Results Of Coupon Tests Research Articles

High-Strength Cold-Formed Steel Stiffened Channel Section: Axial Compressive Strength and Initial Geometric Imperfections

This paper presents a summary of experimental findings from axial compression tests on columns featuring a cold-formed lipped channel section with intermediate stiffeners and return lips, roll-formed from high-strength low-allow steel with a nominal yield strength of 690 MPa (100 ksi). Additionally, the paper provides an analysis of the elastic stability of the studied section, a complete description of the initial geometric imperfections of the tested columns, results of tensile coupon tests, and comparison of the observed strengths of the columns with design predictions. The results provide important additional benchmarks for the wider adoption of high-strength cold-formed steel sections and indicate conditions where existing design methods may be reliably extended.

Calibration of ductile and shear damage models for carbon and stainless steel shear studs

AbstractSteel‐concrete composite beams are commonly used in bridge construction. The corrosion of the supporting steel beams and the shear connectors are however known as a major cause of premature deterioration of composite bridges. Stainless steel beams and shear connectors offer a viable alternative solution to the steel corrosion problem in composite bridges located in harsh environmental conditions. This paper presents experimental and numerical investigations of the tensile and shear behaviour of stainless steel welded shear connectors. The results of tensile coupon and double shear tests on stainless steel and carbon steel shear connectors to characterise the tensile and shear response are reported. Numerical modelling is carried out using the ABAQUS finite element software to develop calibrated ductile damage and shear damage fracture models for stainless steel shear connectors. The development and validation of the numerical models together with the calibration of the fracture models are presented and comparisons are made with those of carbon steel shear connectors.

Lightweight Components Manufactured with In-Production Composite Scraps: Mechanical Properties and Application Perspectives

<div class="section abstract"><div class="htmlview paragraph">In the last years, the design in the automotive sector is mainly led by emission reduction and circular economy. To satisfy the first perspective, composites materials are being increasingly used to produce lightweight structural and semi-structural components. However, the automotive mass production arises the problem of the end-of-life disposal of the vehicle and the reduction of the wastes environmental impact. The circular economy of the composite materials has therefore become a challenge of primary importance for car manufacturers and tier 1 suppliers. It is necessary to pursue a different economic model, combining traditional raw materials with the intensive use of materials from recycling processes. New technologies are being studied and developed concerning the reuse of in-line production scraps with out-of-autoclave process that makes them desirable for high production rate applications.</div><div class="htmlview paragraph">In this frame, a methodology for the reuse of prepreg cutouts coming from in-line ply cutting process is proposed. Production cutouts (scraps, or chops) are used as a charge to manufacture components through the compression molding process. The structure of the final part keeps in meso-scale the same orthotropic orientation of the chops, although it is quasi-isotropic from a macroscopic point of view. Accordingly, standard three-point bending, and tensile mechanical tests were performed to characterize the mechanical behavior of the material.</div><div class="htmlview paragraph">Failure modes and fracture propagation were analyzed too. The chop interface resulted to affect the mechanical performance. Before material failure, multiple damage precursor sites nucleated, generally in correspondence of the chop interfaces. Delamination, brittle fracture of the matrix and debonding between the chops were the main failure modes. The results of the standard coupon tests evidenced good performance of the material in terms of strength and stiffness, despite lower than standard 2x2 twill structure, making the studied material suitable for semi-structural purposes. Accordingly, a prototype of an accelerator pedal frame was produced, in order to evaluate the feasibility, the potential limitations and the aspects to be optimized for the manufacturing of a more complex component.</div></div>

Analysis of fracture behavior of high-strength steels in tension after fire exposure

