Small Diameter Bars Research Articles

Pre-and post-heating bar-concrete bond behavior of CFRP-wrapped concrete containing polymeric aggregates and steel fibers: Experimental and theoretical study

The present research attempted to explore the impact of steel fibers and carbon fiber-reinforced polymer (CFRP) sheets on the pre-and post-heating bond behavior of steel bars in high-strength concrete incorporating waste polyethylene terephthalate (WPET) by conducting the pullout and beam tests and in both pullout and splitting failure modes. To achieve this aim, one hundred and forty-four cubes and forty-eight prisms were cast for the pullout and beam tests, respectively. The variable parameters included the replacement ratio of the fine aggregates with waste polyethylene terephthalate (WPET) particles (0 % and 10 % by volume), steel-fiber content (0 % and 1 % by volume), bar diameter (12-and 16-mm), target temperature (25, 200, and 600 °C), and confinement level (no confinement or CFRP wrapping applied after the thermal regime). Bond strength, bond stress-slip behavior between rebar and concrete, failure mode, and rebar debonding energy were among the parameters investigated after cooling. The results showed that in contrast with the positive effect of CFRP sheets on debonding energy, steel fibers have a positive effect on debonding energy only at 600 °C. Steel fibers did not offset the negative effect of polymeric aggregate, negatively changed the pullout mode to a mixed pullout/splitting failure at 200 °C, and tended to favor splitting failure mode to mixed mode at 600 °C. Moreover, steel fibers negatively affected the bond strength of pullout specimens in both confined and unconfined conditions, especially at 25 and 200 °C, and were less effective than CFRP sheets in avoiding splitting. Small-diameter bars reduced the negative effect of steel fibers on the bond, while polymeric aggregate tended to enhance the bond strength differences between large- and small-diameter bars. The effect of increasing the bar diameter on the effectiveness of CFRP sheets on the bond strength was not clear, but as a general trend, the effectiveness increased with the increase of the bar diameter. A predictive model based on the experimental results of this study and other studies was proposed as well to introduce the positive effect of the CFRP confinement and the dubious effect of steel fibers and polymeric aggregate on bond strength.

Miniature Beryllium Split-Hopkinson Pressure Bars for Extending the Range of Achievable Strain-Rates

Conventional Split Hopkinson Pressure Bars (SHPB) or “Kolsky” bars are often used for determining the high-rate compressive yield and failure strength of materials. However, for experiments generating very high strain-rates (>103/s) miniaturization of the setup is often required for minimizing the effects of elastic wave dispersion in order to enable the inference of decreasingly short loading events from the data. Miniature aluminum and steel bars are often sufficient for meeting these requirements. However, for high enough strain-rates, miniaturization of steel or aluminum Kolsky bars may require prohibitively small diameter bars and test specimens that could become inappropriate for inferring representative properties of materials with large grain size relative to the test specimen size. The use of a beryllium Kolsky bar setup is expected to enable high rates to be accessible with larger diameter bars/specimen combinations due to the inherent physical properties of beryllium, which are expected to minimize the effects of elastic wave dispersion. For this reason, a series of beryllium Kolsky bars have been developed, and, in this paper, the dispersion characteristics of these bars are measured and compare the data with those of similarly sized 7075-T6 aluminum and C350 maraging steel. The results, which agree well with the theory, show no appreciable frequency dependence of the elastic wavespeed in the data from the beryllium bars, demonstrating its advantage over aluminum and steel in application to Kolsky bars.

