Redistribution Of Internal Stresses Research Articles

Short Jute Fiber Reinforced Cement Mortar for Out-of-Plane Strengthening of Masonry Prisms

The retrofitting process contributes to the sustainability of the construction sector, since adopting measures to increase the lifespan of buildings reduces the need for new constructions. However, many of the materials used in this process come from nonrenewable sources and require significant water and energy consumption for production. The aim of this study is to assess the viability of using a more environmentally friendly mortar coating reinforced with short jute fibers (SJFRM) to reinforce ceramic brick masonry walls. Both coated and uncoated prisms were subjected to compression and flexural tests under two-point (line) out-of-plane loading. The reinforcement layer comprised mortar without fibers and mortars reinforced with jute fibers at levels of 2% and 4%, with lengths of 20 mm and 40 mm. Physical and mechanical tests were conducted to evaluate the properties of SJFRM in both fresh and hardened states. Results indicate that the compressive and flexural strengths were enhanced with SJFRM reinforcement due to alterations in the failure mode of the prisms. The fibers impede crack propagation in the reinforcement layer, enabling better redistribution of internal stresses in the prisms. This results in an increase of 6 to 9 times in stiffness under direct compression and up to 42 times in toughness under flexion in the prisms reinforced with SJFRM when compared to uncoated prisms.

On the Potential Role of Viscoelasticity in Fluid‐Induced Seismicity

AbstractFluid‐induced earthquakes adversely affect industrial operations like hydraulic fracturing (e.g., 4.6 Mw in Alberta, Canada) and enhanced geothermal systems (e.g., 5.5 Mw in Pohang, South Korea). Identifying all underlying physical processes contributing to fluid‐induced seismicity presents an open challenge. Recent work reports signatures of event‐event triggering or aftershocks—common for tectonic settings—within the context of fluid‐induced seismicity. Here, we investigate the underlying potential cause of these field observations from a modeling perspective. We extend a novel conceptual model to simulate the characteristics of crustal rheology and stress interactions in a porous medium by combining viscoelastic effects with fluid diffusion and invasion percolation associated with a point source. Our model successfully reproduces realistic aftershock behavior and statistical properties similar to those resulting from tectonic loading indicating that the statistical properties of aftershocks are unaffected by the fluid injection rate. At the same time, the Gutenberg‐Richter relation, the spatial footprint of fluid‐induced events and their dependence on the permeability field are largely unaltered by the viscoelasticity of the medium and the aftershocks it causes. Furthermore, we investigate the impact of varying fluid injection rates on detecting aftershocks and event‐event triggering sequences during viscoelastic stress redistribution. We find that when the injection rate is sufficiently high, aftershock detection and recovery of their statistical properties are only feasible when the underlying internal stress redistribution is directly accessible. This could explain why aftershocks have not been reported in some field studies of fluid‐induced seismicity.

Characteristics of changes in microstructure and mechanical characteristics under high energy load

Purpose. Verification of the hypothesis about the possibility of obtaining a fine-grained structure of a metal as a result of processing with high-density energies. The methods. The research was carried out on cylindrical samples with a diameter of 50 mm and a length of 300 mm, which were made of structural steel 45 in a normalized state. The thickness of the inner coaxial layer BP1 with a detonation speed D=7.5 km/s was 3 mm, the thickness of the outer layer BP2 with a detonation speed D=3.5 km/s was 40 mm. The two-layer BP charge used in the experiment increases the duration of the shock wave and at the same time protects the samples from destruction. Findings. The mechanism of nanostructuring, in general terms, consists in the accumulation of the degree of deformation without destruction, which leads to the defragmentation of the structure with a significant increase in the density of dislocations. One of the methods that allows you to achieve a high density of dislocations, comparable to IPD, is treatment with shock waves. The change in the grain structure in the places of the pores indicates extremely high degrees of inhomogeneous deformation in these areas. During the passage of the shock wave in the middle of the sample, at the boundaries of the interface of phases with different densities, diffraction wave effects occur, which lead to the occurrence of shear deformations. It can be assumed that in the area of pores and microcracks, the deformation conditions are similar to those realized by some methods of intensive plastic deformation. This leads to a sharp grinding of the grain structure and a corresponding change in mechanical properties. The originality. The paper found that the processing of steel parts with the help of high-density energy leads to a sharp grinding of the grain to the nanostructure size and, as a result, to an increase in mechanical properties. The revealed regularities make it possible to obtain optimal parameters of high-energy processing, which lead to an increase in hardness, a redistribution of internal stresses and a decrease in surface roughness. Practical implementation. Obtaining grains with nanostructural characteristics in the structure of the material will allow to create fundamentally new devices and materials. Such materials will have properties significantly exceeding their achieved level – which is important for many fields of engineering, medicine, biotechnology, environmental protection, defense, etc.

