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The flow stress of wire material, the friction coefficient and the sticking capability of the lubrication coating on the wire surface are evaluated with a single test. In this test, the specimen cut off from the end of a wire coil is set on a V-groove die and then is compressed into the V-groove by a punch. Friction coefficient is determined by the ratio of the punch load and the die load. The flow stress curve is calculated using the punch load-punch stroke curve. The proposed method is suitable for the use in the wire manufacturing shops for cold forging. [ABSTRACT FROM AUTHOR]

The prefabricated reinforced concrete (RC) hollow slab bridges, with the advantages of high quality, lower cost and shorter construction period, have been widely used for small-to-medium-span highway bridges in China. Because of environmental deterioration and traffic volume increases, the performance of the bridge system deteriorates gradually. Accurate bridge system evaluation can provide a reliable basis for maintenance and management. A bridge system is composed of multiple interrelated components, which makes the system reliability evaluation become a computationally intractable work. In this paper, an effective method was proposed to evaluate the system reliability of the prefabricated RC hollow slab bridge considering hinge joint damage based on the modified analytic hierarchy process (AHP). Considering the subjectivity of the traditional AHP method in constructing the judgment matrix, this paper proposed an objective construction method of the judgment matrix to modify the traditional AHP. The modified hinge plate method (MHPM) proposed by the previous research was utilized to analyze the effect of hinge joint damage on system reliability. In order to verify the applicability of the proposed system reliability evaluation method, a simply supported RC hollow slab bridge was selected as the case study and the system reliability indexes were compared with the traditional series and parallel methods. The results indicated that the traditional methods were either too conservative or too radical to objectively evaluate the actual system reliability level of the structure. In contrast, the proposed method in this paper was more suitable for evaluating the system reliability of such bridges, and more accurate in providing maintenance decision makers with a relatively reasonable bridge condition information. [ABSTRACT FROM AUTHOR]

The application of yield line analysis to carry out strength design of reinforced concrete (RC) slab systems is mostly limited to solid slabs without beams. In an earlier paper on isolated rectangular beam-slab systems, the authors had demonstrated that such analysis, considering plastic hinges in the beams along with yield lines in the slabs, can result in rational and economical designs. In this paper, it is shown that such yield line analysis can be further extended to beam-slab systems with secondary beams, and the predictions have been validated by tests carried out on four rectangular RC beam-slab systems (each comprising four symmetric grid units), supported at the four corners on pillars. Six possible collapse mechanisms have been investigated. It is established that the critical collapse mechanism is governed primarily by the beam-slab relative strength. It is shown how an economical and rational design can be achieved, making use of the proposed yield line analysis. [ABSTRACT FROM AUTHOR]

Punching Shear under Fatigue Load – European Technical Assessment with Design Concept according to Technical Report EOTA TR 058 Sufficient punching shear resistance of flat slabs has to be ensured. In case of fatigue load the fatigue resistance has to be proved as a part of the design. Eurocode 2 requires in case of reinforced concrete structures separate verifications of the concrete and the reinforcement. In the Eurocode 2 the design concept in the case of a reinforced punching shear area is not presented comprehensively. For the Filigran®‐Punching Shear Reinforcement such a design concept is determined in the European Technical Assessment ETA‐13/0521 based on the Technical Report EOTA TR 058. Accordingly both the punching shear reinforcement on the basis of a S‐N‐Curve and the concrete fatigue resistance, which determines the maximum punching shear resistance, have to be verified. This design concept is described in this article. [ABSTRACT FROM AUTHOR]

The conditions of use of personal protective aids presume impact not only of injuring agents, but also of various environmental factors that affect in no mean degree the level of performance properties that ensure personal safety. This article examines the influence of the rate of penetration of an indenter, the number of layers, and the moisture content on the load of cutting and force of punching of fabrics for body armor and establishes the correlation of these properties. [ABSTRACT FROM AUTHOR]

Highlights • The reliability of the models for the assessment of the punching capacity. • The modification of the failure criterion for the model based on the CSCT. • Relations between ratio V test / V Rc and parameters influencing the punching capacity. Abstract Reinforced concrete flat slabs are structural members frequently used in building construction. Despite their many advantages, such structural systems suffer from several drawbacks. From a safety point of view, the concentration of shear forces at the vicinity of local supports, e.g., columns, edges and corners of walls, can lead to possible structural failure from punching. Punching is a dangerous phenomenon due to its brittle mode of failure and its ability to spread over a whole structure, which can be followed by a progressive collapse. Several models for the assessment of punching capacity have been developed and calibrated using experimental results from laboratory tests. Some models are fully empirical, e.g., EC2 (2004), while other models reflect the physical nature of the phenomenon; however, their safety level was calibrated using experimental data, as the model presented in Model Code 2010 or the CSCT-based model, which is expressed in a closed form. This paper deals with a statistical evaluation of the safety level of the previously mentioned models for punching resistance without transverse reinforcement. A database which includes the results of more than 600 experimental tests of flat slab specimens has been used. The relations between the safety of the model and the quality of the concrete used, the amount of the bending reinforcement, and the effective depth were found using advanced statistical methods. [ABSTRACT FROM AUTHOR]

