Stiffeners geometry

Fracture mechanics characterisation tests have been performed to determine the mixed mode fracture envelope of an epoxy bonded glass/epoxy composite. Analysis of lap shear, and L-stiffener geometries has shown that for this relatively brittle adhesive reasonable first estimations of failure loads can be obtained for both cracked and uncracked specimens. An image analysis technique has been developed which enables failure mechanisms to be... 

Lateral buckling is dependent on stiffener geometry. The requirements for stiffener geometry per CC2286 are as follows ... 

Suppose we want to analyze the stresses in the two stiffeners. The geometry of the sandwich-blade stiffener is actually more complicated and less amenable to analysis than is the hat-shaped stiffener. Issues that arise in the analysis to determine the influence of the various portions of the stiffeners include the in-plane shear stiffness. In the plane of the vertical blade is a certain amount of shear stiffness. That is, the shear stiffness is necfessary to transfer load from the 0° fibers at the top of the stiffener down to the panel. In hat-shaped stiffeners, that shear stiffness is the only way that load is transferred from the 0° fibers at the top of the stiffener down to the panel. Thus, shear stiffness is the dominant issue in the design. And that is why we typically put 45° fibers in the web of the hat-shaped stiffener. 

Epoxy-PVC plastisols are a type of PVC plastisol adhesive that is used in large quantities in the automobile industry. It is used to bond sheet steel to inner stiffener panels and to seal around the crimped panel edges. These adhesives are formulated as high-solids, thixotropic pastes and are applied as discrete dots or droplets to the stiffener surface or panel edge before joining or crimping. These adhesives are called Hershey drops in the trade because of the characteristic geometry of the droplets. 

A first step in the validation of this approach is to test simple specimens under controlled conditions and to compare predictions with measured failure load values. First lap shear geometries were examined, then an L-geometry was studied in more detail. The bond-line in these small specimens was very similar to that in the quasi-unidirectional fracture specimens as the small dimensions allow panels to be pressed uniformly after assembly (which is not the case for industrial top-hat stiffeners). 

Metal ions can serve a variety of functions in the mechanisms of action of metalloenzymes. They may polarize functional groups both in the substrate and in amino acid side chains in the active site. As a result, the reaction being catalyzed can be facilitated. If the metal ion can undergo a change in oxidation number (such as is found for copper and iron), this may further aid in catalysis. Metal ions may also serve as a means of stiffening the geometry of the active site so that appropriate functional groups in it are lined up with respect to the substrate in a finely tuned manner dictated by the stereochemical requirements of the biochemical reaction to be catalyzed. Catalysis proceeds most efficiently in an enzyme when the transition state of the reaction is stabilized with respect to substrate and product. 

Joint simulation test geometry the three stiffeners are numbered in order of welding. 

It is often convenient to stiffen or harden a material, commonly a polymer, by the incorporation of particulate inclusions. The shape ofthe particles is important [see Christensen, 1979]. In isotropic systems, stiff platelet (or flake) inclusions are the most effective in creating a stiff composite, followed by fibers and the least effective geometry for stiff inclusions is the spherical particle, as shown in Figure 41.3. A dilute concentration of spherical particulate inclusions of stiffness , and volume fraction Vj, in a matrix (with Poisson s ratio assumed to be 0.5) denoted by the subscript m, gives rise to a composite with a stiffness E ... 

Local buckling of ring stiffeners may be accomplished by using compact shapes for ring elements. Code Case 2286 and Section VIII, Division 2, Part 4 include geometry requirements (used from AISC) to ensure local buckling of ring stiffeners is avoided. 

Although widely being explored, the majority of the automated production of 3D braids is often limited to fabricate constant cross-sectional 3D braid geometry. However, the production of a tubular or bifurcated structure requires variations in the geometry of the cross sections. This leads to manual interference in the production process, which slows the production process and constrains the use of 3D braids to products with small quantities. Thus, development of a fuUy automated process will clear the way towards the production of 3D braids in large quantities and allow the use of 3D braids in wide areas of application. Examples are the preforms in composites, for example, stmctural stiffeners in car bodies or as stents in a medical devices. 

One-shot manufacturing of complex shaped parts can be considered one of the best solutions [7,8] for the fast production of composite pieces dedicated to the railway and automotive industries. Fig. 16.2(a) represents a cross stiffener made of metallic welded tubes. This chapter outlines the replacement of metallic cross stiffeners with their composite counterpart, using a one-shot manufacturing methodology. Fig. 16.2(b) and (c) describe the geometry designed to achieve a composite cross stiffener. 

Some part geometries, such as stiffener-reinforced panels, require preparing sub-structures (preforms) prior to lay-up of the part. These could, for example, consist of a C-channel stiffener made from several prepreg plies. Such a preform can be manufactured by the same lay-up techniques as described above, e.g. by depositing ply by ply into a C-shaped mould. As an alternative, preforms can also be made by the process of hot forming. 

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