Action Of External Load Research Articles

Experimental study on mechanical characteristics of sandstone containing arc fissures

Arc fissure is one of the basic forms of defective rock, where the expansion and evolution mechanism plays an important role in the stability of engineering rock mass under the external load action. Uniaxial compression experiments of sandstone samples that contained various angles of arc fissures (sandstone sample was 80 mm × 160 mm × 30 mm) were performed in order to investigate the effect that arc angle α had on the mechanical properties, the failure mode, and the fracture evolution process of sandstone. The results showed that when arc angle α was increased, the peak strength and the strain of the sandstone samples initially decreased before increasing and the minimum peak strength and strain were reached when α = 15°. The deterioration of the bearing capacity and the number of cracks that appeared during the sandstone loading process decreased as the arc angle of the fissure increased. The arc fissure destruction was primarily initiated from the fragile area of the arch tip. The tensile cracks appeared on the fissure tip and non-tip as the axial force increased. The various arc angle α played an important role in the initiation stress and the rupture evolution of the specimen.

A Novel Polyaxial Strength Criterion for Rock Materials Under General Stress Condition

Yielding or failure of rocks under the action of external loading is complicated due to the dependence on pressure sensitivity and Lode angle. In this study, a generalized hyperbolic strength criterion is proposed to describe the strong nonlinear characteristics of rocks over a wide range of confining pressures. The relationship between failure stress and instantaneous friction angle of rocks is analyzed based on nonlinear Mohr strength envelope. In order to reflect the influence of intermediate principal stress on the strength of rock materials, the generalized hyperbolic criterion has further been extended to complicated stress state. The failure criterion allows the possibility of transitions from an equilateral triangle to circle, which greatly improves the durability and applicability to describe the strength characteristics of various rocks under complicated stress state. The validity of the proposed criterion is verified by comparing predictions with experimental results of rocks.

Energy Evolution Mechanism and Confining Pressure Effect of Granite under Triaxial Loading-Unloading Cycles

Rock mass undergoes some deformational failure under the action of external loads, a process known to be associated with energy dissipation and release. A triaxial loading-unloading cycle test was conducted on granite in order to investigate the energy evolution pattern of rock mass under the action of external loads. The study results demonstrated: (1) The stress peaks increased by 50% and 22% respectively and the pre-peak weakening became more apparent in the ascending process of the confining pressure from 10MPa to 30MPa; the area enclosed by the hysteresis loop corresponding to 30MPa diminished by nearly 60% than that corresponding to 10MPa, indicating a higher confining pressure prohibits rock mass from plastic deformation and shifts strain toward elastic deformation. (2) In the vicinity of the strength limit, the slope of dissipation energy increased to 1.6 from the original 0.7 and the dissipation energy grew at an accelerating rate, demonstrating stronger propagation and convergence of internal cracks. (3) At a pressure of 70% of the stress peak, the elastic energy of the granite accounted for 88% of its peak value, suggesting the rock mechanical energy from the outside mostly changes into the elastic energy inside the rock, with little energy loss.(4) Prior to test specimen failure, the axial bearing capacity dropped with a decreasing confining pressure in an essentially linear way, and the existence of confirming pressure played a role in stabilizing the axial bearing capacity.

Bamboo-imitated pipes for continuous fiber reinforced polyethylene

Bamboo-imitated pipes for continuous fiber reinforced polyethylene were prepared, and the influences of the bamboo joints and process conditions on the mechanical properties of the pipes were also studied. The results show that the flexural and impact strengths of the bamboo-imitated pipe are significantly improved due to the addition of bamboo joints, and the mechanical properties are gradually improved with the reduction of the bamboo joint spacing. The solid structure of the bamboo joints suppresses the effect of oval deformation for the section under the action of external load, and the suppression effect on the oval deformation of the pipe section is more obvious with the reduction of bamboo joint spacing. At the same time, the flexural strength and the impact strength of the pipe increased firstly and then reduced with the increase of the die temperature.

Analysis of Rock Damage Characteristics Based on Particle Discrete Element Model

Rock is a heterogeneous medium that is composed of minerals of various sizes. Under the action of external loads, the generation, propagation and coalescence of microdefects in the rock mass determines the macroscopic deformation and fracture of rock. To understand the damage law of rock and to reveal the evolution of dynamic failure, a uniaxial compression model was established based on particle flow code. Acoustic emission and energy characteristics of rock damage were analyzed, and the damage constitutive models of rock were discussed. During rock uniaxial compression, acoustic-emission events undergo a relatively quiet, sudden increase and sharp decrease for three periods, which corresponds to the compaction and elastic deformation stage, yield stage and post-peak stage in the stress–strain curve. Before the yield stress is reached, the proportion of bond and strain energies is larger. Friction energy accounts for a small proportion of the total energy, and a reciprocal relationship exists between them. The constitutive model that is based on friction energy can better reflect the variation in stress and strain, then the constitutive model based on acoustic-emission parameters.