Durability evaluation of GFRP rebars in harsh alkaline environment using optimized tree-based random forest model

GFRP bars reinforced in submerged or moist seawater and ocean concrete is subjected to highly alkaline conditions. While investigating the durability of GFRP bars in alkaline environment, the effect of surrounding temperature and conditioning duration on tensile strength retention (TSR) of GFRP bars is well investigated with laboratory aging of GFRP bars. However, the role of variable bar size and volume fraction of fiber have been poorly investigated. Additionally, various structural codes recommend the use of an additional environmental reduction factor to accurately reflect the long-term performance of GFRP bars in harsh environments. This study presents the development of Random Forest (RF) regression model to predict the TSR of laboratory conditioned bars in alkaline environment based on a reliable database comprising 772 tested specimens. RF model was optimized, trained, and validated using variety of statistical checks available in the literature. The developed RF model was used for the sensitivity and parametric analysis. Moreover, the formulated RF model was used for studying the long-term performance of GFRP rebars in the alkaline concrete environment. The sensitivity analysis exhibited that temperature and pH are among the most influential attributes in TSR, followed by volume fraction of fibers, duration of conditioning, and diameter of the bars, respectively. The bars with larger diameter and high-volume fraction of fibers are less susceptible to degradation in contrast to the small diameter bars and relatively low fiber's volume fraction. Also, the long-term performance revealed that the existing recommendations by various codes regarding environmental reduction factors are conservative and therefore needs revision accordingly.

Development of an End-Toothed Disc-Based Quick-Change Fixture for Ultra-Precision Diamond Cutting

With its standardized and unified interface, the quick-change fixture is an important part for maintaining high efficiency without compensation of precision in the metal-turning process because it can conveniently realize high-precision repeated clamping and multi-station conversion without complex positioning and adjustment steps. However, the existing quick-change fixture products and related research cannot fully meet the needs of repeatability and applicability raised from ultra-precision, single-point diamond turning with ultra-high accuracy and ultra-small depth of cut. In this paper, we develop a quick-change fixture for ultra-precision diamond turning, in which the end-toothed disc acts as the positioning element. Specifically, the main parameters of two key components of the end-toothed disc and slotted disc spring are calculated analytically to ensure the positioning accuracy of the designed fixture used in the rotation condition, which is further ensured by controlling the machining tolerance of the tooth profile of the end-toothed disc. Additionally, finite element simulations are performed to investigate the static and modal states of the quick-change fixture, which demonstrate a maximum deformation of about 0.9 μm and a minimum natural frequency of 5655.9 Hz for the designed fixture. Two high-precision sensors are used to detect the radial jump and end run-out values after repeated clamping actions, which are employed to verify the repetitive positioning accuracy of the fixture. Subsequent finite-element simulation of the clamping of small-diameter copper bar, as well as the diamond turning experiment, jointly demonstrate that the designed fixture can achieve a precision of 1 μm. Current work provides an effective quick-change fixture to reduce the deformation of a weak-stiffness workpiece caused by clamping deformation in ultra-precision diamond cutting.

Automatic Ultrasonic Testing of Non-metallic Inclusions Detectable with Size of Several Tens of Micrometers Using a Double Probe Technique along the Longitudinal Axis of a Small-diameter Bar

Automatic Ultrasonic Testing of Non-metallic Inclusions Detectable with Size of Several Tens of Micrometers Using a Double Probe Technique along the Longitudinal Axis of a Small-diameter Bar

Influence of the combined radial shear rolling and rotary forging on the stress-strain state of the small diameter bar stock of titanium-based alloys

The paper focuses on the finite element method used to simulate the stress-strain state of a small-diameter bar stock during hot-forming in a combination of radial shear rolling (RSR) and rotary forging (RF). Simulation was carried out using the rheological model of the Ti-6Al-4V titanium-based alloy with the QForm VX software. A combination of radial shear rolling of a workpiece with a diameter of 15 mm to 12 mm bar in one pass and subsequent rotary forging in one, two and three passes to obtain bars with diameters 11, 10 and 8 mm is simulated. During the simulation, step-by-step accumulation of plastic deformation was taken into account in the conditions of its nonuniform distribution. The intermediate and finite fields of plastic deformation, strain rate and average stress are obtained. It is shown that plastic deformation distribution after RSR has an expressed gradient with a maximum value (3 or more) at the periphery of the cross-section and a minimum value (about 1) at the center. As a result of RF, even with small reductions, the stress-strain state becomes much more uniform compared with a workpiece of the same diameter after radial shear rolling only. In addition, residual tensile stresses due to compressive stresses during rotary forging are reduced. Direct experimental testing of the combined deformation method was carried out for a promising medical-grade Ti-Zr-Nb shape memory alloy when manufacturing 7-8 mm diameter rods in experimental production conditions. Qualitative confirmation of modeling results is obtained by metallographic analysis. It is shown that the combination of radial shear rolling and rotary forging is promising for creating industrial technologies for the manufacture of small-diameter rods with a highly uniform finely-dispersed structure.

