Effect Of Prestress Research Articles

Temperature and Strain Correlation of Bridge Parallel Structure Based on Vibrating Wire Strain Sensor.

Deformation is a ubiquitous phenomenon in nature. This process usually refers to the change in shape, size, and position of an object in the time and spatial domain under various loads. Under normal circumstances, during engineering construction, technicians are generally required to monitor the safe operation of structural facilities in the transportation field and the health of bridge, because monitoring in the engineering process plays an important role in construction safety. Considering the reliability risk of sensors after a long-time work period, such as signal drift, accurate measurement of strain gauges is inseparable from the value traceability system of high-precision strain gauges. In this study, two vibrating wire strain gauges with the same working principle were measured using the parallel method at similar positions. First, based on the principle of time series, the experiment used high-frequency dynamic acquisition to measure the thermometer strain of two vibrating wire strain gauges. Second, this experiment analyzed the correlation between strain and temperature measured separately. Under the condition of different prestress, this experiment studied the influencing relationship of temperature corresponding variable. In this experiment, the measurement repetitiveness was analyzed using the meteorology knowledge of single sensor data, focused on researching the influence of temperature and prestress effect on sensors by analyzing differences of their measurement results in a specified situation. Then, the reliability and stability of dynamic vibrating wire strain gauge were verified in the experiment. The final conclusion of the experiment is the actual engineering in the later stage. Onsite online meteorology in the application provides support.

A general nonlinear magneto-elastic coupled constitutive model for soft ferromagnetic materials

In this study, a new general nonlinear magneto-elastic coupled constitutive model was proposed for soft ferromagnetic materials under magnetic field and pre-stress. The model is based on thermodynamic theory of magnetic materials and Jiles theory on magnetomechanical effect, considering demagnetization field. This model can accurately predict the changes of magnetostrictive strain and magnetization under pre-stress; in particular, it can obviously predict the nonlinear change of magnetostrictive strain according to compressive pre-stress. In addition, this model is concise by not including the inverse function of magnetization relationship and the piecewise function of stress in its mathematical form and can be degenerated to the previous general constitutive model for giant magnetostrictive materials. The prediction result by this model is well-consistent with experimental data. In comparison with the existing constitutive models for soft ferromagnetic materials, this model was demonstrated to have obviously-improved prediction accuracy, particularly in the compressive state. In conclusion, the proposed model can fully describe the effect of pre-stress on magnetostrictive strain and magnetization and the effects of magnetic field and pre-stress on Young’s modulus and relative magnetic permeability, reflecting the effect of demagnetization field on magnetomechanical characteristics.

Prestress effect on the thermomechanical response and fatigue life prediction of viscoelastic plates

Prestress effect on the thermomechanical response and fatigue life prediction of viscoelastic plates

Prestress Effect on the Thermomechanical Response of Viscoelastic Plate Under Harmonic Loading

A statement of the coupled thermomechanical problem on forced resonant vibrations and dissipative heating of hinged viscoelastic elastomeric plate is given with account of prestresses present in the plate. It is assumed the prestress is generated as a result of the manufacturing process or preliminary plate service. The problem statement is based on the standard Kirchhoff-Love hypotheses and concept of complex moduli that are used to describe the viscoelastic material response to harmonic loading. Under these circumstances, the prestress manifests itself as a membrane forces applied in the plane of the rectangular plate. Therefore, the problem of in-plane stress state and problem of forced transverse vibration of the plate can be solved separately. Both steady-state and transient thermal response is investigated. Influence of the prestress is studied in details. Dissipative heating temperature histories are calculated for the variety of the prestress and loading parameters. Temperature criterion is adopted to determine the critical state. The data obtained are used for the plate fatigue life prediction as well as for the investigation of prestress effect on the plate response. The reliability of the values of frequencies on the several lowest resonances was checked. For the most energy-intensive first mode of transverse vibrations, the influence of the preliminary tensile stress state, as well as the amplitude of the transverse distributed load on the amplitude–frequency characteristics and temperature evolution was studied.

Improvements on Evaluation Functions of a Probabilistic Fracture Mechanics Analysis Code for Reactor Pressure Vessels

Abstract In Japan, a probabilistic fracture mechanics (PFM) analysis code PASCAL was developed for structural integrity assessment of reactor pressure vessels (RPVs) considering neutron irradiation embrittlement and pressurized thermal shock (PTS) events. By reflecting the latest knowledge and findings, the evaluation functions are continuously improved and have been incorporated into PASCAL4 which is the most recent version of the PASCAL code. In this paper, the improvements made in PASCAL4 are explained in detail, such as the evaluation model of warm prestressing (WPS) effect, evaluation function of confidence levels for PFM analysis results by considering the epistemic and aleatory uncertainties in probabilistic variables, the recent stress intensity factor (KI) solutions, and improved methods for KI calculations when considering complicated stress distributions. Moreover, using PASCAL4, PFM analysis examples considering these improvements are presented.

