Wide Plate Tests Research Articles

Ductile tearing tests of 316 stainless steel wide plates containing weldments

Twelve wide plate tests have been performed in recent years, as part of the European Fast Reactor development programme, to examine the influence of residual stresses on the fracture behaviour of Type 316 stainless steel plates and weldments. The first ten tests consisted of a study of through-thickness cracks and the last two tests addressed the behaviour of surface cracks. Results obtained from this series of tests are summarised and the ability of the R6 fracture assessment procedure to predict the results is reviewed. Significant amounts of ductile tearing under increasing applied load was shown to have occurred in both the plain plate and weldment through-thickness crack tests, prior to instability conditions being attained. R6 calculations were shown to conservatively underpredict instability applied loads for all through-thickness cracks tested. The through-thickness crack weldment tests indicated that residual stresses should be included in predicting initiation and the earliest stages of crack growth, but that they may be excluded in predicting the later stages of crack growth leading to instability. There was some evidence to suggest however that having to include residual stresses or not may depend on whether the section containing the crack is in contained yield or not. A wide plate test of a semi-elliptical crack in parent material, loaded in tension, indicated that the global limit load, although being slightly overpredictive in terms of applied load, was significantly more accurate than the local limit load approach.

TWI biaxial test program: 1984–1994

The influence of biaxility on the upper-shelf, lower-shelf and the ductile-to-brittle transition regimes has been investigated. A total of 16 biaxial wideplate tests have been conducted. In addition, the effect of biaxility has been investigated using non-linear finite element analysis

Study on Fracture Assessment (3rd Report)

Japan Welding Engineering Society (WES) standard WES 2805 gives procedures for safety evaluation of defects at elastic-plastic condition in welded structures on the basis of the CTOD concept. The essential point of fracture strength assessment in WES 2805 is a relationship between CTOD value and local applied strain, so called “CTOD design curve”. It is important to confirm the applicability of local strain based CTOD design curve to the case of the structural stress concentration, because most of brittle fractures in real structures occur from the defects at the structural stress and strain concentrated region.In this series of studies on fracture strength assessment, an investigation on fracture test results for some kind of structure models with strain concentration was carried out, and modified WES CTOD design curve was proposed. Furthermore, wide plate tests with cracks emanating from a hole and stiffener model tests with a crack in the strain concentrated region were carried out, and applicability of the proposed CTOD design curve was investigated.In this study, wide plate tests with stress concentration using 2-dimensional finite element analysis were carried out, and it was shown that the relationship between CTOD and local strain was varied with the relative size of the plastically deformed region as compared with defect size. It the plastically deformed region size was lagerer than 4 times of crack length, modified WES CTOD design curve under-estimates CTOD value. It has been revealed that the proposed modified WES CTOD design curve is valid for fracture strength assessment of cracks in the stress concentrated region except above mentioned case.

A Strain Gage Analysis of Fracture in Wide Plate Tests of Reactor Grade Steel

A new method of fracture analysis is described. Strains recorded by gages in the immediate vicinity of a propagating crack are analyzed. From the analysis, crack tip position, propagation toughness, and crack velocity are determined. The analysis procedure Is demonstrated using data from the dynamic fracturing of a large-scale, wide plate test. The results are then used to describe the propagation toughness-crack velocity-temperature relation for the 2.25 Cr-1 Mo steel used in the test.

Investigations in fracture mechanics failure concepts with thermomechanically rolled steels

Abstract Thermomechanically rolled steels of quality StE-480 TM and a conventional mild steel (St 52-3) were investigated in instrumented Charpy impact tests, fracture mechanics tests, tension tests with fatigue precracked specimens and wide plate tests with notched specimens (CNT or DENT) up to a maximum load of 4 MN. Several specimens were welded. The results were used for determining various transition temperatures and for checking several actual safety concepts of linear elastic and elastic-plastic fracture mechanics, namely the K I -concept, two methods basing on CTOD (CTOD design curve and PD 6493), and two methods using J -integral (EPRI and R6). Of these methods the new version of the R6 methods seems most promising. J -integral values of wide plates calculated with various finite element programs agreed rather well with one another and with experimental results.

