Stress-displacement Behavior Research Articles

State-of-the-art report: GCL shear strength and its measurement

This paper presents a comprehensive source of information on the shear strength and shear strength testing of geosynthetic clay liners (GCLs). Essential concepts of shear stress–displacement behavior and shear strength interpretation are presented, including long-term performance issues, followed by detailed discussions on the laboratory measurement of the shear strength of GCLs and GCL interfaces. The paper also provides recommendations for the selection of design failure envelopes for stability analyses and checklists to assist users in the specification of GCL shear testing programs. North American practice is emphasized and discussions are focused primarily within the context of landfill bottom liner and cover systems. Conclusions are drawn with regard to GCL shear strength behavior and current GCL strength testing practice, improvements for GCL strength testing and reporting are suggested, and future research needs are identified.

Soil precompression stress: II. A comparison of different compaction tests and stress–displacement behaviour of the soil during wheeling

Precompression stress is often used as a criterion for soil susceptibility to compaction. The objective of this study was to compare precompression stresses derived from different compression test methods and relate these values to measured stress and displacement during wheeling in the field. Precompression stress was measured at three depths at two sites on a Eutric Cambisol in Sweden using in situ plate sinkage test, and by compressing soil cores in the laboratory with sequential loading ( oedometer) and at constant displacement speed, respectively. At the same sites, wheeling experiments were carried out where vertical soil displacement and vertical soil stress were measured simultaneously at three depths. No clear relationship between precompression stress and compression method was found. Precompression stress values derived from the oedometer and the in situ plate sinkage test did generally not differ from each other. Precompression stress derived from the constant speed test was either higher (site A, silty clay loam) or lower (site B, silty clay) compared to the other methods. Precompression stress did not work as a threshold value between reversible and irreversible deformation when precompression stress values derived from the different methods were compared with stress and displacement measured in the field during the wheeling experiment. Even when the observed stress was lower than the precompression stress, a residual displacement was observed. The study demonstrates that the precompression stress is not a sharp value but depends on the compression test method and its analysis, and that compression tests might not represent the soil behaviour in the field sufficiently. There is an urgent need to study soil behaviour in the field and link these experiments to soil mechanical (laboratory) tests.

Observations on plastic strain localization in leonov-panasyuk-dugdale crack model

Method of Westergaard stress functions is applied to analyze the stress distribution around two-dimensional mode I crack in elastoplastic material. The Leonov-Panasyuk-Dugdale model is employed. It is shown that under certain loading conditions, the plastic zone location calculated using commonly accepted criteria of plasticity is inconsistent with initial assumption of thin rectilinear plastic strips. This inconsistency is removed when we assume a linear softening stress-displacement behavior in the plastic zone.

Mechanics of Constant‐Rate Filter Pressing of Highly Flocculated Slurries

The growth of a powder compact from a highly flocculated slurry has been simulated by a computer program that models non‐steady‐state Darcian flow. Computer simulations have been compared with filter‐pressing experiments. Constant‐rate filter‐pressing experiments are divided into two regimes of piston stress—displacement behavior: an initial, almost‐linear, but concave‐up, regime during cake growth, followed by a second region of rapidly increasing piston stress when the piston comes into contact with the cake. Linear piston stress—displacement behavior is expected, from theory based on a uniform cake model. Highly flocculated slurries show highly nonlinear behavior. Nonlinear behavior is shown to be consistent with nonuniform growth of the cake. The permeability and consolidation behavior of the cake has been determined by a consolidometer experiment. Computer simulations indicate that the particle‐packing density profiles during cake build‐up are surprisingly similar during cake growth. Conditions for uniform consolidation can be determined from a general equation for non‐steady‐state Darcian flow. Results are directly applicable to constant‐flow‐rate pressure casting or slip casting.

Influence of interfacial reactions on the fiber-matrix interfacial shear strength in sapphire fiber-reinforced Nial(Yb) composites

The influence of microstructure of the fiber-matrix interface on the interfacial shear strength, measured using a fiber-pushout technique, has been examined in a sapphire-fiber-reinforced NiAl(Yb) matrix composite under the following conditions: (1) as-fabricated powder metallurgy (PM) composites, (2) PM composites after solid-state heat treatment (HT), and (3) PM com-posites after directional solidification (DS). The fiber-pushout stress-displacement behavior con-sisted of an initial “pseudoelastic” region, wherein the stress increased linearly with displacement, followed by an “inelastic” region, where the slope of the stress-displacement plot decreased until a maximum stress was reached, and the subsequent gradual stress decreased to a “fric-tional” stress. Energy-dispersive spectroscopy (EDS) and X-ray analyses showed that the inter-facial region in the PM NiAl(Yb) composites was comprised of Yb2O3,O-rich NiAl and some spinel oxide (Yb3Al5O12), whereas the interfacial region in the HT and DS composites was comprised mainly of Yb3Al5O12. A reaction mechanism has been proposed to explain the pres-ence of interfacial species observed in the sapphire-NiAl(Yb) composite. The extent of inter-facial chemical reactions and severity of fiber surface degradation increased progressively in this order: PM < HT < DS. Chemical interactions between the fiber and the NiAl(Yb) matrix resulted in chemical bonding and higher interfacial shear strength compared to sapphire-NiAl composites without Yb. Unlike the sapphire-NiAl system, the frictional shear stress in the sap-phire-NiAl(Yb) composites was strongly dependent on the processing conditions.

Fatigue life prediction and failure mechanisms of composite materials

Fatigue life prediction and failure mechanisms of composite materials are studied based on the fatigue modulus concept and experimental results. Single-stress level fatigue life is predicted using generalized fatigue modulus degradation model and resultant strain failure criterion. Cumulative damage models defined by fatigue modulus and resultant strains are derived as functions of fatigue cycle and applied stress. This approach can predict accurately the multi-stress level fatigue life in addition to single-stress level fatigue life of composite materials. Fatigue modulus is measured by a cyclic stress-displacement behavior and resultant displacements data. The prediction is also made by the fatigue modulus degradation model and fatigue life prediction results. The comparison shows that the predicted values lie within the experimental scatter band. The relationship between physical damage accumulation and material property (such as fatigue modulus) degradation is induced qualitatively through fractograph...

Stress-displacement behaviour of the fractured rock around a deep tabular stope of limited span : Kirsten, H A D; Stacey, T R J S Afr Inst Min MetallV89, N2, Feb 1989, P47-58

Stress-displacement behaviour of the fractured rock around a deep tabular stope of limited span : Kirsten, H A D; Stacey, T R J S Afr Inst Min MetallV89, N2, Feb 1989, P47-58

Centrifugal Model Tests on Vertical Anchor Plates

The stress displacement behavior of vertical anchor plates and continuous anchor walls in dense sand when subjected to horizontal pull‐out forces is presented. Results of a large number of centrifugal tests on 1 in. (25 mm) and 2 in. (50 mm) models subjected to accelerations of up to 40 gravities are presented and the effects of anchor geometry and embedment are examined. Centrifugal test results are compared with those from conventional small model tests thus enabling potential errors in direct extrapolation of the latter to field scale to be evaluated. Considerable overpredictions of pull‐out resistance and under‐estimations of failure displacements are found for 1/20 and 1/40 scale modellings of 19.7 in. (0.5 m) and 39.4 in. (1 m) anchors. The effects of anchor geometry, defined by dimensionless shape factors appear to be sensibly independent of scale. Experimental results are briefly compared with recent theoretical and semiempirical design formulas using shear strengths derived from plane strain comp...