The effect of FRP prestressing on the fatigue performance of strengthened RC beams

AbstractAlthough Fiber Reinforced Polymer (FRP) prestressing is widely recognized for enhancing the serviceability conditions of strengthened structural elements, there are no available fatigue prediction models encompassing the specificities and advantages of FRP prestressing. In this context, this paper addresses the effect of FRP prestressing on the fatigue performance of strengthened reinforced concrete (RC) beams through the assessment of experimental data, constant life diagrams, and the adjustment of specific stress versus number of cycle (S‐N) curves for RC strengthened with prestressed FRP. First, data obtained through the development of an experimental program give an insight into the long‐term behavior of full‐scale beams subjected to in‐service and severe fatigue loading conditions. Fatigue life prediction models based on the adjustment of S‐N curves are developed using an extensive database of failure data and runouts of fatigue tests. Finally, data of fatigue tests plotted in a constant life diagram evidence the combined effects of stress range, mean stress, R ratio, and reinforcing steel properties on the fatigue life of RC beams strengthened with prestressed FRP. Results highlight the positive effects of FRP prestressing by the improvement of serviceability condition under static loading and the increasing of endurance limit under cyclic loading.

Impact of elevated curing temperature on mechanical properties and microstructure of MgO‐based expansive additive cement mortars

AbstractMgO‐based expansive additive (MEA) is uniquely used in China to compensate for the thermal shrinkage. For mass concrete, its inner temperature can soar up to 60°C due to the accumulation of hydration heat, which will strongly impact the mechanical properties and microstructures. In this paper, the impacts of elevated curing temperatures on the compressive strength developments, the tensile strengths as well as the pore structures of MEA cement mortars are investigated by means of X‐ray diffraction, scanning electron microscope, and mercury intrusion porosimetry. The results show that the external addition of MEA weakens, not eliminates, the crossover effect found in the temperature‐affected strength developments, which is mainly attributed to the accelerated expansion of MEA. For the tensile strength, the weakness of the crossover effect is found more obvious. The ratio of tensile to compressive strength is also positively correlated to the MEA content and the curing temperature. A scattered prestress effect is proposed to explain this phenomenon. The microcosmic evidence proves that the elevated temperature promotes the hydration of MEA and cement, and thereby improves the early‐age microstructures but impairs the late‐age one, which is generally consistent with the mechanical results.

Experimental and numerical investigation on pre-stressed lattice structures

Abstract The effect of pre-stress on the buckling behaviour of geometric unit cells of collinear square lattices is investigated experimentally and numerically. The geometric unit cells are manufactured using fused deposition modelling. Manufacturing strategies are presented which incorporate fibres subjected to pre-stress within the unit cell. The effect of pre-stressed fibres is analysed by comparing the compressive behaviour of unit cells with and without fibre reinforcement. The buckling behaviour of the unit cells is also investigated numerically by employing a parametric study within Abaqus varying the pre-stress in the fibres. The experimental test series shows that the addition of pre-stressed fibres to the system results in an increase in buckling and maximum load of 260%–480% and 220%–350% respectively. The increase strongly relates to the manufacturing quality, i.e. the bonding between the lattice material and the fibres, where a sufficient bonding yields significantly larger loads. The experimental findings on the qualitative and quantitative buckling behaviour correspond well with results obtain from the numerical study.

Numerical Analysis of Segmental Post Tensioned Concrete Beams Exposed to High Fire Temperature

The main objective of this study is to characterize the main factors which may affect the behavior of segmental prestressed concrete beams comprised of multi segments. The 3-D finite element program ABAQUS was utilized. The experimental work was conducted on twelve simply supported segmental prestressed concrete beams divided into three groups depending on the precast segments number. They all had an identical total length of 3150mm, but each had different segment numbers (9, 7, and 5 segments), in other words, different segment lengths. To simulate the genuine fire disasters, nine beams were exposed to high-temperature flame for one hour, the selected temperatures were 300°C (572°F), 500°C (932°F) and 700°C (1292°F) as recommended by ASTM–E119. Four numerical models have been utilized to represent the unburned and the burned specimens at the three elevated temperatures. Calibration and simulation of the experimental work were conducted, while comparisons were made with the experimental results. These included the prestress effect, load-deflection relation under applied load, and load at failure of the reference beam and the beams after the exposure to fire.