Demonstration of crack arrest capability for welds showing low toughness pop-in

Toughness data are presented for three typical structural welds. All the three welds showed significant pop-ins at low toughness (0.02 < δ c < 0.06 mm) in Crack Tip Opening Displacement (CTOD) tests. In spite of this, the structural safety of the welds is demonstrated by their ability to arrest large running cracks at two-thirds yield stress in the double tension wide plate test. A method of deducing an estimate of crack arrest toughness from the CTOD test itself is presented, and shown to be conservative.

Wide-plate crack-arrest tests utilizing prototypical and degraded (simulated) pressure vessel steels

Sixteen wide-plate crack-arrest tests have been completed, ten utilizing specimens fabricated from A533B class 1 material and six fabricated from a low-upper-shelf base material. Each test utilized a single-edge notched specimen that was subjected to a linear thermal gradient along the plane of crack propagation. Test results exhibit an increase in crack-arrest toughness ( K 1a) with temperature, with the rate of increase becoming greater as the temperature increases. When the wide-plate test results are compared with other large-specimen results, the data show a consistent trend in which the K 1a data extend above the limit provided in ASME Section XI.

Study on Fracture Strength Assessment (2nd. Report)

Japan Welding Engineering Society (WES) standard WES 2805 and British Standard Institution (BSI) standard BSI PD6493 were established in 1980. Since then, these standards have been widely used to evaluate fracture safety of structures. They are based on elastic-plastic fracture mechanics (CTOD criterion), because most brittle fracture may occur from defect at structural stress concentration where plastic zone size generally seems to be larger than the defect size.Work on revision to these standards are underway in U. K. and Japan. The BSI are going to provide a new defect assessment. The fracture sections of the revised document will take three levels of assessment. Level 1 is essentially consistent with the PD6493-1980 and treated as a preliminary evaluation. In Level 2 and 3 assessments, brittle fracture and plastic collapse are taken into account by use of a failure assessment diagram (FAD) similar to that proposed originally in CEGB R-6 procedure.In Japan, research on the validity of WES 2805 has been carried out and a modified CTOD design curve and a new method for estimating local strain at stress concentrator were proposed. Work on revisions to WES 2805 has been in progress by taking into account the recent advances in fracture mechanics treatment.In this paper, critical evaluation was carried out for fracture assessment of CTOD and FAD. Wide plate tests with cracks emanating from a hole were carried out and the fracture strength was evaluated by means of WES CTOD and FAD approaches. The FAD analysis based on the WES CTOD was also investigated. The assessment results were almost the same between those two approaches. However, it is said that the WES CTOD method is more practical, because this method is based on the relation between CTOD and local strain. In some practical cases, only the local strain near the region where defect is discovered, is available. The FAD approach is required the global stress condition (plastic collapse load) for fracture evaluation.

Evaluation of toughness requirements in cracked components based on fracture-mechanics methods

Different fracture-mechanics based defect assessment procedures have been checked using results of wide-plate tests. The CTOD-Design-Curve-Approach, the CEGB-R6-routine, the EPRI-approach and methods using Finite-Element-Computations to evaluate the crack driving force lead to safe predictions of the failure behaviour of components as long as the limits of application are considered carefully. Reversing the conventional procedure of defect assessment, the CTOD-Design-Curve approach and the FEM based method can be used to derive toughness requirements. The requirements depend on the component and defect geometry, the strength of the material and the safety criterion. For practical application simple diagrams have been evaluated showing the required toughness e.g. as a function of crack length or material strength.

The Significance of Local Brittle Zones to the Integrity of Large Welded Structures

Abstract An extensive group-sponsored research program has been carried out within the UK, which, supplemented by additional work by British Steel, was designed to study the structural significance of local brittle zones. Charpy impact, CTOD and wide plate tests have been examined in order to compare and contrast their fracture behavior under similar conditions. In order to permit this comparison, two welding conditions were studied giving nominally 30 and 10 percent of coarse-grained HAZ through the thickness of a 50-mm-thick plate. The high percentage of coarse grain condition was tested in the as-welded and PWHT state and the low percentage condition as-welded only. It was shown that low toughness (&amp;lt;0.1 mm CTOD) measurements could be obtained using both through thickness and surface-notched test pieces over a temperature range of −30 to +10°C. Similar minimum toughness values were obtained for all the test conditions studied, but the frequency of occurrence varied. Twenty-two wide plate tests were carried out and nine fractured, four in the as-welded condition (two each for the two welding variables studied) and five in the PWHT condition. A further plate initiated a fracture from a bevel weld procedure which arrested in the parent plate. It is postulated that the requirement for an extreme combination of stress level, defect size and coarse-grained microstructure at the crack tip plus the potential for crack arrest is the reason for the absence of fractures in offshore structures.

