Tham khảo tài liệu 'bruhn - analysis and design of flight vehicles structures episode 2 part 5', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | MEMBRANE STRESSES IN PRESSURE VESSELS In examining the figure to determine what sort of canceling stress system must he supplied we see that the tangential hoop stresses hordering the cutout cannot he canceled hy a self-equllibrating set since they have a radial component. However the radial component of these stresses will actually be supplied by the door or window pressing outward against Its frame. Hence It is only the component of the hoop stresses along a chord which need to be canceled Fig. A16-14b . The Immediate problem becomes one of designing a structure to effectively support a set of uniformly distributed self-equilibrating stresses acting in the plane of the chord connecting the upper and lower edges of the opening Fig. A16-15a . Fig. All that appears necessary to support the stress system is to provide horizontal headers at the top and bottom of the cutout which as beams will carry the loads across to the sides of the frames where the loads cancel Fig. AĨ6-15b . For cutouts of usual sizes In pressurized fuselages the stress system to be supported In this manner is quite large and It proves uneconomical to design a single horizontal frame member of sufficient bending stiffness to resist them. Instead the shell wall Itself is employed to help carry these loads across. The skin is used to form a beam of considerable depth the skin being the web of this beam with the horizontal frame member and one or more longitudinals forming the beam flanges Fig. A16-15c . Because of the heavy shear flows and direct stresses developed the skin is usually doubled In this region. Additional stringers may also be added to relieve the stresses. The rings bordering the cutout and forming part of the frame are extended seme distance above and below the cutout proper unless they coincide with a regular ring location In which case they carry all the way around . Clearly one of the design requirements will be to make the frame sufficiently stiff in bending against