Numerical and Experimental Investigation of Bending Behavior of Pre-Stressed Aluminum Tube

The effect of the pre-stress and internal Pa6 (cast-polyamide) material on the bending behavior of the aluminum tube is investigated experimentally. Finite element studies have been carried out to better understand the effect of pre-stress on the cross-section of tube and to shed light on the experimental studies. From the simulation studies, it was concluded that the effect of the pre-stress on the load carrying capacity of the tube is limited. After finite element studies, experimental studies were performed. In experimental studies, the lower cross-section of the tube was subjected to 175 MPa stress corresponding to 93% of the yield strength of the material. The tensile stress in the tube during the loading is reduced by applying pressure to the lower cross section of the tube beam. In addition, a change in the load carrying capacity of the tube was investigated using a Pa6 ring to delay local buckling. As a result of the experiments, it was found that the pre-stress significantly improved the bending behavior of the tube in the elastic region, while reducing buckling displacement. Application of both pre-stress and internally reinforcement enhanced bending performance of the tube in both elastic and plastic regions. Load carrying capacity of pre-stressed and internally reinforced tube was increased 1.67 times according to the base tube.

Effects of prestressing and saw-cutting on the freeze-thaw durability

There are many factors that affect the freeze-thaw durability of concrete elements, including proper air entrainment system, freeze-thaw durable aggregates, low permeability, and proper curing. While ASTM C666 allows the excising of small freeze-thaw samples from larger sections it doesn't address the issues that can arise when excising samples from prestressed concrete and subsequent testing in freezing and thawing. In order to investigate the effects of saw-cutting, the existence of reinforcement, and use of prestressing, concrete samples of different sizes, with and without saw-cutting, with and without reinforcement, and with and without prestressing were tested in freeze-thaw. The freeze-thaw mechanism was adjusted, from that of ASTM C666, for the larger sample in terms of freezing and thawing rates and the testing method. The results indicate that saw-cutting through plain concrete had minimal effect on the freeze-thaw durability, whereas sawcuts through reinforcement were shown to be very detrimental to the measured durability in the tests.

Temperature dependent magnetoelectric (ME) response in press-fit FeNi/PZT/Ni self-biased ring composite

Magnetoelectric (ME) composites exhibit the magnetoelectric effect, which is a coupling phenomenon resulting from the interaction between the magnetostrictive and piezoelectric phases. This makes ME composites useful as multifunctional devices in a variety of applications. In this work, a press-fit epoxy-free nested ring structured ME composite has been fabricated, in which nickel and FeNi form the magnetostrictive phase and PZT-5A constitutes the piezoelectric phase. To conduct a comparative study, epoxy bonded conventional bilayered and trilayered ME composites of the same material constituents and similar volume fractions have also been made. Magnetostriction measurements are done on individual magnetostrictive materials at varying temperatures in longitudinal and transverse directions. Measurement of the ME coefficient is done on all the prepared composites and their relative response at elevated temperatures is presented. Self-biased behavior of the ME composites resulting out of the applied prestress is also captured. A 2D hysteretic model including the temperature and prestress effects that can capture the behavior of epoxy-free ring composites has also been formulated. The results from the model are in agreement with the experimental results at all the temperatures. The obtained experimental results highlight the suitability of epoxy-free ring composites to be used in high temperature microdevices.

Effects of Prestressing of the Ring Gear in Interference Fit on Flexural Fatigue Strength of Tooth Root

When the gearbox body interference is connected to the ring gear, prestressing occurs in the ring gear, which has a significant impact on the strength and life of the gear. Research on the prestressing of the inner ring gear is in the preliminary stage, and the distribution rule of the prestressing and the influence of each parameter on the interference prestressing have not been derived. In this paper, based on the method of calculating the prestressing of the thick cylinder in interference fit, the ring gear is found to be equivalent to a thick cylinder, and the distribution rule of prestressing of the ring gear in the interference fit is inferred. Then, by modeling and analyzing the gearbox body and ring gear in the interference fit using ABAQUS, the distribution rule of prestressing the ring gear in the interference fit is obtained through a numerical simulation. Finally, the prestressing of the ring gear in the interference fit is measured using X-ray diffraction, and the distribution rule of prestressing of the ring gear in the interference fit is obtained through analysis. Compared with the distribution rule of prestressing in theory, numerical simulation, and experiment, the theoretical distribution rule of prestressing is amended through a statistical method, and a more accurate formula of prestressing is obtained. Through the calculation of the stress and bending moment in the dangerous section of the ring gear through prestressing, the formula for checking the tooth root flexural fatigue strength in the interference fit prestressing is inferred. This research proposes a tooth root bending strength conditional formula for the inner ring gear of the interference fit, which serves as a guide for the design and production of the actual interference joint inner ring gear.

