Hiroshi Suemasu

Bio: Hiroshi Suemasu is an academic researcher from University of Tokyo. The author has contributed to research in topics: Fracture mechanics & Crack growth resistance curve. The author has an hindex of 3, co-authored 5 publications receiving 28 citations.

Probabilistic aspects of strength of unidirectional fibre-reinforced composites with matrix failure

Abstract: In the previous paper [1], the stress distribution and the expected number of successive fibre breakages around broken fibres were calculated. It showed the following results. The fracture process that the crack originates from one isolated broken fibre and propagates due to the stress redistribution following the fibre breakage is unlikely to occur in the real unidirectional fibre-reinforced composite material. The matrix-failure is considered to play an important role in the fracture process of real composite materials. In the present paper, the stress (or strain) distribution and the expected number of successive fibre breakages around broken fibres are calculated when the matrix-damaged regions exist. The stress (or strain) distribution is obtained based on the three-dimensional hexagonalarray shear-lag model. Uniform shear force is assumed to occur in the matrix-damaged region. The expected number of the successive fibre breakages is calculated on the assumption that the flaws in the fibre follow a Poisson process.

Estimation of heat evolution during viscoelastic crack propagation by liquid crystal film technique

Abstract: Heat generated during dynamic crack propagation in viscoelastic solids was investigated by visible liquid crystal film technique to observe the thermal boundary front emanating from a running crack tip. The crack propagation velocity was also measured by the velocity gauge method. The heat so estimated is correlated with the crack propagation velocity.

Heat evolution investigated by a liquid crystal film technique during fracture in metals

Abstract: Heat evolution caused from a running crack front during dynamic fracture in steels, aluminium alloys and titanium alloys was investigated through liquid crystal film visualization, and a correlation between the generated heat and the crack propagation velocity was found. The heat evolution increased with an increase in the crack velocity for an individual metal. The magnitude of heat evolution was largest for steels having the lowest crack velocity, while the titanium alloy produced the smallest heat evolution, but showed the highest crack velocity. In comparison the aluminium alloy gave intermediate values of heat evolution and crack velocity.

An Analytical Study of Nonlinear Response of Shallow Spherical Shells to Random Excitation

Abstract: Probabilistic properties of nonlinear response of shallow spherical shells with clamped edges to random excitation are analytically investigated with the aid of simulation method in order to disclose the effects of the curvature on the acoustic fatigue lives. The deflection is expressed as a series expansion of the axisymmetric normal modes of vibration, and the nonlinear equations of vibration for the generalized coordinates are derived. The equations in the three modes approximation are numerically solved by NEW-MARK'S β method for random excitation forces. The probabilistic quantities of the response are calculated for various combinations of the pressure level and the curvature. The results have revealed the following properties. At high pressure levels the large amplitude vibration includes the snap-through buckling. The change of vibrational mode occurs during the snap-through. At very high pressure levels the probabilistic properties of the center deflection approach those of the flat panel. The fatigue lives of the shells can be shorter than those of the flat plate when the vibration includes the snap-through. The fatigue properties cannot be explained by the mean value and the standard deviation of the stress but explained by its probability density function (PDF), because the PDF is quite different from the Gaussian distribution. Then the static equilibrium load-deflection curves are calculated from the same discretized nonlinear equations and show good agreement with the previous results.

Stochastic Damage Evolution and Failure in Fiber-Reinforced Composites

Abstract: Publisher Summary This chapter describes the stochastic damage evolution and failure in fiber-reinforced composites. The accomplishments in the area of modeling of the mechanical properties of fiber-reinforced composites are reviewed with an emphasis on accurately predicting ultimate tensile strength, stress–strain behavior, and reliability. The model composite studies consists of a volume fraction of continuous cylindrical fibers embedded in a matrix material in a unidirectional arrangement. The reinforcing fibers are generally brittle materials and so are linearly elastic up to the point of failure. The point of failure in any individual length of fiber is determined by the largest flaw or crack in that particular fiber. The interface between the fibers and matrix occupies a vanishing fraction of the total composite volume but plays a critical role in determining many composite properties related to damage and strength. In polymer and metal matrices, the interface becomes important when fibers break. In ceramic matrices, the interface is critical first when the matrix cracks and then again when the fibers break. It is found that increasing stress causes flaws to fail, slip/exclusion zones to form or increase in length, and exclusion zones to increasingly overlap until the entire fiber is subsumed within the exclusion zones and the test saturates. The in situ fiber strength and fracture mirrors are also elaborated.

Tensile Strength of Fiber-Reinforced Composites: I. Model and Effects of Local Fiber Geometry

Abstract: Predictions of the ultimate tensile strength of 3-dimensional fiber-reinforced composites as a function of the fiber statistical strength distribution and fiber geometry (square vs. hexagonal packing) are presented for materials in which the load transfer from broken to unbroken fibers is very localized. The predictions are obtained using a previously-developed simulation model adapted here for hexagonal fiber arrays. The model includes (1) the Hedgepeth and Van Dyke load transfer model to determine in-plane load transfer and (2) fiber slip in the longitudinal direction via a shear-lag model. Results show that, although the load transfer does depend on fiber geometry, the average composite tensile strength and the statistical distribution of strengths do not depend strongly on the fiber geometry. The size scaling of strength is then also shown to be nearly-independent of local fiber geometry. These results are physically reasonable since the critical clusters of fiber damage causing failure are observed to be larger than 15-20 fibers, so that the detailed local geometry at smaller length scales is not crucial to failure. Hence, analytic models developed previously for square fiber arrangements can be used with reasonable accuracy independent of fiber arrangements. Applications of the model to polymer matrix composites are discussed in a companion paper (Part II).

High-Intensity Acoustic Tests of a Thermally Stressed Plate

Abstract: An investigation was conducted in the Thermal Acoustic Fatigue Apparatus at the Langley Research Center to study the acoustically excited random motion of an aluminum plate which is buckled due to thermal stresses. The thermal buckling displacements were measured and compared with theory. The general trends of the changes in resonances frequencies and random responses of the plate agree with previous theoretical prediction and experimental results for a mechanically buckled plate.