Highlights • Effect of punching location on thermo-flow of a metallic lattice is presented. • Similar and distinctive fluid flows induced by the lattices are clarified. • The link between flow and local heat transfer patterns is explored. • New lattices with superior cooling performance are proposed. Abstract This study numerically investigates the effects of the punching location shift on thermo-fluidic characteristics of a metallic lattice fabricated by the metal sheet folding method. By shifting the punching location, new lattices with the identical porosity and surface area density can be fabricated without redesigning the metal sheet or adjusting the fabrication process. The effects of the punching location shift on the flow and heat transfer is totally different when the dimensionless punching location shift (s / d) is below and above 0.55, respectively. When s / d is below 0.55, the flow is composed of the parallel primary flow and the counter-rotating vortex pair; the average overall Nusselt number increases with the increase of s / d ; and both the primary and secondary flows are responsible for the enhanced heat transfer. When s / d is above 0.55, the spiral primary flow and three kinds of secondary flows (i.e., two types of cross-flows and a counter-rotating vortex pair downstream each ligament) dominate the fluid flow behaviors; the average overall heat transfer varies slightly and tends to decline when s / d is above 0.8; and the variation in the secondary flows result in the corresponding heat transfer variation. When s / d is 0.55–0.8, the average overall Nusselt number approximately remains constant and is about 10% higher than that of the ideal X-lattice. The variation of the friction factor as a function of s / d resembles that of the local heat transfer on ligaments because pressure drop is dominated by the form drag induced by ligaments. The overall thermal performance ranked from the inferior to the superior is as follows: the pyramidal lattice (s / d = 0), the lattice with a quarter punching location shift (s / d = 0.25), the X-lattice (s / d = 1) and the other lattices. [ABSTRACT FROM AUTHOR]

Highlights • Small punch test on 3 ODS steels; comparison of hot-rolled vs. hot-extruded ODS. • In-depth analysis of load drops (pop-ins) in the force-displacement curves. • Analogy of secondary cracks (fracture mechanics) and flakes in SP fractures surfaces. • Effect of anisotropy on of the correlation between SP and KLST based DBTTs. Abstract Hot rolling and hot extrusion of oxide-dispersion strengthened (ODS) ferritic steels give rise to anisotropic microstructures and mechanical properties and may provoke related phenomena such as secondary cracking. In this study, we consider the small punch (SP) test – a method, applicable in the case of small amounts of available material and well established for isotropic materials. The SP test was applied to investigate the effect of sample orientation on deformation and cracking for one hot-rolled and two hot-extruded ODS ferritic steels. Existing microstructural evidence is used to rationalize the observed anisotropic fracture behaviour. The SP test results are compared with those from existing fracture mechanics tests based on sub-sized C(T) samples. The applicability of the empirical conversion of SP-based into Charpy-based transition temperatures is evaluated. The fractographic manifestation of load drops in SP load-displacement curves is identified and the analogy to secondary cracking in fracture mechanics tests is shown. [ABSTRACT FROM AUTHOR]

Highlights • A punching shear strength model was proposed for UHPFRC-RC composite flat plates. • UHPFRC overlay increases the load-carrying capacity, but it is limited at a certain point. • The punching shear strength can be defined as a function of the thickness and strength of UHPFRC overlay. Abstract Reinforced concrete (RC) flat plates are vulnerable to punching shear failure due to small effective area for shear resistance. To strengthen the behavior of existing flat plates, use of ultra high performance fiber reinforced concrete (UHPFRC) as a laminate has been pursued. This study focuses on punching shear behavior of RC flat plates retrofitted with UHPFRC overlay (i.e., UHPFRC-RC composite flat plates). To model the axisymmetric UHPFRC-RC composite flat plate, use of the unified strength theory-based punching shear strength model was proposed. Predictions using the proposed model, when compared to existing test results of UHPFRC-RC composite flat plates under concentric load and nonlinear analysis results using ABAQUS, agreed well with the results. Additionally, from the parametric analysis results using the proposed model and nonlinear analysis, the effects of UHPFRC overlay thickness and tensile strength on the punching shear strength were identified. [ABSTRACT FROM AUTHOR]

Highlights • Simplified model to predict the punching shear failure of RC slabs under impact. • Proposed approach is validated with experimental and numerical results. • Review of the response of the concrete slabs under low velocity impact. • Significance of various governing parameters is highlighted. Abstract A simplified analytical approach to predict the punching shear failure of a concrete slab under low velocity (<10 m/s) impact loading has been proposed. The proposed analytical approach has further been validated against a backdrop of experimental results available in the public domain. The efficacy of the proposed approach has further been tested against the results obtained by conducting numerical simulations designed by the authors. The results obtained from this simplified approach have on the whole shown good agreement with the experimental results. Furthermore, on the basis of extensive literature review, a state-of-the-art investigation to examine the structural response of concrete slabs under low velocity impact loading has also been presented in this paper. The paper aims to explore and present a quantum of the undertaken research under the sections dealing with the experimental studies, numerical simulations and the analytical modeling. Thus, in addition to the proposition of a simplified approach for predicting the punching shear failure of a concrete slab under low velocity impact loading condition, the paper also sets forth to establish the current knowledge base in this field and identify the key areas with a need for further research with regard to this domain. [ABSTRACT FROM AUTHOR]

Abstract In recent years, the pre-notched or pre-cracked small punch test (P-SPT) has been successfully used to estimate the fracture properties of metallic materials for cases in which there is not sufficient material to identify these properties from standard tests, such as CT or SENB specimens. The P-SPT basically consists of deforming a pre-notched miniature specimen, whose edges are firmly gripped by a die, using a high strength punch. The novelty of this paper lies in the estimation of fracture properties using dog-bone-shaped specimens with different confinement levels. With these specimens, three confinement variations have been studied. The results obtained enable the establishment of a variation of fracture properties depending on the level of confinement of each miniature specimen and selection of the most appropriate confinement for this goal. Graphical abstract Unlabelled Image Highlights • Influence of confinement levels in the fracture properties has been studied. • New pre-notched dog-bone-shaped specimens has been used. • Different confinement levels tested on P-SPT specimens. • Relationship between fracture toughness and confinement levels has been analysed. [ABSTRACT FROM AUTHOR]

