Kazuaki Inaba

Shock Loading and Failure of Fluid-filled Tubular Structures

We consider the response of fluid-filled tubes to internal shock waves and explosions. The emphasis is on the fluid–solid coupling aspects. The coupling of axial wave propagation in the fluid to flexural waves in the tube may be characterized by a single parameter that depends only on the tube and fluid material properties and dimensions. Using this parameter as a figure of merit, we discuss the limiting cases of weak and strong coupling between the fluid wave motion and tube structural motion. Examples discussed include detonation and shock waves in gas and liquid-filled tubes of metal, polymers, and composites. The results of experiments on elastic and plastic deformation are presented as well as selected results on fracture and rupture. Detonation in gas-filled tubes usually falls in the weak coupling regime except for very thin tubes or cases of deformation that lead to tube rupture. Impact generated axial waves in liquid-filled tubes can range from weak-to-strong coupling cases depending on the tube wall thickness and material. These cases include the well-known phenomenon of water hammer and we describe the relationship of impact studies to previous work on wave-propagation in water-filled pipes.

Flexural Waves in Fluid-Filled Tubes Subject to Axial Impact

We experimentally studied the propagation of coupled fluid stress waves and tube flexural waves generated through projectile impact along the axis of a water-filled tube. We tested mild steel tubes, 38–40 mm inner diameter and wall thicknesses of 0.8 mm, 6.4 mm, and 12.7 mm. A steel impactor was accelerated using an air cannon and struck a polycarbonate buffer placed on top of the water surface within the tube. Elastic flexural waves were observed for impact speeds of 5–10 m/s and plastic waves appeared for impact speeds approaching 20 m/s for a 0.8 mm thickness tube. We observed primary wave speeds of 1100 m/s in a 0.8 mm thickness tube, increasing to the water sound speed with 6.4 mm and 12.7 mm thickness tubes. Comparison of our measurements in the 0.8 mm thickness tube with Skalaks water hammer theory indicates reasonable agreement between the predicted and measured peak strains as a function of the impact buffer speed (1956, “An Extension to the Theory of Water Hammer,” Trans. ASME, 78, pp. 105–116). For thick-walled tubes, the correlation between the experimentally determined peak pressures and strains reveals the importance of corrections for the through-wall stress distribution.

A new method of evaluating interfacial properties of a fiber/matrix composite

Interfacial debonding frequently initiates composite failure in a fiber/matrix composite. A single-fiber fragmentation test and its modifications can be used to evaluate interfacial properties. However, they still have accuracy problems due to fiber impurities and friction work. This paper presents a new method of evaluating interfacial properties using a stress contour of composite matrix. A single-fiber fragmentation test model was developed to simulate the stress contour. The interface was modeled as a cohesive zone model. Four characteristic lengths on the stress contour were found after conducting simulations with many interfacial properties values. The stress contour was then captured from the single-fiber fragmentation test employing a photo-elasticity technique and the four characteristic lengths were measured. Iteration in simulation involved changing interfacial properties until corresponding characteristic lengths from experiment and simulation were obtained. The results were compared with those obtained with existing methods and found to be reasonable.

Evaluation of capillary-induced deformation of thin plates due to liquid column formation

Deformation induced by capillarity is quantitatively evaluated in this study. A pair of polymer plates, fixed at one end and immersed in liquid, bends because of capillary forces from a liquid column formed between the plates. Bending proceeds to either contact or collapse the plates if their gap spacing becomes smaller than 2/3 of the initial plate separation, regardless of plate dimensions. This phenomenon is theoretically validated by proposing a dimensionless number, which is derived from a balance of surface energy, potential energy of a liquid, and strain energy of a plate.

Modeling and validation of evaluation method on IC chip pick-up performance of dicing/die bonding tape

A method to evaluate pick-up performance of dicing/die bonding tapes has been developed numerically and experimentally. In the pick-up process, IC chip with adhesive film is peeled off the base material, by pushing the backside of the base material with protruding needles. As the result of peel test and pick-up test, there were two types of pick-up behaviors correlated to the peeling behaviors. The peel force of one type decreased as the peel speed increased, and the peel initiation was critical in the pick-up test. In the evaluation method, the minimum needle displacement of peel initiation was estimated by the shear stress around protruding needles. The peel force of other type increased as the peel speed increased, and the peel propagation was critical in the pick-up test. In the evaluation method, the peel energy was calculated from the peel force. The finite element method was applied to calculate the energy release rate of the pick-up process for various peel lengths. The minimum needle displacement to complete the peel propagation was estimated by comparing the peel energy and the energy release rate. The predicted minimum needle displacements in both cases were in good agreement with the experimental results.

