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Bauhaus Summer School in Forecast Engineering: From Past Design to Future Decision

22 August – 2 September 2016, Weimar, Germany

Fatigue of lean duplex welded details after post-weld treatments

COOLS Thomas, ROSSI Barbara

TC Construction, Department of Civil Engineering, KU Leuven

Abstract

Duplex stainless steel combines high mechanical properties and excellent corrosion resistance. In recent years, the application of lean duplex has progressed, the effective utilisation of which is however often limited by the fatigue strength of critical welded details. The fatigue resistance of duplex welded details was yet scarcely investigated. In this project, this topic will be studied through experimental investigations comprising the determination of fatigue strength of full penetration single V butt welds and T fillet welds. As-welded details and details submitted to post-weld treatments (PWT) will be studied. Last, one duplex longitudinal stringer welded to a cross girder will be studied under fatigue. A geometrically and materially non-linear finite element model, calibrated against this last test, will be used to calculate the structural stress at the weld toe position and to assess the load bearing capacity and fatigue behaviour, based on currently accepted design rules, to give directions for improvement.

Introduction

Recent years have witnessed an increasing interest in the use of stainless steels in a variety of contemporary architecture owing to their aesthetic appeal, favourable corrosion resistance and low maintenance costs, but also their excellent mechanical properties which allow more slender and lighter designs. Depending on the microstructure, four families of grades exist: martensitic, ferritic, austenitic and austeno-ferritic (duplex) grades. Duplex types, presenting a microstructure made of austenite and ferrite, share the properties of both families, and possess a higher mechanical strength. The lean duplex stainless steel (grades EN 1.4162/1.4062), included in the latest revisions of Eurocode 3 Part 1-4 (European Committee for Standardization (CEN) 2006) is characterized by a lower level of nickel and a higher level of nitrogen, which results in a significant cost reduction compared to other austenitic and standard duplex grades, but also a better price stability. It is further characterized by good weldability and can be welded by the same processes used for the other families, with restrictions in arc energy less tight due to the low alloy and high nitrogen content. That is why it is increasingly used in welded structures exposed to aggressive environments. Examples include bridges (Figure 1), offshore structures, truck sub-structures, wind towers, storage tanks and pressure applications (vessels, reactors, piping, heat exchangers,...). These applications also have in common that they are exposed to a complex range of variable loads.

Figure 1. Two examples of bridges using duplex 1.4162. Left: Likholefossen bridge (Norway);

Right: Solvesborg bridge (Sweden).

COOLS Thomas, ROSSI Barbara / FE 2016 2

Structures exposed to loading cycles are prone to fatigue, the effect of which is a paramount design aspect, especially if the joints are realized by welding. The fatigue verification of structures is a relatively recent requirement. It was first implemented in the ECCS recommendations for steel bridges (Nussbaumer et al.2010) and, while today a number of elaborate design codes for stainless steel exist in other domains like the ASME code for pressure applications (The American society of mechanical engineers (ASME) 2010), in civil engineering, studies have highlighted undue conservatism in their provisions. As an example, two former projects (RFSR-CT-2004-00040 2007) (Hechler et al. 2007) aimed at verifying the technical feasibility of welded bridge using duplex EN1.4462, provided tests results for a few joints underlying that the use of the in Eurocode 3 Part 1-4 (European Committee for Standardization (CEN) 2006), would lead to an uneconomic use of stainless steels in structures. Moreover, the design rules of EN 1993-1-9 (European Committee for Standardization (CEN) 2005b) are applicable to stainless steels if these materials comply with the toughness requirements of EN 1993-1-10 (European Committee for Standardization (CEN) 2005a), where, today, no data can be found about the stainless steel families. In EN 1993-1-4 (European Committee for Standardization (CEN) 2006), there is indeed no record of the fracture toughness of duplex while a number of specifications can be found elsewhere (The American society of mechanical engineers (ASME) 2010; Outokumpu 2013). In the literature, relevant information about the fracture toughness and the fatigue strength of stainless steels can be found but, overall, mostly austenitic grades have been studied. On the other hand, mechanical post-weld treatments (PWT) can provide enhanced fatigue resistance by improving the weld geometry and/or reducing the tensile residual stress. This is illustrated by the table 8.2 of EN 1993-1-9 where the fatigue resistance is given for welded built-up sections; as well as in the literature which abundantly reports the beneficial effects of PWT on high strength steel welded details. To allow for lean duplex to manifest its high material resistance, the use of PWT is promising. Nevertheless, the current scientific knowledge is still scarce and PWTs other than stress relief are today not covered in EN 1993-1-9. To conclude, it can be stated that the research on lean duplex welded details submitted to cyclic loading is today scarce. There is on the one hand a general confusion about the applicability of the current accepted codes to lean duplex. And, on the other hand, there exist substantial differences (between high-strength, lean duplex and carbon steel) to motivate a specific treatment of these grades, especially if submitted to PWTs, for a safer and more economical use of this material in engineering structures. Research objectives The applicability of lean duplex welded joints in structures submitted to cyclic loads necessitates investigating the proneness of welded details to fatigue and the mechanisms underlying it. To build a systematic understanding of the phenomena ruling this domain is a long and tedious task, especially if fatigue tests are conducted. During this thesis, we aim to shed more light on this topic through 3 main realistic tasks, based on experimental and numerical evidence:

1. Proneness to fatigue of as-welded details The first goal is to contribute to an increased knowledge of the fatigue behaviour of as-welded lean duplex details via a comprehensive experimental campaign with detailed analyses of the results, both butt welds and fillet welds will be considered in the beginning. 2. Influence of post-weld mechanical treatments (PWT) The second goal is to study the modification of the fatigue behaviour of the same details after PWT via comparisons with the as-welded specimens. This was achieved only in very recent researches on fatigue (Cheng et al. 2003; Zhang et al. 2015; RFSR-CT-2010-00032 n.d.; Wang et al. 2009; Lakshminarayanan, Balasubramanian 2012; RFSR-CT-2004-00040 2007; Hechler et al. 2007; Di Sarno et al. 2003; Di Sarno et al. 2006; Nip et al. 2010b).


3. Full-scale bridge detail The third goal is to assess the load bearing capacity and fatigue behaviour of a full-scale structural bridge detail made of lean duplex based on experimental and numerical evidence and on well-established theoretical methods, and to put it in perspective with the previous 2 objectives. It can thus be considered as a validation of the previous work. Methodology of the research EN 1993-1-9 requires at least 6 3 tests to achieve a relevant fatigue curve. On the one hand, the tests will sometimes require a relatively high force (up to 100 kN) and, on the other hand, to tackle the slope of the Wöhler curve, a high number of cycles is required. For engineering applications such as bridges, the very high cycle fatigue (above 10

7) is of less interest than the behaviour around the

reference fatigue strength ∆σc (2106 for EN 1993-1-9), but the high-cycle regime will also be

investigated to gain insight into the endurance limit of lean duplex, especially because the PWT effects should be most noticeable in the long-life regime. In ((ISO) 2012; (ASTM) 2012; (ASTM) 2013; (ASTM) 2007), guidance is given on how to thoroughly prepare, conduct, record and analyse fatigue tests. The majority of the tests will be performed within KU Leuven where a number of dynamic hydraulic actuators are today available. The preparation of the specimens will be achieved on the site of the Welding Engineering Centre at Campus De Nayer. The bulk of the fatigue test campaign will be conducted in the Department of Materials Engineering (Campus Gent) and in the Department of Civil Engineering (Campus De Nayer). A limited number of tests will be done at the research centre of Outokumpu in Avesta. Preparatory stage Before actually starting the project, a thorough literature review will be achieved (WP1). In the present document, an overview of the current literature is given for two subjects: Material characterization and Stereovision digital image correlation. Because a substantial amount of welding jobs will have to be performed, the definition of the welding modus operandi (WP2) is of high importance. Metal Arc Welding (GMAW) will be used. A parametric analysis on the welding procedure (i.e. order and welding path, number of passes, speed and heat input) will be carried out on a limited amount of samples (butt welds, grades EN1.4062 and EN1.4162) to investigate the influence of the welding parameters. Methodology followed in the present project The research consists in two major experimental campaigns, supported by one full-scale test and accompanying numerical and theoretical studies.