Highlights • Punching strengthening is required due to design/construction errors, load increase, etc. • Strengthening techniques are compared using the Critical Shear Crack Theory. • A case study is dealt with to give indications for strengthening pre-dimensioning. • Predicted punching strength of strengthened slabs agrees with experimental data. • A design tool is provided to choose which technique better fits the specific case. Abstract Over the years, the flat slab system has become a popular form of construction in many countries, particularly for multi-storey buildings such as offices or carparks. Nowadays, a considerable number of flat slab buildings requires strengthening against punching. Reasons are several, like design or construction errors, poor quality materials, not complying with new codes provisions, or increase of vertical load. This paper discusses different techniques for strengthening of R/C slabs against punching: insertion of post-installed shear reinforcement, application of external fibre reinforced polymers or a bonded reinforced concrete overlay (BRCO) on the slab top surface, enlargement of the support, application of a post-tensioning system. The authors propose a unified approach, based on the Critical Shear Crack Theory (CSCT), to evaluate the effectiveness of each strengthening technique. The attempt is to give a reading key capable of adapting to different strengthening techniques and providing a comprehensive view of the problem. The study shows that the CSCT could be easily adapted to all strengthening techniques and punching strength predictions are in good agreement with literature experimental results. This work also proposes to give designers the tool to choose which strengthening technique suits better to the specific case. [ABSTRACT FROM AUTHOR]

Micro punching process is suitable for mass production of micro parts. It is a challenge to fabricate micro punching mold with complex cross-sectional shape on-machine. The micro punching system's structure design has to meet the requirement of large punching force. In this study, a micro punching system has been developed with a micro electrical discharge machining (EDM) module. A series of machining operations, from the fabrication of micro molds to punching, have been completed with no secondary clamping error. The micro die and reversed electrode are prepared using micro EDM milling. The micro punch is fabricated using reversed electrode. The punching clearance is around 11 μm. Complex shape punched holes and blanked parts have been successfully fabricated on copper, brass, 304 stainless steel, and 3J21 alloy. After punching, there was no damage on the edges of micro die and micro punch. The key dimensional error of blanked part varies by different materials, which is less than 2.5 μm. [ABSTRACT FROM AUTHOR]

The provisions for design of shear reinforcement for flat slabs in the ACI 318 and Eurocode 2 building codes assume that punching failure and flexural failure can be treated as two mutually independent failure modes. However, if the flexural reinforcement yields, then wide flexural cracks will worsen the anchoring conditions for the shear reinforcement and a flexurally initiated punching failure may occur. However, shear reinforcement in the form of inclined stirrups is found to be effective even when wide flexural cracks develop and will, therefore, provide increased capacity and ductility when compared to a design with conventional shear reinforcement. Test results and design recommendations for ductile behavior as well as for maximum punching capacity are presented. [ABSTRACT FROM AUTHOR]

• The residual performance of the flexible barrier is related to the three-stage deflection mechanism of the barrier. • The residual performance of the flexible barrier can be evaluated by the damage identification method and the calculation method of the residual protection capacity. • The damage of the barrier can be identified by comparing the deflection of key components with the ultimate deflection of those components. • The residual protection capacity of the barrier can be estimated by the energy dissipated by dissipators. Currently, there is no effective analysis algorithm to calculate and evaluate the residual performance of flexible barriers after suffering rockfall impact. To solve this problem, a novel approach for assessing and quantifying the residual performance of flexible barriers through the deflection degree of different components is proposed, based on the substantial experimental database from impact tests that were conducted with impact energies between 750 kJ and 1500 kJ, revealing a high correlation between the three-stage macroscopic deflection characteristics and the residual performance. The approach consists of two significant aspects, one is the calculation method of the residual protection capacity, which was established according to the simplified calculation method of the energy dissipation of the dissipators. The other aspect is the damage identification method for the barrier system based on the deflection of key components, which was determined by comparing the deflection angle of the post and the punching deflection of the net obtained from the analytical geometric model with the ultimate deflection of those components calibrated by tests. Utilizing the ultimate force-deflection relationship calibrated by tests, a method to discriminate the system damage based on the analytical calculation value of the deflection of key components is established. Furthermore, both full-scale tests and numerical simulations were conducted to validate the proposed analytical calculation method. The tested flexible barrier had a nominal energy level of 2000 kJ, and the tests included service energy level (SEL) and maximum energy level (MEL) continuous impacts. The analysis results show that the maximum calculation errors for the energy dissipated by the energy dissipators, elongation of the energy dissipator, elongation of the wire ring, and out-of-plane deflection angle of the post are -3%, 10%, 12%, and -8%, respectively. The evaluation results of the residual performance as well as the damage identification both have satisfied agreement with the test results, confirming the reliability and applicability of the analytical method to engineering maintenance decisions. [ABSTRACT FROM AUTHOR]

Highlights • Development of a kinematic theory considering both flexural and translational deformations (two degrees of freedom). • Calculation of shear contributions along the failure crack based on slab deformations. • Validation of the kinematic theory by means of systematic punching test series and databanks. • Discussion of differences between punching shear behavior of slender and compact slabs. Abstract Measurements taken from recent test series with varying slenderness reveal strong differences between fracture kinematics of slender and compact slabs failing in punching. In accordance with the assumptions of the existing kinematic punching shear resistance models, the deformation behavior of slender slabs is governed by flexural deformations. However, in very compact slabs only small flexural deformations occur and the deformation behavior is dominated by translational deformations. In the transition region between slender and very compact slabs, the deformation behavior is influenced by both deformation components. As a consequence, the general application of the existing kinematic models to both slender and compact slabs might yield unexpected results. In this paper, a two-parameter kinematic theory for punching shear in reinforced concrete slabs without shear reinforcement is developed taking into account the aforementioned observations. In the theory, it is assumed that shear forces are transmitted along the failure crack by four shear contributions, namely the contributions of compression ring, aggregate interlock, residual tensile stresses, and dowel action. The magnitude of shear contributions is estimated based on the deformed slab accounting for two degrees of freedom (DOFs). While the first DOF accounts for flexural deformations, the second DOF considers translational deformations. Subsequently, the punching strength is calculated by summation of the contributions. The evaluation of the proposed theory by means of systematic test series and databanks yields good agreement between predictions and experimental results. Especially, the differences between flat slabs and column bases can be explained in a consistent manner by the theory. [ABSTRACT FROM AUTHOR]

