Main Plate Research Articles

Further assessment of the coupling load decomposition technique for the vibration analyses of planar coupled structures

Vibration analyses of various line-coupled structures are conducted in this paper using the newly developed Coupling Load Decomposition technique. Examples are given to illustrate how this approach may be used in practice. Various factors related to the practical application of the technique are investigated. The approach is applied to systems composed of a main plate as the master structure and different substructures. Plate-like structures and beam-stiffened plates are studied and the results are compared to finite element results. Applications to the case of periodic structures or systems with repeated substructures are also investigated. It is shown that the method is very efficient in such cases leading to satisfactory results in low and medium frequency ranges.

Plasma Control with Conducting Plates in the Anchor Region of the GAMMA 10 Tandem Mirror

This paper describes the effect of conducting plates installed in the transition region of the minimum-B anchor-cell of GAMMA 10 for the purpose of the improvement in plasma performance. The conducting plates are fixed closely to the plasma surface where the cross section of the plasma is flatly elongated in the transition region. Electrical characteristics of the conducting plates are investigated by changing the resister connected between the plates and the machine ground. Effects on the plasma parameters of the conducting plates are studied and it is found that the floating condition of the plates leads to the increase of the plasma density during potential formation. It is also find that the effect is reduced in the case that the space of main plates facing each other is widened. Existence of electric current in azimuthal direction of plasma cross section is discussed from the viewpoint of radial loss mechanism.

Comparison of fatigue life for T and cruciform welded joints with different combinations of geometrical parameters

The fatigue life for T and cruciform welded joints containing different extents of lack of root penetration was calculated for different combinations of geometrical parameters, including thicknesses up to 45 mm, by integration of the Paris law and use of stress intensity factor solutions calculated previously. The effect of attachment and main plate thickness, weld leg length and initial lack of penetration size on fatigue life was studied. For T welded joints, the effect of different support span has also been investigated. The results are reported as fatigue life curves for both types of joints. All the curves show higher fatigue life for T joints than for cruciform joints. These curves were then compared with the S– N curves for failure from either weld toe position or on the weld throat, proposed by Eurocode 3. The maximum tolerable sizes for lack of penetration at which weld toe failures would still rule are reported for each case. Results of experimental tests are in good agreement with the predictions.

Geometric regularities of the lithosphere plate structure

Abstract It is shown that the positions of the centres of the main and medium plates display an elegant order and allow us to bring into consideration the special lithosphere reference system (LRS). The following notions are introduced: the lithosphere equator, north and south poles of the lithosphere, etc. The plane of the lithosphere equator is inclined at the angle of 26°7 to the Earth's equator plane and has longitude of the ascending node 3.4° W in the Greenwich (Earth's) reference system (ERS). In the new reference system (LRS), the boundaries of the plates are situated in the zone of latitudes ±70°. The lithosphere belt of the plates is clearly distinguished: the plates are arranged along the equator of the lithosphere. A new phenomenon of pairing of the triple junctions of the plates has been discovered.

The influence of substructure modeling on the predicted vibroacoustic response of a fluid-loaded plate system

When predicting the vibroacoustic behavior of complex systems, one must decide how much effort to spend on modeling the features with dimensions smaller than those of the primary structure. To investigate these issues, this work examines changes in the vibroacoustic response of a semi-infinite fluid-loaded plate due to variations in modeling details associated with an attached substructure. The substructure consists of a smaller plate supported by springs along each edge. To examine the impact of spring scales, the manner in which the elasticity is distributed over the main plate is varied. Substructure modeling issues are examined by varying the number of degrees-of-freedom allowed in the substructure model. Both the combined system response and acoustic radiation from the main plate are computed using the Acoustic Surface Variational Principle and Hamilton’s Principle. Furthermore, sensitivity relationships that express changes in the system response to changes in the scale of the spring elements are presented. For the cases considered, it is shown that details associated with the scale of the spring element are only important for frequencies near or below the resonances of the isolated subsystem. Furthermore, only the dynamics of the substructure that includes rigid-body-type motions is important. [Work supported by Georgia Tech.]