Material characterization – Stainless steel duplex (WP3) The static and hysteretic stress-strain behaviour of the grades EN1.4062 and 1.4162 (base material, weld nugget and heat affected zone (HAZ)) will be characterized using a mixed numerical-experimental method. Uniaxial tensile tests – cyclic tests for the hysteretic behaviour – will be performed whereby the high strain area (for the unwelded samples) and the welded area (including HAZ) are monitored using a stereo-vision camera setup (DIC), either continuously or at intermediate stops. These full-field measurements will be coupled to a Finite Element model (FEM) to obtain the different material parameters. Fatigue tests on “as-welded” samples (WP4) Tests under constant amplitude pulsating tension at different stress amplitudes will be conducted on the base material followed by a series of welding jobs. Full penetration single V butt welds and single T fillet welds (Figure 2) will be envisaged (according to the previous analysis, WP2).


Figure 2. Left: Single V butt weld; Right: Single T fillet weld The welds quality will be characterized using metallographic cross-sections images, to investigate flaw detection, HAZ, inadequate penetration, mismatch, cracks and inclusions. The residual stresses will be measured (WP4). The microstructure of the base material, the microstructural changes and the toughness near the welds will be characterized in the research centre of Industeel in Le Creusot. The results of these analyses will be put into perspective to the subsequent comprehensive fatigue testing campaign of the same as-welded details (WP4). To enhance the quality of the test predictions, DIC will be used to measure the strain concentration factors in and near the welds. It is an uneasy task but has been proven feasible (Koster et al. 2014; Pérez et al. 2014; Pérez et al. n.d.). The samples will also be instrumented with strain gauges. Special emphasis will be placed on the crack initiation measured via non-destructive acoustic techniques (capture of high frequency elastic waves). The fracture analysis of selected samples will be achieved to comprehend the cause of failure. With the above test results, it will be possible to carefully characterise the specimens’ microstructure and initial imperfections, to establish appropriate constitutive models for the base material and fatigue Wöhler curves for the welded samples. Fatigue tests on post-weld treated samples (WP5) The intention is to evaluate the influence of three selected PWTs on the fatigue strength. Shot (or hammer) peening using glass, stainless steel or carbon steel beads (followed, in this case, by decontamination of the treated surface), brushing, removing the reinforcement bead, passivation and electrolyte polishing will preliminary be envisaged leading to the selection of three PWTs (WP5). TIG dressing should not be used for duplex due to the risk of microstructure degradation ((IMOA) 2014). PWTs are an essential part of this project and will be achieved under the guidance of several Flemish companies. Different treatments yield different surface qualities (roughness, coarse aspect, defects), metallurgical aspects (grain deformation, hardness, HAZ) and residual stresses, having an effect on the final fatigue limit. The same methodology as the one used for the “as welded” specimens will be followed and a similar test campaign will be carried out, based on which the improvement of the fatigue strength will be measured and the optimal PWT will be obtained (WP5). The test campaign on the T fillet welds will be limited to one weld preparation and one PWT (derived from the experience on the butt welds). Full-scale joints (WP6) Two full-scale fatigue tests on a duplex longitudinal stringer welded to a cross girder (Figure 3) will be carried out as a final task of the experimental work (WP6): once as-welded and once with a suitable PWT. It will be put in perspective with the FE modelling (WP7) of the same stiffener and will serve as real-life validation of the findings of the previous tasks. The state-of-art on the behaviour of duplex welds (at microstructure level) together with the results of WP3, WP4 and WP5 (single T fillet weld) will help comprehend the specificities to be taken into account in the FEM. It will include an accurate geometrical description of the strain and stress concentration and the particularities of duplex constitutive models (virgin material, HAZ and residual stresses) (WP7). The FEM will be used to evaluate the position of the most detrimental structural stress near the weld toe and to assess the fatigue life based on currently accepted design rules. During the experiments, DIC will be used to measure the strain intensity and to compare them with the FEM results.


