Wide Plate Specimens Research Articles

Residual Stresses in Welded Moment Frames and Implications for Structural Performance

Welding-induced residual stresses are usually regarded as secondary stresses and therefore not accounted for in the structural analysis. This treatment, however, was brought into question with the welding research community by the discovery of a widespread structural damage in the 1994 Northridge earthquake. Brittle fracture was identified in many of the prequalified weld joints in steel moment frames. Welding-induced residual stresses are believed to be one of the factors contributing to the brittle fracture. In this paper, a detailed investigation on residual stresses in welded moment frame connections is presented. Both the actual connection configurations of the moment resistant frames and local weld details are considered by means of advanced residual stress analysis techniques. Then, the effects of triaxial residual stress state on plastic deformation capacity are discussed based on finite-element results on a wide-plate specimen loaded in tension. Finally, a series of fracture mechanics analyses were carried out to assess the effects of residual stresses on the fracture behavior. As a result, a great deal of insight has been obtained on the fracture behavior of the moment frame welds. Among other things, the results indicate that welding-induced residual stresses significantly increase the fracture driving force due to the presence of high tensile residual stresses. The high triaxial residual stress states identified in these joints can greatly reduce the plastic deformation capability, consequently promoting brittle fracture. Therefore, it seems reasonable to postulate that weld residual stresses could have played an important role in the occurrence of brittle fracture in the pre-Northridge weld joints.

加硫天然ゴムにおける疲労き裂伝ぱの破壊力学的研究

Fatigue crack propagation tests in vulcanized natural rubber sheets were conducted by using narrow, wide plate specimens under the constant displacement condition. The J integral was kept constant during fatigue crack propagation. The fatigue crack propagation rate was expressed as a power function of the J-integral range, and the power exponent was 1.81 under the ratio R=0 of the minimum to maximum displacement. When R is greater than 0.23, the crack propagation rate is lower than that predicted by the power function. This reduction may be caused by the fiber structure of molecules formed at the crack tip which is not relaxed even at the minimum load. Microcracks are formed ahead of the tip of a crack propagating at high rates. Fatigue fracture surfaces are rough and are accompanied by secondary cracks. No fatigue striation corresponding the crack propagation rate was observed on the fatigue fracture surface.

CTOD design curve in consideration of material strain hardening

In this paper by means of the plane-stress CTOD crack growth driving force analysis in the tensile wide plate specimen, a CTOD design curve is deduced for the material in consideration of the stress–strain relation following the Ramberg–Osgood law. The feature of the new CTOD design curve is that the material strain-hardening exponent n, material constant α and plate thickness coefficient κ are introduced to the design curve, and the mechanical heterogeneity of the welded joint is separated from the design curve. The uncertainty of the safety coefficient on CTOD design is improved. The CTOD design curve may be used to analyze the elastic–plastic fracture problem rather accurately for engineering structure.

Effects of crack size and weld metal mismatch on the has cleavage toughness of wide plates

The heat affect zone (HAZ) is in many cases considered to be the most critical part of a weldment. In this paper, the effect of crack size and weld metal mismatch on the HAZ cleavage toughness of wide plate specimens with X-groove has been investigated by the J- Q- M theories and a simple micromechanism for cleavage fracture. Two crack sizes have been studied ( a w = 0.1 and 0.3). In the analyses, the HAZ yield strength is assumed to be higher than the base metal. For each crack size, weld metal local overmatch and local evenmatch with respect to the HAZ are considered. For a given global strain, the results indicate that weld metal overmatch and evenmatch yield the same crack tip loading in terms of J-integral for a w = 0.3 . For a w = 0.1 , overmatch gives lower crack tip loading than evenmatch. For a given crack tip loading, weld metal local evenmatch in general results in less effective crack tip loading than the overmatch. Overmatch is detrimental to HAZ toughness, but this detrimental effect becomes less significant when the crack size decreases.