Two-dimensional and three-dimensional magnification factors, Mk, for non-load-carrying fillet welds cruciform joints

Two-dimensional M k factors at the weld toe of non-load-carrying transverse welded attachments are derived indirectly using the principle of superposition and stresses obtained from boundary element analysis. The results are in good agreement with that obtained by Maddox and Andrews [1] for different ratios of l/ T, where l is the weld toe to weld toe distance, and T is the main plate thickness. Further three-dimensional boundary element analysis using realistic crack shapes, confirm that l/ T is the most important parameter. Two-dimensional edge cracks analyses overestimate and underestimate the deepest and surface points M k values by as much as 15% and 65% respectively. Parametric equations for three-dimensional M k are proposed for design purposes.

Comparison of the stress intensity factor of T and cruciform welded joints with different main and attachment plate thickness

The present study compares the stress intensity factor of T and cruciform welded joints containing Lack of Penetration defects and gives new results in the form of parametric equation coefficients for the T joint case. Cruciform and T welded joints with equal and unequal attachment and main plate thickness have been analysed by the finite element method. For the T welded joints the effect of different support spans has also been studied. Comparison of the results shows that in nearly all cases, the stress intensity factor of the cruciform joint is higher than the T joint.

Relationships between local and structural stress in the evaluation of the weld toe stress distribution

This paper deals with the problem of determining, by proper stress analyses, the stress fields near arc-welded joint toes and the use of such distributions in fatigue strength predictions. In particular, the relationships between the local stress field and the structural (geometrical) stress field are investigated under the hypothesis that highly stressed zones remain under linear elastic conditions. The local stress distribution is given for different joints in terms of the relevant notch stress intensity factors (NSIFs), having modelled their weld beads like re-entrant sharp corners. The structural stress distribution is, in contrast, the stress field linearly distributed through the thickness of the welded plates (and sometimes on the plate surfaces), beyond the zone affected by local effects due to the beads. The aim of the proposed methodology is to provide an explicit link between NSIF values and structural stress at a well-defined distance from the weld toe. Such a distance is chosen equal to the main plate thickness. The expressions obtained allow a direct comparison with the well-known “hot-spot stress” approach; it is demonstrated that there are circumstances of practical interest in which the usual hot-spot stress (which is the simple linear extrapolation at the weld root of the structural field) is not able to predict accurately the fatigue behaviour of the joints, whereas the combination of structural field and NSIF-based field is more advantageous. The complete methodology can be simplified for rapid calculations involving weldments of different types. Some examples are also reported and discussed.

Fatigue behaviour of a box‐welded joint under biaxial cyclic loads

Multiaxial fatigue behaviour of box‐welded (wrap‐around) joints in a JIS SM400B steel (12‐mm‐thick plate) was examined using a biaxial fatigue test facility. For the specimen, two stiffeners were attached to a main plate by a CO2 semi‐automatic welding procedure. Residual stress measurements and finite element (FE) analyses were also performed. Fatigue tests were performed under both uniaxial and biaxial (mainly out‐of‐phase) cyclic loads, and both results were compared and examined.It was found that fatigue cracks in the biaxial fatigue test specimens were initiated at the boxing‐weld toes and propagated almost in the direction of the lateral loads. This is considered to be due to the dominant direction of tensile residual stresses from welding and the stress concentration in the vicinity of the boxing‐weld toe.From the relation between the strain range near a weld toe, Δε5 , and the fatigue lives, it was found that crack initiation life, Nc , was almost equivalent in the biaxial and uniaxial fatigue tests, while the failure life, Nf , was slightly longer in the biaxial tests. However, when the fatigue lives are put in order using the stress range near a weld toe, Δσ5 , the crack initiation life, Nc , in the out‐of‐phase biaxial tests (phase difference of π) is ~30% lower than in the in‐phase biaxial and uniaxial tests, while the failure life, Nf , was almost equivalent in the biaxial and uniaxial tests. From these results, it is concluded that an increase in Δσ5 (lowering of the minimum value of σ5 ), induced by the out‐of‐phase lateral loads, leads to an increase in fatigue damage where the high tensile welding residual stresses exist in the vicinity of the boxing‐weld toe.Finally, a simple life estimation for the biaxial fatigue tests was made using FE analyses and the results of the uniaxial fatigue tests, proving that the effects of the lateral loads should be taken into consideration.