High-strength steels have been widely applied in high-rise and long-span structures. Exposure to high temperatures due to fire may lead to reduction in material properties and fracture behavior of high-strength steels, greatly affecting the post-fire behavior of high-strength steel structures. This paper investigates the post-fire fracture behavior of high-strength steels in tension to pave the way for safety assessment of high-strength steel structures after fire. The fracture models of Chinese high-strength steels (Q460, Q550, Q690, Q890) and European high-strength steels (S460, S690 and S960) are calibrated and validated against limited experimental results of tensile coupon tests in an exposure temperature range of 200 °C to 1000 °C. The effect of air-cooling and water-cooling methods on the post-fire fracture behavior of high-strength steels is investigated. The fracture behavior is represented by the post-necking true stress-strain curve, toughness index (resistance to fracture initiation) in the stress modified critical strain model (SMCS) and damage evolution law. It is found that different types of high-strength steels with similar yield strength may exhibit quite different fracture behavior after exposure to high temperatures. The maximum exposure temperature and cooling method are two critical factors influencing the post-fire fracture behavior of high-strength steels. The true stress-strain curves after onset of necking can be simply expressed by a straight line with a slope, which becomes temperature dependent when the exposed temperature exceeding a critical level (e.g. 600 °C). The toughness index in SMCS model is subjected to great reduction in a temperature range of 800 °C to 900 °C for Q460-Q890 steels and 750 °C to 900 °C for S460-S960 steels. The most rapid evolution of damage occurs after being exposed to temperatures in a range of 650 °C to 900 °C. Compared to air-cooling method, the water-cooling method may lead to great reduction in the slope of post-necking true stress-strain curves (by 50%), significant reduction in toughness index (by 80%), and even change of fracture mode from ductile fracture to brittle fracture. It is recommended to choose reasonable and appropriate post-fire material properties for fracture prediction of different high-strength steels.

Damage in CFRP composites subjected to simulated lighting strikes - Assessment of thermal and mechanical responses

Damage is inflicted upon Carbon Fiber Reinforced Polymer (CFRP) composite laminates using simulated lightning strikes to investigate the resulting residual mechanical properties. Seven different CFRP laminate specimens were exposed to simulated lightning strikes using three different electric waveforms. The three waveforms imposed were the 10/350 μs waveform, which simulates the first return stroke during a direct strike according to IEC 61400–24 Ed1.0. The second was a unipolar long stroke component, and the third was a combination of the first return stroke and the long stroke. After exposure to lightning, coupon specimens were prepared for mechanical testing. The test specimens were subsequently subjected to compression and shear loading to determine the post-strike mechanical properties. The compression tests were conducted using uniaxial coupons in accordance with ASTM standard D6641. The shear tests were conducted using V-notch specimens utilizing an Iosipescu test rig in accordance with ASTM standard D5379. Digital Image Correlation was used to capture the strain fields on the surface of the specimens. The results of the material coupon tests are compared with test results from pristine CFRP coupon samples that were not exposed to any electrical current. The shear and compression strengths, compressive and shear stress-strain curves, compressive and shear moduli, and the maximum temperature on the CFRP specimens during lightning tests are presented and discussed. Key results include that the largest reduction of strength occurred in the specimens that were subjected to the largest current and specific energy. The specific energy correlated more closely to the observed reduction of residual strength than the charge, and the damaged specimens displayed a higher degree of nonlinear stress-strain behavior than the pristine specimens.

Effects of fibre orientation and layup on the mechanical properties of the pultruded glass fibre reinforced polymer tubes

Pultruded glass fibre reinforced polymer (PFRP) tubes are becoming popular in civil engineering applications due to their unique features. The focus of this paper is on column applications. It addresses the understanding of the correlation between the mechanical properties of PFRP tubes and their material constituents. The burnout, tensile, compressive and shear tests were undertaken for square and circular PFRP tubes. Full scale compressive test was also conducted to compare the axial behaviour of pultruded FRP tubes. Moreover, a finite element analysis was carried out to simulate the compressive behaviour of full-scale specimens and to predict the axial behaviour of FRP columns of different length-to lateral dimension ratios. The results of compressive coupon tests are compared with those of full-scale tests which are used to check the accuracy of finite element simulation in terms of load-deflection curves, load capacity and failure mode. Results show that the strength and modulus depend on the fibre orientation and percentage of fibres in the axial direction. It further states the behaviour of full scale specimen is linear up to failure and the post peak behaviour of square tubes is affected by the continuity of non-axial fibre layers at corners. The numerical study reveals that the compressive behaviour of FRP tubes can be predicted reasonably.

The effect of manufacturing process on the post-fire mechanical response of thin-walled ultra-high strength steel (Grade 1200) tubes

This study aims to investigate the effect of manufacturing process on the post-fire mechanical response of Grade 1200 ultra-high strength steel (UHSS) tubes. To this end, the post-fire mechanical properties of “direct-quenched” UHSS (UHSS-DQ) standard tensile coupons are compared to those made of “quenched and tempered” UHSS material (UHSS-QT) with similar original room temperature stress-strain responses. Thus, to compare the post-fire compression behaviour of UHSS-DQ tubular stub columns with those made of UHSS-QT material, a finite element (FE) model is developed in ABAQUS FE software with precise material properties extracted from the results of the post-fire tensile coupon tests. Quasi-static compression tests are then conducted on UHSS-QT tubular stub columns cooled from different fire temperatures to room temperature to validate the FE analysis. Using the results of the tensile coupon tests and the FE analysis on UHSS stub columns, it is shown that the manufacturing process substantially affects the mechanical properties of UHSS stub columns under cooling phase of a fire.

