Tensile Side Research Articles

Cyclic Fatigue Properties of Titanium Alloys for Application in Dental Implants.

The present study investigated the cyclic fatigue properties of titanium alloys (Ti-6Al-4V and Ti-6Al-7Nb) as implant materials and compared their properties with those of commercially pure titanium. Ti-6Al-4V and Ti-6Al-7Nb cylinders with diameters of 3.0 mm were examined. The surfaces of the cylinders were roughened by sand blasting with alumina particles and acid etching. Static and cyclic tests were performed according to ISO 14801:2016. The yield force in the static test (YS) was measured in 5 specimens of each alloy using a universal testing machine. The yield force in a cyclic test (YC) was measured in 20 specimens of each alloy using the staircase method, which involved applying a cyclic load at a frequency of 10 Hz for 106 cycles. After the cyclic loading tests, cross-sections of the specimens were examined under an optical microscope. The YS values for Ti-6Al-4V and Ti-6Al-7Nb were 1463 N±93 N and 1405 N±79 N, respectively, and the YC values were 870 N±58 N and 853 N±202 N, respectively. Microscopic observation revealed cracks on the tensile side of some of the specimens, including run outs and failures. The results of this study suggest that the YC values for Ti-6Al-4V and Ti-6Al-7Nb were 40% less than those for YS. The yield force of Grade-4 Cp-Ti significantly decreased after cyclic loading. The YC values for Ti-6Al-4V and Ti-6Al-7Nb were approximately 900 N, which was markedly greater than that for commercially pure, Grade-4 titanium (700 N).

Minimally processed recycled yttria-stabilized tetragonal zirconia for dental applications: Effect of sintering temperature on glass infiltration

This study aimed to develop a recycling process for the remnants of milled 3Y-TZP and enhance their properties using glass infiltration. 3Y-TZP powder was gathered from the vacuum system of CAD–CAM milling equipment, calcined and sieved (x < 75 μm). One hundred twenty discs were fabricated and pre-sintered at 1000 °C/h. These specimens were then divided into four groups, categorized by glass infiltration (non-infiltrated [Zr] or glass-infiltrated [Zr-G]) and sintering temperature (1450 °C [Zr-1450] or 1550 °C [Zr-1550]/2h). After sintering, the specimens were characterized by X-Ray Diffraction (XRD), relative density measurement, and scanning electron microscopy and energy dispersive spectroscopy (SEM-EDS). The biaxial flexural strength test was performed according to the ISO 6872 and followed by fractographic analysis. Subsequent results were analyzed using Weibull statistics. Relative density values of the sintered specimens from Zr-1450 and Zr-1550 groups were 86.7 ± 1.5% and 92.2 ± 1.7%, respectively. Particle size distribution revealed particles within the range of 0.1–100 μm. XRD analysis highlighted the presence of the ZrO2-tetragonal in both the Zr-1450 and Zr-1550 groups. Glass infiltration, however, led to the formation of the ZrO2-monoclinic of 9.84% (Zr-1450-G) and 18.34% (Zr-1550-G). SEM micrographs demonstrated similar microstructural characteristics for Zr-1450 and Zr-1550, whereas the glass-infiltrated groups exhibited comparable infiltration patterns. The highest characteristic strength was observed in the glass-infiltrated groups. Fractographic analyses suggested that fracture origins were related to defects on the tensile side, which propagated to the compression side of the samples. Both the sintering temperature and glass infiltration significantly influenced the mechanical properties of the 3Y-TZP recycled.