Dynamics of Cavitating Flow and Flexural Waves in Fluid-Filled Tubes Subject to Axial Impact

We have experimentally studied the coupling of flexural waves in water-filled tubes with cavitating flow. To examine the cavitation events in the tube, we used a transparent polycarbonate (PC) tube. The flexural waves are generated by stress waves in the water propagating along the tube axis. A steel impactor is accelerated by gravity and strikes a polycarbonate buffer placed on top of the water surface within the tube. Strain gages measure hoop strain along the polycarbonate tube and a piezoelectric pressure gage measures the pressure at the bottom of the tube. The events were visualized by a high-speed video camera synchronized with the strain and pressure measurements. The impact of the projectile creates a stress wave propagating along the tube and coupled to the pressure wave in water. A sequence of traveling waves results and when the pressure in the waves drops below the vapor pressure, cavitation occurs in the tube. When cavitation bubbles are present, the tube vibrates at the natural frequency of the second mode of the circular ring. The duration of the cavitation can be estimated from a balance between the buffer kinetic energy and the work done in accelerating the fluid. Cavitation does not occur uniformly or simultaneously; cavitation events are observed near the bottom surface of the buffer, the middle of the tube, and at the bottom (closed) end. High-speed video of the cavitation events reveals that the cavities are clusters of bubbles that have a rosary or grape-bunch appearance.Copyright

Effect of Tensile Stress on Cavitation Erosion and Damage of Polymer

Cavitation erosion tests for epoxy, unsaturated polyester, polycarbonate, and acrylic resin were conducted under various tensile stress conditions (Tensile-Cavitation test). A new testing device was designed to conduct the Tensile-Cavitation test and observe specimen surface during the experiment based on ASTM G32. When tensile stress of 1.31 MPa was loaded on epoxy resin, cracks occurred on the specimen after 0.5 hours during cavitation erosion. When no tensile stress was loaded on the epoxy resin, the damage was general cavitation erosion only. As well as the epoxy resin, unsaturated polyester resin applied tensile stress of 1.31 MPa and polycarbonate resin of 6.54 MPa indicated erosion damages and cracks. When tensile stress of 6.54 MPa was loaded on acrylic resin, the erosion damage was almost the same as the results without tensile stress. We confirmed that anti-cavitation property of epoxy resin was higher than those of acrylic and polycarbonate without tensile stress while the damage of epoxy resin was much serious than that of acrylic resins under tensile stress loadings.

Interaction of Serum Proteins with Hemodialysis Membrane: Comparison with De-adhesion Process of AFM Probe from Adhesive Tapes

Adhesive properties of several serum proteins to the hemodialysis membrane surface previously studied by atomic force microscopy were compared with a more general case of adhesion/de-adhesion process of adhesive tapes and films. The three different tapes and film samples showed de-adhesion curves with different level of tack and flow properties. The two types of de-adhesion force curves of serum albumin from the hemodialysis membrane can be explained in terms of the difference in the physical process of de-adhesion and in a general perspective of self-cohesive force of the adhesives.

Wave Propagation Across Solid-Fluid Interface With Fluid-Structure Interaction

This paper reports on investigations conducted with a view towards developing a theoretical model for wave propagation across solid-fluid interfaces with fluid-structure interaction. Although many studies have been conducted, the mechanism of wave propagation close to the solid-fluid interface remains unclear. Consequently, our aim is to clarify the mechanism of wave propagation across the solid-fluid interface with fluid-structure interaction and develop a theoretical model to explain this phenomenon. In experiments conducted to develop the theory, a free-falling steel projectile is used to impact the top of a solid buffer placed immediately above the surface of water within a polycarbonate tube. The stress waves created as a result of the impact of the projectile propagated through the buffer and reached the interface of the buffer and water (fluid) in the tube. Two different buffers (polycarbonate and aluminum) were used to examine the interaction effects. The results of the experiments indicated that the amplitude of the interface pressure increased in accordance with the characteristic impedance of the solid medium. This cannot be explained by the classical theory of wave reflection and transmission. Thus, it is clear that on the solid-fluid interface with fluid-structure interaction, classical theories alone cannot precisely predict the generated pressure.Copyright

Dynamic buckling tests of cylindrical tubes with and without pellets

In this study, the dynamic buckling tests using cylindrical tubes with and without internal pellets were carried out to investigate the impact behaviour. Various materials of cylindrical tubes and pellets were used to examine the buckling mode and the maximum loads at several impact velocities. The tubes with low stiffness pellets behaved similarly to the empty tubes, but high stiffness pellets caused different behaviours of tubes. At low impact velocity buckling deformations were suppressed by the strengthening effect of the pellets, while at high impact velocity a fracture occurred due to the constraint effect of pellets on plastic deformations.