A comparative study on corrosion kinetic parameter estimation methods for the early stage corrosion of Q345B steel in 3.5wt% NaCl solution

Corrosion kinetic parameters play an important role in researchers’ ability to understand and predict corrosion behavior. The corrosion kinetic parameters of structural steel Q345B specimens immersed in 3.5wt% NaCl solution for 1–2 h were determined using linear polarization resistance (LPR), Tafel-curve multiparameter fitting, electrochemical impedance spectroscopy (EIS), and electrochemical frequency modulation (EFM) methods. The advantages and disadvantages of each method were investigated and discussed through comparative investigation. Meanwhile, the average corrosion rate was examined using traditional coupon tests. The results showed that the corrosion current density values estimated by EFM at a base frequency of 0.001 Hz and those obtained by Tafel-curve four-parameter fitting (TC4) are similar and consistent with the results of coupon tests. Because of their slight perturbation of the corrosion system, EIS and EFM/TC4 in collaborative application are the recommended techniques for determining the kinetics and the corresponding parameters for the homogeneous corrosion of the naked metal. In our study of the electrochemical kinetics, we obtained much more abundant and accurate electrochemical kinetic parameters through the combined use of different electrochemical methods.

High temperature full-scale tests performed on S500M steel grade beams

In recent publications, the results of coupon tests performed on high-strength steel (mainly S460M and S460N) have been presented. Some of these tests led to ratios between the coupon resistances at elevated temperatures and at room temperature lower than the Eurocode reduction factors. The authors of these publications have consequently questioned the validity of these factors for these steel grades, without referring to any full-scale fire tests.Two experimental full-scale fire tests have been performed at the University of Liege in order to assess the mechanical resistance of S500M steel grade at high temperatures. Two similar 4.4m-long steel beams have been respectively subjected to fast (standard ISO curve) and slow (fixed 5K/min heating rate) elevations of temperature under a constant mechanical loading. The tests have been successfully reproduced in subsequent finite element analyses using Eurocode 3 steel material law at elevated temperatures, in which a creep component is implicitly taken into account.

Simulation of ductile fracture in welded tubular connections using a simplified damage plasticity model considering the effect of stress triaxiality and Lode angle

In the experiment of the welded CHS–RHS X-joint, ductile fracture initiated on the chord near the saddle position along the brace-to-chord intersection which led to punching shear failure mode. The initiation and extension of the ductile fracture reduces the punching shear resistance of the remaining intact material. In order to estimate the accurate strength and the failure mode of tubular connections, this paper proposes a new fracture model by extending the existing damage-mechanics based models to predict the ductile fracture failure in tubular connections. The proposed model considers not only the effect of the stress triaxiality but also the effect of the Lode angle on the fracture strain, so as to make an enhanced estimation on the “shear fracture mode”. To facilitate its engineering application, this paper proposes a simplified method to calibrate the material parameters solely from experimental results of common coupon tests. Besides, to examine the engineering application of the proposed fracture model to other types of welded tubular connections, this paper applies the proposed fracture model in analyzing the fracture failure in a welded CHS-plate X-joint, and further two I-beam-to-tubular-column connections reported by previous researchers. The numerical simulation predicts accurately the actual failure sequence observed in the experiment.

Supersonic particle deposition as a means for enhancing the structural integrity of aircraft structures

The paper presents the results of experimental studies into the application of supersonic particle deposition (SPD) for repairing and enhancing the airworthiness and integrity of aging aircraft structures. Presented are the results of coupon tests on the application of SPD doublers to mechanically fastened joints and to simulated corrosion damage tested under constant amplitude fatigue loads. These successful tests are then supported by an application to an F/A-18 Hornet wing attachment centre barrel laboratory test article.