Multi-objective optimal design for carbon and basalt fibre-reinforced hybrid composites under flexural loading

This paper presents a study on the optimal design of hybrid composites reinforced by woven carbon and basalt fibre fabrics. The investigation focuses on evaluating the flexural properties of these hybrid composites through finite element analysis (FEA)-based simulations. To determine potential optimal stacking sequences, design rules are employed. For each stacking sequence, a regression model is developed to establish the correlation between the flexural strength and the fibre volume fractions. Using these regression models, solutions meeting the minimum required flexural strength are found for each stacking sequence. With the objectives of minimising both cost and weight, the optimal solutions are found from these solutions. It is shown that for most optimal solutions, basalt/epoxy and carbon/epoxy plies should be placed on the compressive and tensile sides, respectively. When the minimum required flexural strength is high (800 MPa or 900 MPa), sandwich type stacking sequences with carbon/epoxy plies on both the compressive and tensile sides can also be the optimal solutions. Key findings from this study include.1. Stacking sequences [C]8, [B2C6], [B2C2BC3], [B2C2]2, [B2C2B3C], [B2CB4C], and [B7C] are optimal solutions for all minimum flexural strengths.2. Stacking sequences [B3C]2 and [B]8 are optimal solutions when the minimum flexural strength is up to 800 MPa.3. Stacking sequence [BC7] can be one of the optimal solutions when the minimum flexural strength is 600 MPa or 700 MPa.4. Stacking sequence [C4B2C2] is one of the optimal solutions when the minimum flexural strength is 800 MPa or 900 MPa, and stacking sequence [C3B3C2] is one of the optimal solutions when the minimum flexural strength is 900 MPa.

Analyzing the impact of veneer layup direction and heat treatment on plywood strain distribution during bending load by digital image correlation (DIC) technique

In this study, radiata pine veneers and phenol-formaldehyde resin were used to prepare specimens of 5-ply plywood with different layup directions and heat treatments of veneers. The physical and flexural properties of the plywood specimens were assessed, and digital image correlation (DIC) analysis was employed to determine the strain distribution of the plywood under bending loads. The results of the static mechanical strength and DIC tests showed that the plywood with a small-angle veneer layup ([0]5 and [0,22.5,0,22.5,0]) exhibited a better longitudinal modulus of rupture (MOR//), while [0,45,0,45,0] plywood showed the least bending strength and most strain. Moreover, the results revealed that for plywood composed of veneers that were fully heat treated at 200 °C (5T200), the moisture content was efficiently decreased, and the modulus of elasticity parallel to grain (MOE//) was the highest. The DIC images indicated that the largest strain along the x-direction (εxx) was concentrated on the tensile side of untreated plywood (5N) and on the opposite side of plywood composed of heat-treated veneers, except for the plywood composed of veneers treated at 220 °C (5T220). Of these, 5T200 plywood showed the least strain. In addition, the plywood with 200 °C heat-treated veneers instead of face and core layers (NTNTN200) or crossband layers of untreated veneers (TNTNT200) had larger strain values than 5N and 5T200 plywood specimens, with NTNTN200 plywood having the greatest strain. According to the above results, appropriate layering and heat treatment of veneers can effectively improve the dimensional stability and flexural properties of plywood.

Magnetostriction and volume magnetostriction of sputtered Tb20Fe24Co56 film

The magnetostriction and volume magnetostriction of sputtered amorphous Tb20Fe24Co56 (TFC) films are investigated. In recent years, knowledge of volume magnetostriction is needed in terms of actuator applications utilizing the volume magnetostriction effect. This TFC film with the composition selected in this study is known to exhibit small Joule magnetostriction in Tb-Fe-Co system, and the volume magnetostriction of Tb-Fe-Co thin film systems may be observed more significantly. A bilayer cantilever structure is used to evaluate the magnetostriction performance, which indicates that the largest magnetostriction coefficient and volume magnetostriction of the TFC films are 54 and 48 ppm at an external magnetic field of 7490 Oe, respectively. The Ar gas pressure during sputter deposition is selected to be in the range of 0.7 to 8 Pa in consideration of the deposition quality of the TFC film. The residual stress shifts to the tensile side as the Ar gas pressure increases while the stress field affects the magnetostriction performance. The value of the Joule magnetostriction of the TFC film is almost as same as the volume magnetostriction, which shows that the volume magnetostriction is the dominant mechanism of the magnetic field-induced strain. The homogeneous distribution of elements in the amorphous TFC films possibly makes the Joule magnetostriction small. Since the magnetization of the TFC film is sensitive to strain, the stress field in the in-plane direction strongly constrains the magnetic moment in the out-of-plane direction, and this constraint affects the magnetostriction and magnetization properties. This strain-sensitive magnetic film opens up new possibilities for microdevices using magnetostrictive TFC films via volume magnetostriction.