To achieve large-scale preparation of high-performance carbon materials for electrochemical energy storage with a simple and cost-effective method remains a challenge. Here, we report a novel approach to synthesize hierarchical porous carbon with a low melting point metal tin (Sn) as pore forming agent. An aqueous processed tin chloride-polyethylene glycol (SnCl 2 -PEG) gel is used as precursor to form Sn/Carbon (Sn/C) composites with homogeneously distributed ultrafine Sn particles (<2 nm) by pyrolysis. After etching Sn nanoparticles, hierarchical porous carbon with high specific surface area (SSA: 846 m 2  g −1 ) and abundant pore structure (coexistence of mesopore and micropore) was obtained. The SSA, pore size distribution and pore volume were successfully tuned by controlling the size of the Sn nanoparticle. The capacitive performance of the as-prepared hierarchical porous carbon was evaluated in 1 M H 2 SO 4 , which exhibits excellent specific capacitance of 240 F g −1 . In order to further increase the electrochemical performance, N-doped porous carbon was fabricated by thermal nitridation in ammonia, which shows favorable features for electrochemical energy storage such as high specific surface area (1175 m 2  g −1 ), uniform micropore volume (0.46 cm 3  g −1 ) and rich nitrogen-doping (4.45 wt%). This N-doped sample exhibits outstanding specific capacitances of 360 F g −1 and excellent cycling stability in aqueous electrolytes. The above achievements indicate that combining low melting point metal as pore forming agent with a sol-gel protocol can be a unique and reliable method for preparation of high performance supercapacitor electrode materials. [ABSTRACT FROM AUTHOR]

Among stainless steel, type-304 austenitic stainless steel is the most widely used because of high corrosion-resistance as well as favourable mechanical properties due to strain-induced martensitic transformation (SIMT). In order to utilize the application of type-304 austenitic stainless steel in dynamic loading condition, the fracture behaviours with the effect of the local distribution of SIMT in the bending deformation using a relatively small specimen need to be investigated. The effect of SIMT as well as thermal softening phenomenon at a high deformation rate has been examined insufficiently and mechanism for rate-sensitivity of fracture-mechanical characteristic is still unclear. In present study, experiment and FE simulations are performed for the SP test at different deflection rates for type-304 austenitic stainless steel. In order to describe the damage and fracture process of materials, a modified version of the Johnson–Cook damage model is applied. After confirming the validity of computation, the rate-sensitivity of fracture-mechanical characteristics of the steel is examined at room temperature. In addition, the effects of temperature and SIMT on the force-deflection curve and fracture properties are discussed to clarify the mechanism for an improvement of impact fracture-mechanical characteristics of the steel. [ABSTRACT FROM AUTHOR]

A punching shear strength mechanical model for RC flat slabs with and without shear reinforcement, based on a beam shear model previously developed by the authors, is presented. The differences in resisting actions between beam shear and punching shear have been identified and incorporated into the governing equations and failure modes, resulting in simple but accurate punching design equations. The model consistently explains and quantifies some experimentally observed phenomena, such as the higher contribution of the concrete to the punching shear strength of slabs than in the case of beams subjected to shear, mainly due to the multi-axial state of stresses that takes place near the support. Furthermore, the model provides physical meaning to some parameters used in the design, such as the position of the critical perimeter or the effective stress of the punching reinforcement, among others. Very good agreement has been obtained between the model predictions and the results of 560 punching tests of concentrically loaded slabs, with and without shear reinforcement, included in two available large databases. The mechanical character of the model allows its extension to post-tensioned flat slabs, border or corner columns, steel fiber and FRP reinforced concrete slabs or different strengthening systems in a consistent way. [ABSTRACT FROM AUTHOR]

In this study, the feasibility of sound signal for monitoring the micro-piercing process is investigated. The effect of piercing parameters, i.e., sheet material, sheet thickness, and clearance to the power spectrum of emitted sound, is observed. The potential of sound in detecting the abnormal condition is also examined. The results show that the cutting process with different sheet material, sheet thickness, and clearance consistently shows a larger respond in similar frequency range, i.e., 3 to 4 kHz. In this region, the effect of variation of punch force history due to the different parameters is noticeable. A higher amplitude is noticed for piercing with a higher strength of sheet material, greater thickness, and greater clearance. During the experiments which are conducted until the breakage of punch, the fluctuation of signal power in this frequency range is the most salient. Before the punch breakage, the signal power of all the observed frequency ranges increases, but the increment in frequency 3 to 4 kHz is the most significant. The results show that the trend of signal power in this frequency range may reveal the trend of the process. The trend of the power in this frequency is in accordance with the trend of punch force and the growth of burr formation. These results evidence the correlation between the sound signal emitted by the piercing process and the tool condition. It can be concluded that the sound signal is potential for monitoring the micro-piercing process. [ABSTRACT FROM AUTHOR]

Laser-accelerated metallic flyers can be used in microscale manufacturing processes by providing high-speed impact and shockwave to target materials. This study conducted microscale punching experiments using a laser-accelerated flyer for various mold sizes, workpiece thicknesses, and flyer thicknesses to investigate performance and failure characteristics of the punching process. In the case of a single flyer impact, punching was successful when the ratio of mold diameter to workpiece thickness exceeded 3. High-speed punching advantages, which improve punching quality as the shear zone increases and burrs become smaller, were validated. When flyer thickness was significantly reduced, punching performance deteriorated although higher speed could be realized, because the thinner flyer was difficult to maintain flatness during acceleration, resulting in inefficient forming pressure transfer to the workpiece. When the ratio of mold diameter to workpiece thickness was less than 3, punching was achieved through multiple flyer impacts. However, pressure transfer efficiency from the flyer to the workpiece was further reduced. Thus, punching performance could be improved by reducing the relative size of the flyer to the mold diameter. [ABSTRACT FROM AUTHOR]