Effect of fiber prestressing on mechanical properties of glass fiber epoxy composites manufactured by vacuum-assisted resin transfer molding

The mechanical properties of fiber-reinforced polymer composites depend on several aspects such as the characteristics of constituents, fiber volume fraction, and manufacturing techniques. Fiber prestressing is considered a very attractive manufacturing technique that can be used to produce fiber-reinforced polymer composites with high mechanical properties. This technique has the potential to eliminate or reduce some manufacturing problems like fiber waviness. In the present study, a new approach was used to prepare prestressed fiber-reinforced polymer composites. Unidirectional E-glass fiber-stitched mats were impregnated with epoxy matrix through vacuum-assisted resin transfer molding process. Once the infusion was done, a pre-calculated tensile force was applied to the fiber mats through a hydraulic tensile machine. The impregnated fiber mats were left under tension and vacuum during curing of the epoxy matrix (24 h). Five prestressed samples were prepared by using five different prestressing levels 20, 40, 60, 80, and 100 MPa. In addition, non-prestressed (control) sample was prepared for the purpose of comparison. The influence of fiber prestressing on fiber waviness, fiber volume fraction, and void content was investigated. Flexural, tensile, and compression tests were performed to observe the effect of fiber prestressing on the mechanical properties. The results have shown the success of this new approach in producing prestressed fiber-reinforced polymer composites with high mechanical properties comparing to non-prestressed composites. The microstructure analysis has shown dramatical reduction in fiber waviness for the prestressed samples over control sample. All prestressed samples have shown higher fiber volume fraction and lower void content comparing to the control sample. Also the results have shown as the prestressing level increases, fiber volume fraction increase and void content decreases. Prestressing levels of 40 and 60 MPa were found to be the best candidates, they have led to an increase in tensile strength, compressive strength, and flexural strength by 24.2%, 72.5%, 28% and 28.6%, 100.4%, 26.1%, respectively, comparing to the non-prestressed sample. Ease of implementation and promising results of this new approach would attract the attention toward it. Automotive industry is one potential nominee to apply this approach during manufacturing of fiber-reinforced polymer leaf spring.

Effect of Pre-stress in Steel Strips to Strengthen Unreinforced Brick Masonry Walls under Axial Loads

Using steel strips to strengthen the existing unreinforced masonry walls has competitive advantages, which includes no wet work, avoidance of formwork, time saving, ease of installation, minimal increase of dimensions, no requirement for material strength of the existing walls and good reversibility. In this paper, seven specimens were fabricated and tested under axial loads for obtaining the effect of pre-stress in steel strips to strengthen unreinforced brick masonry walls. Test results showed pre-compression stress in the vertical steel strips could increase the load of cracks in the single brick in the wall, otherwise steel strips only improved the load of continuous cracks and the failure load, and the axial stiffness of the wall; when the transverse steel strips were pre-tensioned, it could further improve the failure load and the later axial stiffness of the strengthened wall.

Influence of prestress on ballistic performance of bi-layer ceramic composite armors: Experiments and simulations

The effect of prestress on the ballistic performance of bi-layer ceramic composite armors was explored both experimentally and numerically. Three types of target plate with different prestress levels were prepared using the method of shrink-fit, and tested with ballistic experiments. Residual velocity and length of the projectile were recorded and failure mode of each target was examined. A numerical technique was also proposed to explore the penetration process of projectile and the enhancement mechanism of prestress, with the effectiveness of simulation results validated by experimental measurements. Prestressing the ceramic led to more kinetic energy dissipated by plastic deformation and erosion of the projectile, causing more than 25% increase in ballistic limit. The effects of key geometrical parameters – thickness and diameter of ceramic tile – on ballistic limit were systematically explored, and a critical tile thickness for the influence of prestressing on ballistic performance was identified.