Experimental study of in-plane shear strength of confined concrete masonry walls with joint reinforcement

Six full-scale confined masonry walls made with multi-perforated concrete units were subjected to reversal cyclic lateral loads. The only variable investigated was the amount of joint reinforcement. All other variables were fixed, the height to length aspect ratio was set to one. The reinforcement, placed in the bed joints every two courses, consisted in small diameter bars with 588 MPa nominal yielding stress. Numerous strain gages were installed on the rebars to monitor deformation and subsequently estimate the lateral strength contributed by the reinforcement. The strength due to the masonry was estimated as the difference between the total lateral strength and the strength attributed to the reinforcement. The results show that the contribution of the reinforcement to the lateral strength increases with the amount of reinforcement to a certain limit and that the contribution of the masonry decreases. The limit is related to the masonry compressive strength. The experiments and results are presented in detail, followed by a discussion and conclusions.

Effects of tensile steel bars arrangement on concrete cover separation of RC beams strengthened by CFRP sheets

This study was conducted to investigate the effect of reinforcement arrangement in strengthened RC beams on the concrete cover separation. For this purpose, 12 beam specimens with the dimensions of 250 mm × 300 mm × 2200 mm and different reinforcement ratios were prepared and tested under four-point bending. From the standpoint of the strengthening technique, the specimens were categorized into two groups: six specimens were strengthened by Externally Bonded Reinforcement (EBR) method and the other six specimens were strengthened using Externally Bonded Reinforcement on Grooves (EBROG). On the condition that the reinforcement ratio is constant, reducing the diameter and increasing the number of bars increased the probability of concrete cover separation. The specimens with low and medium ratios of reinforcement, in which small-diameter bars are used, demonstrated a higher load carrying capacity sustaining more deflections at mid-span before debonding of FRP sheets.

Evaluation of Dynamic Fracture Toughness in Ductile Steel by Means of a Split Hopkinson Pressure Bar 3PB Technique

The objective of this work is the tune of a methodology for the determination of the fracture toughness in ductile materials at high strain-rate by means of dynamic 3 Point Bending (3PB) tests. The specimens made in high strength steel have been pre-cracked in fatigue with a single edge notch. The dynamic loading conditions have been reached by means of a modified Split Hopkinson pressure Bar setup, in which two small diameter bars are used as transmitted bars instead of the standard single one. In order to obtain the maximum amount of information from each test, different measuring systems have been adopted, in addition to the strain measurements on the bars performed using semiconductor strain-gages. On the specimen surface, one or two crack-gages (one for each side for specimens) have been bonded for obtaining data about the crack propagation and the crack tip position vs. time curve. Moreover, a high speed camera has been used for obtaining the measurements of the Crack Opening Displacement (COD) and the opening velocity: digital images have been processed using tracking techniques following some points on the specimen notch and input bar tip. Starting from the experimental measurements in term of force, displacement and crack-gage data, a protocol for fracture toughness calculation at the initiation stage of the crack growth in dynamic condition has been defined and a hybrid experimental – numerical methodology has been used. One of the key variables for the determination of dynamic initiation fracture toughness is the crack time to initiation. Many efforts have been done in order to better determine a precise method to experimentally measure this entity: this datum has been obtained from the analysis of both the force and crack-gage vs. time signals and the COD measurement on high speed video. Good agreement has been found between the two methodologies. At this stage, a 3D model, which simulates the SE(B) specimens during the Hopkinson 3PB test, has been done in order to determine the toughness (J integral) as a function of time. Knowing the initiation time, the fracture toughness at crack initiation can directly be determined.