The frictional receding contact problem for two graded layers pressed by a rigid punch is considered in this paper. The punch is subjected to both normal and tangential loads thereby resulting in frictional contact with the upper layer. It is also assumed that the contact between the layers is frictional and the lower layer is fixed. It is further assumed that the gradation in the layers follows an exponential variation through the thickness with different profiles while Poissons ratios are taken as constants. Using standard Fourier transform, the contact problem is converted to a system of two singular integral equations in which the contact pressures and the contact widths are the unknowns. The integral equations are then solved numerically using Gauss–Jacobi integration formula. The Finite Element Method was additionally employed and both exponential and power law material gradation is used to solve the investigated problem and the obtained numerical and analytical results are in good agreement. The primary intention of this paper is to investigate the effect of material gradation, friction coefficients, layers thicknesses and material property mismatch at the interface between the layers on the contact pressures and contact widths. [ABSTRACT FROM AUTHOR]

Punching strengthening of reinforced-concrete slabs using a bonded reinforced-concrete overlay (BRCO) is an efficient alternative to traditional strengthening systems such as post-installed shear reinforcement, enlargement of the support column, or bonded fibre-reinforced polymer strips. The BRCO technique allows for both the flexural stiffness and shear strength of existing slabs to be increased. Shear strength increases due to the greater slab thickness, while an increase in flexural stiffness is also provided by the added reinforcement. Particular attention must be paid to the interface between the existing slab and the BRCO, because performance gains can only be achieved if the existing slab and the new concrete layer work monolithically. Interface performance can be improved through surface preparation and mechanical connectors; the latter is recommended to avoid premature debonding failure. This paper presents an ad hoc design approach for flat slabs strengthened with BRCO based on the critical shear crack theory, which accounts for slab rotation after strengthening. This is a fundamental parameter to assess the punching capacity of the strengthened slab. The efficiency of the proposed method is confirmed by the agreement between analytical results and experimental data collected during an experimental campaign carried out at the Universidade Nova de Lisboa. [ABSTRACT FROM AUTHOR]

Limited research work exists on assessment of punching shear of reinforced concrete (RC) flat slabs made with blended cement incorporating ground-granulated blast-furnace slag (GGBS). This research is aimed at analyzing the punching shear strength of RC flat slabs cast from blended cement having GGBS in different proportions as partial replacement of cement. Four flat slabs supported on the ends were tested under column load such that one flat slab was cast from normal concrete with no GGBS and the remaining three flat slabs were cast with 30, 40, and 50% replacement of cement by GGBS. Experimental punching shear, midspan deflections, strain in the steel bars, and cracking pattern of the slabs were determined. The results of punching shear of flat slabs from the tests were compared with the nominal punching shear capacities proposed by BS 8110, BS EN1992-1-1/EC2, and ACI 318. The provisions of these building codes for the punching shear were observed as safe and conservative for the RC flat slab made from blended cement incorporating GGBS. [ABSTRACT FROM AUTHOR]

This paper presents findings from a study on punching shear capacity of high‐performance concrete slabs reinforced with macrobasalt fibers. The punching shear failure is simulated through a simple method introduced by Hassan et al. The test specimens comprised 14 small‐scale slabs with circular notches. To investigate the effect of fiber content, 5 different fiber volume fractions of 43 mm macrobasalt fibers have been studied. The results show that the punching shear capacity and the ductility of the slabs were slightly improved with increasing the fiber content. Furthermore, the results also indicate that the outcome of the experimental method is valid when the rotation of the slabs is negligible. [ABSTRACT FROM AUTHOR]

Fracture resistance of concrete column-slab connections, with low reinforcement ratios and strengthened by carbon fibre reinforced polymer (CFRP) plates, is often governed by debonding failure modes. In this paper, a three-dimensional finite element model is conducted to predict the punching behaviour of concrete column-slab connections which incorporate bonded non-prestressed and prestressed CFRP plates to the tension surface of the slab. The adopted interfacial behaviour, between the FRP materials and concrete, takes into account the effect of mixed mode behaviour on the displacement fields at the critical diagonal cracks (CDC). Results are then presented in terms of the ultimate load capacities, load-strain relationships in the FRP and internal steel reinforcement, load-interfacial stress relationships, and stress distributions in the FRP reinforcement. It can be stated that by adopting the mixed mode behaviour at the interface between the fibres and concrete, the onset of debonding is effectively captured by the FE analysis, which is very difficult in a laboratory test. [ABSTRACT FROM AUTHOR]

Uniaxial stress–strain relations of ductile materials are the most fundamental requirement for the design and safety assessment of structures. In this paper, a novel small punch testing (SPT)-related stress–strain relation (SPT-SR) model is proposed to predict the stress–strain relations of materials on the basis of equivalent energy principle. To examine the validity of the model, numerical simulations by finite element analysis (FEA) with a series of hypothetical materials with different Hollomon's material parameters were carried out. The results demonstrate that the uniaxial stress–strain relations predicted by SPT-SR model from simulated load-displacement curves are in good agreement with the properties of hypothetical materials used in FEA. Furthermore, SPT experiments and tensile tests for four steels (P92, DP600, Q345B, A508-III) at room temperature and 300   °C were conducted. The stress–strain relations predicted by SPT-SR model agree well with the tensile results generated from finite-element-analysis aided testing (FAT) method. Compared with the tensile strengths obtained by uniaxial tensile tests, they can also be well determined based on the strength coefficient and strain hardening exponent predicted by SPT-SR model. [ABSTRACT FROM AUTHOR]

