Toru Kamita

Structural health monitoring of a full-scale composite structure with fiber-optic sensors

Structural health monitoring systems capable of assessing structural integrity during manufacture and service would allow us to keep them up-to-date and to increase their lifetime and safety in use. We installed fiber-optic sensors into a full-scale composite structure of a Japanese experimental re-entry vehicle and monitored temperature and strain distributions of the fuselage during the manufacturing process. The results obtained us with important information about the process control and the structural quality. The sensing system used in the manufacture could measure strain also in structural tests with static load. Although the strain measured by the fiber-optic sensor was averaged data depending on the spatial resolution, the overall deformation of the structure could be found, because strain was acquired extensively and continuously along the sensing fiber. The achievement of this study shows applicability of fiber-optic sensors to structural health monitoring for composite structures.

Mechanical Behavior of Composite Lattice Cylinders

The effect of local rotational deformation of the ribs on compressive buckling behaviors of lattice cylinders is investigated. This type of local deformation may not be embraced in the context of either the global buckling based on smeared/homogenized conventional shell analysis or the local Euler buckling analysis, which are used in the current design methodology of lattice cylinders. Experimental evaluation of the compressive behavior of representative lattice cell structure demonstrated that the rib rotation actually may take place. Beam elements are used in the finite element modeling in order to include the effect of local rib rotational deformations. The consequence of considering the effect is the possibility of non-negligible decrease in the buckling load estimation compared to that based on combined methodology of conventional shell buckling, rib local Euler buckling and rib failure strength. The addition of thin skin to the lattice structure is also proposed in order to prevent or reduce the infection of the local deformation nature of the ribs. The merit of supplementing the skin may also arise when the lattice structure is applied to the aircraft fuselage with cabin containment or pressurization requirements.

A Challenge of Modeling Thermo-Mechanical Response of Silica-Phenolic Composites under High Heating Rates

We have been building up a brand new ablation analysis code which is intended to predict simultaneously thermo-chemical and thermo-mechanical response of the SilicaPhenolic (SiFRP) ablator. In this paper, the model is applied to the RTG tests, FTE tests and the laser heating tests for model validation. The comparison to the SiFRP’s actual thermomechanical behavior shows that the present model gives better match by introducing the dependence of the elastic coefficient on the pore pressure in the high temperature region.

Low cost fabrication of HOPE-X all-composite prototype structure

Two strict requirements were to be adhered to in the development of HOPE-X: to shorten the manufacturing lead-time and to reduce the fabrication cost for the lightweight prototype structure of HOPE-X. To meet these requirements, the design team adopted an all-composite monocoque structure instead of a conventional aluminum skin, stringer-frame structure. The all-composite structure was made of several large parts in order to reduce the total number of parts. These large parts were made by using the non-autoclave curing technique and assembled by bonding into a monocoque structure. The high-accuracy large lay-up tool and the custom-made oven played important roles particularly during these manufacturing processes, leading to reduction in both lead-time and cost. The structural design and the manufacturing strategy for the prototype structure are described in this paper. The development of the lay-up tool and the oven, which helped to realize low fabrication cost, is described here.

Experimental and Numerical Simulation Study of Liquid-Propellant Draining from Rocket Tanks

Nomenclature a = vertical acceleration, m=s Fr = Froude number h = liquid height from baffle at center of tank, m hc = critical height, m h0 = liquid height from baffle at surface dip, m Q = drain volume flow rate, m=s r = drain line radius, m Rb = baffle radius, m u = liquid radial velocity at surface dip, m=s v = liquid velocity in drain line, m=s Vf = liquid volume at fixed point in tank, m 3 Vr = liquid volume remaining in tank at gas ingestion, m 3 = width of control volume, m = liquid density, kg=m

Stability of Skin Added Lattice Structure

Composite lattice structure, consisting of helical and hoop ribs intersecting each other in a regular pattern, is considered to be a superior candidate as the lightweight aerospace structure such as payload attachment adapter and inter-stage structure of launch vehicles. The present study focuses on the buckling behaviors of lattice cylinders under compressive loading. The buckling modes of lattice structures are deeply affected by the local rotational deformation of the ribs. In order to prevent this local rotation effect, the addition of thin skin to the lattice cylinders is proposed. The buckling load of the skin-added lattice cylinders significantly increases. A parametric study is also carried out to obtain the optimal designs of skin thickness and cross-sectional dimensions of the ribs. It is shown that the addition of skin has different effects on the improvement of bucking loads depending on the rib dimensions. As a result of parametric study, the new lattice model which has no hoop ribs is proposed and the buckling behavior of the structure is investigated. The elimination of hoop ribs is also meaningful from the manufacturing point of view. It may leads to the drastic reduction of the fabrication cost.

Experimental investigation on thermochemical phenomena in SiFRP

This study focuses on understanding and modeling the physical phenomena that occur in degraded zones of silica-phenolic (SiFRP) materials under exposure to high-temperature gasses when applied to a liquid rocket engine (LRE) combustor. Although understanding and modeling these phenomena is considered essential in designing an LRE combustor, few studies on these fields can be found in the available literature. Basically, it is well known that when ablators are heated, a pyrolysis reaction proceeds in them, forming three distinct zones: a charred, a decomposed, and a virgin zone. The obtainable information for the thermal response of SiFRP in ground-firing tests is classified in two categories. The first category involves the equilibrium state characteristics after a long time has elapsed following burnout. This refers to the degraded thickness distribution, which reflects 3D information (the combustor’s inner surface x the thickness direction) regarding the heat load distribution over the entire combustor’s inner surface, owing to the highly insulating nature of SiFRP. The second category involves the transient characteristics of the propagation of the degraded zones in SiFRP, which can be detected using an ultrasonic testing (UT) method. In this paper, the progress of in-depth phenomena of SiFRP and their physical variations were intentionally studied. Our aim was to clarify and specify the quantitative threshold values of the interface points that characterize each degraded zone and the UT reflection point, and then express these values in terms of physical quantities that could appear in a numerical analysis.