Research on residual stresses after hydrobulging of spherical vessels

This paper describes the residual stress distributions on wide plate specimens intended to simulate the hydrobulging process for the 200 m 3 spherical vessel which is the first set for storage of liquefied petroleum gas (LPG) manufactured using dieless hydrobulging technology. The results show that on the inside surface of the spherical vessels after they are hydrobulged, the transversal residual stress is in a compressive state; the longitudinal residual stress has a very small tensile value and sometimes is in a compressive state. These distributions of residual stresses are favourable to prevent the spherical vessel from stress corrosion cracking (SCC) and embrittlement fracture and can improve its fatigue strength. This is a significant advantage of the new dieless hydrobulging technology in guaranteeing safety.

Research on the residual stresses of hydrobulged spherical vessels

This paper describes the residual-stress distributions of wide plate specimens for simulating the hydrobulging process of a 200 m 3 spherical vessel, which latter is the first set for the storage of liquefied petroleum gas (LPG) manufactured by die-less hydrobulging technology. The results show that on the inside surface of the hydrobulged spherical vessels, the transverse residual stress is in the compressive state: the longitudinal residual stress usually has a very small tensile value, but is also sometimes in the compressive state. These distributions of residual stresses are favourable for preventing the spherical vessel from stress-corrosion cracking (SCC) and embrittlement fracture and can improve its fatigue strength. This is a significant advantage of the new die-less hydrobulging technology, in ensuring safety.

An investigation into the plastic formability of welded joints

This paper deals with the plastic formability of welded joints simulating the dieless hydro-bulging process of spherical vessels using wide-plate specimens. The effect of welding factors such as weld strength, profile of the weld, toe etc., on the stress-and strain-distributions of the welded joints are analyzed by elasto-plastic FEM. The results show that the plasticity of the welded joints can satisfy the requirement of metal-forming processes, on condition that some technological measurements are adopted.

Load bearing and deformation behaviour of dynamically loaded wide plate specimens

For the testing of large-scale specimens, a 12 MN-High Loading Rate Tensile Testing Machine was designed and built at MPA Stuttgart. The aim was to determine the influence of high loading rates on the stress and strain behaviour of unwelded and welded components of ferritic and austenitic materials. This new generation of testing machines is driven by a propellant charge, and generates a maximum tensile force of 12 MN with a piston velocity of 25 m/s after a stroke of 20 mm, or a maximum velocity of 60 m/s after a stroke of 400 mm. In a first test programme, welded and unwelded wide plate specimens made of material X 6 CrNi 18 11 were tested at room temperature with different strain rates from 10 −3 /s to 63/s. In addition to a description of the 12 MN-High Loading Rate Tensile Testing Machine, the results of the high loading rate tensile tests performed will be presented and compared with quasistatically tested wide plate specimens.

Applications of adina to viscoplastic-dynamic fracture mechanics analysis

Nonlinear rate-dependent effects in crack run-arrest events in ductile materials are being investigated through development and applications of viscoplastic-dynamic finite element analysis techniques. This paper describes a portion of these studies wherein various viscoplastic constitutive models, dynamic crack-propagation algorithms, and proposed nonlinear fracture criteria have been installed in the general purpose ADINA finite element computer program. The predictive capabilities of the nonlinear techniques are evaluated through analyses of crack-arrest tests of nonisothermal wide-plate specimens. Values of fracture parameters calculated by elastodynamic and viscoplastic-dynamic techniques are compared to assess the impact of including viscoplastic effects in the computational models. Mesh refinement studies are presented that examine whether the proposed fracture parameters converge to nonzero values in viscoplastic-dynamic analyses or whether they are controlled by element dimensions. Plans are reviewed for additional computational studies to assess the utility of viscoplastic analysis techniques in constructing a dynamic inelastic fracture mechanics model for ductile steels.