Significantly improved interfacial mechanical properties in boron nitride nanosheet/Ti composite via nano-configuration: A molecular dynamics study

Boron nitride nanosheets (BNNSs) reinforced titanium (Ti) matrix composites possess a combination of high strength and ductility due to the in-situ synthesized nano-configurations consisting of BNNSs, titanium boride (TiB) and titanium diboride (TiB2). The mechanisms for the outstanding properties, however, are yet fully unraveled. In this study, BNNSs/Ti composites with various nano-configurations are investigated by molecular dynamics (MD) simulation. Results show that the tensile strength and ductility of the composites increase with the number and length of titanium borides (TiBx). The excellent ductility is attributed to the crack-blocking and internal stress redistribution effects of the well-bonded TiBx nanophases. The strength enhancement mainly arises from the improved dislocation strengthening and load-transfer efficiency brought by the nano-interlocking structure. This work can benefit the optimization of BNNSs/Ti composites for fulfilling the strengthening and toughening potential of BNNS.

Nanomodified Basalt Fiber Cement Composite with Bottom Ash

Directed control of the process of structure formation of a cement composite from modern positions must be carried out taking into account the synergistic effect of its components. In particular, the cement composite, when applied with pozzolanic additives and fiber reinforcement, is transformed into a more complex material with excellent performance. The aim of the article is to study the combined action of nanomodified basalt fiber (NBF) and bottom ash (BA) as structural elements of concrete. To achieve this aim, a number of tasks were performed, including the development of nanomodified-basalt-fiber–bottom-ash–cement concretes, as well as the study of their fresh, physical and mechanical properties (flowability, average density, compressive and flexural strength, elastic modulus and crack resistance) and durability characteristics (water, frost and abrasion resistance). A series of nanomodified basalt-fiber-reinforced concretes (from 0 to 7 wt.% NBF) were developed, in which the economical Portland cement CEM I 32.5 N was replaced by up to 45 wt.% mechanically activated bottom ash residue (400 m2/kg). An economical superplasticizer with a high water-reducing capacity (35%) made it possible to achieve uniform flowability of the mixes (slump 20–22 cm and slump flow 45–52 cm). The combined effect of BA and NBF provides control over the structure formation of cement materials, which ensures the redistribution of internal stresses from shrinkage deformations throughout the entire volume of the composite; under loading, the process of crack formation slows down, the stress concentration near structural defects decreases, and stresses are redistributed in the microstructure of the cement composite between its components. Perfect values of mechanical properties (compressive strength up to 59.2 MPa, flexural strength up to 17.8 MPa, elastic modulus up to 52.6 GPa, critical stress intensity factor 0.507 MPa m0.5) are explained by the complex action of the ash residue and nanomodified basalt fibers. A mix with 30 wt.% BA and 5 wt.% NBF is characterized by water resistance grade W18, frost resistance class F400 and abrasion resistance 0.59 g/cm2, which confirms the high wear resistance of the developed materials.

