Main Tensile Stress Research Articles

Short dental implant biomechanics in the mandible bone tissue

The aim of the study was to assess the stress-strain state of «short dental implant - lower jaw bone tissue» system in the its osseointegration area under different stress options, of an experimentally developed bone tissue model. Using the finite element analysis method, we investigated a three-dimensional model of an implant with 5.0 mm diameter and 6.5 mm height integrated into the quasi-elastic model of the lower jaw segment with a total deformation modulus of 14 400 MPa and a Poisson's ratio of 0.24 for the cortical layer, for the spongy layer, the general deformation module of 0.2 MPa, Poisson's ratio 0.4. The values of equivalent stresses according to the Genki-Mises criterion for the implant body amounted to 50-76 MPa in the cervical region from the end and inner sides of the implant interface and along the upper edges of the thread edges in the upper third of the implant. Minimum values of 0.1-20 MPa are distributed over the implant body from its cervical part to the top in the lower 2/3. The equivalent von Mises stresses in the bone at the joints of the threaded implant part are minimal - 5-15 MPa. Values of shear stresses in the bone - 2 - 3 MPa, normal vertical stresses - up to 5-13MPa, main tensile stresses - up to 20 MPa, compressive stresses - up to 30-40 MPa. Thus, installing this implant in such model, should not occur irreversible deformations. In our opinion, the structural stability is ensured by the bone tissue features architectonics within 3 mm of the cortical layer, where the maximum stress is redistributed in the future throughout the cortical bone, which can expand the indications for short dental implants use, especially in patients with a limited alveolar bone volume.

Analysis on stress state of box-girder web under prestressing effect

In order to study the effect of prestressed box girder webs stresss state, determining the stress distribution within a web, research and analysis of vertical prestressed box girder, curved beam prestressed sensitivity under the web. Establishing the finite element model of the box girder web vertical prestressing effect is analyzed, results show that the principal tensile stress of the web is sensitive to the vertical prestress, applying the vertical prestress can effectively reduce the principal tensile stress of the web; with the decrease of the effective vertical prestress, the neutral axis above the principal compressive stress decreases rapidly, while below the neutral axis decreases relatively slow; Under the same vertical preloading stress level, the roots of cross section of the compressive stress of web reserves than L / 4 section of the web. Calculation and analysis of curved beam under bending point, different bending angles and bending radius of principal stress effect on the web, Results show that the set of curved beam web when the curved beam bending stress concentration easily, appear the main tensile stress; Increase the bending radius can effectively reduce beam cross-section of web principal tensile stress, along with the rising of the next corner, principal tensile stress peak value increases gradually, thus setting bending beam, should try to reduce the bending angle.

涪陵江东边坡治理方案有限元分析

边坡失稳易导致山体滑坡，抗滑桩被广泛应用于边坡治理工程中。依托于涪陵江东边坡治理工程，结合群桩承台基础、扶臂式挡墙及斜坡护岸结构体系对边坡进行治理。选取典型剖面建立计算模型，采用有限元程序CORE3D针对边坡在结构体系作用下的变形与稳定性进行了计算，对比分析了4排桩与5排桩体系作用下滑坡体与抗滑桩的变形与受力特性，为工程实践提供参考。研究结果表明：与5排桩结构体系相比，4排桩体系作用下边坡、挡墙的竖向与水平向位移较大；抗滑桩最大主拉应力与压应力亦较大。抗滑桩表现出明显的“S形”变形，并形成土拱效应。滑坡体单宽推力自后缘起逐渐增加，至抗滑群桩前推力达到峰值。推荐采用4排桩方案，注意在节点处加强纵向受力钢筋与箍筋作用。 Slope instability is easy to cause landslides, and anti-sliding piles are widely used in slope treat-ment. Based on the slope treatment project of the eastern Fuling River, the slope was treated by the system which coupled the pile groups, retaining wall and the slope revetment structure. The calculation model of the typical profile was established, and the finite element program CORE3D was used for calculating the deformation and stability of slope, and the deformation and stress characteristics of landslide and anti-sliding piles were compared between 4 piles and 5 piles sys-tem, which provide a reference for engineering practice. The results show that compared with the 5 piles system, the vertical and horizontal displacement of the slope and the retaining wall of the 4 piles system were larger, and the main tensile stress and compressive stress of anti-sliding pile were larger too. The anti-sliding piles showed “s-shaped” deformation, and the soil arching effect was formed. The single wide thrust of the slope increases gradually from the post, and attained the peak before the anti-sliding piles. It is recommended that 4 pile system is better, and the longitudinal rebar and stirrup at the nodes should be reinforced..