Late-event viscoplasticity in wide-plate crack-arrest tests

A primary objective of the crack-arrest studies being conducted by the Heavy-Section Steel Technology (HSST) program is to understand pressure vessel conditions that would initiate growth of an existing crack and conditions that would lead to arrest of a moving crack. In meeting this objective, the HSST program is generating crack-arrest data over an expanded temperature range through tests involving large cylinders, pressure vessels and wide-plate specimens. The role of nonlinear rate-dependent effects in the interpretation of crack run-arrest events in ductile material is being investigated by the HSST program through development and applications of viscoplastic-dynamic finite element analysis techniques. This paper describes the portion of those studies that relate to the installation of two viscoplastic constitutive models and several proposed fracture criteria into the ADINA finite element program. The formulations of the Bodner-Partom and the Perzyna constitutive models that were installed in ADINA are presented, including a compilation of material parameters for these models obtained from dynamic stress-strain data for A533 grade B class 1 steel. This is followed by a description of path-area integrals J′, T ∗ (from Nishioka and Atluri) and J ̂ (from Kishimoto) and of the function γ (representing energy flow to the crack tip) installed in the ADINA program. Finally, the combined predictive capabilities of these techniques are applied to the analysis of one of the recently completed HSST wide-plate crack-arrest tests.

Determination of fracture mechanics properties of welded joints and comparison with the failure behaviour of wide plates

Fracture behaviour of different welded joints of 15 MnNi 6 3 and 20 MnMoNi 5 5 steel is studied by testing Charpy-V impact, fracture mechanics specimens as well as wide plate specimens of different sizes. The influence of welding conditions and stress relief heat treatment on the failure behaviour of the heat affected zones is examined. Fracture mechanics test data are used in order to predict failure loads of the wide plates by the R6-procedure and by FE-calculations.

HSST crack-arrest studies overview

An overview is given of the efforts underway in the Heavy-Section Steel Technology (HSST) Program as of October 1985 to better understand and model crack-arrest behavior in reactor pressure vessel steels. The efforts are both experimental and analytical. The experimental work provides K Ia data from laboratory-sized specimens, from thick-wall cylinders which exhibit essentially-full restraint and from nonisothermal wide-plate specimens. These data serve to define toughness-temperature trends and to provide validation data under prototypical reactor conditions. The analytical efforts interpret and correlate the data, plus provide LEFM, elastodynamic and viscoplastic analysis methods for analyzing crack run-arrest behavior in reactor vessels. The analysis methods are incorporated into finite element computer programs which are under development at three separate laboratories.

Some advances in fracture studies under the heavy-section steel technology program

Recent results are summarized from HSST studies in three major areas that relate to assessing nuclear reactor pressure vessel integrity under pressurized-thermal-shock (PTS) conditions. These areas are irradiation effects on the fracture properties of stainless steel cladding, crack run-arrest behavior under non-isothermal conditions, and fracture behavior of a thick-wall vessel under combined thermal and pressure loadings. Since a layer of tough stainless steel weld overlay cladding on the interior of a pressure vessel could assist in limiting surface crack extension under PTS conditions, its resistance to radiation embrittlement was examined. A stainless steel overlay cladding, applied by a submerged arc, single-wire, oscillating-electrode method, was irradiated to 2 × 10 23 neutrons/m 2 (> 1 MeV) at 288°C. Yield strength increases up to 27% and a slight increase in ductility were observed. Charpy V-Notch data showed a ductile-to-brittle transition behavior caused by temperature-dependent failure of the 8-ferrite phase. The type 308 cladding, microstructurally typical of that in reactor pressure vessels, showed very little degradation in either upper-shelf energy or transition temperature due to irradiation. Crack-arrest behavior of A533 grade B class 1 steel was examined for temperatures extending above the onset of Charpy upper-shelf. Crack-arrest experiments that use wide-plate specimens have shown crack arrest occurring prior to transition to tearing or tensile instability. High values of crack-arrest toughness have been recorded (static values above 400 MPa m that are well above the maximum value that safety assessment criteria assume such materials can exhibit. A validation experiment was performed by exposing an intentionally flawed HSST intermediate test vessel to combined pressure and thermal transients. The experiment addressed warm-prestressing phenomena, crack propagation from brittle to ductile regions, and crack stabilization in ductile regions. Test and analysis results are summarized.