Combined effect on properties and durability performance of nanomodified basalt fiber blended with bottom ash-based cement concrete: ANOVA evaluation

A control of a cement composite structure formation from modern positions should be carried out taking into account the synergistic effect of its components. The goal of the article is to study the combined effect of nanomodified basalt fiber (NBF) and bottom ash (BA) as structural elements of concrete using a two-factor analysis of variance ANOVA. The tasks for achieving this goal are the development of nanomodified basalt fiber bottom ash-cement concretes, as well as the study of their fresh, physical and mechanical properties (slump, slump flow, average density, compressive and flexural strength, elastic modulus and crack resistance) and durability performances (water, frost, and abrasion resistance). Nanomodified basalt-fiber-reinforced concretes (from 0 to 7 wt % NBF) have been developed, in which the economical Portland cement CEM I 32.5 N is replaced by up to 45 wt % mechanically activated bottom ash (400 m2/kg). Achieving uniform flowability of the compositions (slump 20–22 cm and slump flow 45–52 cm) was carried out by varying the dosage of an economical superplasticizer with a high water-reducing ability (35%). The joint effect of the BA and NBF provides control over the structure formation of cement materials, which ensures the redistribution of internal stresses from shrinkage deformations throughout the entire volume of the composite; during loading, the process of crack formation is retarded, stress concentration near structural defects is reduced, and stresses are redistributed in the microstructure of the cement composite between its components.High values of mechanical properties (compressive strength up to 59.2 MPa, flexural strength up to 17.8 MPa, elastic modulus up to 52.6 GPa, limit stress intensity factor 0.507 MPa m0.5) are explained by the complex effect of bottom ash and nanomodified basalt fibers. For the composition with 30 wt % BA and 5 wt % NBF, W18 water resistance grade, F400 frost resistance grade, and the abrasion resistance of 0.59 g/cm2 were achieved, which characterizes the high durability of the developed materials.

Effects of treated corrosion reinforcement on structural behavior of concrete beams

Structural degradation phenomena like reinforcement corrosion in concrete structures imply a consequent reduction in time of the safety level. Corrosion causes a reduction of the sectional area, ductility and strength of rebars, bond strength between steel and concrete. The subsequent redistribution of internal stresses induces a reduction in ductility at ultimate limit state and a variation of the deformational behavior in serviceability conditions. In this paper, an experimental investigation was carried out to study the effect of treated corrosion reinforcement on structural behavior of concrete beams. In this investigation, phosphoric acid and vinegar solution are used to treat the corroded steel bars and compared the bending strength of concrete beams with treated and untreated corrosion reinforcement. A finite element computer software (ANSYS) has been used to compare the experimental results. From the experimental and analytical results, it was observed that performance of concrete beams with treated corrosion reinforcement is better than the concrete beams with corrosion reinforcement,

Anomalous diffusion driven by the redistribution of internal stresses.

This article explores the mathematical description of anomalous diffusion, driven not by thermal fluctuations but by internal stresses. A continuous time random walk framework is outlined in which the waiting times between displacements (jumps), generated by the dynamics of internal stresses, are described by the generalized Γ distribution. The associated generalized diffusion equation is then identified. The solution to this equation is obtained as an integral over an infinite series of Fox H functions. The probability density function is identified as initially non-Gaussian, while at longer timescales Gaussianity is recovered. Likewise, the second moment displays a transient nature, shifting between subdiffusive and diffusive character. The potential application of this mathematical description to the quaking observed in several soft-matter systems is discussed briefly.

Tailoring of Magnetic Softness and Magnetoimpedance of Co‐Rich Microwires by Stress Annealing