Residual Stress Reduction and Fatigue Strength Improvement by Controlling Welding Pass Sequences

The effects of residual stress on fatigue strength at a weld toe in a multi-pass fillet weld joint were evaluated. The residual stresses in the weld joints were varied by controlling the sequence of welding passes. The residual stress at the weld toe was 80 MPa in the specimen whose last welding pass was on the main plate side, but it was 170 MPa in the specimen whose last pass was on the attachment side. The fatigue strength was nearly the same at high stress amplitude for both specimens, but the fatigue strength of the specimen whose last weld pass on the main plate was higher than that of the other specimen at low stress amplitude. This difference is due to the magnitude of the initial residual stress and the relaxation of the residual stress under fatigue cycling. The effects of the residual stress were shown in a modified Goodman diagram, in which residual stress is treated as a mean stress. [S0094-4289(00)01701-1]

Results from geodetic measurements in the western part of the African–Eurasian plate boundary

Since 1988 the Astronomical Observatory (University of Porto) and the Institute for Geodesy and Navigation (University of the Federal Armed Forces, Munich) have been involved in a common project to establish and maintain a high precision geodetic network in the area of the Azores triple junction, along the Western boundary of the Eurasian plate. The network has stations on three of the main plates — North American, Eurasian and African. This is a long-term project, with planned re-observations every three years. First epoch measurements were done in 1988, using the Global Positioning System (GPS). A second GPS campaign was conducted in 1991, during which the network was enlarged to include more stations on the African plate in order to monitor also the Azores–Gibraltar plate boundary. Further strength of the network was obtained by the establishment, in 1992, of a gravimetric network in the Azores archipelago; the gravimetric network comprises two absolute stations and relative measurements on all the nine islands of the archipelago. Re-observation campaigns, with GPS and gravity measurements, took place in 1993 and 1994. This paper focuses on comparison of the GPS results achieved in the different campaigns. Annual values for point displacement, direction and magnitude, are computed for some of the stations and analyzed in light of the results derived from geological and geophysical data interpretation. Our preliminary geodetic results show ocean spreading across the Mid-Atlantic Ridge at rates consistent with those determined from 3MY averages (NUVEL-1). In addition, there is marginal evidence for a leaky transform boundary transversing the central Azores islands. Possible directions for future research on the dynamics of this plate boundary are also presented.

Improvement of Fatigue Strength through Residual Stress Reduction by Controlling the Sequence of Welding Pass.

The effects of residual stress on fatigue strength at a weld toe in multi-pass fillet-welded joints were evaluated. The residual stresses in the specimen were varied by controlling the sequence of welding passes. The residual stress at the weld toe was 80 MPa in the specimen whose last welding pass was on the main plate, but it was 170 MPa in the specimen whose last pass was on the attachment. The fatigue strength of the specimens was nearly the same at high stress amplitude, but the fatigue strength of the specimen whose last welded pass on the main plate was larger than that of the other specimen at low stress amplitude. This difference is due to the magnitude of the initial residual stress and the relaxation of the residual stress under the cyclic loading. The effects of the residual stress were shown in the modified Goodman diagram, in which residual stress is treated as a mean stress.

