Metallic Structural Components Research Articles

Thermal and Geometrically Nonlinear Stress Analyses of an Adhesively Bonded Composite Tee Joint with Double Support

Carbon fiber reinforced plastics (CFRP) can be successfully joined to metal or composite structural components using the adhesive bonding technique [Semerdjiev, S. (1970). Metal to Metal Adhesive Bonding, Business Books Ltd., London.]. The stress and deformation fields occurring in the adhesive joints due to the thermal loads as well as the structural loads play an important role on the joint strength since the thermal and mechanical properties of the adhesive and adherends are different. Previous thermal stress analyses of the adhesive single-lap joints with simple geometries assumed a uniform temperature distribution through the adhesive joint, consequently predicted uniform thermal strain and stress distributions. In this study, the thermal stress analysis of an adhesively bonded tee joint with double support made of unidirectional CFRP was carried out for variable thermal loading conditions along its outer boundaries and different plate edge conditions. The large displacement and rotation effects were considered using the small strain-large displacement theory. The stress fields in the adhesive layer and the composite members of two tee joints bonded to a rigid base and a flexible plate were investigated. In the thermal analysis, a reference uniform temperature was attributed to all joint members for its stress free state, and air streams with different temperature and velocity were specified along the outer surfaces of the adhesive joint. In addition, the air streams were specified in the vertical or horizontal directions to the composite plates and adhesive layer. The consideration of convective and conductive heat transfer showed that nonuniform temperature distributions occurred in the adhesive tee joints. High heat fluxes took place along the free surfaces of the adhesive fillets at the free ends of the adhesive layers. Geometrical nonlinear stress analyses of two tee joints were carried out using the calculated temperature fields for two different plate edge conditions. Since the adhesive joints consist of materials with different thermal and structural properties, the thermal strains become incompatible along the adhesive layer–plate interfaces. Consequently, the stress concentrations occurred inside the adhesive fillets around the adhesive free ends, and in the regions near the adhesive layer–composite plate interfaces. The adhesive fillets, middle region of the horizontal plate, the elbow sections of the left and right supports appeared as most critical regions of the tee joints. In addition, the support length did not have similar effect of reducing the normal and shear stresses at these critical adhesive and adherend locations.

Shape optimization of bonded patch to cylindrical shell structures

AbstractAdhesive bonding has been widely used to join or repair metallic and composite structural components to achieve or restore their designated structural stiffness and strengths. However, current analysis methods and empirical databases for composite bonded patch repairs or joints are limited to flat structures, and there exists a very limited knowledge on the effect of curvature on the performance and durability of composite bonded joints and repairs. Recently, a novel finite element formulation was presented for developing adhesive elements for conducting 2.5‐D simplified stress analysis of bonded repairs to curved structures. This paper presents the work on optimal shape design of a bonded curved composite patch using the newly developed adhesive element. The Sequential Linear Programming (SLP) method is employed as the optimization algorithm in conjunction with a fully implemented mesh generation algorithm into which new features have been incorporated. The objective of shape optimization is to minimize the maximum stress in the entire adhesive layer to ensure that the bonded patch effectively works together with the parent structure in service. Several different objective functions, related to possible failure mechanisms of the adhesive layer, are proposed to optimize the shape of a bonded patch. Copyright © 2003 John Wiley & Sons, Ltd.

Nonlinear stress analysis for bonded patch to curved thin-walled structures

Adhesive bonding has been widely used to join or repair metallic and composite structural components to achieve or restore their designated structural stiffness and strengths. However, current analysis methods and empirical databases for composite bonded joint design and composite bonded patch repair are limited to flat plate and/or flat laminate geometries, and the effects of curvature on the performance and durability of composite bonded joints and repairs is not known. This paper presents a novel finite element formulation for developing adhesive elements and conducting 2.5-D simplified stress analysis of bonded repairs to curved structures. Both large deflections of the parent structures and nonlinear adhesive behavior are incorporated in the formulation. An in-house software called BPATCH has also been developed. A variety of numerical examples are presented to illustrate the effects of curvature, moderately large deflection and adhesive nonlinear behavior on stresses in the adhesive layer. Illustrative examples also indicate the effect of patch location, i.e., internal and external patches, patch size and patch thickness.

