Composite Wedge Research Articles

Rivet Structural Design and Process Optimization for the Double-Sided Countersunk Riveting of Composite Wedge Structures

Within the double-sided countersunk riveting process of aircraft wings with a composite wedge structure, riveting consistency is poor, and composite damage is severe, which seriously affects the performance and reliability of the aircraft structure. This paper used the principal stress method to establish a stress model of countersunk riveting, and, based on the analysis of the stress on the structure during the pressure-riveting process, a composite structure rivet was designed. A finite element simulation model of the double-sided countersunk riveting of composite wedge structures’ composite rivets was established. The influences of the structure and the matching parameters of composite rivets on both the plastic flow of pressure riveting and the compressive stress of the structure during the pressure-riveting process were analyzed. The structural parameters and riveting process of composite rivets were optimized. The results show that the composite rivet structure could significantly reduce the contact-compressive stress at the riveting joint by more than 20%, thereby reducing the damage caused by the riveting to the composite material. For 4 mm rivets, an aperture of 4.04~4.06 mm can achieve precise relative interference riveting at 0.6% to 1.0%. Employing a 2.6 mm rivet elongation can exactly fill the countersunk hole of the wedge.

Experimental study of the effectiveness of stress reduction near V-shaped notch filled with a certain material

A variant of healing a V-shaped notch in an elastic body using an elastic material to fill the notch cavity is considered. The filling material changes the stress singularity at the apex of the V-shaped notch. The degree of changes depends on the correlation of mechanical and geometric parameters of the elastic filler with the mechanical parameters of the base material. Previously, this problem was comprehensively investigated based on the comparative analysis of the results of numerical modeling of the stress singularity exponents for a closed bimaterial wedge and a homogeneous wedge with stress-free edges at different ratios of the opening angles and elastic moduli of the homogeneous parts of the composite wedge, and at different values of Poisson's ratios. It was found that for a closed bimaterial wedge, the stress singularity in the symmetrical (with respect to the bisector of the opening angle) stress state disappears when the value of the Poisson's ratio of the material of one part (with a smaller opening angle) reaches 0.5. By means of numerical models it has been shown that the singulaity of stresses and, as a consequence, stress concentration can be eliminated even when the values of the elasticity modulus of the filling weakly compressible material is several orders of magnitude lower than the elasticity modulus of the base material. This finding made it possible to eliminate the stress singularity at the apex of the V-shaped notch when its cavity was filled with a material, whose Poisson's ratio is close to 0.5. In this work, an experimental study was carried out to substantiate and verify the effectiveness of reducing the stress concentration near V-shaped notch by filling its cavity with a material whose Poisson's ratio is close to 0.5.

Optimization of anchorage and deviator for concrete beams prestressed with external fiber-reinforced polymer tendons

This paper focuses on the optimization of anchorage and deviator for concrete beams prestressed with external basalt fiber-reinforced polymer (BFRP) tendons. A composite-wedge (CW) anchorage for BFRP tendons was first developed. The dimensions of the wedge were optimized using finite element (FE) analysis. Additionally, a three-dimensional deviator-tendon FE model was established, and the ratio of the curvature radius of the deviator to the radius of the tendon (Rd/Rp) and the bending angle (θ) of the BFRP tendon were optimized. Furthermore, an experimental study on the flexural behaviors of a non-prestressed concrete beam and a beam prestressed with external BFRP tendons was conducted. The results show that the proposed CW anchorage achieved an anchor efficiency factor of 85%. The recommended lower limit value of Rd/Rp is 200, and the upper limit value of θ is 5°. The RC beam prestressed with external BFRP tendons exhibited enhanced flexural behaviors, compared with the non-prestressed RC beam. The BFRP tendons at the anchor zones and tendons at the deviators remained intact at the ultimate load of the beam. The results validate the effectiveness of the anchorage and deviator parameters.