Behavior of large-scale concrete columns reinforced with high-strength and high-toughness steel bars under axial and eccentric compression

In this paper, combined with the current era background of energy saving and emission reduction, low carbon and environmental protection, the mechanical performance of new high-strength and high-toughness steel bars (HSHTSB) in concrete structural members is studied, and HSHTSB is expected to be popularized. To investigate the compression behavior of large-scale concrete columns reinforced with HSHTSB under axial and eccentric compression, thirteen reinforced concrete (RC) columns were designed in this paper, including the five columns under axial compression and the eight columns under eccentric compression. The effects of different types of steel bars, transverse steel bar spacing, the configuration of transverse steel bars, and eccentricity on failure modes, load-deformation curves, load-strain curves, ultimate bearing capacity, deformation capacity, and energy absorption capacity were studied in detail. The results show that the cracks are more uniform for concrete columns reinforced with HSHTSB. When the transverse steel bar spacing is less than 80 mm, concrete columns reinforced with HSHTSB with eccentricity ≤200 mm (including eccentricity = 0) have obvious secondary bearing phenomenon, and significantly improve ductility and energy absorption capacity; HSHTSB as longitudinal steel bars can reach yield strength for RC columns under axial compression. For RC columns under eccentric compression, HSHTSB could not reach yield strength on both the tensile and compression side. For the RC columns of Group II, III, and IV, when the eccentricity increases from 100 mm to 400 mm, the ultimate bearing capacity decreases by 76.1%, 75.2%, and 75.1%, respectively. Different from the ordinary RC columns, the ductility decreases with the increase of eccentricity for concrete columns reinforced with HSHTSB. Compared with ordinary RC columns, the energy absorption capacity and deformation capacity of concrete columns reinforced with HSHTSB under axial compression are increased by 120.9% and 116.9%, respectively. Compared with RC columns using transverse steel bars with single-leg, the energy absorption capacity and ductility for multiple-leg can be increased by 111.5% and 103.2%, respectively. When the eccentricity increases from 100 mm to 400 mm, the ductility for columns of Group II and III decreases by 73.5% and 65.9%, respectively. The use of HSHTSB can save the number of longitudinal steel bars and the transverse steel bar spacing while maintaining the bearing capacity, and further improve the deformation capacity. Based on the section strain analysis, the analytical models of the ultimate bearing capacity for the concrete columns reinforced with HSHTSB were established with high accuracy.

Failure Analysis for Gold Wire Bonding of Sensor Packaging Based on Experimental and Numerical Methods.

There is an increasing demand for the use of automotive sensors where complex working environments may easily lead to failure. Wire pull and shear test models based on finite-element analysis are established to evaluate their reliability by investigating the failure mode and mechanism of gold wire bonding. The effect of shear force position and pull force position on failure is also analyzed. The bonding failure was verified by experiments, which is consistent with the simulation result. The results show that: (1) The three-dimensional quantitative modeling reveals the process of bonding delamination and stress concentration. (2) The bonding-slip method (BSM) is adopted in the gold ball detaching process. The concept of three states, including deformation accumulation, cracking, and disengagement, was put forward to reveal the interface stress evolution trend according to the shear testing results. The results indicate that in the interface, the stress in the deformation accumulation state decreases from the tensile side (or compression side) to the center, and the stress in the cracking and disengagement states reduces gradually from the tensile side to the edge. When the interface is completely separated, the failed shear force concentrates on 42 g. The concept and theory proposed in this work can effectively reveal the failure mechanism of bonding interface and help to establish a new failure criterion.

