Hidemitsu Hojo

Erosion damage of polymeric material by slurry

Abstract An attempt was made to reveal the erosion mechanism of a plastic material in slurry containing glass beads of approximately 176 μm in diameter. The experimental observations were interpreted in terms of parameters such as the impact velocity Vp, the impact angle α of the beads and the striking efficiency η. A theoretical flow analysis for a solid-liquid two-phase flow was made and it was found that the trajectories of the particles curved as they approached the specimen, indicating that the actual surface onto which the particles were impinging was much narrower than that which would be expected for sand erosion in an air stream. In the slurry erosion the impact velocity and impact angle differed greatly at different positions of the specimen. This is possibly due to the differences in the density and viscosity of liquid and air. Two distinctly different types of erosion were observed: a typical brittle behaviour occurred near a stagnant point, after an initial incubation period, whereas at a distance from the stagnant point only a slight surface roughness was produced. These two different types of erosion produced a clear boundary. Erosion rates depended on the positions of the specimen and were found to be proportional to (Vp sin α)2.6. This suggested that the normal component of the impact velocity of the particle determined the erosion rate of the plastic material due to slurry.

Erosion Behavior of Polystyrene

Erosion tests of polystyrene were made by impingement of glass beads at various attack angles and impact velocities. Two erosion damage peaks near the angles of 20 and 50°, which have never been observed on other materials, were found. In the erosion process near the peak of 50°, a characteristic ring-like damage pattern on the surface was recognized. To explain the experimental results, a new erosion mechanism based on the initiation and propagation of transverse cracks beneath the surface at the tip of longitudinal cracks was introduced. And by this mechanism, the erosion rate could be given by R = ρhS*/Mo where h, S*, and Mo are the factors describing the characteristics of the ring-like damage pattern and ρ is the density of material. The theoretical values agreed quite well with the experimental ones.

Form and rate of corrosion of corrosion-resistant FRP resins

The corrosion behavior and mechanism of matrix resins for FRP in aqueous solutions were investigated, comparing these with the corrosion of metals. Three forms of corrosion were found, namely surface reaction type, corrosion layer forming type and penetration type. In surface reaction type corrosion, which was recognized in the corrosion of epoxy resin cured with phthalic anhydride in alkaline solution, the ester bonds in the resin were attacked by hydrolytic reaction with liquid and then dissolved from its surface uniformly. In the corrosion layer forming type corrosion, observed in the corrosion of unsaturated polyester in alkaline solution, the ester bonds in the main polymer chain were corroded by the same mechanism, but crosslinked polymer chain remained. Then the corrosion residual layer was formed. In penetration type corrosion, a large quantity of environmental liquid was absorbed until an equilibrium state was reached, and then the strength of the specimen decreased quite remarkably. This type of...

Corrosion of plastics and composites in chemical environments

The degradation of polymeric materials with chemical reaction in which the molecular chains is cut is called corrosion. In this paper the behavior, the forms and mechanisms of corrosion of resins and GFRP (glass fiber reinforced plastics) under several aqueous solutions are reviewed based on our experiments. Three types of corrosion exist: the surface reaction type, the corroded layer forming type and the penetration type. Each form was determined by the chemical structures of the resin, the reactivity between resins and environments, and also the diffusivity of environmental media into the resins. The concept of the corrosion rate of metals could be applied even in plastics and fiber reinforced plastics for each corrosion form.

Local yielding of polyethlene in active environments

Abstract A study has been made by tensile testing to clarify the effects of notch length, temperature, environment, and blowup ratio on the local yielding criterion in polytylene, and also to investigate the fracture criterion. Double-edgenotched (DEN) speicimens of blown high-density polyethylene film were tested at several temperatures mainly in proply alcohol. As a result of testing, it was found that the general or local yield strength of transverse specimens was higher than that of longitudinal ones. By photographic examination during stretching, the local yielding zone size ahead of crack tip, crack opening displacement (COD), and crack length were observed. The growth rate of the local yielding zone increased with increasing strain, but it stopped abrutptly at or near a peak of stress-strain curve. With this relation and assuming an elastoplatic crack with a plastic zone, the modified Westergaards equation could satisfactorily be applied to estimate the critical stress for local yielding. Using th...