Features of the Masonry Structure Calculation with Vertical Ring Beams based on the European Standards

The design of masonry structures should remain a combination of traditional and modern knowledge. The Eurocodes in the field of the design of earthquake-resistant masonry structures, carry mostly acceptable and expected recommendations and requirements. This paper shows that they contain less acceptable principles, which require further experimental and analytical studies. Particularly it should be noted that Eurocode knows only a shearing mechanism by the horizontal coupling, although during the seismic load, the fracture usually occurs due to exceeding the main tensile stress, which manifests by opening diagonal cracks. The mechanism of the horizontal shearing by Eurocode is treated as critical for the seismic resistance of most masonry buildings, thus the masonry structure is attributed as sufficiently secure, although its actual seismic resistance would be far below from the required.

Нагрузки, разрушающие строительные конструкции в результате аварийных взрывов

To determine the bearing capacity limits of main structures of buildings and constructions with explosive productions it was analyzed data on destruction and damage rate of various constructive elements of buildings and constructions which took place as due to emergency explosions inside production premises so due to external explosion; it were also used results of tests of structures under the action of explosive loads. The analysis of past accidents shows that one of the most vulnerable spots of brickwork created during construction of buildings are sections at seams which cohesion is often insufficient to provide shearing resistance, breaking strength or resistance to the main tensile stresses. Advantages of large-panel industrial buildings before brick buildings, in regards to their explosion stability, are proved. Recommendations on designing of collapsible reinforced concrete structural frames of buildings with explosive productions are given. Data on bearing capacity of structures of industrial buildings obtained on the basis of materials on emergency explosions, analysis of results of researches stated in literary sources and also data on loadings causing destruction of constructions and structures of various degree and character are presented. Classification of building structures according to their damage rate is given. Data on explosive loads which cause destruction of different types of the main building structures that can be used for creation of the explosion protection system of buildings (using construction methods) with explosive productions are given. Behavior of structures in case of emergency explosions, tests and calculations of structures is defined; permissible loads on the bearing and filler structures with the purpose to obtain the initial data for recommendations on design of buildings for explosive productions is determined.

Geometrically necessary twins in bending of a magnesium alloy

Evidence for the formation of geometrically necessary twins (GNTs), or twins that accommodate a strain gradient in a multi-axial stress state, in quasi-static, room temperature three-point bending of a rolled magnesium alloy is presented. Electron backscatter diffraction analysis showed that {101¯2}<101¯1¯> extension twins (rather than {101¯1}<101¯2¯> contraction twins) form in arcs in the tension zone, and that twinned grains have very low Schmid factors. The main tensile stress component in the tension zone was nearly perpendicular to the c-axis of the parent grains. The mechanism for such unusual twinning behavior was analyzed from the perspective of strain components that are generated by {101¯2}<101¯1¯> twinning. After twinning, an extension strain component along the c-axis and a contraction strain component perpendicular to the c-axis of the parent lattice are generated simultaneously due to the misfit between the parent and the twin lattice. The contraction strain component by twinning provided an extra strain accommodation for the compressive strain in the tension zone produced by the bending, despite the fact that the local stress state strongly disfavored the {101¯2}<101¯1¯> twinning. Thus, the {101¯2}<101¯1¯> twins in the arcs in the tension zone of the bent specimen present the characteristic of being geometrically necessary, similar to geometrically necessary dislocations and boundaries.