Large deflection deformation behavior of a Zr-based bulk metallic glass for compliant spinal fixation application

A novel compliant spinal fixation designed based on the concept of compliant mechanisms can reduce the stress-shielding effect and adjacent segment degeneration (ASD) effectively, but propose higher requirements for the properties of the used materials. Bulk metallic glasses (BMGs), as a kind of young biomaterials, exhibiting excellent comprehensive properties, which are attractive for compliant spinal fixation. Here, according to the practical service condition of the basic elements in compliant spinal fixation, large deflection deformation behaviors of Zr61Ti2Cu25Al12 (at.%, ZT1) BMG beam, including elastic, yielding and plastic were investigated systematically. It was shown that the theoretical nonlinear analytical solution curve as the benchmark not only with the capacity to predict the nonlinear load-deflection relation within the elastic deformation regime, but also assists to capture the yielding event roughly, which can be used as a powerful design tool for engineers. To capture the beginning of the yielding event exactly, bending proof strength (σp,0.05%) accompanied with tiny permanent strain of 0.05% was proposed and determined for BMGs in biomedical implant applications, which is of significance for setting the allowable operating limits of the basic flexible elements. By approach of interrupted loading-unloading cycles, plastic deformation driven by the bending moment can be classified into two typical stages: the initial stage which mainly characterized by the nucleation and intense interaction of abundant shear bands when the plastic strain below the critical value, and the second stage which dominated by the progressive propagation of shear bands and coupled with the emergence of shear offsets on tensile side. The plasticity of BMG beam structures depends on the BMG's inherent plastic zone size (rp). When the half beam thickness less than that of the rp, the plastic deformation of BMGs will behave in a stable manner, which can be acted as the margin of safety effectively.

Effect of neutral layer migration on bending force of AZ31B magnesium alloy sheet during bending

In this paper, they are based on the micro-element stress equilibrium condition in the plastic deformation theory and the Yoon-2014 yield criterion, which can reflect the tension and compression asymmetry of AZ31B magnesium alloy, a bending force model is established to predict the required bending force at different angles according to the neutral layer migration in the bending process of magnesium plate. The offset and bending force values of the neutral layer were verified by FEM and corresponding experiments. The results show that the bending force of a magnesium plate is related to the geometrical size of the scale, the yield limit of the material, and the height of the elastic zone of deformation. The model’s prediction accuracy is better than that of the conventional calculation formula, which can realize the reliable prediction of the required bending force of the magnesium plate. In the bending process, the magnesium plate is affected by the asymmetry of tension and pressure, and the neutral layer migrates to the tensile side. The deviation degree of the neutral layer is the most obvious when the magnesium plate is bent to 90°, and the required bending force is the largest.

Measurement techniques for self-sensing cementitious composites under flexure

Intrinsic self-sensing concrete has gained substantial interest recently as a promising construction material for smart structures. Most of the research focuses on testing their sensing behaviour under pure compression, but in practice, damage to concrete structures due to bending is more commonly seen. It is thus necessary to also test the sensing performance of the composites under flexural loading. Due to the variation of the stress distribution in a concrete element subject to bending, the influence of the geometry of electrodes on measured results is more complex. This study investigated the self-sensing behaviour of prismatic graphite-cementitious specimens under three- and four-point bending with different electrode placements. Composites were tested both in the elastic and plastic range by applying cyclic and monotonic flexural loading. Prisms with different sample depth, sample width, electrode penetration and electrode diameter were further modelled numerically using Finite Element Analysis (FEA) to study the electrical behaviour. Experimental results show that to obtain accurate measurements for composites under flexure, the electrodes need to be at close spacings with shallow penetration at the tensile side of the specimen in order to measure behaviour in the tensile zone. An equation for the relationship between the measured resistance and the geometry variables has been found through numerical simulation that can estimate the influence zone within the sample and hence enable optimisation of the electrode placement for self-sensing cementitious composites under flexure.

Dynamic response of concrete-filled square steel tubular columns under lateral impact load at flat or corner zone

The dynamic response of columns under lateral impact is of great significance for guiding structural design under accidental loads. The present study aims to investigate the effect of different impact directions on the dynamic response of square concrete-filled steel tubular (CFST) columns by conducting drop hammer tests at flat or corner zones. The main experimental parameters included hammer mass, drop height, indenter radius, built-in steel bars, shear span ratio, width-thickness ratio, and column sizes. The experimental results showed that the impact zone has a significant effect on the dynamic response of CFST specimens. Under higher impact energies, specimens impacted at corner zones were more likely to fracture on the tensile side of the steel tube than specimens impacted at flat zones. And the specimens impacted at the corner zone were more sensitive to the change of indenter radius. Smaller shear span ratios, built-in steel bar, and larger column sizes improved the impact resistance of tested specimens. The 3D finite element models were developed and analyzed by ABAQUS/Explicit to explore dynamic behavior further.

