Kozo Ikegami

Analysis of stress-strain relations by use of an anisotropic hardening plastic potential

Abstract A method of analyzing plastic behavior by use of an anisotropic hardening plastic potential is proposed. The plastic potential surface in deviatoric stress space is assumed to be the same as the equi-plastic-strain surface. Stress-strain relations in combined loading and in multi-axial cyclic loading are calculated by use of the anisotropic hardening plastic potential and the normality rule of the plastic strain increment vector to the plastic potential surface, which are experimentally determined or confirmed by subjecting thinwalled tubular test specimens of 60 40 brass to combined axial load, internal pressure and torsion. The calculated results agree fairly well with the experimental observations.

Dynamic deformation of lap joints and scarf joints under impact loads

The propagation of stress waves and the concentration of dynamic stress under impact loading in single lap joints, tapered lap joints and scarf joints, which were bonded adhesively, were investigated analytically and experimentally. Viscoelastic properties of cured adhesive resin were obtained from the variation of strain waves which propagated in a rod of cured resin. The compliance of the cured adhesive resin depended on the frequency of the strain waves. The viscoelastic properties obtained in the test were formulated by Voigt viscoelastic models. The stress distribution and the time variation of stress and strain in the joints under tensile impact loading were calculated using the finite element method, considering the viscoelastic properties of the adhesive. Stress concentration occurred in both the edges of the adhesive layers of the single lap joints and the tapered lap joints. The stress concentration in the scarf joints was relatively small. The stress occurred in the taper lap joints was smaller than that in the single lap joints when the taper lap joints had enough taper length. Impact test on the joints, which had adherends of aluminum alloy, was conducted to verify the pertinence of the analyses. The deformation of the tapered lap joints and the scarf joints showed good agreement on the analytical results. The deformation of the single lap joints was more complicated than the analytical results.

Benchmark tests on adhesive strengths in butt, single and double lap joints and double-cantilever beams

The RC99 committee of the Japan Society for Mechanical Engineers conducted the benchmark tests on strengths of adhesive joints using different testing methods. The effects of joint configuration, loading mode, adherend yield strength and so on, on the strength and data scatter were investigated using two typical epoxy adhesives. The strengths obtained by various tests were compared with each other. The relationships among strengths of butt, single lap and double lap joints and fracture toughness were given. Thirteen member institutes of the committee participated in this project. The benchmark results allow us to recognize that the joint strengths are strongly affected by the curing process. The key to obtaining the appropriate joint strength, is precise temperature control inside the adhesive layer for curing. Toughened adhesives do not always give higher joint strengths than untoughened adhesives. The yield strength of adherends much affects the observed lap joint strength of adhesives.

Strength of adhesively-bonded butt joints of tubes subjected to combined high-rate loads

Abstract The dynamic strength of adhesively-bonded joints was investigated experimentally. The strength of the bonded joints under combined high rate loading was measured using the clamped Hopkinson bar method. Tubular butt joints bonded by epoxy resin were used for the experiment. Combined stress waves of tension and torsion were applied to the specimens. The strength of the adhesively-bonded joint was determined by measuring the stress waves propagated in the load output tube of the specimen. It was found that the dynamic strength of the adhesive joints was greater than the static strength under tensile and shear load.

Effect of creep prestrain on subsequent plastic deformation

Abstract The effect of creep prestrain on subsequent plastic deformation is experimentally investigated. The experiments are performed by subjecting thin-walled tubular specimens of stainless steel SUS 304 after creep prestraining to combined axial load and torsion at room temperature to 600°C. The stress-strain relations subsequent to creep prestrain are determined under combined stress state with and without temperature changes in prestraining and subsequent plastic straining. On the experimental results, the plastic hardening effects by creep prestrain are discussed under various temperature conditions. The subsequent stress-strain relations are compared with the calculated results on the equi-plastic strain surfaces.

Strain measurement for Raman-inactive substrates with PbO thin films using Raman Coating Method

A new method of Raman spectroscopy to measure strain of Raman-inactive materials deposited with Raman-active thin films was proposed. This method is denoted as the Raman Coating Method. This is the application of Raman spectroscopy, in which thin films of PbO are deposited on the surface of resins and metals using physical vapor deposition (PVD) as the pretreatment to measure strain. The relation between peak shift of PbO thin films and tensile strain was experimentally examined. This relation was independent of the mechanical properties of materials on which PbO thin films were deposited. The residual stress in PbO thin films was also measured. The absolute values of residual stress in the films on resins were much greater than those on metals. As an application of the proposed method, the tensile strain in carbon fiber of carbon fiber reinforced plastics (CFRP) was measured by Raman spectroscopy.

Experimental Studies of the Strength of an Adhesive Joint in a State of Combined Stress

The adhesive strength of a butt-type specimen of two cylinders is experimentally studied. Combined stresses are applied on the adhesive layer by subjecting the specimen to combined axial load, torsion and internal pressure. The effects of the surface roughness, the thickness of adhesive layers and the combined stresses on the adhesive strength are examined for the specimens of various metals bonded with epoxy resin. The adhesive failure locus under the combined stress state are represented by a polynominal equation of stress tensors.

Tensile Strength of Single Lap Joint and Scarf Joint between CFRP and Carbon Steel

Abstract The strength of single lap joints and scarf joints between carbon cloth laminated plastics (CFRP) and carbon steel bonded with epoxy resin was investigated both analytically and experimentally. The stress and strain distributions under tensile loads of the joints were analyzed by applying the elastic finite element method. The strength of the joints was predicted by applying the strength law of CFRP, metal, adhesive layer and their interfaces to the calculated stress distributions. The predicted strength was compared with the experimental strength of the joints. The critical positions of the joints and the effects of the overlapped length on the joints were examined.

Failure criterion of angle ply laminates of fibre reinforced plastics and applications to optimise the strength

Abstract The failure criterion of fibre reinforced plastics is experimentally determined by subjecting filament-wound tubes with various ply angles to axial load, torsion and internal pressure. The material of the tubes is a composite of glass rovings and epoxy resin. Expressions for the failure criterion under a combined stress state are derived for various ply angles. Using these results, the optimum ply angles are determined for the maximum strength and for the maximum strain energy. The maximum strength results are used to optimise the strength of rotating discs.

Fracture toughness evaluation for multidirectional CFRP by the Raman coating method

The Mode I fracture toughness for multidirectional carbon-fiber-reinforced plastics (CFRP) was investigated by using double-cantilever beam (DCB) specimens with Raman spectroscopy. A thin PbO film was deposited on the specimen surface by physical vapor deposition (PVD) as the pretreatment for strain measurement, and then the fracture toughness was determined from the results of Raman spectroscopy measurement. These results agreed with the results by conventional experimental methods and numerical analyses. The fracture surfaces of DCB specimens were observed by scanning electron microscope (SEM); the fracture surfaces differed because of different critical energy release rates.