Fatigue behavior of boxing welded joint under biaxial cyclic loads

Multiaxial fatigue behavior of boxing welded joints of a JIS SM400B steel (12 mm thick plate) was examined using a biaxial fatigue test system. For a specimen, two stiffeners were attached to a main plate by a CO2 semi-automatic boxing welding. Residual stress measurement and finite element (FE) analyses were also done. Fatigue tests were performed under both uniaxial and biaxial (mainly out-of-phase) cyclic loads, and both results were compared and examined.It was found that fatigue cracks in the biaxial test specimens were initiated at the boxing weld toes and propagated almost in the direction of lateral loads. And the relation between stress range near a weld toe, Δσ5, and crack initiation life, Nc, was almost common in the biaxial and the uniaxial tests, proving that the increase of Δσ5 due to the lateral loads is fully effective to the increase of cyclic fatigue damage because of the high tensile welding residual stress near the boxing weld toe. On the other hand, failure life, Nf, was slightly longer in the biaxial tests than in the uniaxial ones.Finally a simple life estimation for the biaxial tests was made using the results of the FE analyses and the uniaxial tests, giving a little conservative results due to overestimation of stress range Δσ5 and the difference in crack propagation life between the uniaxial and the biaxial tests.

Load-Carrying Fillet Welds Using Dual Boundary Element Method

The fatigue behavior of load-carrying cruciform fillet welded joints has been studied extensively using the dual boundary element method. This method, which incorporates two independent boundary integral equations, uses the displacement equation to model one of the crack boundaries and the traction equation to model the other. As a consequence, the analysis of the welded joints can be performed effectively in a single-region formulation. It is shown that the stress intensity factors (SIFs) at the weld toe and at the weld root are approximately equal when γ and λ are equal to 1.0 and 1.7, respectively, where γ and λ are the ratios of the embedded crack length 2a, and weld leg length w, to the main plate thickness T. In other words, the weld size, w, should be <1.7 times the main plate thickness in order for the crack to propagate from the weld root. Using these conditions, the magnification factor, Mk, and the SIFs, K, at the weld root, are calculated using the J-integral in the analysis. They are compared...

Ultimate Compressive Strength of Orthogonally Stiffened Steel Plates

An approximate method to predict ultimate strength is presented for orthogonally stiffened steel plates subjected to uniaxial compression, based on the orthotropic plate theory. The present method can treat all collapse modes which occur on the orthogonally stiffened plates; for example, overall buckling of the main plate together with longitudinal and transverse stiffeners, and overall buckling of the main plate between the adjacent transverse stiffeners together with longitudinal stiffeners. In addition, the method includes the effect of the local buckling that occurs on the longitudinal stiffeners and/or the plate panels bounded by both the longitudinal and transverse stiffeners. Thus the method can be used for the practical design of actual steel stiffened plates; i.e., subjected to eccentric compression, nonuniformly stiffened, or having large stringers together with longitudinal stiffeners. Many test results of longitudinally and orthogonally stiffened steel plates subjected to uniaxial compression are used for comparing with the ultimate strength predicted by the present method. It is found from comparison that the present method shows a good agreement with the test results.

Localised impact of Sitka spruce (Picea sitchensis (Bong.) Carr.) on soil permeability

A typical upland soil catena afforested with Sitka spruce (Picea sitchensis (Bong.) Carr.) was chosen to examine the localised effect of trees on soil permeability. A borehole permeameter was used to measure soil permeability at 0.2 m and approximately 2 m distance from the stem of 20 trees at a fixed measurement depth of 0.25 to 0.45 m. In the case of the ‘near-tree’ measurements, this corresponded to soil beneath the main root plate of each conifer. Two principal elements of the soil catena: the ferric podzol of the mid-slope and histosol soil of the foot-slope were investigated.

Study on Design Technology of Multiblade Fan. (2nd Report. Basic Study on Simple Numerical Model for Dynamic Analysis of Rotating Fan Shaft System).