Composite-Wedge Anchorage for Fiber-Reinforced Polymer Tendons

A novel composite-wedge anchorage is proposed here for prestressing fiber-reinforced polymer (FRP) tendons. The composite wedge was designed and optimized in terms of the length and elastic modulus of the wedge segments via finite-element analysis. The manufacturing technologies for the composite wedge involving a molding process, are presented in detail. Static, creep, and fatigue tests on basalt FRP (BFRP) tendons with the proposed anchorages were conducted. The tensile capacity, long-term deformation, and fatigue life of the tendon–anchor assemblies were analyzed. The experimental results show that the proposed anchorage exhibits an anchor efficiency factor of up to 91%; the corresponding value for a conventional steel–wedge anchorage is only 80%. The tendon–anchor assembly displays a creep behavior similar to that of BFRP tendons. Furthermore, the system survives 200 million cycles of fatigue load at a maximum fatigue load of 0.5 Fu (Fu is the tensile capacity of the tendon–anchor assembly) and a load range of 0.05 Fu. Wedge–sleeve and tendon–wedge sliding under a sustained load or cyclic load cannot cause considerable prestress loss in practical engineering. The results validate the effectiveness of the proposed anchorage under service loads and demonstrate the application prospects of this anchorage.

Numerical investigation of stress concentration at the tip of the V-notch partially filled with material

One of the ways to reduce the stress level in the vicinity of V-shaped notches is to fill them with material. The effectiveness of achieving this result is largely determined by the mechanical characteristics of the filling material. The study of the stress state in the vicinity of the tip of a V-shaped notch is generally related to consideration of the composite wedge problem, which in the framework of the classical theory of elasticity, can have singular solutions with infinite values of stresses at the wedge vertex. The paper presents solutions for a composite closed wedge, which allows us to determine the range of mechanical characteristics and angles of the composite wedge, at which there is no stress singularity at the vertex. The proposed variant of the computational procedure, which is based on the finite element method, makes it possible to find a relationship for stresses in the vicinity of the wedge vertex, providing the evaluation of the stress singularity indices and constants known as stress singularity intensity factors. In real industrial technologies currently used for filling notches with another material, a small region (cavity) generally remains unfilled in the vicinity of the notch tip. This defect becomes more pronounced at small notch angles. In the presence of a cavity at the notch tip, a singular solution exists at any mechanical characteristics of the filling material. The developed algorithm has been used to calculate the values of the intensity factor of singularity for a V-shaped notch partially filled with materials, which either eliminate or preserve the stress singularity in the case of complete filling. The results obtained demonstrate that at the tip of the notch partially filled with another material the singularity intensity factor can be significantly reduced.

Anti-plane impact of a composite wedge with radial cracks

The Laplace transform of stress field in a cylindrically anisotropic elastic wedge, fixed at an edge and traction-free at the other, containing a screw dislocation with time-dependent Burgers vector is obtained by means of integral transform method. Energy dissipation in the wedge is modeled by viscous damping. Furthermore, solution to an intact wedge subjected to the dynamic anti-plane point load is obtained. These solutions are utilized to construct integral equations for a wedge weakened by several radial cracks subject to anti-plane impact loads. The integral equations are of Cauchy singular type. The stress analysis around a crack tip in cylindrically anisotropic material reveals that power of stress singularity depends upon the ratio of material stiffness coefficients. Therefore, a general definition for crack Stress Intensity Factor (SIF) is rendered for any power of stress singularity at a crack tip. Moreover, the numerical procedure for the solution to Cauchy integral equations is extended to solve integral equations with general power of singularity of solution. The procedure is utilized to obtain Laplace transform of the cracks SIFs. In the case of a cracked wedge under impact loads the inverse Laplace transforms of SIFs are determined numerically. To verify the formulation the quasi-static case of all the examples is solved by means of a different procedure. The results of latter case are compared with the dynamic solutions as time tends to infinity. Interaction between cracks, effects of structural energy dissipation, and wedge geometry on cracks SIFs are studied.

The stress singularity order in a composite wedge of functionally graded materials under antiplane deformation

In this paper, finding the order of singularity in multi-wedge systems containing elements made of functionally gradient material (FGM) with an angular gradient under antiplane deformation is studied. These elements are proposed to be modeled by means of multi-wedge composite, where the shear modulus changes from wedge to wedge according to a certain functional dependence (in

Stress Analysis of Orthotropic Wedge Loaded on the Apex

The complex variable function including a material parameter is analyzed for the solving the mechanic problem. Typical stress boundary condition for a wedge is considered to orthotropic materials. By constructing new stress function, the mechanic analysis of the wedge subjected to a concentrated force is carried out. The stress boundary problem and the governing equation are studied. The formulae of the stress fields in rectangular and polar coordinates are derived for the composite wedge.