Functionally graded rod with small concentration of inclusions: Homogenization and optimization

This work is devoted to strain analysis and optimal design of a Functionally Graded (FG) rods and beams with small inclusions. The homogenization procedure plays a key role in our investigations. The method is illustrated using an example of the rod longitudinal deformation and bending of a beam. We consider the cases of FG inclusion sizes and FG steps between inclusions separately. Particular problems of optimal design are discussed in some details. The mathematical model of the bending beam, which adapts to the external load action, is proposed and an illustrative example of the adaptation process is given.

The Use of Eurocode Model of Reinforcing Steel Behavior at High Temperature for Calculation of Bars Elongation in RC Elements Subjected to Fire

The Anderberg model introduced in Eurocode 1992-1-2 gives stress-strain relationships of reinforcing bars for high temperature values at multiples of 100oC. This model was based on tests performed at steady temperature conditions. Therefore, the elongation predicted by this model only accounts for simultaneous action of external load and high temperature. The steel free thermal strain is not included. However, reinforcement of RC elements exposed to fire is subjected to unsteady temperature conditions. This paper presents the Eurocode model in temperature-strain coordinates. The sum of elongations caused by stress and free steel thermal strain is shown against temperature for various stress levels. This model might be useful for estimation of reinforcing bars elongation during advanced analyses of RC structures exposed to fire.

Stresses in the material with multilayered coating under impulse thermal loading

The two-dimensional model of mechanical behavior of the specimen with multi layered coating is formulated. The parametric analysis was carried out for various types of boundary conditions. Stress intensity depending on time was studied. The influence of impulse parameters on the temperature and stresses was investigated. It was revealed that radiation heat losses reduces the action of external loading.

Design Procedure by Strength Criteria of Asphalt Layers on a Rigid Base Taking into Account the Simultaneous Action of External Loads and Thermal Stresses

The article gives the definition of a generalized solution of the thermal stress in the asphalt layer on a rigid base at heating and cooling, taking into account the rheological properties of asphalt concrete pavement. The equation for determining the stress state of the asphalt layer on a rigid base caused by the combined effect of temperature deformation and external load is presented. The design procedure by the strength criteria of asphalt layers on a rigid base, taking into account the adhesion strength of the asphalt layer and the rigid base, the temperature cracking resistance, as well as the shear resistance of the asphalt layer is given.

Structure and properties of water film adsorbed on mica surfaces.

The structure profiles and physical properties of the adsorbed water film on a mica surface under conditions with different degrees of relative humidity are investigated by a surface force apparatus. The first layer of the adsorbed water film shows ice-like properties, including a lattice constant similar with ice crystal, a high bearing capacity that can support normal pressure as high as 4 MPa, a creep behavior under the action of even a small normal load, and a character of hydrogen bond. Adjacent to the first layer of the adsorbed water film, the water molecules in the outer layer are liquid-like that can flow freely under the action of external loads. Experimental results demonstrate that the adsorbed water layer makes the mica surface change from hydrophilic to weak hydrophobic. The weak hydrophobic surface may induce the latter adsorbed water molecules to form water islands on a mica sheet.

Topology optimization of reinforced concrete structures considering control of shrinkage and strength failure

To take into account the shrinkage effect in the early stage of Reinforced Concrete (RC) design, an effective continuum topology optimization method is presented in this paper. Based on the power-law interpolation, shrinkage of concrete is numerically simulated by introducing an additional design-dependent force. Under multi-axial stress conditions, the concrete failure surface is well fitted by two Drucker–Prager yield functions. The optimization problem aims at minimizing the cost function under yield strength constraints on concrete elements and a structural shrinkage volume constraint. In conjunction with the adjoint-variable sensitivity information, the enhanced aggregation method is utilized to efficiently reduce the computational effort arisen from large-scale strength constraints. Numerical results reveal that the proposed approach can produce a reasonable solution with the least steel reinforcements to ensure the structural safety under the combined action of external loads and shrinkage.

Adaptive mechanical properties of topologically interlocking material systems

Topologically interlocked material systems are two-dimensional granular crystals created as ordered and adhesion-less assemblies of unit elements of the shape of platonic solids. The assembly resists transverse forces due to the interlocking geometric arrangement of the unit elements. Topologically interlocked material systems yet require an external constraint to provide resistance under the action of external load. Past work considered fixed and passive constraints only. The objective of the present study is to consider active and adaptive external constraints with the goal to achieve variable stiffness and energy absorption characteristics of the topologically interlocked material system through an active control of the in-plane constraint conditions. Experiments and corresponding model analysis are used to demonstrate control of system stiffness over a wide range, including negative stiffness, and energy absorption characteristics. The adaptive characteristics of the topologically interlocked material system are shown to solve conflicting requirements of simultaneously providing energy absorption while keeping loads controlled. Potential applications can be envisioned in smart structure enhanced response characteristics as desired in shock absorption, protective packaging and catching mechanisms.