Deterioration of bond–slip due to corrosion of steel reinforcement in reinforced concrete

Corrosion of steel reinforcement in reinforced concrete members is a common occurrence and a major concern, as it can significantly affect both the serviceability and ultimate limit states. In order to simulate the effects of corrosion through mechanics, it is necessary to quantify the effects of corrosion on the material bond–slip properties, which is the subject of this paper. A large database of 377 data points was used to quantify the effect of corrosion on bond strength and bond–slip in a form that can be used in numerical analyses. This research concentrates on the changes in bond strength and bond–slip due to corrosion, and hence the changes relative to the uncorroded properties because these are already well quantified. Furthermore, it does not consider the clamping action of stirrups encasing the reinforcement. As an illustration of the application of these bond properties of corroded steel reinforcement, they are used in a mechanics analysis to show that large-diameter bars are much more susceptible to the effects of corrosion than small-diameter bars.

Analysis of a Three-Bar Kolsky Apparatus for High-Rate Three-Point Flexure

A Kolsky bar method is described that is suitable for measuring the flexural strength of ceramics under valid testing conditions in a high-rate three-point bending configuration. A three-bar arrangement is used—one input bar and two output bars—to provide measurements of force and displacement at each loading point. Small diameter bars are used to improve the force measurement made by the incident bar which in many cases would be inaccurate. An analytical model is formulated to predict the desired incident pulse based on the conditions of the experiment and the desire for a particular prescribed strain-rate. A finite element analysis is also conducted to determine suitable specimen geometries that will yield valid data at the desired rate. It is shown that stiff beam geometries improve specimen equilibrium and can reduce inertial effects. However, the use of small diameter bars necessitates unusually precise pulse-shaping. To achieve additional flexibility in pulse-shaping, a tapered striker is used in conjunction with a ductile wave-shaper to generate the desired incident pulse. A down-side of this approach is that a suitable taper geometry must be determined. It is shown that this geometry can be designed quickly and accurately using a simple one-dimensional finite element approach. The methods are demonstrated by measuring the dynamic flexural strength of α-SiC.

On the strength and ductility of lapped splices of reinforcing bars in tension

AbstractWhen designing a reinforced concrete member for strength, ductility and robustness, it is essential that the tensile reinforcement at the critical section can not only develop the yield strength of the steel f sy, but that it can sustain this level of stress as deformation increases. At a lapped splice, each bar must be fully anchored beyond the lap length. The minimum lap lengths of deformed reinforcing bars in tension specified in the Australian Standard for Concrete Structures AS3600-2009 were recently revised and a procedure similar to, but less conservative than, the provisions in Eurocode 2 was adopted. The new provisions require longer lap lengths for small diameter bars in slabs, but considerably shorter lap lengths for larger diameter bars in beams and columns. This paper reports on several series of tests that examine the efficacy of the AS 3600-2009 provisions from the perspectives of adequate strength and ductility. Over 50 specimens containing both contact and non-contact lapped splic...

The Strength and Ductility of Lapped Splices of Reinforcing Bars in Tension

When designing a reinforced concrete member for strength, ductility and robustness, it is essential that the tensile reinforcement at the critical section can not only develop the yield strength of the steel f sy, but that it can sustain this level of stress as deformation increases. At a lapped splice, each bar must be fully anchored beyond the lap length. The minimum lap lengths of deformed reinforcing bars in tension specified in the Australian Standard for Concrete Structures AS3600-2009 were recently revised and a procedure similar to, but less conservative than, the provisions in Eurocode 2 was adopted. The new provisions require longer lap lengths for small diameter bars in slabs, but considerably shorter lap lengths for larger diameter bars in beams and columns. This paper reports on several series of tests that examine the efficacy of the AS 3600-2009 provisions from the perspectives of adequate strength and ductility. Over 50 specimens containing both contact and non-contact lapped splices have been tested. The aim was to assess the current Australian provisions and to examine the reliability and consistency of the factors of safety associated with lapped splices. It is concluded that the strength requirements of AS3600-2009 are adequate for small diameter bars in slabs but may not provide an adequate factor of safety for large diameter bars in beams. Also, the AS3600 provisions may not ensure sufficient ductility of a lapped splice in members that use high strength concrete. Further tests are required to investigate these aspects.