Determination of the Strength and Orientation of Destruction Concrete's Surfaces for Different Types of Bulk Stress State

Criteria of concrete strength and their dependence on the character of deterioration at the volume tense state types: 3-axial compression, cases of the compression-extension and 3-axial extensions are described. The compression tensions are taken as negative. In the case of 3-axial compression the criterion of the strength is presented as the functions from the main tensions σ1, σ3 and from the Lode-Nadai μσ parameter, which allows to take into account the influence of the middle tension σ2 on the concrete strength. It was shown that the analogy is possible between the offered criterion of concrete strength at 3-axial compression and the Coulomb-Mohr strength criterion, if you take that every Lode-Nadai μσ parameter corresponded its threshold value envelope of Mohr cycles, and the family of the envelopes has unlinear character. Criteria of the strength at the availability of the tensile stresses are represented as unlinear functions from the main tensions σ1, σ2, σ3. The deterioration character in these cases is tied with the formation of cracks at the main tensile stresses surfaces (areas). Criteria of the strength coincides on the borders of the tensile states and forms general criterion of the concrete strength at the volume tensile state in common.

ADIÇÃO DE FIBRAS DE LATA DE ALUMÍNIO E AÇO EM CONCRETO

The use of staple fibers with reinforcing function in some cases is better than conventional equipment with rods and wires. As in the case of thin sheets which do not contain reinforcement in the form of rods, fibers serving as the main armor, and the rate exceeds 5% by volume. Another case is the control of cracking due to humidity and temperature variations, where the fibers act as secondary armor. Although the concrete will gain strength with the addition of fibers, it is important to note that this gain is not specific varying according to the approximation of the fibers relative to the direction of the main tensile stress, so its primary function is to contain or avoid the appearance of cracks that impair the concrete structure, and that its use provides increased toughness and energy absorption capacity, where the voltage drop is accompanied by large deformation. This work aims to present an analysis of the use of steel fibers obtained by recycling aluminum cans added to the concrete fibers. Checking the possible changes in the mechanical behavior of concrete.

Prestressed Concrete Continuous Girder Bridge Reinforcement Simulation Analysis and Carrying Capacity Assessment

This article simulates prestressed concrete continuous girder bridge reinforced many times and evaluates carrying capacity after reinforcement. Taking the FuFeng bridge for an example, we analyze the bridge’s stress state in using by Midas software, evaluate the concrete ability of crack resistance, check the reinforced concrete structure ultimate carrying capacity, the cracking resistance and the stiffness, assess reinforcement effect and verify the accuracy and reliability of the simulation results. The maximum main compressive stress, maximum compressive stress, maximal main tensile stress and maximum tension stress of mid-span cross-section of the bridge are 1.6Mpa, 1.6Mpa, 0.3~0.5Mpa, and -1.2Mpa respectively, the mid-span center cross-section of deflection is 2.89cm. Reinforcement suppresses the development and expansion of the crack; the mid-span deflection tends to stabilize; the ultimate bearing capacity meets the Standard requirement basically; the emergency capacity is not enough; and the car whose weight over 55 tons is prohibited from passing.

Influence Analysis of Crack Depth and Position on Asphalt Pavement Structure with 3D Finite Element