Herein, detailed studies on the influence of stress annealing on the magnetic softness and giant magnetoimpedance (GMI) ratio of Co69.2Fe3.6Ni1B12.5Si11Mo1.5C1.2 glass‐coated microwires are provided. As‐prepared microwire presents linear hysteresis loops, moderate GMI ratio with double‐peak magnetic field dependence and low coercivity (4 A m−1), typically observed for wires with transverse magnetic anisotropy. However, after conventional annealing magnetic hardening and transformation of linear hysteresis loop into rectangular with coercivity about 90 A m−1 is surprisingly observed. It is shown that stress annealing allows preventing magnetic hardening and remarkably improving GMI ratio. Properly stress‐annealed samples present better magnetic softness: almost unhysteretic loops with coercivity about 2 A m−1 and magnetic anisotropy field about 35 A m−1. Observed stress‐annealing‐induced anisotropy is affected by the tensile stresses, applied during annealing and by the annealing temperature. From the frequency dependence of the maximum GMI ratio, the optimum frequency ranges for as‐prepared and stress‐annealed samples are determined. The observed stress‐annealing‐induced magnetic anisotropy and associated changes in magnetic properties and GMI effect are discussed in terms of internal stresses relaxation and related modification of the magnetostriction coefficient, “back stresses,” structural anisotropy, redistribution of internal stresses, and change of spatial distribution of magnetic anisotropy.

Experimental Evaluation of Strut-and-Tie Model of Anchorage Zone in Posttensioned Concrete Structures

Abstract This article presents a series of experimental investigations assuming the strut-and-tie model (STM) for anchorage zones in posttensioned concrete structures. The test design for concrete samples is based on finite element analysis for a prestressing process. For end anchorage specimens, the relative location of the reinforcement centroid with respect to the bursting force center was investigated. The test results indicate that the specimen with the coincident reinforcement centroid shows the best performance in resisting the tension load. The presence of spiral reinforcement in the region below the bearing plate results in a redistribution of internal stresses in the anchorage zone. Therefore, Mörsch’s model should be refined by moving the STM configuration down by a distance of a quarter of the anchor size. For the interior anchorage zone, the test results confirm that the modified International Federation for Prestressing model offers a safe but economical STM scheme for the interior anchorage zone.

Effect of temperature on the transverse impact performance of preloaded CFRP wire

This paper experimentally investigated the effect of temperature on the transverse impact response of preloaded carbon fiber reinforced polymer (CFRP) wire. The CFRP wires with a glass transition temperature of 99 °C were tested in the temperature range of −40 to 80 °C using a drop-weight impact test system. The results show that the maximum impact force, maximum wire tension and transverse deflection at fracture of the wire increased as the temperature increased from −40 to 80 °C, due to the ductility of the resin, effective redistribution of internal stresses and reduced stress concentration in the wire at high temperatures; and the energy dissipating capacity was also improved resulting from the low impact damage at high temperatures. A temperature-dependent function to quantify the effect of temperature on the impact response of CFRP wire was established, and formulas for predicting the impact resistance of preloaded CFRP wires at various temperatures were provided.

Issues of further development and improvement of design standards for wood structures

The current state of design of wooden structures against the background of the historical development of design standards is analyzed, the tasks of their further development are formulated. The strength criteria ensuring progress in the design of unique and spatial wooden structures are considered. Examples of unique large-span coatings, principles of their design with providing a spatial scheme are presented. In addition, the methodology for the nonlinear analysis of such systems with due regard for the duration of action of the load and of redistribution of internal stresses, especially under unsymmetrical loads, including with due regard for the coverings between the ribs experiencing a complex stress state is proposed. The application of the calculation method considered provides material savings and at the same time increases the reliability and survivability of the structure. Some possible additions and proposals on the structure and content of the new version of the norms are proposed. Taking into account continuity and achievements of the technical progress the necessity of development of new standards on the basis of advanced technologies of production, design and calculation of designs on the computer is proved.

Identification and Space-Time Evolution of Vortex-Like Motion of Atoms in a Loaded Solid

The paper studies the redistribution of internal stresses and atomic displacements in a preloaded copper crystallite using the molecular dynamics method. It is shown that relaxation within the crystallite volume is accompanied by the formation of dynamic structures in which atomic displacements produce a coherent system of vortex lines. In so doing, the displacement of atoms in neighboring vortex structures has the opposite sign of the angular velocities. The evolution of the dynamic vortex structures is analyzed using an original technique for identifying the vortex motion in the space of a vector variable with a discrete step. It is shown that a system of dynamic vortices and antivortices can propagate inside the crystallite, ensuring the transfer of stresses from the bulk of the loaded material to its unloaded periphery in order to preserve continuity. The developed technique has revealed that the lifetime of such defects depends on their size and ranges from fractions to tens of picoseconds. The simulation results correlate well with the experimental electron microscopy data on the estimation of spatial parameters and lattice curvature during strain localization in the region of elastic distortions.