Time dependent ductile crack extension in A533B class I steel

Four wide plate specimens manufactured in A533B Class I, 90 mm thick by 500 mm wide containing through-thickness or semi-elliptical surface fatigue cracks were tested at +70°C. These specimens were subjected to a series of increasing applied loads, each of 100 h duration, until failure. Testing was performed using a computer interactive 40 MN load controlled tensile testing rig. Values of the fracture toughness parameters J and crack tip opening displacement (CTOD) were derived from the recorded values of applied load, plate extension and crack mouth opening displacement. The influence of loading rate, degree of yield containment and crack orientation on the time dependent behaviour is assessed and compared with data obtained from wide plate and bend tests under monotonic loading and from bend tests conducted with a variable loading rate, with hold periods, under crack mouth opening control. Interpretation of the results provides a clearer understanding of low temperature time dependent ductile crack extension and enables the identification of the conditions under which this phenomenon is apparent, to allow the necessary adjustments to failure assessments.

Fatigue Life of Welded and Bolted Repair Parts

Fatigue crack propagation and residual stress measurement tests were conducted by using deep‐notched wide plate specimens with repaired parts. The main purpose of this study was to evaluate numerically the effects of some weld repair methods and a mechanically patching method with high strength grip bolts on residual fatigue life. The test results proved that the conventional welded repair method with no special treatment reduced fatigue life due to high tensile residual stress induced by welding repairs. However, through application of adequate treatment to cracks, compressive residual stress was induced in repair welds to increase the fatigue life. The remaining fatigue life of welded repair parts was further investigated using Fracture Mechanics. The patching method with high strength bolts and welded splice plates, on the other hand, had a remarkable effect on retarding the fatigue crack growth rate by decreasing it after bolted repairs to about 1/100‐1/1,000.

Influence of yielding behaviour and stress-strain law on the failure analysis

The yielding behaviour and its influence on failure have been investigated for different structural steels. The yield strength and the flow stress of bcc steels as a function of temperature and strain rate was described quantitativly with the mechanism of thermally activated flow. A description of strain hardening behaviour of materials has to distinguish between a purely mathematical approximation of the stress-strain curve (Ramberg-Osgood, Ludwik's equation) and the real strain hardening of the material ( dσ t dϵ t ). The estimation technique according to Shih and Kumar and the Two-Criteria-Approach, which take into consideration the strain hardening of the material with increasing plastic deformation, was used to estimate the critical loads of center cracked wide plate specimens.

Experimental Investigation on the Relationship between Brittle Fracture Initiation and Arrest Toughnesses of 9% Ni Steel

The objective of this paper is to investigate the relationship between fracture toughnesses of 9% Ni steel at brittle crack initiation and at brittle crack arrest. It is the authors' point of view that the difference between these fracture toughnesses is due to the difference in strain rates. Based on this assumption, the effect of strain rate on the fracture initiation toughness was investigated by three-point bend test, while the fracture arrest toughness was investigated by Compact Crack Arrest (CCA) test. On comparing fracture initiation toughness, Kc, with fracture arrest toughness, Kca, it was found that Kca was almost equal to or higher than Kc. The cause is considered to be the effect of ductile lips left below the plate surfaces. This led the authors to the conclusion that an initiated brittle crack can inevitably be arrested after a short extension even if external force does not fall.To verify the finding, a notched very wide plate specimen was tested. The result showed that only a pop-in type of fracture could occur, that is, an initiated brittle crack was arrested after the extension comparable to plate thickness. The notched wide plate test also verified that the reinitiation of brittle fracture from the arrested crack could not take place without the substantial increase in external load.

Elastic-plastic analysis of local and integral straining behaviour in a cracked plate