Elasticity Solution of Composite Material Wedge Loaded with a Concentrated Moment

The complex variable functions are used and analyzed for the solving the mechanic problem of composite plates. The stress boundary condition for composite material wedge is considered. By constructing new stress function, the mechanic analysis of the composite material wedge subjected to a concentrated moment is conducted. The stress boundary problem is studied and the basic governing equation is solved by using the complex function method. The formulae of the stress fields are derived for the wedge loaded with a concentrated moment.

Effect of a wedge-shaped insert of the functionally graded material on the stress singularity in a composite wedge structure under antiplane deformation

Effect of a wedge-shaped insert of the functionally graded material on the stress singularity in a composite wedge structure under antiplane deformation

Composite wavelength tunable wedged interference structures with increased free spectral range

In the present paper, we propose a compact composite wedge interference structure by combining wedges with different geometry. We use interferential wedges with optical thickness from several micrometers to several hundred micrometers and apex angles of the order of tens microradians. The aim of the conducted study is to prove that such a structure exhibits improved optical properties in comparison to a conventional wedge. We have carried out simulations and experiments with a structure built from two wedges. We have shown that, instead of multiple transmission peaks observed for a single interferential wedge, the composite structure provides selection of a single resonance in transmission within the impact area of a large diameter monochromatic beam and enables wavelength tuning when a small diameter multi-wavelength beam is used. The first property ensures analysis of light beams characterized with a wide spectrum. The second feature allows for increase of the wavelegth tuning range at keeping spectrally narrow transmission peak if the structure is formed by a thin and a thick interferential wedges. Two such structures have been realized using a technique which we have developed. The experiments made with this structures show that the produced transmission peak is narrowed spatially and spectrally at the expense of lower transmission which achieves 50–60% of transmission ensured by the used interferential wedges.

Database of pleistocene periglacial featuresin France: description of the online version

A database of Pleistocene periglacial features in France has been compiled from a review of academic literature and reports of rescue archaeology, the analysis of aerial photographs and new field surveys. Polygons, soil stripes, ice-wedge pseudomorphs, sand wedges and composite wedge pseudomorphs are included in the database together with their geographic coordinates, geological context, description and associated references. It is hoped that this database, which aim is to be integrated in broader studies, will stimulate further work on past permafrost reconstruction and will favour greater understanding of the climatic events that lead to the formation of the periglacial features. The database is available online on the AFEQ-CNF INQUA website (https://afeqeng.hypotheses.org/487). A folder that contains photographs and sketches of the features is also available on request.

A strip cut in a composite elastic wedge

Integral equations of new three-dimensional problems concerning a cut in the plane of symmetry of a composite elastic wedge are obtained. The wedge consists of three wedge-shaped layers with a common apex, connected by a sliding clamp: in the middle there is a compressible layer with a cut, to the sides of which two identical incompressible layers are pressed. For the case of a strip cut emerging on the edge of the composite wedge, using the method of paired integral equations, the problem is reduced to Fredholm integral equations of the second kind. An expression is obtained for the stress intensity factor.

Stress singularity in a top of composite wedge with internal functionally graded material

The antiplane problem of the composite wedge consisting of two homogeneous external wedge-shaped areas and an intermediate zone of the interphase is studied. The interphase material is assumed functionally graded. It is shown that the problem in each area is harmonic within the quadratic law of inhomogeneity of the material in the transverse direction. The influence of the interphase on the stress state at the top of the wedge is analyzed. As compared to the ideal contact of external materials, the presence of the interphase leads both to decrease and increase in the singularity exponent. Moreover, the stress asymptotic may have two singular terms for some values of the composite parameters.

Evaluation of Ceramic Composite Wedge for High Speed Combustor Applications

Ultra high temperature ceramic based Zirconium composite “Wedge” was fabricated with suitable dimensions required for high speed combustor using centrifugal thermit process. The wedges are normally used in the application of the ‘flame holding’ and ‘fuel injection’ of the combustor. The basic requirement of the wedge is that it has to have a very high thermal shock resistance along with near erosion free control surface in un-cooled conditions. Also it has to withstand ultra high temperatures of the order of 2000K under extreme heat flux of 10 MW/m2 and high velocity of gas injection. Wedge shaped strut was machined with special techniques to get the required shape. It was fastened inside the water cooled rectangular duct using tungsten carbide dowel pins. The wedge was tested at the High Speed Combustor Test Facility (HSCTF), with the air flow conditions of 5bar pressure and with an average temperature of 1900K. The flow velocity was at Mach number 2 for the duration of 20seconds. Experiments were repeated many times with the same inlet flow conditions. Thermal shock conditions were created by abruptly bringing down the flow temperature from 1900K to 300K with in short duration of 5seconds. The strut was intact even after several repeated tests except for oxidation coating. The mechanical properties and microstructure characteristics of fuel strut specimens after the combustor test have been investigated and compared with just fabricated material before the test. X-ray radiography also corroborates the flaw less condition of the strut. These results have been discussed in light of the integrity and surface micro structure mechanisms involved in the evaluation process.