Static Structural Analysis of the Blood Pump Rotor System

In order to study the impact of external forces of the influence of the structural characteristics of axial flow blood pump rotor system.Using the blood pump rotor system as the research object,use ANSYS software,Use the method of static structure.the stress and strain analysis nephogram of the blood pump rotor system was obtained under the external load.through the study: The deformation of the blood pump rotor system which under the action of external load was mainly concentrated in the external contact of blade wheel rotor and ceramic shaft,but the deformation is small.So the blood pump rotor system design is reasonable. The vulnerability part of the blood pump rotor system was obtained.it provide date support for the further optimization of the blood pump rotor system and it also lay the foundations for the subsequent dynamic analysis.

Transformation of the Structure of Refractory Alloy 0.45C – 26Cr – 33Ni – 2Si – 2Nb During a Long-Term High-Temperature Hold

The continuous variation of structure and the kinetics of dissolution of the initial phases with formation and dissolution of intermediate phases at the temperature of long-term operation of cast refractory alloy 0.45C – 26Cr – 33Ni – 2Si – 2Nb are studied. The behavior and succession of phase transformations in Fe – Cr – Ni-base alloys at a temperature of 0.85 – 0.90 of their solidus, including the case of the action of external load, is determined. The effect of high-temperature transformations of structure on the operating properties of the alloy is estimated.

Evolution Model of Concrete Failure Surface under the Action of Load and Frezee-Thaw Cycles

Concrete failure surface is the most important tool to predict concrete strength under complicated load. Most concrete structures in cold regions are subjected to both external loads and freezing-thawing, while now most researchers focused on the freeze-thaw durability of concrete without external loads. To make up the deficiency, the degradation of compressive strength of concrete under the simultaneous action of external loads and freezing-thawing are experimentally investigated in this research. Finally, a concrete failure criterion is adopted to establish an applicable failure surface in principal stress space for concrete.

Influence of external loads on the redistribution of hydrogen in the metal near stress concentrators

To study the influence of elastic strains caused by the action of external forces and internal hydrogeninduced stresses in the metal on the redistribution of hydrogen near stress concentrators, we propose a system of gradient-type differential equations. On the basis of this system, we develop a general algorithm and analytic relations for the investigation of the accumulation of hydrogen near technological and structural defects. The redistribution of hydrogen near circular stress concentrators, cracks, and rigid inclusions under the action of external loads is studied for hydrogenated elastic bodies.

A method for computing the stress fields in a deformable elastic half-space with a polysynthetic twin near the surface

The problem of computing the stress fields around a polysynthetic twin near the surface under the action of a lumped or distributed load on the boundary of an elastic half-space is solved without using the thin twin approximation. It is found that the action of external stresses leads to the stress redistribution such that the stress localization is observed not only in the region of the external load action but also far from the vertices of the twins of the polysynthetic twin.

Analysis of Vortex-Excited Resonance for Main Stay Bar on One Large-Span Bridge

In this paper, the vortex-excited resonance analysis are performed for main stay bar of a new type large-span bridge and the structural maximum displacement response in resonance state is calculated by programming , to be obtained the maximum displacement response and its occurring position of main stay bar in the vortex-stimulated resonance state caused by wind. The bottom of the main stay bar is fixed connection and the top is hinged. Because the bottom of the main tower fixed with better conditions, the maximum displacement should occur the place where are up middle of the main stay bar under the action of external loads. The analytical results show that the real compute results are better consistency with this judge. The results of this paper provide the base for the wind-resistant design of large-span bridge and can be to references for the coming bridge

Automated thermal-strength calculations of ceramic cutting plates

An automated system for thermal-strength calculations of ceramic cutting plates is proposed. This system is based on microstructural and mathematical models and provides information regarding the thermal state and stress-strain state of cutting plates under the action of external loads. The structural nonuniformity of the ceramic is taken into account.

Analysis of Multi-Pylon Cable-Stayed Bridges with Intersecting Cables

For the intermediate pylons of multi-pylon cable-stayed bridges can’t be connected by backstays to fixed points, it is possible to produce greater horizontal displacements in the top of towers under the action of external loads. Therefore, it is an important problem to obtain adequate structural stiffness in the design of multi-pylon cable-stayed bridges. In this paper, methods of improving stiffness of multi-pylon cable-stayed bridges are discussed. Multi-pylon cable-stayed bridges with intersecting cable are studied. Some useful recommendations were given for the design of multi-pylon cable- stayed bridges by numerical calculation.