For components of the primary coolant system of the German LMFBR prototype reactor SNR-300, integrity against anticipated accidents (Bethe-Tait) has to be shown for a cracked structure. Within this programme a number of tests with cracked wide plate specimens yielding overall limit strains of approximately 15% have been run; finite element calculations have been initiated for the wide plate geometry. The paper discusses the straining behaviour of a cracked plate by considering the numerical simulation of structures strained up to such high levels. The stress-strain diagram of the weldment of the austenitic stainless steel X6 CrNi 18 11 at 450°C has been used. Plane strain and stress conditions have been prescribed. The original plate dimensions ( t=thickness=40 mm; h=height=400 mm) have been used as well as a similar, but smaller plate of t=8.8 mm width. The crack length is defined as 0.1 t. The results show that for a cracked plate under high plastic strain the near-crack-tip-field values still govern the structural mechanical behaviour. Concerning the absolute dimensions the effects known for elasticity retain their influence in the plastic regime; however, the crack location becomes more unimportant with increasing strain, i.e. the appropriate pure geometry factor tends to unity in the plastic regime. The center-crack, defined as 2 a=0.1 t, corresponds to an equivalent edge crack of depth a=0.05 t in the elastic case. It can be shown that for high plastic strains this correspondence remains fully valid.

厚板６０ｋｇ／ｍｍ?Q２?R高張力鋼溶接部のぜい性破壊発生特性 Ｉ 切欠角変形付広幅引張試験による検討

Brittle fracture initiation characteristics of manual arc and submerged arc welded joints of 60 kg/mm2 high strength thick steel plates were investigated by testing wide plate tension specimen with angular distortion and with a surface notch. The test results were analized by fracture mechanics. The results are summarized as follows.:(1) The lowest V-charpy impact toughness in the weld zone was obtained at the weld fusion line.(2) At temperatures above 0°C, the fracture initiation stress obtained from the wide plate specimens was not so lower than the yield strength of the steel.At lower temperatures, however, the fracture initiation stress was greatly lowered. The decrease was particularly remarkable below -10°C in transversely welded W(1) joints and below -5°C in T-type welded W(1)+W(2) joints and also repair welded joints with some residual stress.(3) The fracture toughness was calculated quantitatively from the fracture initiation stress. The values calculated in the transversely welded W(1) joints, the T-type welded joints and the repair welded joints decrease in a single band as a function of temperature.(4) The fracture toughness in the weld fusion line of the welded joints for 60 kg/mm2 high strength thick steel is high value above 0°C, but it is remakably lowered in the temperature range of -5-20°C and shows larger dependency on temperature than that for, 80 kg/mm2 high strength thick steel. And this steel does not show the embrittlement by stress relief annealing. Therefore, there is little difference in frecture toughness between as-welded spcimen, stress relieved specimen and repair welded specimen.(5) The fracture toughness values of the manual arc welded metal and of the submerged arc weld fusion line are almost equal to that of the manual arc weld fusion line.

厚板80kg/mm<SUB>2</SUB>高張力鋼溶接部の脆性破壊発生特性(第3報)

Effects of residual stress and repair welding on the brittle fracture initiation in weld fusion line of the manual arc welded joints for 80kg/mm2 high strength steel were investigated using the wide plate tension test specimen with an angular distortion and a surface notch. And the results were analyzed by application of the fracture mechanics. The main results are summarized as follow:(1) The maximum residual stress of T-shaped welded joints is about 50kg/mm2 in the direction of weld line. That of repair weld zone is about 35kg/mm2 in the direction of right angle with weld line and is about 50kg/mm2 in the direction of weld line.(2) The brittle fracture strength of the T-shaped welded wide plate specimen with a surface notch, is lower than that of the transversely welded W(1) specimen. The test results with the specimen in which residual stress is superimposed can be adjusted quantitatively by taking stress intensity factor KR of Eq. (4) into consideration. The fracture toughness obtained by the above procedure agrees with that of a transversely welded W(1) specimen without residual stress.(3) The fracture toughness of the repair welded wide plate specimen almost equals to the minimum values of stress relieved welded joints when the notch tip is heated to the temperature range, 300-550°C, in repair welding. Therefore, the fracture stress of the repair welded joints is extremely lowered if defects remain in the fusion line. But it is as high as the fracture stress of the transversely welded W(1) joints as welded, when the maximum temperature of notch tip is below 250°C in repair welding.(4) It is important that the maximum heat temperature of fusion line is below 250°C in repair welding. Removal ofhydrogen by heating is effective, but its temperature should be below 250°C.(5) We calculated relation between fracture stress and crack length of T-shaped welded joint and repair weld zone for welded structure.