In recent years the research on Surface-initiated longitudinal cracking along wheelpath (or Top-Down cracking) is become a fresh hotspot in the field of pavement damage focused by international asphalt pavement engineering.Because the traditional load is the vertical surface load with uniform tire pressure, this loading is applied at only one position and no effort is made to distinguish between tire pattern.The traditional method can’t explain the mechanism of the top-down cracking. In order to discuss the mechanism of TDC, this paper establish a 3D finite element model of semi-rigid pavement structure and use the large finite element software Abaqus. The analysis shows that, in the crack beginning stage, the main tensile stress appears under the center of the load on the sub-base of the pavement,and its value increases with the time. When cracks appear in the base, the position of the main tensile stress appears at the bottom of the surface layer, under the outside edge of wheel path. The value of the main shear stress increases at the stage of the cracks beginning, but the increase is small. The value of the main shear stress decreases when the cracks appear in the middle of the surface layer, and the position of the main shear stress changes with the depth of the cracks. With the increase of the cracks’ depth, the adverse influence of the shear stress becomes weaker and weaker.So the key of controlling the cracks in the surface layer is prevention. To prevent the development of the cracks, the tensile strength of the layer’s material should be enhanced in any way. The stress and its value resulted from the vehicle loaded on the structure layer is bigger than the other cases when the position of the cracks is at the edge of wheel path, and the stress is much bigger than the shear strength and the fracture toughness of the material of the layer. As the shear strength of the material is not enough, the vertical cracks are easier to appear at the edge of wheel path under the load of the vertical. Once it appearing, the cracks will extended into the layer because of the load of vertical. Eccentric load generates greater stress in the structure than the load loaded upright. In fact, though, non-channeling can reduce the appearance of the tracks, eccentric load enhance the development of the cracks in the surface because of the existence of the cracks in the surface layer.

Influence Analysis of Crack Depth and Position on Asphalt Pavement Structure with 3D Finite Element

In recent years the research on Surface-initiated longitudinal cracking along wheelpath (or Top-Down cracking) is become a fresh hotspot in the field of pavement damage focused by international asphalt pavement engineering.Because the traditional load is the vertical surface load with uniform tire pressure, this loading is applied at only one position and no effort is made to distinguish between tire pattern.The traditional method can’t explain the mechanism of the top-down cracking. In order to discuss the mechanism of TDC, this paper establish a 3D finite element model of semi-rigid pavement structure and use the large finite element software Abaqus. The analysis shows that, in the crack beginning stage, the main tensile stress appears under the center of the load on the sub-base of the pavement,and its value increases with the time. When cracks appear in the base, the position of the main tensile stress appears at the bottom of the surface layer, under the outside edge of wheel path. The value of the main shear stress increases at the stage of the cracks beginning, but the increase is small. The value of the main shear stress decreases when the cracks appear in the middle of the surface layer, and the position of the main shear stress changes with the depth of the cracks. With the increase of the cracks’ depth, the adverse influence of the shear stress becomes weaker and weaker.So the key of controlling the cracks in the surface layer is prevention. To prevent the development of the cracks, the tensile strength of the layer’s material should be enhanced in any way. The stress and its value resulted from the vehicle loaded on the structure layer is bigger than the other cases when the position of the cracks is at the edge of wheel path, and the stress is much bigger than the shear strength and the fracture toughness of the material of the layer. As the shear strength of the material is not enough, the vertical cracks are easier to appear at the edge of wheel path under the load of the vertical. Once it appearing, the cracks will extended into the layer because of the load of vertical. Eccentric load generates greater stress in the structure than the load loaded upright. In fact, though, non-channeling can reduce the appearance of the tracks, eccentric load enhance the development of the cracks in the surface because of the existence of the cracks in the surface layer.

The Discussion on Deflected Pre-Stressed Tendons and Diagonal Cracks of Webs in PSC Box Girders

Abstract In order to find the relationship between deflected pre-stressed tendons and diagonal cracks of webs and provide basis to design and construction of bridges, a characteristics section model of a long span pre-stressed concrete continuous box girder, which is now under construction in Chongqing is analyzed by using nonlinear finite element program Midas-FEA. A numerical simulation analysis to the tensile stress in the webs was down based on the actual construction situation. As the research shows: 1, Stress concentration exists at the point where pre-stressed tendons are anchored, and the stress value was higher in anchorage area, which accord with the Saint-Venant Principle.2, The main tensile stress of webs in the anchorage area is lower than 1.04MPa, which did not surpass the standard 2.74MPa of the concrete tensile stress of C55, as a result, webs would not craze from finite element analysis. 3, Cracks brought by other normal or abnormal reasons existed in the process of casting the cantilever...