The most common failure criterion in sheet metal forming operations is the forming limit diagram (FLD). Typically, the FLD is evaluated with the Nakajima test, which is a stretch forming-based test that allows the analysis of stretching under different stress conditions. The results of the Nakajima tests are considered ideally achieved under linear strain path deformation. However, due to the hemispherical form of the punch, the induced strain path starts in biaxial condition and switches to a linear path after the first contact between punch and specimen. In addition, the strain distribution is evaluated on the outer surface of the specimen. Consequently, the results are affected by a non-linear strain path and a bending component due to the sheet thickness and punch diameter. These effects have a consequence on the FLD, and thus it is not directly comparable with the ideal FLD that is analytically evaluated since the analytical models in the literature do not consider the process effects like bending and the biaxial pre-straining. In this paper, a study of biaxial pre-straining and bending effects is observed for different stress conditions and materials. The investigation of the bending will be considered under the experimental and numerical aspect. Nakajima tests are conducted with different punch diameters to discover the effects of different material thickness to punch radius ratios. The results are also compared with the outcomes of a numerical model, used for the analysis of the strains on the outer, middle and inner layers. The biaxial pre-stretching is analysed by comparing the outcomes of the FLD achieved by the Nakajima punch with the results of the Marciniak test. In this paper, an efficient method based on the correlation coefficient for the evaluation of pre-straining is presented. The biaxial pre-stretching will be compared to the strain paths and the tendencies will be analyzed. Finally, considerations about the phenomenology of the effects in dependency of the material classes are given. [ABSTRACT FROM AUTHOR]

Conventional punches used in tube hydroforming (THF) are hollow to facilitate supply of pressurized fluid to the die cavity. The fabrication of hollow micro-punches for micro-THF which can sustain punch loads presents a challenge. This study proposes different types of micro punch designs that can be used in conjunction with floating based micro-tube hydroforming (THF) die set-up. Finite element analysis was carried out to determine the feasibility of the proposed punch design variants followed by Micro-THF experiments. The experiments were carried out to hydroform Y, T, and bulge shaped parts from SS 304 1 mm and 2 mm tubular blanks. The study has demonstrated that notched punches can effectively be used in micro-THF. The major benefit of using notched punches is that, longer micro-punches with the desired strength can be fabricated with ease using electrical discharge machining (EDM). [ABSTRACT FROM AUTHOR]

Obtaining square cups with the radius at the bottom corner lower than the thickness of original plate via a single-step hot forming process is a challenge. In this paper, a processing way was proposed by combining local-thickened plate and friction control, to manufacture square cups with small corner radii. Through finite element (FE) simulations, the metal flow during hot forming of square cups was optimized by varying the shape of the local thickened section and adjusting the friction conditions at the interfaces between blank and tools. It was found that the filling ratio of the bottom corner can be significantly improved by increasing the friction coefficient at the interfaces between the blank and the upper punch, and that between the blank and the central zone of counter punch. The established flow dividing surface (FDS) model is capable for describing the variation of metal flow with the friction coefficients. Base on the simulation results, hot forming experiments were also carried out, and square cups with small radii of 2 mm at the bottom corners were successfully manufactured. [ABSTRACT FROM AUTHOR]

During the punching process of high strength lightweight materials such as 2024T4 aluminum alloy, the severe die wear and edge fracture of the punched part are one of the main concerns of manufacturing industries and the scientific community. Researches have found that the electric current can reduce the metals’ flow stress, improve their ductility, and promote the dislocation annihilation below the annealing temperature. Therefore, the electric current was proposed to help improve the punching process of 2024T4 aluminum alloy sheet in this paper. The experiments of electropulsing assisted punching (EAP) were carried out by applying different values of electric current on the specimens at different punching phases. For convenience to compare the punching results, the punching load, the surface quality of the punched profile and edge strain hardening (ESH) were analyzed under different electropulsing ways. In addition, the uniaxial tensile tests of punched parts were carried out to evaluate the influence of electropulsing on the ultimate tensile load of punched specimen with a hole. The results show that the electropulsing has a significant effect on reducing the punching load and improving the surface quality of the punched profile. Moreover, the anisotropy of material and the ESH of the punched edge, which are characterized by the level or distribution of microhardness, are eliminated partially due to the electropulsing induced annealing effect. The ultimate tensile load has been effectively enhanced by electropulsing, which may stem from the fact that elimination of ESH and the healing and arrest of microcracks and microvoids near punched edge. [ABSTRACT FROM AUTHOR]

Punching is an efficient and economical process for producing a hole in structures for functional requirements, repair, maintenance, and so forth. Toward extending the use of punching to new materials, the punching of multilayer CFRP laminates and CFRP/metal hybrid composites was investigated. In this paper, the effect of the unidirectional (UD) prepreg size on the shear behavior of pseudo-ductile CFRP laminates and CFRP/metal hybrid composites is discussed on the basis of experimental observations. CFRP laminates were individually fabricated using standard (149 g/m 2 ) and thin-ply (62 g/m 2 ) prepregs, and were bonded with three metals (aluminum alloy A6061, magnesium alloy AZ31, and advanced high-strength steel SPFC980) by utilizing an autoclave (co-curing) and adhesive glue for hybrid composite application, then punched by a circular die and punch tool at room temperature. The effects of the UD prepreg size on the punch force, punching resistance (Ks) , quality, and sheared surfaces of the through-holes are discussed. The shear behavior for punching in different composites was also studied by microscopic examination. Our results are expected to enable quantitative design for the development of punched CFRP laminates and CFRP/metal hybrid composites. [ABSTRACT FROM AUTHOR]

In an attempt to investigate the effects of punching process on crystal orientations, magnetic and mechanical properties in non-oriented silicon steel, the steel sheet was punched for circular shape of Φ40 mm. The crystal orientations and small-angle grain boundaries were characterized by electron backscatter diffraction (EBSD). The results indicated that the initial crystal orientations within a distance of 200 μm away from the sheared edge were significantly changed after the punching process. In this area, the fractions of the directions with a high value of magnetocrystalline anisotropy energy E a , 〈1 1 1〉, 〈2 1 2〉 and 〈1 1 2〉 can reach up to 0.619. However, the fractions of the directions 〈0 0 1〉 and 〈1 1 3〉 accounts for only 0.096, which have a lower value of E a . Moreover, the fraction of small-angle grain boundaries markedly increased in the area of about 200 μm from the sheared edge, which is mainly attributed to the dislocations multiplication and dislocations motion. The magnetic domain structures were characterized by an optical microscope according to the Bitter method. The results showed that the width of magnetic domain in the sheared edge was much larger than that in the center and the patterns also existed a big difference. The Vickers HV 0.1 method was employed to measure the microhardness of the sheared edge. It was found that the values of microhardness within a distance of 400 μm away from the sheared edge decreased from 259 to 167 due to the effect of work hardening, which is mainly caused by the dislocations pile-ups near the grain boundaries. [ABSTRACT FROM AUTHOR]