Quality Evaluation of Molded Epoxy Resin and Particulate Filled Composites by Ultrasonic Technique

Epoxy resin and its particulate filled composites are being used widely in many fields of industry. High quality as well as reliability are especially necessary for electric and electronic products such as heavy generators and IC packages. For quality assurance, therefore, it is important to detect or evaluate the quality of these materials without causing destroying them. The purpose of this study is to establish a non-destructive evaluation method for the quality of cast epoxy resin and its particulate filled composites. This paper describes the results of an investigation made to clarify the relation among structure, physical and mechanical properties and ultrasonic characteristics of these materials by using an ultrasonic pulse reflection technique.

Evaluation of Corrosion Behavior of Rigid PVC Used for HNO3 Absorption Tower.

13年間使用した硬質ポリ塩化ビニル製硝酸吸収塔 (直径2.6および2.0m, 高さ15m, 厚さ20mm) の腐食状況について検討した.試験片は塔壁マンホール部から, 外層, 中間層および内層について試料を採取し, それらについてクリープ破断強さ, 引張り, 曲げ, 衝撃強さなどの機械的強度を測定し, さらに赤外スペクトル (IR) 分析を行った.IR分析により大気側 (外層) では-OHと>C=O基の生成が, また, 接液側 (内層) では>C=O基とニトロ基の生成が認められた.ステアリン酸バリウムのIR吸収に注目した結果, 外層の大気劣化層, 内層の腐食層の厚さは, それぞれ250および500μmであることが明らかになった.これらの結果より, 硝酸の製造装置用材料として, 従来のステンレス鋼に代わり, 硬質ポリ塩化ビニルが有効であることがわかった.

Thermal Shock Tests of Epoxy Resin with Disk Type Specimens

ABSTRACT The crack of LSI packages caused by thermal shock like the solder reflowing, gives serious problem in electronic industry. Two types of specimen were tested, and these thermal shock fracture behavior and cyclic life were investigated from the point of reliability. As a result of the ring model testing, cyclic life was found to obey the Weibull distribution. On the other hand, thermal shock tests for LSI model indicated that there were two patterns of cracking, circular type and diagonal type. LSI model was also evaluated its life statistically considering failure mechanism, and data agreed well with Weibull distribution. The life indicated maximum value when solder bath temperature was 240 °C, because of the affair of thermal stress and resin degradation.

Evaluation of Thermal Shock Resistance for Cast Epoxy Resin with Various Toughness.

Previously the present authors proposed the testing method of thermal shock resistance using a notched disk type specimen of brittle type epoxy resin and its evaluation method based on fracture mechanics. In order to examine their applicability, some practical epoxy resins for casting were tested in this study.For brittle alicyclic epoxy resin, irrespective of the cooling bath temperature, the nondimensional stress intensity factor calculated by the experimental results agreed well with that of theoretical estimation.In the case of mixed resin of bisphenol A epoxy having certain toughness and very brittle alicyclic epoxy, the critical temperature difference ΔTC was clearly recognized for all resin systems with various mixture ratios, and the resin with higher bisphenol A epoxy content showed higher thermal shock resistance. For the bisphenol A type epoxy resin with longer molecular chains (larger number of repeated units) indicated higher resistance. The analysis agreed well with the experiments for these both resin systems.For the epoxy resin modified with a low content of plasticizer, the same evaluation method of thermal shock resistance was found to be applicable. But over 20phr content, plastic flow occurred markedly, and so the critical temperature difference could not be obtained. For such cases, it is still possible to evaluate the thermal shock resistance by using a large size specimen.