Figure 3. Full-scale fatigue test: longitudinal stringer, welded to a cross girder (t ≤ 12 mm)

Overview of the test matrix of WPs 3, 4 and 5 In sum, the proposed test matrix is shown below:

Table 1. Summary of the tests of WP3

Base material HAZ Fusion zone

Monotonic stress-strain behaviour 20 tests 28 tests 28 tests

Cyclic stress-strain behaviour 8 tests 17 tests 17 tests

“DIC tests” 15 tests 15 tests 15 tests

More information on the previous test matrix is given in the last chapter of this paper. In WPs 4 and 5, for each combination, one Wöhler curve with 63 samples (‘SN’) will be achieved, covering the range of 10

4 to 10

7 cycles

Table 2. Test matrix of the tests of WP4 and 5

Single V butt weld Single T fillet weld

Influence of welding parameters

(3 estimated parameters: welding

procedure, number of pass, speed/heat

input)

3 to 5 cyclic tests per

parameter NT

“As welded”

SN 3 thicknesses: 6, 8 and

10 mm to investigate the size

effect

SN on one thickness only

Selection of post-weld treatments (10mm)

(3 estimated PWTs) 3 to 5 cyclic tests per PWT NT

Post-weld treatment 1 = same as full-scale

detail SN SN

Post-weld treatment 2 SN NT

Post-weld treatment 3 SN NT

SN = 63 cyclic tests

NT = not treated

Literature review Material characterization To identify the stress-strain behaviour of welded lean duplex stainless steel hot-rolled plates (LDSS) (EN 1.4162 and EN 1.4062), monotonic and cyclic tension and compression tests will be conducted. The main goal is to determine the monotonic and cyclic stress-strain behaviour of the base material, the fusion zone and the heat-affected zone (HAZ).


In the literature, some results on the monotonic stress-strain behaviour of LDSS can be found. In (Graziano et al. 2015), test results are given on the mechanical properties of the base material and the welded components (fusion zone and heat-affected zone). Tensile tests were conducted on welded (MIG and SAW) and base material LDX 2101 (EN 1.4162) plates with a thickness of 10 mm. The average mechanical properties of the base material and of the welded components did not show any difference. In (Afshan et al. 2013; Saliba, Gardner 2013a; Saliba, Gardner 2013b), results of tensile and compression tests on the base material in the rolling and transverse direction on LDSS (EN1.4162) are provided for thicknesses ranging from 4 mm to 20 mm. All these tests were performed according to EN ISO 6892-1 ((ISO) 2009) and its former version EN 10002-1 (European Committee for Standardization (CEN) 2001). These experimental stress-strain curves, along with data for other families of stainless steel, are used in (Arrayago et al. 2015) to propose improved parameters to analytically describe the stress-strain behaviour of different stainless steel grades. This material model is the simplified (by Rasmussen (Rasmussen 2003)) two-stage Ramberg-Osgood model, also included in EN 1993-1-4 (European Committee for Standardization (CEN) 2006). Generally it can be stated that the data on monotonic stress-strain behaviour of LDSS (EN 1.4162 and EN 1.4062) is relatively scarce. Not only the data on the material characteristics of the base material are limited, but also on the material characteristics of the fusion zone and the HAZ. In order to define the monotonic stress-strain behaviour of the base material and the fusion zone, the EN ISO 6892-1 ((ISO) 2009) gives the necessary guidance to perform these tests. Due to the inhomogeneous character of the HAZ (different characteristic zones depending on different thermal history), it is impractical to measure the stress-strain behaviour by simply testing a part of this HAZ. Therefore, as described in (Guo et al. 2016; Liu et al. 2015; Lu et al. 2015), a welding simulator or a Gleeble simulator, will be used to simulate one specific zone within the HAZ on a larger specimen of base material. The HAZ is generally composed of different characteristic zones, each with a specific microstructure and mechanical property. After identification of the different characteristic zones, within the HAZ through micro-hardness testing and optical microscopy (Lu et al. 2015), the thermal history of these specific zones is measured during welding. Later, a specimen (for example a dog bone made of base material) is submitted to this thermal cycle profile with a certain heating rate, peak temperature and cooling rate, to create a specimen with the microstructure of one specific zone within the HAZ (Figure 4). By developing specimens for all characteristic zones, a complete representation of the stress-strain behaviour of the HAZ can be created.