Introduction of Ningbo Tongmuo as a Leading PM Industry in China

Ningbo Tongmuo New Materials Co., Ltd. (NBTM), which specializes in manufacturing PM components, has been enjoying rapid growth since 1995. This article gives a brief introduction of NBTM, as one of the largest manufacturers of sintered metal structural components in China.

An efficient complex variable technique for the boundary element solution of stress concentration problems arising in notched creeping metallic structural components

The present paper presents, for the first time, a direct formulation of the boundary element method using complex variable theory techniques for the solution of the inelastic stress concentration problem arising in V-notched creeping metallic structural components in the presence of high temperature gradients. The application of this method is illustrated by obtaining stress and strain components distribution fo specimens with a single edge notch subjected to tension and bending loading conditions. The stress-strain constitutive relations are assumed to be described by an internal state variable viscoplastic model. Numerical examples presented and solved by the proposed methodology are further compared with other numerical solutions obtained for different loading rates.

Tensile yield load solutions for centre cracked bilayer (clad) plates with and without repair welds

Bilayer metallic structural components in the form of clad plates are often used owing to their superior environmental and mechanical properties. During the service life of these components, cracks or cracklike defects may be developed in the clad layer and may grow into the substrate. To repair the damaged regions, local repair welding techniques are often used. The presence of this repair welded part may affect the deformation behaviour, and hence yield load level, of the structure. Therefore, in the present paper, new analytical tensile yield load solutions for centre cracked clad steel plates (austenitic cladding on a ferritic substrate) with a repair weld have been developed and these provide good agreement with experimental results. Additionally, a previously reported tensile yield load expression for a centre cracked clad plate (without a repair weld) has also been verified using the experimental results.

Viscoplastic D/BEM analysis of metallic structures with dependence on thermomechanical history

The feasibility of advanced viscoplastic models for non‐linear boundary element analysis of metallic structural components with dependence on thermomechanical history is investigated. Several numerical examples are presented using the boundary element implementation of two different internal state variable viscoplastic models to the solution of time‐dependent inelastic problems arising in creeping metallic structural components under the combined action of high temperature loading gradients and quasi‐static mechanical loading conditions. To demonstrate the efficiency of the implemented viscoplastic models, the results obtained using the direct boundary element methodology are compared with those obtained by both analytical and finite element solution as well as, for different numerical results of plane strain thermoviscoplastic deformation problems under general thermomechanical loading.

Boundary element approach to creep deformation of edge notched and cracked specimens

A direct formulation of the boundary element method using a complex variable numerical approach is presented for the time-dependent inelastic stresses in edge notched and cracked creeping metallic structural components subject to high temperature gradients. Particular attention is focused on the numerical evaluation of energy rate contour integrals in single edge cracked specimens in tension. The constitutive models used in the numerical calculation are internal state variable creep–plasticity or elastic power law creep model. Numerical results are compared with solution obtained from other methods for different loading rates.

Viscoplastic BEM fracture analysis of creeping metallic cracked structures in plane stress using complex variable techniques

This paper extends a boundary element approach developed earlier by the present author to the solution of viscoplastic fracture problems arising in creeping cracked metallic structural components undergoing plane stress deformation conditions. By using a plane stress viscoplastic formulation this work adopts the procedure of Lyness and Moler to express the derivative of displacement rate as the ratio of the imaginary part of the displacement rate to the imaginary part of a complex variable representing the coordinates of a collocation point. In this manner the evaluation of creep stresses at internal points is greatly simplified. The results thus obtained are highly accurate in comparison with conventional BEM. The application of the present BEM approach is illustrated by obtaining creep stress and strain distribution for center cracked and standard CT fracture specimens subjected to remote tensile and shear stress loading under plane stress deformation conditions.