An enhanced method of predicting effective thickness of corroded steel plates

Many steel bridge infrastructures in the world are getting older, and a large number of these structures are in need of maintenance, rehabilitation or replacement. Most of them are subjected to corrosion due to exposure to aggressive environmental conditions and inadequate maintenance, causing reduction of their carrying capacities. In order to have an adequate bridge management, it is of paramount importance to develop an efficient, accurate and rapid condition assessment method which can be used to make reliable decisions affecting the cost and safety. Therefore, a simple and accurate method of calculating remaining yield and tensile strength by using a concept of representative effective thickness with correlation of initial thickness and maximum corroded depth is proposed in this study, based on the results of many tensile coupon tests of corroded plates obtained from a steel plate girder with severe corrosion, used for about 100 years. Furthermore, a strength reduction diagram which will be very useful for bridge inspection engineers to make rational decisions about the maintenance management of aged steel bridge infrastructures is presented.

Development of an Efficient Maintenance Strategy for Corroded Steel Bridge Infrastructures

The potential for structural capability degrading effects caused by corrosion is of profound importance and must be both fully understood and reflected in bridge inspection and maintenance programs. As the number of steel bridge infrastructures increases throughout the world, it is an exigent task to conduct regular and detailed corrosion surface investigations to evaluate their residual strength capacities and to develop analytical models to understand their current conditions and critical locations, as well as yield and ultimate behaviors. This paper presents a simple, accurate, and rapid assessment method and an effective maintenance management strategy developed by using the results of tensile coupon tests conducted on numerous corroded plates obtained from a steel plate girder used for about 100 years with severe corrosion and an finite element method (FEM) analytical approach proposed by measuring only the maximum corroded depth, which can be used to make reliable decisions affecting cost and safety.

Interlaminar Strength of CFRP Curved Beam with Different Toughened-Material Systems

Various toughened-material systems to reinforce interlaminar strength of CFRP have been proposed on the basis of the results of coupon tests. In this paper, an applicability of toughened-material systems to structural model such as curved beam subject to static bending was examined. Two kinds of CFRP with different toughened-material system were selected, and both microscopic observation and numerical FEM simulation using VCCT were performed for test results. A difference between coupon and structural model tests was found for the case of the curved beam with artificial anomaly, and the cause was considered due to the difference of delamination pass between coupon and curved beam tests. From a view point of numerical simulation for predicting the strength behavior of the curved beam, an adoption of different fracture toughness from that by coupon test was necessary.

Fatigue–Strength Surface: basis for structural analysis under dynamic loads

The relation between fatigue strength and number of load cycles to failure is usually represented by Wohler curves. The four-parametric Weibull function shows a good relation between the static and dynamic strength in the low- and high-cycle fatigue range for a constant stress ratio R (minimum stress/maximum stress) (see Jarosch and Stepan in Fatigue properties and test procedures of glass reinforced plastic rotorblades. American Helicopter Society, 25th Annual National Forum, Paper No. 370, 1969; Och in Fatigue strength, AGARDograph No. 292, helicopter fatigue design guide, 1983; Bansemir and Emmerling in Fatigue substantiation and damage tolerance evaluation of fiber composite helicopter components, applied vehicle technology panel: applications of damage tolerance principles for improved airworthiness of rotorcraft, Corfu, Greece, 1999). However, in addition to the number of load cycles to the failure, fatigue strength also depends on the stress ratio R as well. In predicting the lifetime of a component, a more proper way for the presentation of fatigue life test data is the Goodman approach. This often used method affords the user to predict lifetime at any stress ratio, but does not represent the real material behaviour fully. The Goodman diagram does not take into account the combined effect of low-cycle fatigue and high-cycle fatigue. One better way to build an accurate relation between the fatigue strength, number of load cycles to failure and the stress ratio is to add the third dimension. The result is a three-dimensional view of the fatigue strength as a function of number of load cycles to failure and stress ratio R. Hence, the mathematical description of the fatigue strength as a kind of a surface function depending on the number of load cycles to the failure and the stress ratio is of high interest and indeed the focus of this study. The surface function represents the real material behaviour in low-cycle fatigue range as well as in high-cycle fatigue range more accurate compared to basic Goodman approach. For the determination of the Fatigue–Strength Surface, a so-called F–S Surface, test points with different stress ratios are necessary. The surface function can be adapted to the test points using a nonlinear regression analysis based on least square method. Therefore, it is advisable to use either the three-dimensional Weibull function or a surface function which consists of Tschebyscheff Polynomials. To enhance the regular two-dimensional Weibull function to a three-dimensional model, the four Weibull parameters are described as functions of the stress ratio. This method can be used to analyse the material behaviour based on the results of coupon or component tests. In case of coupon tests, this method is applied and validated as described in the paper. Furthermore, the use of material F–S Surface is compared with Goodman approach. For this purpose, mean surfaces of coupon test specimens with a survival probability of 50% are used. Especially in high-cycle fatigue range and for the stress ratios greater than zero, Goodman approach shows a slight deviation from the actual fatigue strength. In order to consider such effects, lifetime calculations are performed in Eurocopter Deutschland GmbH by using the reduced, so-called working S–N curves which are based on component test results. It has been found that the F–S Surface tends to describe the real fatigue strength in a more accurate way. This may lead to a longer lifetime of components and the possibility to extend the margins of components. This paper is developed from the Diploma thesis “Prediction of the dynamic strength behaviour of structural elements based on S–N–R surfaces created by nonlinear regression analysis of experimental data” (see Weinert in Prediction of the dynamic strength behaviour of structural elements based on S–N–R-surfaces created by nonlinear regression analysis of experimental data Technische Universitat Dresden 2011).