Figure 4. Left: Thermal history of a region of the HAZ; Right: Welding simulator


The stress-strain behaviour obtained from a monotonic test differs from that of a cyclic test. Johann Bauschinger was the first to study the hysteretic behaviour of metals (Bauschinger 1886). In order to determine the cyclic stress-strain curve, constant strain range tests like low cycle fatigue tests are used, for which the procedures are covered in standards such as ASTM E606 ((ASTM) 2012). Besides, a code of practice for the determination of cyclic stress-strain data exists (Hales et al. 2002). This document describes different testing procedures that can be used: single-step tests (SST) (according to low cycle fatigue tests), multiple-step test (MST) or incremental-step tests (IST) (Figure 5). The single-step test procedure is the most comprehensive method that will generate most of the material characteristics. However this procedure is time consuming and is hence mostly combined with one of the two other methods. During the SST, the specimen is submitted to a specified number of cycles at a constant strain range (fully reversed, i.e. strain ratio = -1, is commonly used in low cycle fatigue). This test will result in one stabilized hysteresis loop. The tips from a family of stabilized hysteresis loops (at different strain ranges) can be connected to form the cyclic stress-strain curve, hence multiple tests at different constant strain ranges are required for this procedure. The IST uses strain ranges that are incremented every half cycle until a specific maximum strain range is reached, than the strain ranges is decreased again. This is repeated until the tips of the different hysteresis loops are stabilized. Finally the MST, which is similar to the IST, uses several cycles of equal strain ranges in each loading block. In all these procedures, it is highly recommended to use triangular waveforms, instead of sinusoidal waveforms, because these last can cause ‘rounding’ of the hysteresis loops at the tips (Hales et al. 2002).

Figure 5. From top to base: SST; IST; MST


In (Polak, Hajek 1991; Belattar et al. 2012; Sivaprasad et al. 2010; Nachtigall 1977), the three different testing procedures (SST, MST and IST), along with other loading sequences, are used to determine the cyclic stress-strain behaviour of metals. The methods are compared to each other. These papers clearly state that the cyclic curve is not unique and depends on the loading history. Specifically on the cyclic stress-strain behaviour of LDSS (EN1.4162), a small number of results can be found in the literature. In (Strubbia et al. 2012; Strubbia et al. 2016), low cycle fatigue tests were used to obtain cyclic stress-strain curves under fully reversed total strain control, applying a triangular waveform at a constant total strain rate. Results show an initial small cyclic hardening, followed by cyclic softening. Recently, research was conducted on the hysteretic behaviour of LDSS (EN1.4162) under cyclic loading (Zhou, Li 2016). The tests were strain controlled and were recorded using a digital extensometer. Different loading schemes were used, such as the MST, wherein each strain amplitude was repeated for five cycles, until a saturated response was obtained. The specimens used to perform these tests were round coupons, cut in the rolling direction. This research showed the dependence of the shape of the cyclic stress-strain curve to the loading history. No data could yet be found on the cyclic stress-strain behaviour of welded LDSS EN 1.4162 or EN 1.4062. The cyclic stress-strain behaviour can be modelled by the cyclic form of the Ramberg-Osgood equation (Skelton et al. 1997). Besides this simplified model, a number of constitutive models exist to describe particular aspects, like ratcheting or Bauschinger effect of the cyclic deformation response (Hales et al. 2002; Lee et al. 2014; Khutia et al. 2014). For both monotonic and cyclic compression tests, anti-buckling jigs are generally used to avoid buckling of the specimen (Figure 6). In (Zhou, Li 2016; Nip et al. 2010a) as well as in ASTM E9 ((ASTM) 2000), examples and recommendations for the shape and dimensions of these anti-buckling jigs are provided.