Study on effect of tunnelling blasting on existing adjacent tunnel

Based on the actual tunnel excavation projects, a three‐dimensional finite element model of tunnel excavation is set up, and the particle vibrations and stress distributions are analysed at the existing adjacent tunnel concrete linings. The results of calculation show that in the whole range of investigation, the vertical peak particle vibrations are bigger than those in the other two directions, but the main tensile stresses in the tunnel vault crown and bottom are in the horizontal direction, which prove that the vertical peak particle vibrations cannot totally represent the stress states of rocks. In actual projects, the blasting peak particle vibrations should be controlled, and the stress states of rocks should be analysed as well. During our actual tunnel excavation, the maximum peak particle vibration calculated is 0·0494 m s–1, which is lower than the 0·05 m s–1 required in projects; and the maximum tensile stress in the tunnel vault crown is 0·54 MPa. That is to say, the tunnel concrete linings are not affected.

Theoretical Analysis of Designed Internal Forces of Jiamusi Highway Prestressed Concrete Bridge before Strengthening in China

The objective of this study is to calculate and analyze the internal forces under designed dead and live loads to evaluate the structural performance of corbels and T-shaped cantilever structure of the main span of Jiamusi highway prestressed concrete bridge to evaluate the state of the structural members of the bridge. Two software are used in this analysis. The first software is Dr. Bridge Ver. 2.95 which is used to analyze the internal forces of T-shaped cantilever structure under different load combinations. The second software is Ansys Ver. 10 which is used to analyze the internal forces in the corbel. The results of analysis show that at the dead load stage, the maximum compressive stress at the upper and bottom edge of all sections of T-shaped cantilever structure satisfies the allowable values of standard. The tensile stress doesn’t appear. At the normal service stage, there is enough reserve of compressive stress in the all sections, and the compressive stress is smaller than the allowable value of the standard. There is no tensile stress for all the controlled sections. The maximum main compressive stress and maximum main tensile stress of all controlled sections is smaller than the allowable value of standard. The bending strength of all sections satisfies the allowable values of standard, and there is big reserve of strength. The steel settled in the oblique section of 45° in the web of the corbel has enough reserve for the tensile strength. If the prestressed steel in the corbel is inefficient, the resistance of the oblique section given by the ordinary steel in the corbel and it can be resisted the loads. The longitudinal positive stress of vertical section a-b, vertical shear stress, main tension stress and main tension stress of oblique section a-c of 45 satisfy the allowable values of standard.

Failure analysis of a crude oil pipeline

The transversal cracking of a seamed API 5L X46 steel tube belonging to a crude oil pipeline was investigated. The main cracking nucleated in the internal surface of the tube, at the boundary between the heat-affected zone (HAZ) and the weld metal, propagating in a stable mode along the radial and longitudinal directions. Stress raisers, such as welding defects and corrosion pits, were associated to the cracking nucleation. The internal surface of the tube and the cracking surfaces presented a deposit layer, which was rich in Fe, O and S. Diffractometry on the internal identified the presence of a multi-layered corrosion deposit, formed by iron oxide (Fe 2O 3 and Fe 3O 4) and iron sulphides, such as pyrrhotite, mackinawite and pyrite, indicating the action of a H 2S corrosion assisted mechanism. The crack propagation path did not depend on the welding macrostructure, growing perpendicular to both the internal surface and main tensile stresses. Crack propagation was, however, microstructure sensitive, with a more intense branching occurring inside the base metal rather than the HAZ region. Both regions presented cracking (blistering) of the sulphide/matrix interface and microfractographic examination indicated the action of a ductile fracture mechanism linking the H 2 blisters, reinforcing the idea that atomic hydrogen association rather than hydrogen embrittlement was the active mechanism during the cracking of the pipeline. These observations indicated that failure of the pipeline occurred by a stress-oriented hydrogen-induced cracking (SOHIC) mechanism.