Viscoplastic BEM analysis of creeping metallic structural components in the presence of temperature gradients

A boundary element formulation for the solution of time-dependent inelastic problems arising in creeping metallic plates at high temperatures is presented. The formulation allows the use of models of inelastic deformation using state variables for characterizing the time-dependent behaviour of metals and alloys under thermal loading conditions. The deformation of the plate is simulated using a viscoplastic model developed by Hart to describe the material behaviour. The accuracy and efficiency of the proposed method is demonstrated by obtaining stress and strain distributions for selected sample problems of cylinders under radial temperature gradients. The simulation portrayed by the present formulation is further compared with analytical and finite element solutions obtained for different thermal stressing rates.

Microwave Nondestructive Detection of Corrosion Under Thin Paint and Primer in Aluminum Panels

Detection of corrosion, under paint and primer, in various metallic structural components, particularly when used in moist and salty environments is an important practical concern. Moreover, nondestructive testing techniques that do not require paint removal are desired. Near-field microwave nondestructive inspection techniques, employing open-ended rectangular waveguide probes, have shown tremendous potential for detecting and evaluating the presence of corrosion under paint in steel substrates. The objective of this investigation has been to investigate the potential of these techniques for detecting corrosion under paint and primer in aluminum substrates. To accomplish this goal, an electromagnetic formulation, simulating detection of corrosion in layered structure using open-ended rectangular waveguide probes, was used to gain an insight into the functionality of measurement parameters such as the frequency of operation and standoff distance. In conjunction with this simulation, the dielectric properties of paint, primer, real and chemically produced aluminum oxide were measured in a wide range of microwave frequencies (2.6–18 GHz). The results showed that the dielectric properties of paint, primer and aluminum oxide are very similar to each other. Subsequently, the theoretical simulation was conducted in a wide frequency band (8.2–40 GHz). The overall result of the simulation effort was that higher frequencies and standoff distances of a few mm are more optimal for detecting thin corrosion layers under paint. Two specially prepared aluminum panels with induced areas of corrosion and surface pitting were produced as well. Using these panels and several phase sensitive measurement systems, experiments were conducted producing 2-D images of various areas of these panels. Images were produced at different standoff distances and at frequencies of 9, 11.725, 24.1, and 33.5 GHz. The overall results of the experimental investigation were extremely promising when detecting the thin regions of corrosion in these panels. This paper presents the approach and results of this investigation.

Optical fibre sensors for health monitoring of bonded repair systems

In the aircraft industry the use of externally bonded composite repairs has become an accepted way of repairing fatigue, or corrosion, damaged metallic structural components. However, current NDI and damage assessment techniques for composite repairs are passive and generally performed on ground. The challenge is to develop new techniques utilising recent analytical and experimental tools. This report examines the use of optical fibre sensors. Optical fibres offer a means of monitoring the load transfer process in these repairs, and can therefore be used to provide an indication of the integrity of the repair. This paper describes the use of an array of fibre Bragg grating strain sensors (FBGs) for the in situ monitoring of bonded repairs to aircraft structures and, in particular, the monitoring of crack propagation beneath a repair. In this work the FBGs have been multiplexed using a combination of wavelength and spatial techniques employing a tunable Fabry–Pérot (FP) filter to track individual gratings. The multiplexed FBGs were then surface-mounted on a boron–epoxy unidirectional composite patch bonded to an aluminium component. The sensors were located so as to monitor the changing stress field associated with the propagation of a crack beneath the patch. The ability of relating experimental results to sensor readings is then confirmed using both a thermo-elastic scan of the patch and 3D finite element analysis.

Three-Dimensional Mesoscale Self-Assembly

Three-Dimensional Mesoscale Self-Assembly

Strength, longevity, and failure of structural materials under multicycle loading (review)

This review provides a brief historical outline of the development of research on fatigue strength. Basic attention is focused on studies of the strength, longevity, and failure of metallic materials and structural components under cyclic loads, which have been conducted at the S. P. Timoshenko Mechanics Institute, National Academy of Sciences of Ukraine during the years of its existence. Developments of related organizations are touched upon briefly only to that degree in which they are associated with the problems under consideration.