Figure 6. Buckling jig

To conclude, data on the stress-strain behaviour of both LDSS EN 1.4162 and EN 1.4062 grades is today relatively rare, especially concerning their cyclic behaviour. Stereovision digital image correlation DIC is an optical-numerical measuring technique that offers unique opportunities to determine the complex full-field displacement and strain distribution at the surface of objects under arbitrary loading in 2D and 3D, depending on the number of cameras used – a single camera in the case of 2D, two or more cameras in the case of 3D. In 1983, Sutton et al. (Sutton et al. 1983) developed and tested 2D-DIC, upon which numerous research domains started applying this method. In 1993, stereovision DIC was pioneered by Chao et al. (Luo et al. 1993). Unlike 2D-DIC, a stereovision camera system is not limited to in-plane displacements, but allows for the displacement and strain evaluation at the surface of 3D shapes.


The basic principle is as follows. Charged-Coupled Device (CCD) cameras take synchronized images of a specimen in the undeformed and deformed state. Afterwards, these images are computationally compared (correlated) in a correlation software (representing the numerical part of DIC) to obtain the complete displacement field at the surface of the specimen under consideration, and, by derivation, also the strain field. It should be noted that the correlation procedure is only feasible if the surface of the specimen is covered with a random pattern. In general, one applies paint onto the specimen’s surface with an aerosol to obtain a random speckle pattern. This random pattern generates a unique signature for each subset so that it can be retrieved from the deformed image. As the DIC method relies on digital images to measure deformation, the quality of the images determines the quality of the measurements. The image quality depends on the experimental setup and on adequate preparations in order to minimise errors. It is hard to unambiguously define the accuracy of the DIC technique however it is generally accepted that an accuracy between 2% and 5% of the pixel size can be achieved in decent experimental conditions. Both 2D- and 3D-DIC have been used in a variety of civil engineering applications. For example, Küntz et al. (Küntz et al. 2006) employed DIC to gather information on the development of cracks in a reinforced concrete beam of the Saint-Marcel bridge during a static loading test. Yoneyama et al. (Yoneyama, Ueda 2012) and Malesa et al. (Malesa et al. 2010) measured deflections of steel bridge girders whilst a heavy cargo truck or a train was passing on. Malesa et al. (Malesa et al. 2010) also measured the displacements of a girder close to a connection. DIC was applied by Koltsida et al. (Koltsida et al. 2013) and Santini-Bell et al. (S Santini-Bell et al. 2011) for monitoring, respectively, a masonry arch bridge and a steel girder composite bridge. Besides structural health monitoring or inspection, this method was implemented for measurements during in situ and laboratory tests. Tung et al. (Tung et al. 2014) used DIC to measure deformations during an in situ pushover test of an old building columns retrofitted with steel plate. In laboratory, DIC has been used to study various materials, e.g. canvas paintings (Kujawinska et al. 2011), composites (De Roover et al. 2002; Featherston et al. 2008), aluminium (Braga et al. 2016) and the most common construction materials: concrete and steel. In (Ferreira et al. 2011; Dutton et al. 2014; Souid et al. 2009; Smith et al. 2011; De Wilder et al. 2015), stereovision DIC was used to obtain the displacement field in concrete beams. Ghafoori and Motavalli (Ghafoori, Motavalli 2011) investigated the fatigue and fracture behaviour of a steel I-beam. They employed DIC to illustrate the stress evolution pattern and the plasticity zone around the crack tip. Hild et al. (Hild et al. 2011) applied DIC to identify the behaviour of steel beams prior to and after the initiation of local buckling. Kujawinska et al. (Kujawinska et al. 2011) tested a metal-plate arch and monitored displacement maps with DIC. Sozen and Guler (Sozen, Guler 2011) investigated a bolted steel connection and compared in-plane displacement distributions computed through DIC and strain gauges. Shih and Sung (Shih, Sung 2014) tested a five-story shearing steel structure under dynamic loading and measured the responses by means of a single camera with 3D images. Tran et al. (Tran et al. 2015) executed a compression test on a down scale model of a steel tubular wind turbine tower to study buckling around the door opening of the tower using DIC. DIC has also been used in several researches in which fatigue tests were performed (Aparna et al. 2015; Salvati et al. 2016; Crupi et al. 2015). An extensive list of applications of both 2D- and stereovision DIC in various research domains can be found in (Orteu 2009) and (Sutton et al. 2009). WP3 Material Characterization – Test programme in details Because of the limited data on the material behaviour of lean duplex, an extensive test programme has been designed in order to characterize the material stress-strain behaviour, under both monotonic and cyclic loading. Test will be conducted on plate thicknesses of 10 mm and 25 mm. Dog-bones will be machined out in order to perform tensile and compression tests. The test program does not limit itself to the characterization of the base material, but also to the welded zone (weld nugget or fusion zone (FZ)) and the HAZ.