Microstructure–texture–mechanical properties relationship in multi-pass warm rolled Ti–6Al–4V Alloy

In the present study, high strength bulk ultrafine-grained titanium alloy Ti–6Al–4V bars were successfully processed using multi-pass warm rolling. Ti–6Al–4V bars of 12mm diameter and several metres long were processed by multi-pass warm rolling at 650°C, 700°C and 750°C. The highest achieved mechanical properties for Ti–6Al–4V in as rolled condition were yield strength 1191MPa, ultimate tensile strength of 1299MPa having an elongation of 10% when the rolling temperature was 650°C. The concurrent evolution of microstructure and texture has been studied using optical microscopy, electron back scattered diffraction and x-ray diffraction. The significant improvement in mechanical properties has been attributed to the ultrafine-grained microstructure as well as the morphology of α and β phases in the warm rolled specimens. The warm rolling of Ti–6Al–4V leads to formation of 〈101¯0〉α//RD fibre texture. This study shows that multi-pass warm rolling has potential to eliminate the costly and time consuming heat treatment steps for small diameter bar products, as the solution treated and aged (STA) properties are achievable in the as rolled condition itself.

NONLINEAR FE MODELLING OF ANCHORAGE BOND IN REINFORCED CONCRETE

The transfer of forces from the surrounding concret e to the reinforcing bars in reinforced concrete (R C) can be influenced by several parameters. In this paper an attempt has been made to study the influence of specimen geometry, bar di ameter, strength of concrete, lateral confinement and embedment length on the bon d properties of concrete. The embedment length of t he bar was varied between 50mm and 400mm by varying the diameter of the bar, strength of concrete and lateral confinement. The d ifferent bar diameters of 16, 20 and 25mm were selected along with three differen t concrete strengths of 25, 40 and 65MPa. The speci mens with the above parameters were modeled by using a nonlinear finite element analysis package. It has been found that fthe same geometry, the specimens with small bond length exhibited high bon d strength. With the range of bar diameters conside red the bond strength of concrete decreases as the diameter of the bar incre ases. The splitting failure has been observed in un confined concrete, while the pullout failure was predominant when the concrete l aterally confined. In case of large embedment lengt h, the post peak plateau is prolonged with small diameter bars when compared to the large diameter bars. The descending branch of the bond stress-slip response with large diameter bars has been found to be steep.

Some Remarks Towards Surface Reinforcement Used in Concrete Members

The present paper deals with the special situations, when the cover of reinforcement of structural members exceeds 50mm, and it may be appropriate to provide a surface reinforcement. The new Model Code 2010 [1,2] mentions such a reinforcement, but doesn’t specify its type, cover and the area amount. However such a surface reinforcement is able to increase the bending and especially shear resistance of structural members, subjected to bending and shear. In addition to that the surface reinforcement reduces an expansion and width of cracks.According to Eurocode 2 [3], Part 1-1 in Annex J – Detailing rules for particular situations – there are some special cases when such a surface reinforcement should be used. It is necessary to use this reinforcement type when:•diameter of designed bars is greater than 32mm, or equivalent diameter of bundled bar exceeds this limit;•cover to reinforcement is greater than 70mm (for enhanced durability);•crack widths without using surface reinforcement exceed allowed limit;•reinforced concrete structure is subject to fire and there is a risk of falling off of a concrete in the later stage of a fire exposure according to Part 1-2 of Eurocode 2 [5,6].The surface reinforcement should consist of wire mesh or small diameter bars and should be placed outside of links.This paper analyses different values of the surface reinforcement cover and the increase of bending and shear resistance due to surface reinforcement of RC beams. It also includes an explanation of the effect of the surface reinforcement on expansion and width of cracks.

