σ+T T having shear and normal stress points τ and σ respectively. This is difficult to do with sufficient accuracy to obtain reliable results. Instead we determine the value of the ratio, cohesion C to tension T, which we first show to be a constant, K, for any particular powder in the great majority tested—nearly 40. We do this by measuring graphically the static angle of internal friction ψ, which again we show to be constant for any given powder and related to K by K = ny [ W W−ny ] (n−1)/n where W = 1+tan (ψ 2 1−tan(ψ 2 and y = tan ψ. All individual loci are first reduced to a single “specific” locus by dividing all τ and σ points by σ L. the consolidating normal stress for each locus and then, using the above relationship, satisfactory values for n and T s are found by reiteration using a curve-fitting optimisation procedure. The indications are that this method will not only produce more reliable hopper design solutions, but will determine the essential powder flow properties with the precision necessary for a general classification of flowability.

Dilatancy Characteristics Of Sand

Dilatancy characteristics of sand under cyclic loading including cyclic mobility behavior and behavior at large strains after liquefaction is investigated. Series of torsional shear test data and torsional simple shear test data, including both monotonic and cyclic loading, have been processed. First, stress-dilatancy relationship is developed using drained test results based on normalized shear work. Volumetric strain characteristics in wide range of confining pressure including low confining pressure levels are then investigated using undrained test data and stress-dilatancy model established using drained test data. It is shown that volumetric strain characteristics are similar to the one after liquefaction, except that the range of low stiffness region is smaller than that. This indicates that conventional constitutive model may not be able to simulate the behavior of sand at low confining pressure. It is also recognized that material properties deteriorate gradually with the application of cyclic load.