Failure Mode of GFRP Bar RC Beams Using GFRP Sheet as Shear Reinforcement

The objectives of this study are to analyze the pattern crack and failure mode of the GFRP concrete beam by using GFRP sheet as shear reinforcement (GFB) compared with the two types of the conventional reinforced concrete beam (CB and GB). One of the conventional reinforced concrete beams is reinforced with the steel bar (CB) and the other is the GFRP bar (GB) as longitudinal reinforcement. The nine beams were cast from one concrete batch with dimensions of 150 mm width, 250 mm depth and 3300 mm length. This study focuses on a simply-supported beam using a roller and pinned supports at the end of the beam. Control beam (CB) that using steel reinforcement shows three phases of deformation based on the deflection load curve, ie before crack, after crack, and after yield, while GB and GFB beams that use GFRP bar reinforcement only show two phases of linear deformation namely the deformation phase before cracking and after cracking. From the crack pattern, CB beams experience the flexural cracks which starting from the mid-span on the tensile side of the constant moment region and propagated to the compression region along with the increase in load. All GB beams show the crack starts from the mid-span and then propagates towards the support. Whereas GFB beam show the flexural cracks that occur in the constant moment region and in the shear span, also diagonal cracks that divide the GFRP sheet occurred. From the failure mode, CB experienced flexural failure, while GB experienced compression failure and shear failure in all GFB beams.

Influence of surface finishing and printing layer orientation on surface roughness and flexural strength of stereolithography-manufactured dental zirconia

ObjectiveTo evaluate the effect of surface finishing and printing layer orientation on the surface roughness and flexural strength of three-dimensionally (3D) printed 3 mol% yttria-stabilized zirconia manufactured by stereolithography (SLA). MethodsNinety bar-shaped zirconia specimens (1 mm x 1 mm x 12 mm) were 3D-printed via SLA. After debinding and sintering, they were randomly divided according to the printing layer orientation: parallel (PR) or perpendicular (PD) to the tensile surface for bending test. Each group was submitted to a surface finishing protocol (n=15/group): unpolished (subgroup 0), with polished tensile surface (subgroup 1), and with polished lateral and tensile surfaces (subgroup 3). Roughness of tensile surface was determined using a contact sensor and surface morphology was analyzed under Scanning Electron Microscopy (SEM). Flexural strength, apparent elastic modulus, and Weibull parameters were assessed using a 3-point bending test. Fractured specimens were examined to identify failure origins. Finite element analysis was used to evaluate tensile stress peaks and failure risk. ResultsPR orientation exhibited higher strength, higher apparent elastic modulus, higher maximum principal stress peaks, and lower failure risk. For both layer orientations, groups with polished lateral and tensile sides (PR3 and PD3) were the strongest. SEM revealed that polishing led to changes in defect type, location, and size. SignificanceSLA zirconia shows different mechanical properties according to surface roughness and defects. Orienting the printed layers parallel to the tensile side improves its mechanical performance. Polishing can significantly improve its flexural strength. It is necessary to reduce the final product's surface roughness and large pores for its best performance.

