Optimum design and testing of a postbuckled stiffened panel

The efficient, industrially used, linear elastic preliminary design software VICONOPT is employed to design a stiffened panel with a post-buckled reserve of strength. The initial buckling mode is a local skin mode in longitudinal compression with allowance being made for the effects of an initial overall imperfection. The resulting panel has been analyzed using the non-linear FE package ABAQUS and four laboratory specimens have been tested to failure. The similarity of the experimental failure with the VICONOPT and ABAQUS predictions suggests that VICONOPT can give a satisfactory preliminary design. While neither model matches completely the boundary conditions found in a real aircraft compression panel, it is suggested that the VICONOPT model may be a better representation than either the ABAQUS model or the experimental tests

Postbuckling of stiffened panels using strut, strip, and finite element methods

Postbuckling results are presented for isotropic stiffened panels loaded in compression. Comparisons are made between single-bay and double-bay nite element (FE) models (where “bay” denotes a repeating portion, between supports, in the load/length direction) and a new strut model, following a Shanley-type approach, for single-bay and multibay panels. The strut model has been incorporated within the strip programVIPASA with CONstraints and OPTimization (VICONOPT) to design a multibay example panel with postbuckling reserve of strength in its skins, assuming linear elastic material properties. The panel has been shown by VICONOPT to have a stiffener buckling failuremode when an overall sinusoidal imperfection causing increased stiffener compression is present. The failure is con rmed by the double-bay FE model, which is shown to be an imperfect representation of the multibay case. Single-bay analysis using the strut model shows good agreement with the single-bay FE results. The VICONOPT code is able to design a metallic panel of realistic dimensions and loading using 50 strip elements (compared with the 9600 shell elements required by the nite element model) but cannot correctly account for material nonlinearity. The important phenomenological difference between postbuckling of single-, double-, and multibay panel models are indicated

Analysis and testing of a postbuckled stiffened panel

The suitability of using the ef cient, linear elastic design softwareVICONOPT for the analysisof a stiffened panel with a postbuckling reserve of strength is investigated. A longitudinallycompressed panel, which initially buckled in a local skin mode, was analyzed with allowance being made for the effects of an initial overall imperfection. The panel was also analyzed using the nonlinear nite element package ABAQUS, and four laboratory specimens that represent the panel were tested to failure. The similarity of the experimental failure with the VICONOPT and ABAQUS predictions indicates that VICONOPT can give satisfactory analysis results for use in preliminary design

Optimum design and testing of a post-buckled stiffened panel

The efficient, industrially used, linear elastic preliminary design software VICONOPT is employed to design a stiffened panel with a post-buckled reserve of strength. The initial buckling mode is a local skin mode in longitudinal compression with allowance being made for the effects of an initial overall imperfection. The resulting panel has been analyzed using the non-linear FE package ABAQUS and four laboratory specimens have been tested to failure. The similarity of the experimental failure with the VICONOPT and ABAQUS predictions suggests that VICONOPT can give a satisfactory preliminary design. While neither model matches completely the boundary conditions found in a real aircraft compression panel, it is suggested that the VICONOPT model may be a better representation than either the ABAQUS model or the experimental tests

Oxidation of the alarmin IL-33 regulates ST2-dependent inflammation

In response to infections and irritants, the respiratory epithelium releases the alarmin interleukin (IL)-33 to elicit a rapid immune response. However, little is known about the regulation of IL-33 following its release. Here we report that the biological activity of IL-33 at its receptor ST2 is rapidly terminated in the extracellular environment by the formation of two disulphide bridges, resulting in an extensive conformational change that disrupts the ST2 binding site. Both reduced (active) and disulphide bonded (inactive) forms of IL-33 can be detected in lung lavage samples from mice challenged with Alternaria extract and in sputum from patients with moderate-severe asthma. We propose that this mechanism for the rapid inactivation of secreted IL-33 constitutes a 'molecular clock' that limits the range and duration of ST2-dependent immunological responses to airway stimuli. Other IL-1 family members are also susceptible to cysteine oxidation changes that could regulate their activity and systemic exposure through a similar mechanism