Effect of lightning impulse prestress on AC partial discharge characteristics in cast resin transformer

AbstractIt is crucial for cast resin transformer to detect void and delamination existing in the cast resin because these defects reduce insulation performance of cast resin equipment. Furthermore, defects are likely to be mixed in cast resin because of several surface boundaries between resin and conductor. It is considered that detecting partial discharge (PD) is effective to diagnose equipment of power equipment. However, it is reported that withstand lightning impulse voltage test may give influence on AC partial discharge test, especially partial discharge inception voltage. This paper deals with accumulated charge in a void under AC voltage to investigate the effect of the impulse voltage prestress on subsequent AC PD characteristics in cast resin transformer. AC PD characteristics were compared before and after impulse application. In addition, recovery of PD characteristics was measured to investigate charge decay. As a result, the mechanism of prestress effect is revealed and surface charge density is estimated quantitatively in cast resin transformer.

Rayleigh wave at the surface of a prestressed elastic medium with arbitrary anisotropy

The propagation of harmonic plane waves is considered in a general anisotropic elastic medium, in the presence of prestress. A system of three homogeneous equations governs the existence of a Rayleigh wave at the stress-free plane boundary of the medium. This requires solving a complex secular equation for the implicit real phase velocity of the Rayleigh wave. For the presence of the radical, this irrational equation is never easy to solve by any standard analytical or numerical method. In this study, the system of three equations is transformed to get a real secular equation for the propagation of a Rayleigh wave, which can always be solved numerically for the real phase velocity of the Rayleigh wave. This phase velocity defines a complex slowness vector, which is used to calculate the polarisation of the Rayleigh wave at different depths in an elastic half-space. Effects of prestress and anisotropic symmetry on the phase velocity of the Rayleigh wave and associated particle motion are analysed by a numerical example.

Compression behavior of expansive concrete-encased-steel filled square CFRP tubes

The concrete-encased-steel filled FRP tube (CSFFT) is a composite that enables taking advantage of combined effects of material properties of FRP, concrete and steel. Such composites outperform the conventional concrete or steel structures, by integrating outer FRP wrapping as lateral confinement and chemical barrier to concrete core and encased steel section, as well as the load-carrying capacity of concrete and steel section. While the CSFFT composites exhibit a great potential for broader applications, the issues associated with concrete shrinkages and stress hysteresis experienced in FRP confinement as observed by previous studies could weaken their performance at some cases. Therefore, to overcome these drawbacks, this study was to investigate active confinement on the CSFFT composites using expansive concrete-generated prestress. A total number of 24 concrete-encased-steel filled square CFRP tube (CSFSCT) specimens were casted and tested under axial compression. The variables studied included the number of CFRP layers (one, two and three layers), and the area of the section steel (type A and B). Test results showed that the CSFSCT failed by the rupture of the CFRP in the hoop direction. For test specimens with the same sectional area of steel and CFRP layer, the normalized ultimate load capacity of the prestressed specimen was 1.03–1.13 times that of the non-prestressed specimen, which indicated that the pre-stress effect made the tube specimens had higher strength enhancement ratio. As the number of CFRP layer increased, the ultimate load capacity and ultimate axial strain increased, and the slope of the second linear segment of the load-strain curve increased. Moreover, it was revealed that the area of the steel was effective in increasing the Pu/Po and strain reduction factor of tube specimens. The models of ultimate stress and axial strain of confined concrete were formulated to account for both FRP-induced passive confinement and expansive concrete-generated active confinement and were validated by the experimental data.

Experimental Analysis of Continuous Vibrations in Dielectric Elastomer Membrane Actuators via Three-Dimensional Laser Vibrometry

Dielectric elastomer (DE) membrane transducers are well known for exhibiting large deformations when subject to high voltage. Furthermore, DEs are characterized by an actuation bandwidth of several kilohertz, which allows their use in high-frequency applications, e.g., acoustic ones. The frequency response of DE membranes depends on many parameters such as geometry, pre-stress, and electrode pattern. By properly designing such parameters, it is possible to control vibration modes and resonance frequencies of the membrane, opening up a number of application scenarios. Motivated by this fact, this work presents the first experimental study of continuous vibrations generated in DE membranes via high-voltage excitation. The system under investigation consists of a squared DE membrane with a circular electrode, preloaded out of plane with a linear spring. Vibrations are generated by applying a broadband high-voltage signal to the DE membrane. A 3D laser vibrometer is used to reconstruct the three-dimensional oscillations of scanning points on the membrane surface. Experimental investigations are performed to study the effects of DE geometry and pre-stress on the membrane motion, in terms of resulting frequency spectrum and vibration modes.