Residual stress relaxation by bending fatigue in induction-hardened gear studied by neutron Bragg edge transmission imaging and X-ray diffraction

The compressive residual stress on the gear tooth’s surface, a vital parameter to control mechanical properties, such as strength, has a beneficial effect on the component’s fatigue life. A novel procedure, double induction quenching (DIQ), effective for improving the fatigue strength of gear products, has been used for producing gears with steep gradients of compressive residual stress generated in the tooth surface. We performed a Bragg edge imaging experiment at a pulsed neutron source to determine the spatial distribution of the {110} lattice spacing (d110) and the broadening of the {110} Bragg edge (w110) on the DIQ gear product after tooth-bending fatigue tests to which different loading cycles were applied. No significant difference occurred in the d110 and the w110 at Hofer’s critical section (tensile side) of the teeth with different loading conditions within the accuracy of data analysis. However, we detected a decrease in the w110 and changes in the residual lattice strain distribution in the axial direction (through the thickness) along the tooth root directions at the opposite side of Hofer’s critical section for both teeth after 3 × 105 and 8 × 105 cycles, relieving the compressive residual stresses during the fatigue process. The residual stress close to the gear tooth surface determined by X-ray diffraction using sequential polishing showed a slight relaxation and redistribution from the tensile side in the hoop direction, complementary to the neutron Bragg edge imaging information in the axial direction.

Fire resistance evaluation of laminated bamboo lumber column under eccentric compression

Given the fact that laminated bamboo lumber (LBL) is a combustible material similar to timber, evaluating the fire resistance of LBL column accurately demonstrates its importance. The load-bearing capacity and fire resistance of LBL column under eccentric compression were conducted in this paper based on the experimental investigation and theoretical derivation. Considering charring layers falling off the bilinear relationship between charring depth and exposure time was proposed for flatwise orientation with the furnace temperature following the requirements of ISO 834. The failure mode of LBL column in the ultimate state exhibited fiber breaking in the tensile side and the loss of the load-bearing capacity at normal and elevated temperatures. Ultimate state based model (USBM) and reduced cross-section method were introduced to calculate fire resistance of LBL column under eccentric compression, which conformed well to the experimental results.

Impact Strength Enhancement of PMMA base Denture Material by Fibre Addition

Prostheses used temporarily are flexible based on function. Given the paucity of empirical knowledge flexural strength of temporary resins, choosing the right material for their manufacturing is challenging. Dentures have been reinforced with partial fibres both during the production process and during repairs. Polymer's fiber-rich phase in the denture base can either form a distinct structure or the reinforcing fibres can be dispersed equally throughout the material. In this work, the static three-point flexural strength and modulus of denture base polymer reinforced with various fibre reinforcements were determined. PMMA base material can currently be strengthened by adding fibre reinforcement. The creation of bar-type specimens complied with standard 27 of the American National Standards Institute and the American Dental Association. After being immersed in artificial saliva at 37°C for 10 days, the specimens were broken under 3-point loading with a crosshead speed of 0.75 mm/min in a universal testing machine. The highest breaking weights were expressed in Newton’s. The mean flexural strengths were measured in MPa (n = 10 per group). Results were compared using variance analysis and Duncan's multiple ranges testing (P.05). Impact strength of The Glass and Natural fibre (Jute, Sugarcane, Banana etc.) group with 1% and 0.5% composition respectively composition have the maximum value. This group shows the maximum value of flexural strength, compression strength and tensile strength. The findings imply that fibres that are impregnated or re-impregnated strengthen the denture base polymer more than fibres that are not impregnated. When compared to the same amount of fibre reinforcement placed on the compression side, the fibre reinforcement applied on the tensile side produced much higher values for flexural strength and flexural modulus.

Effect of U-bending deformation on pitting corrosion of 2205 duplex stainless steel under wet-dry cycling of chloride salt droplets

The pitting behavior of 2205 duplex stainless steel after U-bending deformation was investigated under wet-dry cycling of droplets. At the tensile side, the average critical relative humidity for pitting (RHpit) was increased from 44.5% to 55.6%, the critical relative humidity (RHrep) for repassivation was correspondingly increased from 59.9% to 76.6%. The compressive strain increased the critical relative humidity to 52.9% (RHpit) and 73.3% (RHrep), respectively. Compared to the hemispherical pits without deformation, selective dissolution of the ferrite phase with irregular pits appeared on the tensile side. The decrease in pitting resistance and the formation of irregular pit morphology were discussed.

