Structural Performance of Orthogonal and Bias Stitched Sandwich Structures with Rigid Close-cellular Foams

Sun

et al. 2009

A thermal expansion process was applied to prepare stitched sandwich structures using the pressure generated by the foam core inside a closed mold. In this way, buckling of stitches was avoided. The mechanical properties of the specimens prepared by thermal expansion process were significantly improved when compared to that of specimens prepared using the hot press. In order to increase the thermal expansion pressure, the foam cores were pre-compressed, and then stitched with the face sheets. The pre-compressed foam cores underwent thermal expansion easily and their thermal expansion pressure increased with increase in pre-compressive ratio.

“…Here, ÁV E 2 is the volume change of mold cavity at T 2 due to the pressure increase, in cm 3 . The volume change of foam core is given by Equation (5):…”

Section: Model Of Thermal Expansion Processmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Thermal Expansion Process for Manufacturing of Stitched Sandwich Structures

Sun

et al. 2009

“…Even if the mechanical gain seems to be significant, the X-truss/foam sandwich structure has received minimal attention so far. Singh [9], Potluri [6,7], and Lascoup [10] prepared bias stitched sandwich structures with RTM or VARTM processes. They considered its characterizations compared to the traditional sandwich, as well as the relationship between mechanical performance and structure parameters.…”

Section: Introductionmentioning

confidence: 99%

“…Among them was the effective method of inserting small diameter fiber rods (stitches or Z-pins) into the foam core at a specific angle to form a truss, by which the face sheets were linked together. For example, X-cor TM and K-cor TM developed by AZTEX, Inc. in 2001 [5], as well as the bias stitched sandwich panel studied by Potluri [6,7] in 2003. Because of their similar architectures, they can be generally called X-truss/foam sandwich structures.…”

Section: Introductionmentioning

confidence: 99%

The Influence of Preparing Method on Novel X-Truss/Foam Sandwich Structure

et al. 2008

Novel X-truss/foam sandwich structures were prepared by Z-pin inserted and bias stitching method, respectively, in order to improve the transverse mechanical behavior. With such reinforcements, the collapse resistance capability of the core and the bonding strength between the core and the skins are obviously increased. Thus the principal disadvantages of conventional sandwich structures are solved. The Z-pins and stitches embedding in rigid polyurethane foam configured a truss, which was made of carbon fiber/epoxy resin. The architectures of specimens made from Z-pin inserted and bias stitching methods are very similar but not identical, which make their mechanical performances different from each other. In order to evaluate these two methods, out-of-plane mechanical tests, such as compression, shear, and tension were practiced and failure modes were compared. In some conditions, the specimens made from the Z-pin inserted process have a higher compression modulus, but a lower tension and shear strength compared to that made from the bias stitching process. Moreover, there are big differences in their failure modes.

“…Compared to some high performance honeycomb cores widely used in aeronautic and astronautic fields, polymer foam cores are not strong enough [1,2], which limits their application in some fields. In order to increase the load carrying capacity of foam core sandwich construction, a number of strategies have been explored [3][4][5][6][7][8][9], one of which is embedding small diameter rods (metallic, ceramic, or polymeric fiber) into the foam core at a specific angle forming an X-truss by Z-pin inserted or bias stitching processes [10][11][12][13][14][15]. With these X-trusses, not only are the mechanical properties of the core improved, but also the delamination strength is enhanced since there are reinforcements bridging the foam and the skins.…”

Section: Introductionmentioning

confidence: 99%

Mechanical Performance of X-Truss/Foam Sandwich Construction

et al. 2008

In order to improve the transverse mechanical performance of ordinary foam core sandwich, Z-pins of carbon fiber were inserted into the foam core forming a novel X-truss/foam sandwich construction. Mechanical behaviors of this new composite are mainly determined by its structure parameters, which offer many degrees of freedom to designers. Here, flatwise compression, shear, and bending tests were carried out to investigate the influence of structure parameters on mechanical behavior. These structure parameters include Z-pin inserted angle, volume fraction, and orientation of X-truss, etc. Based on the rule of mixture, equations have been derived to estimate the compression and shear properties, which conform to experimental results. With the increase of Z-pin inserted angle, compression performance is improved, while shear and bending performance decrease. The 45° angle offers the best properties of shear and bending behavior, whereas the 90° angle presents the best compression performance. In addition, using the theory of the Winkler foundation beam, a prediction equation of compression strength has been derived which indicates that larger diameter Z-pins can offer more efficient enhancement than smaller diameter ones in terms of compression behavior.