Ductal – A High-Performance Material for Resistance to Blasts and Impacts

Reactive Powder Concrete (RPC) is a cementitious material consisting of cement, sand, silica fume, silica flour, superplastiser, water and high strength steel fibres. The material, developed by Bouygues the parent company of VSL, is marketed under the brand name of Ductal®. Production in Australia commenced in early 2003. Ductal is almost self placing, has a compressive strength of 160–200 MPa and a flexural strength of 30–40 MPa. In structural applications, Ductal is generally used without any passive reinforcement. Very fine high strength steel fibres are able to withstand secondary tensile stresses. Prestressing counterbalances the main tensile stresses due to bending. The durability properties of Ductal and its resistance to aggressive agents are orders of magnitude better than conventional high performance concrete. A predicted design life in marine environments of several hundred years is achievable. The unique characteristics of Ductal, including exceptionally high energy absorption capacity and resistance to fragmentation, make it ideal for panels and components that need to perform under explosives, impact or shock loads. The flexural toughness is greater than 200 times that of conventional fibre reinforced concrete. In May 2004, the performance of seven Ductal panels was evaluated in two large explosive trials performed at Woomera (South Australia). The panels performed remarkably well, exhibiting high levels of ductility and no signs of fragmentation. In further tests, 100mm thick Ductal blast resistant panels have been shown to effectively resist impacts by blast produced fragments using fragment simulated projectile tests. These panels can also withstand impacts from the highest class of rifle projectiles in the Australian Standard AS 2343. In June 2005, the first Ductal protective panels manufactured to provide resistance to blast were supplied to the Australian Government and installed on an Australian Government building in a high risk international location.

Effect of Cyclic Loading on Crack Propagation of X-70 Pipeline Steel in Near-Neutral pH Solution

Crack propagation of X-70 pipeline steel in near-neutral pH solution was studied under different modes of cyclic loading. A revised equation of crack growth rate vs. Δ K was obtained. Average crack growth rate increased with cycles under conditions of different R values. Linear shape notch specimen made cracks much easier to initiate and propagate than V-shaped notch specimen did. For different R values, the curves of crack growth rate with cycles were similar, but the platform propagation period and quick propagation period were different obviously. Crack growth rate at both periods increased and thus failure time decreased markedly with decrease of R value. The propagation directions of cracks were different under different cyclic loading conditions. Under mode I (single tensile stress) cyclic loading, cracks were straight and perpendicular to the tensile stress axis, while under mixed-mode I/III (tensile/shear stress) cyclic loading, cracks were sinuous and did not propagate in the direction perpendicular to the main tensile stress axis.

Failure of OT4-1 and D16T alloys during cyclic loading over a wide range of frequencies

1. For both forms of loading over the whole range of working frequencies nucleation and propagation of the fatigue crack in OT4-1 alloy is observed in a direction perpendicular to the action of the applied tensile stresses, i. e., in this case nucleation and development of the crack are of the normal breaking crack type. 2. In D16T alloy for both forms of loading over the whole range of working frequencies the fatigue crack is nucleated similarly to the normal breaking crack, and the length of the section of the nucleating crack normal to the main tensile stress decreases with increase in the amplitude of the cyclic stress. The fatigue crack develops at an angle of 45° to the main tensile stress, and this corresponds to a transverse shear type of crack. 3. During uniform extension-compression the propagation rate of the crack in the cycle dl/dN in its nucleating part is lower for D16T alloy than for OT4-1 alloy. 4. For both materials under conditions of uniform extension-compression change in the loading frequency has little effect on the velocity of the crack in the cycle. 5. In the case of high loading frequencies the relief of the fracture in the investigated alloys is smoother on account of increase in the ductility under the influence of local heating of microvolumes of the material.