Design Of Components For Applications Research Articles

Metallurgical Analysis of a Failed 17-4 PH Stainless Steel Pyro Bolt Used in Launch Vehicle Separation Systems

Abstract Precipitation hardenable stainless steels are widely used in aerospace applications because of their excellent combination of strength and corrosion resistance. In view of this advantage, Fe-17Cr-4Ni (17-4 PH) steel is used in pyro bolts in space ordnance systems for stage separation in a satellite launch vehicle. These systems typically consist of a pyro charge to sever a given material resulting in stage separation, and these materials are exposed to high strain rates. In one such application, although perfect severance took place, secondary cracks were noticed longitudinally, which are not desirable. This steel, in view of its composition, has delta ferrite in a martensitic matrix in the hardened and tempered condition. In wrought products worked unidirectionally, delta ferrite gets oriented along the direction of thermomechanical processing. The effect of delta ferrite orientation on the impact properties of 17-4 PH stainless steel was studied in various heat-treatment conditions with a view to understand the effect of microstructure on impact properties. It was found that the transverse impact properties are severely affected by the presence of highly oriented delta ferrite stringers for any given heat-treatment condition. This has been attributed to the weak delta ferrite–martensite interface, which facilitates easy crack propagation. Finally, it was suggested that the anisotropy in impact properties need to be carefully considered in the design of components for applications that involve high strain rates.

The effect of fabric and fiber tow shear on dual scale flow and fiber bundle saturation during liquid molding of textile composites

In Liquid Composite Molding (LCM) processes, a fibrous reinforcement preform is placed or draped over a mold surface, the mold is closed and a resin is either injected under pressure or infused under vacuum to cover all the spaces in between the fibers of the preform to create a composite part. LCM is used in a variety of manufacturing applications, from the aerospace to the medical industries. In this manufacturing process, the properties of the fibrous reinforcement inside the closed mold is of great concern. Preform structure, volume fraction, and permeability all influence the processing characteristics and final part integrity. When preform fabrics are draped over a mold surface, the geometry and characteristics of both the bulk fabric and fiber tow bundles change as the fabric shears to conform to the mold curvature. Numerical simulations can predict resin flow in dual scale fabrics in which one can separately track the filling of the fiber tows in addition to flow of resin within the bulk fabric. The effect of the deformation of the bulk fabric due to draping over the tool surface has been previously addressed by accounting for the change in fiber volume fraction and permeability during the filling of a mold. In this work, we investigate the effect of shearing of the fiber tows in addition to bulk deformation during the dual scale filling. We model the influence of change in fiber tow characteristics due to draping and deformation on mold filling and compare it with the results when the fiber tow deformation effect is ignored. Model experiments are designed and conducted with a dual scale fabric to characterize the change in permeability of fiber tow with deformation angle. Simulations which account for dual scale shear demonstrate that the tow saturation rate is affected, requiring longer fill times, or higher pressures to completely saturate fiber tows in areas of a mold with high local shear. This should prove useful in design of components for applications in which it is imperative to ensure that there are no unfilled fiber tows in the final fabricated component.

Mechanical Properties of Hard Materials and Their Relation to Microstructure

The design of components for applications requiring high stiffness, hardness and wear resistance under extreme conditions of load and temperature leaves little choice for materials selection outside the realm of hard materials. But a combination of advances in materials and process development has led to a significant reduction in the uncertainties and risks associated with the estimation of mechanical failure probabilities and component for brittle materials in service.

Frequency response of thermo-optic tuning mechanism of planar silica optical multiplexer

The thermo-optic mechanism provides a simple means of tuning the wavelength of interferometric optical multiplexers constructed from planar silica waveguides upon a silicon substrate. Frequencydomain measurements of the tuning response permit an understanding of the tuning mechanism that is relevant to the design of components for applications in which wavelength-tracking error and cross-talk penalty are important. Measurements on a prototype device have shown a primary low-pass breakpoint at 360 Hz but have also highlighted the possibility of secondary mechanisms affecting the low-frequency response. A continually increasing phase lag at higher frequencies has also been detected and must be allowed for in control-circuit design.