HSST wide-plate test results and analysis

Fifteen wide-plate crack-arrest tests have been completed to date, ten utilizing specimens fabricated from A533B class 1 material (WP-1 and WP-CE series), and five fabricated from a low upper-shelf base material (WP-2 series). Each test utilized a single-edge notched specimen that was subjected to a linear thermal gradient along the plane of crack propagation. Test results exhibit an increase in crack-arrest toughness with temperature, with the rate of increase becoming greater as the temperature increases. When the wide-plate test results are combined with other large-specimen results the data show a consistent trend in which the K Ia data extends above the limit provided in ASME Section XI.

The history, development and application of a uniformly applied load wide plate testing machine

The paper describes early attempts to use a rigid end wide plate testing machine to investigate the behaviour of centre cracked flat plates. Confusing and inconsistent results arising from the above tests lead to a detailed investigation of the loading characteristics of rigid end machines in general and the difficulties which can arise in the interpretation of data obtained by the used of such machines. In order to overcome the above difficulties which stem largely from uneven load distribution, a versatile testing machine was designed which by use of cheap and easily obtainable components allows the application of a uniformly distributed applied load to a centre cracked test plate. The machine which was commissioned in its original form in 1975 was initially capable of testing plate of 820 mm width and 25 or 48 mm thickness up to maximum stress levels of 488 or 254 MPa respectively. The ease of adaptability of the machine has since permitted its capacity to be increased to handle plate up to 2032 mm wide and 76 mm thickness and by use of double-banked hydraulic jacks stress levels up to 350 MPa can be achieved on plate of these dimensions. The configuration of the machine allows adequate access for strain gauging, crack tip observation and measurements, and temperature control, tests having been conducted in the temperature range —40°C to 290°C. Advantages and potential for further development of the machine are given together with details of two of a number of fracture studies which have been conducted since its commissioning.

Fracture control in the transition-temperature region of structural steels

Abstract This paper describes the applicability of current research on the crack-tip opening displacement (CTOD) methodology to engineering approaches to fracture control in steel structures in the transition-temperature region. review of the four (not three) broad areas of fracture response that structural steels exhibit throughout their transition-temperature region is presented and the standard fracture toughness test methods applicable to each region are described. These four regions are the lower-shelf (linear-elastic K Ic type behavior), lower-transition (elastic-plastic behavior with no stable crack growth prior to brittle fracture), upper-transition (stable ductile tearing followed by brittle fracture),and upper-shelf (full fibrous ductile tearing). Correlations and relations between Charpy V-Notch impact energy results, K ID , K Ic , J-integral and CTOD test results are described. The importance of loading rate in understanding fracture control is demonstrated using the Standard Oil Development (SOD) wide plate test results of the early 1950s. Finally, actual CTOD test values, in combination with nonlinear finite element analyses, are used to predict the burst pressures of notched pressure vessels. The burst pressures computed agree to within 7% of experimental burst pressures in all five vessels analyzed.

Behaviour of A533B under biaxial loading at +70°C

Fracture analyses have generally assumed that biaxial loading can be assessed conservatively using uniaxial data. However, although there have been many analytical studies examining the response of cracks to biaxial loading, few large-scale tests have been carried out. This paper describes work carried out on a large biaxial test rig enabling the development of crack tip plasticity to be studied in 25 and 50 mm thick 500 mm square A533B plates. To date, tests under uniaxial (k = 0) and biaxial ( k = 1 2 and 1 ) conditions confirm that, in the linear elastic regime, the stress intensity factor K is not influenced by the loading ratio, k. However, the onset of plasticity in the wide plate tests occurs at different stresses as the loading ratio varies. Crack tip opening displacement resistance curves appear insensitive to loading ratio for the semi-elliptical part wall defects tested. However, once through-thickness cracks are developed, there are indications that the resistance curve is lower under equibiaxial conditions than for uniaxial loading.

High-temperature crack-arrest behavior of prototypical and degraded (simulated) reactor pressure vessel steels

Sixteen wide-plate crack-arrest tests have been completed, ten utilizing specimens fabricated from A533B Class 1 material and six fabricated from a low-upper-shelf base material. Each test utilized a single-edge notched specimen that was subjected to a linear thermal gradient along the plane of crack propagation. Test results exhibit an increase in crack-arrest toughness ( K Ia ) with temperature, with the rate of increase becoming greater as the temperature increases. When the wide-plate test results are compared with other large-specimen results, the data show a consistent trend in which the K Ia data extend above the limit provided in ASME Section XI.