Periglacial structures within fluvio‐aeolian successions of the end of the Last Glaciation – examples from SE Poland and NW Ukraine

The nature of permafrost and related environmental conditions in the Weichselian Late Pleniglacial and Lateglacial are reconstructed based on the assessment of frost structures that are best documented in the Loess Belt and in plateau areas composed of glacial till. Investigations were conducted in the central‐eastern part of the European Sand Belt (SE Poland and NW Ukraine) on a fluvio‐aeolian sedimentary succession and took into account its chronological context given by luminescence dating. Various generations of periglacial structures found in these deposits indicate not only the development of permafrost (ice‐wedge pseudomorphs) and decreased humidity (composite wedge casts) but also the degradation of permafrost (large‐scale involutions) and, finally, the establishment of deep seasonal frost (frost cracks). The diversity of structures in the study region appears to result from local conditions rather than increasing continentality of climate towards the east.

A Crack Emanating from a Wedge In Dissimilar Anisotropic Materials Under Antiplane Shear

A crack in a composite wedge consisting of two dissimilar anisotropic materials under concentrated antiplane loads is analyzed. The problem of a crack in an isotropic composite wedge is solved first by using the Mellin transform and the Wiener-Hopf method. Using a linear transformation of the original composite wedge into an isotropic composite wedge consisting of dissimilar isotropic materials, the antiplane displacement and stresses for the anisotropic composite wedge are obtained from the solution for the transformed wedge. The stress intensity factor for the crack in the original anisotropic composite wedge is obtained from the solution of the crack in the transformed wedge. Special attention is given to the asymptotic problem of a wedge crack in an anisotropic bimaterial. Numerical computations are carried out to obtain the energy release rate for various apex angles and anisotropic parameters as a function of crack angle.

Interfacial wedge cracks in dissimilar anisotropic materials under antiplane shear

An interfacial crack in an anisotropic bimaterial wedge under antiplane shear is investigated. An interfacial wedge crack in an isotropic bimaterial with concentrated forces is first solved by using the Mellin transform and the Wiener–Hopf technique. The solution of an interfacial crack in an anisotropic composite wedge is then derived from the isotropic solution based on a linear transformation method. An expression for the stress intensity factor for the interfacial crack is obtained. The asymptotic problem of an interfacial wedge crack is also analyzed. The stress intensity factor is obtained in terms of the stress intensity factor of a wedge without cracks. Numerical calculations of the stress intensity factor are carried out for various wedge types such as symmetric and asymmetric wedges as well as wedges with edge cracks and kinked cracks.

Analysis of a wedge in an anisotropic bimaterial under antiplane loads

An anisotropic bimaterial wedge under antiplane shear is investigated. The problem is formulated by using a linear transformation method. Employing complex function representations of elastic fields, a complete form of elastic fields near the apex of an anisotropic composite wedge is derived. An anisotropic composite wedge subjected to concentrated loads is also analyzed. The transformed isotropic bimaterial wedge is first solved, and the solution for the anisotropic wedge is then obtained based on the linear transformation method. Expressions of the stress intensity factor for the composite wedge are obtained. Numerical computations are carried out to obtain the order of stress singularity and the stress intensity factors for three types of wedge shapes.

H-Polarized Diffraction Coefficients of a Composite Wedge Composed of a Perfect Conductor and a Lossy Dielectric

The H-polarized diffraction coefficients of a composite wedge composed of a perfect conductor and a lossy dielectric are constructed using the hidden rays of diffraction (HRD) method. The usual principle of geometrical optics is employed to trace not only ordinary rays in the physical region but also hidden rays in the complementary region. In particular, the modified propagation constants are adopted to represent the non-uniform plane wave transmission through the lossy dielectric. The HRD diffraction coefficients are expressed by the sum of the cotangent functions, of which the angular period is adjusted to satisfy the edge condition. Some HRD diffraction coefficients are plotted here.