This article aims at modeling the WIM sensor electrical behavior to provide a better understanding of the mechanical and electrical proprieties of piezoelectric sensors. The model is considered in the frequency domain, supposing any sinusoidal solicitation with constant frequency or any other type of solicitation. Tests, having real WIM sensors placed on the pavement of a test track at IFSTTAR/Nantes was used to verify the nature of the electro-mechanical (EM) behavior of the real sensors over punching, flexural and extension effects. Also, two different pavement numerical simulations deliver the mechanical response using linear elasticity and viscoelastic proprieties. The output of these two simulations are compared with two WIM signals obtained at same load and speed at two different temperature conditions. [ABSTRACT FROM AUTHOR]

The die roll of fine-blanking parts is an important indicator when evaluating quality of parts. In this paper, the formation of die roll during the punching process is analyzed through the difference of the velocity of material between the die roll area and center area. At first, an assumption is made that every die roll is determined by the volume proportion of the part and waste area in the circular affected zone, and it is proved by simulation. In addition, the introduction of insertion block can prevent the fracture on the shearing surface without V-ring. In consideration of waste affect area and insertion block, a novel combined method is designed to decrease the die roll. It turns out that the height of die roll can be reduced by as much as 70% in both FEM simulation and actual experiment, which shows a great potential in fine-blanking industry. [ABSTRACT FROM AUTHOR]

Punching is one of the most important phenomena to be considered during the design of reinforced concrete flat slabs. Three main factors affect the punching behavior. These factors are concrete compressive strength, horizontal flexural reinforcement, and vertical shear reinforcement in the form of stirrups, studs or other forms. This paper is part of an ongoing research program conducted at the concrete laboratory of the Faulty of Engineering, Cairo University to assess the contribution of horizontal flexural reinforcement and vertical shear reinforcement on the punching behavior of reinforced concrete flat slabs. In the current research, seven half scale specimens are cast and tested. The specimens had dimensions of 1050 × 1050 mm and a total thickness of 100 mm. All specimens were connected to a square column of dimensions 150 × 150 mm and loaded at the four corners with a span 950 mm. The parameters considered in this research included spacing between vertical stirrups, width of the stirrups, number of stirrups branches and the ratio of the horizontal flexural reinforcement. During testing, ultimate capacity, steel strain, cracking pattern and deformation were recorded. The experimental results were analyzed and compared against values estimated from different international design codes. [ABSTRACT FROM AUTHOR]

Punching shear resistance of column footings and foundation slabs varies significantly in different standards. The reason for this is because standards define differently the position of the critical perimeter in which the punching shear resistance should be determined, and quantify the influences of the main parameters like effective depth, shear slenderness, compressive strength of concrete, longitudinal reinforcement ratio and tension yield stress of reinforcement in different ways. In order to quantify the level of safety in Eurocode 2 and in fib MC 2010, their design results are compared with the test results of the series of footings tested in completely realistic boundary conditions in terms of the subgrade soil. Besides the performed tests results, the analysis of the other investigations of the footing punching rested on the real soil is also included. Thus was obtained the answer to the question how individual characteristics of the footings and of the soil affect the punching bearing resistance and how accurately Eurocode 2 and fib MC 2010 predict the bearing capacity of the tested column footings. At the end, based on the test results and on the tests of others, and on and performed numerical analyses, a possible modification of Eurocode 2 in the field of reinforced concrete footing was proposed. [ABSTRACT FROM AUTHOR]

The article evaluates durability of punches and cutting tools when cutting of the cut-outs. Durability of punches made of the same material without coating, with the TiCN-MP coating and with the TiN coating is compared. Durability is evaluated by the tolerance of the cut-outs. Border durability, which requires grinding of the tool, is a determined durability, at which the deviation of the tolerance of a cut-out is at the lowest border. By comparing the dependency of change of the holes' dimensions on the number of strokes in the case of all three types of punches, it can be stated that the durability increased by 10-12 times in the case of the tools with coatings. [ABSTRACT FROM AUTHOR]

In this study, a new method of backward extrusion through rotating die and open punch, named rotating backward extrusion (RBE), is proposed. In this new process, a torque is imposed on the die that drives billet rotating. The rotating billet was backward extruded with the use of the punch with end face groove. To investigate the capability of this process, the experiment and finite element (FE) analysis were carried out for AZ80 magnesium alloy used as experimental material. The effects of rotating speed on the effective strain and process load were analyzed. The effective strain of the final part and process load were compared for cup extrusion by both the conventional and the new process respectively. The results showed that the average effective strain through the processed sample was approximately higher in 3 times the value of the sample processed via the conventional backward extrusion. The reduction of process load is about 20% in maximum in comparison with the conventional backward extrusion process. This new process has proven to be promising for the hollow parts production because of lower process force and imposing higher effective strain. The potential for grain refinement and mechanical properties improvement are required to fully evaluate for the new process. [ABSTRACT FROM AUTHOR]

In this study, various reinforcement and strengthening details for the improvement of the punching-shear behavior of concrete footings were developed. Eight test specimens of reinforced-concrete (RC) footings were constructed and tested to investigate the punching-shear behavior of the concrete footings with the developed details. The test parameters include the additional placement of a longitudinal reinforcement around the column-footing connections, the inclination of the shear reinforcement, an additional cast of high-strength concrete, and an additional concrete cast with amorphous metallic fibers (AMFs). The test specimens were supported on a bed of steel car springs that simulate the elastic behavior of soil. The test results show that the punching strength was significantly enhanced by the additional placement of the longitudinal reinforcement around the column-footing connections and by the addition of the retrofit materials (high-strength concrete and AMF-reinforced concrete). Contrarily, the shear reinforcement that was placed around the connections did not significantly affect the punching-shear strength of the footings. The test results were also compared with strength predictions for which the current design codes and the existing theoretical models were used. [ABSTRACT FROM AUTHOR]