The monotonic loading will be both in tension (T) and in compression (C), the cyclic loading will be fully reversed (i.e. strain ratio = -1). For the base material, the anisotropic behaviour of the plates, due to hot rolling, will be quantified. Therefore, specimens will be taken from the plates in three different directions: parallel to the rolling direction (RD), at 90° to the rolling direction (TD) and at 45° to the rolling direction (45°). After characterization of the base material, the FZ and the HAZ will be studied under the same loadings. The influence of a number of parameters during welding on the FZ and on the HAZ will be evaluated. For both the HAZ and FZ, a reference situation is defined by a specimen taken in the middle of the welded plates (REF), compared to the edge of the welded plates where residual stresses can have a significant influence. For the REF specimen, gas metal arc welding (GMAW) will be used and a welding procedure specification (WPS), defining the required number of passes (NOP) and heat input (HI), along with other parameters will be followed. After defining the behaviour of the FZ and the HAZ in this reference situation, five other situations will be studied, each time changing one parameter (highlighted in italic in Table 4 and 6). Doing so the influence on the mechanical behaviour of each parameter can be evaluated. Table 3, 4, 5 and 6 give an overview of the planned tests.

Table 3. Monotonic tension-compression – Base material

Thickness RD TD 45°

10 mm 3 T + 3 C 1 T + 1 C 1 T + 1 C

25 mm 3 T + 3 C 1 T + 1 C 1 T + 1 C

TOTAL: 20 tests

Table 4. Monotonic tension-compression – HAZ and fusion zone

Thickness REF

Mid

specimen

HAZ/FZ 1

GMAW

HI 1

NOP 1

Edge

specimen

HAZ/FZ 1

GMAW

HI 1

NOP 1

Mid

specimen

HAZ/FZ 2

GMAW

HI 1

NOP 1

Mid

specimen

HAZ/FZ 1

SAW

HI 1

NOP 1

Mid

specimen

HAZ/FZ 1

GMAW

HI 2

NOP 1

Mid

specimen

HAZ/FZ 1

GMAW

HI 1

NOP 2

10 mm 3 T + 3 C 1 T + 1 C 0 1 T + 1 C 1 T + 1 C 0

25 mm 3 T + 3 C 1 T + 1 C 1 T + 1C 1 T + 1 C 1 T + 1 C 1 T + 1C

TOTAL: 28 tests

Table 5. Cyclic fully reversed tension-compression – Base material

Thickness RD TD 45°

10 mm 2 1 1

25 mm 2 1 1

TOTAL: 8 tests

Table 6. Cyclic fully reversed tension-compression – HAZ and fusion zone

Thickness REF

Mid

specimen

HAZ/FZ 1

GMAW

HI 1

NOP 1

Edge

specimen

HAZ/FZ 1

GMAW

HI 1

NOP 1

Mid

specimen

HAZ/FZ 2

GMAW

HI 1

NOP 1

Mid

specimen

HAZ/FZ 1

SAW

HI 1

NOP 1

Mid

specimen

HAZ/FZ 1

GMAW

HI 2

NOP 1

Mid

specimen

HAZ/FZ 1

GMAW

HI 1

NOP 2

10 mm 2 2 0 2 2 0

25 mm 2 1 2 1 1 2

TOTAL: 17 tests


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