5 research outputs found
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