Influence of corrosive phenomena on bearing capacity of RC and PC beams

The attack of environmental aggressive agents progressively reduces the structural reliability of buildings and infrastructures and, in the worst exposition conditions, may even lead to their collapse in the long period. A change in the material and sectional characteristics of a structural element, due to the environmental damaging effects, changes its mechanical behaviour and varies both the internal stress redistribution and the kinematics through which it reaches its ultimate state. To identify such a behaviour, the evolution of both the damaging process and its mechanical consequences have to be taken into account. This paper presents a computational approach for the analysis of reinforced and prestressed concrete elements under sustained loading conditions and subjected to given damaging scenarios. The effects of the diffusion of aggressive agents, of the onset and development of the corrosion state in the reinforcement and the corresponding mechanical response are studied. As known, the corrosion on the reinforcing bars influences the damaging rate in the cracking pattern evolution; hence, the damage development and the mechanical behaviours are considered as coupled phenomena. The reliability of such an approach is validated in modelling the diffusion of the aggressive agents and the changes in the mechanical response of simple structural elements whose experimental behaviour is reported in Literature. A second set of analyses studies the effects of the corrosion of the tendons of a P.C. beam and explores potentially unexpected structural responses caused by corrosion under different aggressive exposition. The role of the different types and of the different positions of the damaging agents is discussed. In particular, it is shown how the collapse mode of the beam may switch from flexural to shear type, in case corrosion is caused by a localized chloride attack in the shear span.

Simulation Research for the Effect of KDP Crystal Defect and Initial Internal Stress on Sawing Stress

KDP (KH2PO4) crystal is a kind of excellent nonlinear optical crystals, which has been widely used in nonlinear optical and Inertial Confinement Fusion (ICF) engineering. KDP crystal with the characteristics of low hardness, high brittleness, easy deliquescence and temperature-sensitive is easy to crack during the crystal growth, taken out from crystallizer, and the process of slicing. Stress concentration caused by the initial internal stress redistribution and the growth defect in KDP crystal is an important reason of KDP crystal cracking during sawing process. The numerical simulation model of the KDP crystal containing spherical cavity defect and sawing with fixed abrasive wire saw is established by finite element method in this paper. The effects of initial internal stress, spherical cavity defect on sawing stress are investigated. The maximum tensile stress near the defect during the sawing process is simulated and analyzed. The results show that sawing stress changes smoothly during sawing process, and the fixed abrasive wire saw slicing belongs to low stress cutting way. The sawing stress at sawing kerf is increased obviously. The crystal defect leads to local stress concentration during sawing process. The coupling effect of sawing stress with initial internal stress and the effect of stress concentration are enhanced when the sawing kerf approaches to the defect.

Micromechanical modelling of twinning in polycrystalline materials: Application to magnesium

In this work, a crystal plasticity constitutive model is proposed to describe the mechanical behavior of metallic materials for which twinning plays a significant role in the deformation process. Constitutive relations are obtained from a micromechanical approach that explicitly considers the interactions between twinned and untwinned domains. Then, based on a thermodynamical analysis of the problem, a new expression for the driving force for the expansion of twinned domains is proposed. Finally, to account for the polycrystalline nature of metallic materials, the constitutive model is implemented in a FFT spectral solver.In the second part of this paper, the model is used to study the mechanical behavior of a AZ31 magnesium alloy under compression, for which a significant amount of experimental data is available in the literature. The comparison between numerical and experimental data allows for discussion of the influence of the different deformation modes on the development of both crystallographic texture and lattice strains. The evolution of lattice strains is found to be largely influenced by the internal stress redistribution process associated with the expansion of twinned domains. Also, the polycrystalline plasticity model provides a correct description of how the morphological texture is strongly altered during the deformation process due to the important activity of twinning systems.