Enhancing the behavior of reinforced concrete box girders under Two-point Loading: Numerical and experimental investigations

Reinforced Concrete Box Girders: RCBGs are considered in concrete bridges as significant members and they have been closely accepted as bridge systems due to their structural efficiency: economical construction, serviceability, high stability and aesthetic requirements. The aim of the current research is determining the best way to enhance the behavior of RCBGs, which includes the outcomes of practical and numerical programs of 15 samples tested under bending. The use of ferrocement laminate on the tensile side or in the form of a U-shape, the number of meshes, as well as their type (welded or expanded), and the use of composite materials: Carbon Fiber Reinforced Polymer and Glass Fiber Reinforced Polymer (CFRP and GFRP) were all considered. For composite materials, the strengthening was applied at the tensile side only and wrapping the composite material around the web like a U-shape along the total beam’s length or as strips with different sizes and spacing. The results indicated that wrapping GFRP and CFRP sheets like a U-shape along the total beam’s length gave the same ultimate loads and it represents the highest load of the tested beams. It increased by ∼ 78 % than the control beam. The numerical model gave good results in comparison with the test results. The difference between them does not increase ∼ 13 %.

Novel Reinforcing Techniques and Bearing Capacity Analysis for Tunnel Lining Structures with Extensive Corrosion

Affected by the erosive environment, tunnel lining concrete in the long-term service zprocess often exhibits engineering diseases such as concrete corrosion degradation and loss of strength, decreasing the stability of the tunnel lining structure and the traffic safety. Based on HTG tunnel project, the basic distribution rule of tunnel lining corrosion and macro mechanical properties of corroded concrete were explored in this paper through engineering disease site investigation. Then, on this basis, aiming at large-scale corrosion of tunnel lining structure, two reinforcement and repair schemes are proposed, corrugated steel plate reinforcement method and channel steel reinforcement method. Indoor component tests are carried out on the two reinforcement schemes. The failure characteristics and stress and deformation law of tunnel lining members after reinforcement and repair were verified. The analysis showed that the failure process of the reinforced specimens on the tensile side could be divided into the non-cracking stage and the working stage with cracks, and the cracking load and failure load of the specimens were significantly increased. The bearing capacity of the reinforced specimens was divided into the ultimate bearing capacity against cracking and the ultimate bearing capacity during failure. Finally, the calculation methods of the bearing capacity of the channel steel reinforcement method and the corrugated steel plate reinforcement method were derived. Comparative analysis shows that the results of numerical simulation, experimental testing and theoretical simplification methods are close to each other, and the maximum deviation is less than 8%. The established method for calculating the bearing capacity of corroded components after reinforcement is reliable and can be used for the design calculation of corroded lining reinforcement.

Mechanical and Durability Performances of Alkali-resistant Glass Fiber-reinforced Concrete

Concrete, being the most widely used construction material in the world, lacks strength in direct tension and flexure. Attempts to reinforce concrete in tension include the use of steel rebars to strengthen the tensile side of concrete as well as the use of discrete fibers as a reinforcing medium. The study conducted in this manuscript details the effects of including alkali-resistant glass fibers in concrete. Mechanical strength, such as strength in compression and flexure, chord modulus of elasticity and bond pull-out strength, have been measured along with porosity and resistance to accelerated carbonation. Five different water to binder ratios in a range of 0.4 to 0.6 had been used to prepare the design mix proportions. The optimum fiber dosage was found to be 1.5% by weight of cement used. The same had been adopted in the design mix proportions. The average increase in compressive strength and flexural strength was 13% and 28%, respectively. Alkali-resistant glass fiber concrete showed less resistance to carbonation when compared to control mix. Results indicate that glass fibers play a predominant role in providing flexural strength to concrete. The pull-out strength of fiber was added to extra post-cracking flexural strength. The inclusion of alkali-resistant glass fibers imparted a maximum addition of 44% increase in the flexural strength compared to control concrete. The inclusion of alkali-resistant glass fibers in concrete paves the way for a leaner mix and eradicates the possibility of congestion of steel reinforcement for certain structures. KEYWORDS: Alkali-resistant glass fibers, Accelerated carbonation, Bond strength, Compressive strength, Flexural strength.