Prediction of residual strength of corroded tensile steel plates

Recently, the damage due to deterioration of materials in many old steel bridge structures, which causes unavoidable strength reduction, is becoming a serious problem in Japan and all over the world. Therefore the remaining load-carrying capacities must be carefully evaluated in order to understand the feasibility of those steel structures for the current usage and to evaluate the necessity of retrofitting of selected corroded members to strengthen the existing structure. This paper proposes a new method to calculate the remaining yield and tensile strengths by using a concept of representative effective thickness (teff) with the correlation of initial thickness (t0) and the maximum corroded depth (tc,max), based on the results of many tensile coupon tests of actual corroded plates. Further, the feasibility of establishing of an analytical methodology to predict the residual strength capacities of a corroded steel member with fewer number of measuring points is also discussed.

A Basic Study of CFRP Laminates with Embedded Prestrained SMA Foils for Aircraft Structures

This paper presents some basic research results for the application of the smart materials and structural systems to aircraft structure. The authors conducted quasi-static load-unload tests and fatigue tests on several kinds of quasi-isotropic carbon fiber-reinforced plastic (CFRP) laminates with embedded prestrained shape memory alloy (SMA) foils. The damage behavior and the fatigue behavior were evaluated based on the effects of the recovery stress of SMA, and the relationship between the applied strain and the transverse crack density is discussed. It was found that the developed smart materials achieved a maximum improvement of 34% in the onset strain of the transverse cracks and a maximum improvement of 60% in the onset strain of delamination as compared with the standard CFRP laminates in the static condition. However, the fatigue properties of the smart material were not improved due to the material degradation of the 90°-ply at 80°C. The fatigue test by the multistep strain method using a structural element specimen was used to verify the results of coupon tests. The results indicate the possibility of using coupon data as a design database.

Characterizing Guardrail Steel for LS-DYNA3D Simulations

Finite-element models have three parts: geometry, connections, and material properties. As the visible parts of a model, geometry and connections are generally carefully considered. Material properties often are not chosen with the same degree of care although they are equally important to obtaining good results. Accurate simulations of vehicles striking roadside hardware require an understanding of both the material behavior and the mathematical material models in LS-DYNA3D. A method for comparing LS-DYNA3D simulations with typical ASTM materials tests is described. The behavior and modeling parameters of guardrail steel (AASHTO M-180 Class A Type II) are examined in this study. Experimental and simulation results of quasistatic coupon tests are compared for AASHTO M-180 Class A Type II guardrail steel, and parameters for guardrail steel are recommended.

Inelastic Buckling of Steel Plates

An experimental investigation on inelastic buckling of plates simulating simply supported webs and flanges was conducted. The test results are compared with values predicted using the results of standard tensile coupon tests and inelastic orthotropic material properties suggested by various investigators. A set of orthotropic material properties, derived semi-empirically as a result of this study and in good agreement with test results, is suggested. Agreement between predicted values of buckling loads and test results obtained in this investigation and from other researchers validates the use of these material properties for predicting inelastic plate buckling behavior.

Evaluating the potential for contaminating drinking water from the corrosion of tin‐antimony solder

This paper presents a theoretical analysis of antimony corrosion, tin corrosion, and galvanic coupling relationships. Results of coupon and field tests conducted to verify the theory are included. The theoretical and experimental results obtained in this study indicate that 95–5 tin‐antimony solder has a potential for replacing lead‐based solders in plumbing systems.