This study aims to clarify deformation and stress generation mechanisms in a multiblade fan under static and dynamic torsional moments, and to establish a simple lumped inertia model for the dynamic analysis. Static and dynamic torsional tests were carried out to investigate the deformation and stress of the blades. Numerical calculations of the deformation and stress using the finite element method were also carried out under the same loading conditions. By comparing the experimental results with the numerical ones, the generation mechanisms of the deformation and stress of the blade were clarified. The results of these investigations are as follows. The relative displacement between the main and side plates causes the bending deformation in the flatwise and edgewise directions and the torsional deformation of the blade under the static and dynamic torsional moments. The stress caused by the deformation in the flatwise direction mainly governs the strength of the blade. Good coincidence is found between the static stress distribution and the dynamic one in the first mode. This means that the simple lumped inertia model is suitable for further dynamic analysis of the rotating fan shaft system.

Fatigue Life Estimation of Welded Joints of an Aluminium Alloy under Superimposed Random Load Waves (a follow-up report)

Fatigue behavior of boxing welded joints of JIS A 5083 P-O Al-Mg alloy was examined. For a specimen, a 20 mm thick stiffener was attached to a 20 mm thick main plate by a MIG boxing welding. Previous to fatigue tests, residual stress measurement, a static loading test and an elastic finite element analysis (FEA) were carried out. The residual stress in the fatigue stress direction was 135 MPa at a distance of 5 mm from a boxing weld toe, and the FEA gave a fairly good estimation for the elastic strain distribution near the boxing weld toe.Then fatigue tests were performed under both constant amplitude and random loads by 3-point bending. For a load wave in the random loading fatigue tests, a direct current component, a zero-mean narrow band random process, and a high frequency component were variously and selectively combined and superimposed.As a result, a reference stress 65, which was determined as the stress at a distance of 5 mm from a boxing weld toe, was proved effective in reducing the amount of scattering in the fatigue test results. And it is also found that the crack initiation lives determined by the 5% drop method largely scattered because of the determination error brought by the 5% drop method itself, showing to be unsuitable for putting the fatigue test results in order as in a S-N diagram.With regard to the effects of high frequency components, it was found that a simple handling of fatigue data using the RMS value of stress is not available while arrangement using a representative frequency is effective, and that neither the range count method nor the peak to peak count method are suitable to those superimposed wide band stress waves.Finally the life estimation procedure proposed in the former report, which comprises a 2-dimensional rainflow method, the modified Goodman's relation and the modified Miner rule, was shown to be valid also in this study.

Vibration Control of Plates by Plate-Type Dynamic Vibration Absorbers

In this paper, a new plate-type dynamic vibration absorber is presented for controlling the several predominant modes of vibration of plate (mainplate) under harmonic excitation, which consists of a plate (dynamic absorbing plate) under the same boundary condition as the main plate and with uniformly distributed connecting springs and dampers between the main and dynamic absorbing plates. Equations of motion of the system in the modal coordinates of the main plate become equal to those of the two-degrees-of-freedom system with two masses and three springs. Formulas for optimum design of the plate-type dynamic vibration absorber are presented using the optimum tuning method of a dynamic absorber in two-degrees-of-freedom system, obtained by the Den Hartog method. Moreover, for practical problems regarding large-scale plates, an approximate tuning method of the plate-type dynamic absorbers with several sets of concentrated connecting springs and dampers is also presented. The numerical calculations demonstrate the effectiveness of the plate-type dynamic absorbers.

γ Precipitates in Cu-Zn-Al Alloys Studied by High Resolution Electron Microscopy

A HREM study of small γ-phase precipitates in β Cu-Zn-Al single crystals is presented. The images taken at atomic resolution show the perfect coherency of the precipitates are located at the antiphase boundaries of the matrix. In turn, several microdomains separated by internal antiphase-like boundaries are present inside the precipitates. Nevertheless, the study of the boundaries at atomic level shows that the shift associated to the boundary (one atomic plane along ) is not a translations vector of the lattice. When the precipitates are embedded in a martensitic (18R) matrix, the precipitates loose the coherency. A mechanism of martensite/precipitate accomodation based on the formation of a small nanoplate at the interface between the main martensite plate and the precipitate, together with the formation of dislocations, has been observed