This article deals with the interactions between a central crack and a pair of outer cracks situated at the interface of an orthotropic elastic half-plane bonded to a dissimilar orthotropic layer with a punch. The problem is reduced to the solution of three simultaneous singular integral equations that are finally solved using Jacobi polynomials. The phenomena of crack shielding and crack amplification have been depicted through graphs for different particular cases. [ABSTRACT FROM AUTHOR]

Assembly for a structural material such as a composite panel cannot be avoided. Typically, composite panels are assembled using a fastener through a drilled hole. The main problem of drilling is delamination, which affects the strength of the assembly. In addition, the cost of drilling is high because of repeated regrinding of the drill bit. The main goal of this research is to develop a new method as an alternative to drilling hole preparation. In this study, a new simpler method to determine delamination is based on the profile measurement technique. The 2D profile of the punched hole obtained through the focus variation technique is utilized to determine the delamination. A comparison to the developed measurement method shows a good agreement. [ABSTRACT FROM AUTHOR]

Laser drilling has swiftly become an economical and well-regulated substitute to conventional hole drilling methods such as wire EDM, punching, broaching, or other prevalent destructive processes, because of cleanliness, accurate results, precise holes, fast material removal rate, and possibility to make holes. Prompt expansion of laser technology in current years gave us facility to regulate laser input factors such as lamp current, pulse frequency, air pressure, and pulse width. The dimensional accuracy and quality of holes are very important for some specific applications of holes. Circularity of drilled hole at entry and exit, and taper are very important attributes which influence the quality of a drilled hole in laser drilling. For this reason, the experimentation based on central composite design is carried out on austenitic stainless steel for examining the effect of laser parameters, i.e., lamp current, pulse frequency, gas pressure, and pulse width, on the quality of drilled holes. A total of 31 experiments were carried out. Later, the models were predicted for output responses using response surface methodology and then tested for adequacy. It is found that the response surface methodology (RSM) predicted models are in close agreement with the experimental values. Hence, the models may be further used for optimization of process parameters using evolutionary algorithms. [ABSTRACT FROM AUTHOR]

Punching shear is a possible type of failure that occurs in reinforced concrete flat slabs, which can develop with an ultimate load below flexural capacity. Several researchers have studied the punching resistance of flat slabs over recent years. Although they have made great advances, there are codes that show different approaches to a singular design. Some codes show that there exist contradictions, even in the simplest situations, such as concentric loads. Most codes prescribe empirical expressions based in a theoretical model to analyze punching strength, but for flat slabs with holes around the column and shear reinforcement there are divergences between codes, justifying research in this area. This paper presents an experimental analysis of nine square reinforced concrete flat slabs under concentric loading (width: 1800 mm; thickness: 130 mm). The main variables used in the tests were: a) two square openings (150 mm) adjacent to the smallest side of the column and b) the use of shear reinforcement containing 3 layers, with 6 or 8 elements in each layer and radially distributed around the column. The research concludes that openings adjacent to the column affect punching shear strength, while the correct use of the shear reinforcement can minimize and even compensate this loss. [ABSTRACT FROM AUTHOR]

In this study, a comprehensive 3D non-linear finite element modelling procedure is presented for the simulation of reinforced concrete flat plates, retrofitted with externally bonded carbon fibre-reinforced polymer (CFRP) strips and subjected to punching shear loads. The presented modelling procedure may be used to conduct parametric numerical analyses on the response of reinforced concrete elements similar to considered in this study. The modelling procedure is applied on: (i) a solid, un-retrofitted flat plate and (ii) eight flat plates with openings and retrofitted with externally bonded CFRP strips. In the procedure, debonding of CFRP strips from concrete surfaces is accounted for by defining appropriate bilinear shear stress–slip and normal stress–gap relationships. In the model, the corner lift-offs observed at the corners of the flat plates are also considered by defining appropriate restrains and frictional support conditions. Results obtained from the proposed modelling procedure are verified using experimental data available in the literature. From the verification, accuracy of the proposed modelling procedure is confirmed in terms of structural responses such as load displacement relationships and crack propagations of the test specimens. [ABSTRACT FROM PUBLISHER]

Three-dimensional (3-D) finite element analysis (FEA) in ABAQUS software examines the punching shear behaviour of reinforced concrete slabs. Four interior reinforced concrete slab-column connections (one slab is without shear reinforcement, while the other slabs are with shear bolts) previously tested under static loading are analysed. The shear reinforced slabs differ in the amount of the shear bolts. The coupled plasticity damaged model previously calibrated is considered for modelling the concrete. In this paper, parametric studies are presented to examine the effect of the amount and placement of the shear bolts. The amount of shear bolts is increased by adding more rows of shear bolts and also decreased by considering less shear bolts in each row. Also, two different arrangements are studied: rectangular and radial. The adopted FEA model is used to analyse and investigate the failure modes, loads and the crack patterns of the slab-column connections. The numerical results are compared to two current design codes for punching shear (ACI 318-14 and EC2-2004). [ABSTRACT FROM AUTHOR]

In this work, a micro punching equipment was designed and assembled for punching components with micro hole array. Micro hole array in 800 μm scale was punched successfully on blanked parts using this equipment. Punch experiments under different punch conditions were conducted to explore the effect laws of cavity depth, punch force and punch speed on punching process and quality of punched holes. To improve the process performance of the developed equipment, an ultrasonic vibration module was designed and assembled to the existing system based on its function of softening materials, the equipment's process parameter scope such as cavity depth was optimized then. The results in this work proved the practicability of the developed micro punching equipment for punching components with micro hole array, the influence mechanism of punching conditions on punching process, and the optimization function of ultrasonic vibration on micro punching process, which could be useful in improving machining efficiency and cost of punch fabrication. [ABSTRACT FROM AUTHOR]