Suspension of work on fatigue standards proposed by ISO

Twelve wide plate tests have been performed in recent years, as part of the European Fast Reactor development programme, to examine the influence of residual stresses on the fracture behaviour of Type 316 stainless steel plates and weldments. The first ten tests consisted of a study of through-thickness cracks and the last two tests addressed the behaviour of surface cracks. Results obtained from this series of tests are summarised and the ability of the R6 fracture assessment procedure to predict the results is reviewed. Significant amounts of ductile tearing under increasing applied load was shown to have occurred in both the plain plate and weldment through-thickness crack tests, prior to instability conditions being attained. R6 calculations were shown to conservatively underpredict instability applied loads for all through-thickness cracks tested. The through-thickness crack weldment tests indicated that residual stresses should be included in predicting initiation and the earliest stages of crack growth, but that they may be excluded in predicting the later stages of crack growth leading to instability. There was some evidence to suggest however that having to include residual stresses or not may depend on whether the section containing the crack is in contained yield or not. A wide plate test of a semi-elliptical crack in parent material, loaded in tension, indicated that the global limit load, although being slightly overpredictive in terms of applied load, was significantly more accurate than the local limit load approach.

Ductile Instability of Long Arrested Crack under R-Curve Concept

To prevent the catastrophic failure of a large storage tank, it is necessary to ensure not only that the long brittle crack will be arrested by the material toughness, but also that the arrested crack will subsequently be stable. After the long and fast running crack is arrested, the bulging force applied to the crack flanks will grow and re-initiate the unstable ductile crack.R-curve concept combined with J-integral is adopted as a theoretical tool and wide plate tests are carried out to estimate the fracture resistance of a material for LPG storage tanks. The tested material is the 34 mm thickness 2 1/2% Ni steel plate manufactured by the special thermomechanical process, SHT-DAC. The specimens are 3 m in width and 4. 6 m in length so as to reproduce long arrested cracks in storage tanks. The specimens were loaded in the 10, 000 tonf test rig under the room temperature and as the ductile crack extended, they were unloaded in less than 10% for measuring the crack growth.The applied driving force is calculated from J-integral, the Battelle's equation on the bulging effect.The ductile resistance of the test material is 200 N/mm2 as dR/da for long arrested cracks. For a large LPG storage tank of 40 m in diameter, the strake height should be limited under 3. 2 m to avoid the ductile instability of the long arrested crack.

Dynamic analysis of a crack-arrest specimen

Under pressurized thermal shock (PTS) loading conditions arrest of running cracks at temperatures that range up to or above those corresponding to the onset of Charpy upper shelf is of particular interest. Only few crack arrest toughness ( K Ia) data above 200 MPa√m obtained from rather expensive PTS-experiments and wide-plate tests are available. In the present paper the capabilities of a relatively small panel crack arrest specimen for yielding K Ia data in excess of 200 MPa√m under conditions of a rising K I-field are investigated. For this purpose static and dynamic finite element analyses are performed. It is shown that dynamic effects cannot be neglected for this specimen type and K Ia-values up to about 300 MPa√m can be expected from measurements in suitably conducted experiments.

Evaluation of ductile vessel rupture by [formula omitted] analysis using CT specimens and wide plate tests

A large volume, thin-walled vessel was weakened by the introduction of a longitudinal slit sealed from the inside. With the help of compact-tension specimens and wide plates, attempts were made to analyse the failure by means of elastic-plastic fracture mechanics, taking into account the bulging of the vessel by the use of the so-called ‘Folias factor’. With J R curves obtained from wide plate tensile tests, the crack driving force curves provide stresses at crack initiation and instability which are approximately 20–30% below the corresponding values of the internal pressure test. With regard to stable crack growth, very good agreement was achieved.

Wide plate tests and critical crack lengths at general yield

A proposal related to experimental fracture mechanics suggested by Professor W. Soete, Gent University, Belgium, is investigated in the present paper. The concept of two critical crack lengths of general yield is proposed, and their physical meaning and engineering application are presented. Based on the experiment and analysis, an engineering method for the assessment of defects in pressure vessels is suggested.