Research on the Relative Stable Time and Stable Value of Concrete Creep

The safety coefficients of structures change due to the creep behavior of concrete, which causes increased deformation and cracks in structures, redistribution of internal stresses, and the loss of prestress. It is an important and significant problem to determine when concrete creep is stable and how much of the creep will occur once it is stable over the projected life of the structure. The relationship between compressive concrete creep and time was obtained during creep experiments, which were conducted using the compressive concrete cube with stress levels of 0.160, 0.261, 0.370, 0.470, 0.568, and 0.668, a loading age of 126 days, and a time under loading of 589 days. The creep compliance function model of linear and non-linear compressive concrete creep under stress levels lower than 0.8 was unified by introducing a creep compliance function amplification coefficient Aj. Relative stable time and relative stable value of concrete creep, with different stress levels, were obtained according to the creep model and regular relative stable time.

Geogrid pullout behaviour according to the experimental evaluation of the active length

In reinforced earth structures, the main function of the included reinforcement is to redistribute stresses within the soil mass in order to enhance internal stability. Redistribution of internal stresses in reinforced soil can be very complex. In order to simulate the behaviour of geosynthetic reinforcement, large-scale laboratory pullout tests are carried out. Once a pullout load has been applied, the tensile force is transferred along the geogrid (from the front to the free end) and reduced through interaction with the soil. The active length is the portion of the geogrid on which the mobilisation of interaction mechanisms withstands the applied pullout load. Evaluation of the active length can allow for the understanding of the interaction mechanisms and can therefore be important for the design of the soil–geosynthetic interface. This paper describes the interpretation of pullout test results based on an experimental and theoretical evaluation of the active length. This approach has been used to analyse several large-scale pullout tests performed on two extruded geogrids embedded in a compacted granular soil, varying the specimen lengths and the applied effective vertical pressures.

Numerical simulation of the fracturing processes in masonry arches

AbstractMasonry arch structures, and, more generally, vaulted structures, are traditionally assessed using a well‐established approach, such as linear elasticity or limit analysis, whereby system behaviour at the intermediate stage – which occurs when the material's tensile strength has been exceeded but the collapse mechanism has not yet formed – is disregarded. A more accurate interpretation requires a thorough analysis that can take into account the intermediate cracking stage and uses a constitutive law providing a closer approximation to the actual behaviour of the material. In this paper, an evolutionary fracturing process analysis for the stability assessment of masonry arches is presented. This method makes it possible to capture the damaging process that takes place when the conditions evaluated by means of linear elastic analysis no longer apply and before the conditions assessed through limit analysis set in. Furthermore, the way the thrust line is affected by the opening of cracks and the redistribution of internal stresses can be checked numerically. The results obtained with the described approach are compared with a numerical simulation performed with the finite element code Diana (TNO, The Netherlands) adopting discrete cracking with cohesive laws. Finally, the case study of the arch of the Mosca Bridge over the Dora River in Turin, Italy, is described. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)

An analytical model for bending and springback of bimetallic sheets

Springback is an inevitable phenomenon due to elastic redistribution of internal stresses occurring in sheet metal forming operations. Most of the research reported in this area has been concerned with the components formed from single metal. This article deals with the analytical solution for prediction of springback in bending of bimetallic sheets. A mathematical model is derived based on Woo and Marshall's constitutive equation, considering logarithmic strain (nonlinear) distribution across the thickness and thickness change during bending. Analytical modeling, based on logarithmic strain distribution across the thickness, can be used for accurate springback predictions in the case of smaller bend radius to the thickness ratio. The results of the springback and thickness change are validated using experimental results for the aluminum sheet layered with steel. Further, springback variation in bimetallic sheets is studied, with a change in material properties and thickness of each layer.