ASM metals reference book

This reference book makes it easy for anyone involved in materials selection, or in the design and manufacture of metallic structural components to quickly screen materials for a particular application. Information on practically all ferrous and nonferrous metals including powder metals is presented in tabular form for easy review and comparison between different materials. Included are chemical compositions, physical and mechanical properties, manufacturing processes, applications, pertinent specifications and standards, and test methods. Contents Overview: Glossary of metallurgical terms Selection of structural materials (specifications and standards, life cycle and failure modes, materials properties and design, and properties and applications) Physical data on the elements and alloys Testing and inspection Chemical composition and processing characteristics

Structural design criteria for HTR — a summary report —

Abstract The results of the German research and development project ‘HTR Design Criteria’ has been presented during the workshop on ‘Structural Design Criteria for HTR’. The work is organized in four areas: (1) technical safety boundary conditions, (2) metallic structural components, (3) prestressed concrete pressure vessel, and (4) graphitic structural components. In this summary report some essentials are discussed for all four areas. On basis of these results, the formulation of structural design (KTA) rules are in preparation.

An investigation of the feasibility of the use of stabilizers in a nuclear waste canister with specific emphasis on evaluation of radiative properties

This paper investigates the feasibility and the effectiveness of using stabilizers i.e., internal metal structural components, in augmenting the heat transfer characteristics of a nuclear waste canister. The present work complements and enhances the results of a prior investigation by the authors in this area. The problem is modeled as a transient two dimensional heat transfer in two physical domains — the stabilizer and the heat producing spent-fuel rods. The results show that, for typical conditions in a waste package design, the stabilizers are quite effective in reducing the overall temperature in a nuclear waste canister. The results also show that increasing the stabilizer thickness from the present design conditions has a negligible effect on the temperature distribution in the canister. Furthermore, the results show that the presence of the stabilizers shifts the location of the peak temperature in the nuclear waste canister.

Maintenance of iron and other micronutrients in hydroponic nutrient solutions

Abstract The chelating agents DTPA, EDTA, EDDHA, HEDTA and others have been used as sources of iron in hydroponic nutrient solutions. Commercial hydroponics would be impossible without them. Although these have resulted in some success, micronutrient balance remains as an important problem in commercial hydroponic operations. Our results suggest that for a given plant species, it does matter which chelating agents are used. For some plant species, the low stability Fe chelates give advantage. The results also suggest that all of the Fe, Zn and Cu depending on pH may be chelated with good results and good control of micro‐nutrients. In commercial uses of hydroponic nutrient solutions, particularly in the Nutrient Film Technique (NFT), Fe, Zn and Cu concentrations increase with time of recycling. These micro‐nutrients can enter the system via contamination mostly through the air. Soil dust is a major contributor but Zn in metallic structural components in greenhouses is perhaps the prime contributor of Zn. ...

Shear properties of polyimide adhesives at various temperatures

In composite material structures, one of the primary limitations in minimising structural weight is the joining of various structural components. In composite structures joining is largely limited to employing adhesive bonding 1 or mechanical fasteners, 2 such as bolts or rivets, or possibly a combination of the two. Since mechanical fastening requires intermittent load paths, resulting in large stress concentrations, as well as the cutting of fibres to make the necessary holes, adhesive bonding is considered far more desirable for joining composite structural components to either other composite or metallic structural components. Concerning various adhesive systems, in order to design, analyse and optimise bonded structures 3–13 it is necessary to know the mechanical properties of the adhesives in both shear and tension. Furthermore, it is necessary to know these properties for each temperature and moisture level to which the structure will be subjected, because the adhesives today are polymeric, and therefore subjected to ‘hygrothermal’ effects, i.e. the deleterious effects of combined high moisture and high temperature. 8,10,11 Unfortunately, not many of the moderate temperature adhesives, which are mostly epoxies, have been characterised. However, a few dozen have been characterised to some extent. 11–13,15,16 One of the reasons for this lack of material property data is the lack of standardization of a suitable shear and tension test-piece configuration. However, more and more, the thick adherend shear test specimen is being accepted as the means to obtain shear properties because of the constancy of the shear across most of the length of the joint in this test configuration. 11–13,15,16