Development of new Hopkinson’s device dedicated to rib’s bone characterisation

This study presents an original approach for the design of adapted Hopkinson device dedicated to the characterisation of human ribs’ cortical bone. The quasi-static study carried out on flat samples coming from this anatomical part highlighted the importance of the critical effect of sample shape and location on the accuracy of identify mechanical behaviour. The access to higher rates of strains, Hopkinson bars technique are classically required whatever compression or tension loadings. Classical designs of measurement bars are not suitable for this purpose due to the complexity of specimen’s geometry (thickness variation). In this context, a new design of SHTB is studied here on the basis on a Finite Element approach of the set measurement bars/biological coupon. Finite Element simulations have been conducted using Abaqus explicit code by varying the design configuration. The comparison on input and output elastic waves suggests a set of small diameter bars in polyamide 66 for a better signal measurement.

Evaluation of the Adequacy of Development Length Requirements for 500 MPa Reinforcing Bars

This paper compares the development length requirements of several international codes for 500 MPa steel reinforcing bars with test results obtained from eighteen reinforced concrete beams. These beams were designed specifically to allow the pull out of bars in the tension zone before bar yielding in order to determine the anchorage capacity and hence the development length necessary to obtain yield. After introducing the background to development length requirements and summarizing eight different international code provisions, this paper reports the results of the eighteen beam tests and compares these results with the code provisions. Following the development length comparison among the international standards, several conclusions are drawn. Of all the approaches examined in this paper, AS3600-2001 is always the most conservative one and has the worst correlation with the test data in most conditions, while AASHO has the lowest factors of safety for the smaller bars. These factors are considered reasonable and appropriate. ACI318-05 and ACI Committee 408 are more conservative and provide worse agreement for the larger bars. CEB-FIP Mode Code 1990 and Eurocode 2 always follow a similar trend and have lower, appropriate factors of safety, and also provide a better agreement with the test data in most conditions. GB50010-2002 has the similar factors of safety to CEB-FIP Mode Code 1990 and Eurocode 2. However, it doesn't provide good agreement with the test data for larger diameter bars. Of all the approaches examined here, AS3600-2009, which brings the Australian Standard into line with FIP Mode Code 1990 and Eurocode 2, provides better consistent agreement with the test data and is a significant improvement on the method provided in AS3600-2001. All current codes appear to be over conservative for small diameter bars.

CARPENTER CUSTOM 475

Abstract Custom 475 stainless is a premium melted, high-strength, martensitic, precipitation-hardenable stainless steel. It provides good corrosion resistance and was designed to achieve a tensile strength up to 2000 MPa (290 ksi), combined with good toughness and ductility when in the H975 condition, peak aged at 525 deg C (975 deg F). Other combinations of strength are possible by applying aging temperatures up to 595 deg C (1100 deg F). The alloy is available in strip, wire, and small diameter bar. This datasheet provides information on composition, physical properties, hardness, and tensile properties. It also includes information on corrosion resistance as well as forming, heat treating, and machining. Filing Code: SS-974. Producer or source: Carpenter Technology Corporation.

High-Speed Steels Produced by Conventional Casting, Spray Forming and Powder Metallurgy

Powder metallurgy (PM) and spray forming (SF) have been reported as important alternative routes for tool steel production. The ability to promote refined and more uniform microstructures is their main advantages, leading to improved properties and larger isotropy. While PM application is a completely established technology, the SF process may be considered as a not totally explored field. Therefore, the present work aimed to study the potential of both processes, focusing at high-speed steel (HSS) production. AISI M3:2 highspeed steel was produced by conventional casting, spray forming and powder metallurgy. Conventional ingots and a 400 mm diameter SF billet were rolled to small diameter bars, with cross section around 110 mm. The PM material was evaluated in the as-HIPed condition, in comparative diameters. Large diameter HSS bars are used mainly in cutting tools, but are also applied in cold work tooling when high wear resistance is required. In the present characterisation, microstructures and bend test analysis were used, both in transverse and longitudinal directions. The results show that the as-HIPed PM material presents finer and more uniform carbide distribution, leading to a complete isotropy and higher toughness than conventional steel. In the SF material, carbides are also finer, have good distribution and the isotropy is considerably higher than that for conventional HSS.