Kanji Ono

Temperature Dependence of Dispersed Barrier Hardening

This paper examines the temperature dependence predicted by theories of dispersed barrier hardening. Most of interaction potentials employed in the theories are similar. It is not possible to select one of several interaction potentials on the basis of an experimentally obtained stress‐temperature relationship. This paper discusses limitations of the theories and clarifies several misconceptions on the theories.

Fracture mechanism characterization of cross-ply carbon-fiber composites using acoustic emission analysis

Abstract The sequence of microscopic fracture mechanisms in locally loaded cross-ply carbon-fiber composites was studied by analyzing acoustic emission (AE) signals in combination with the modal analysis of Lamb waves, using microscopic and ultrasonic examination of the specimen after load interruption. The first 70 AE events were analyzed, which were detected during the initial loading segment when the first sudden load drop and gradual load recovery were observed. Characteristics of the detected waves were compared with the S 0 - and A 0 -mode Lamb waves produced by a spot- or line-focused YAG laser. The internal damage progression of the composite specimen was determined to be the fiber fracture in the front lamina, transverse cracks in the mid-lamina, delamination and splitting.

Modal Analysis of Hollow Cylindrical Guided Waves and Applications

Dispersion behavior of guided waves in hollow cylinders (cylindrical waves) was evaluated theoretically and experimentally. Observed dispersion behavior suggests an assignment, different from the traditional one, of longitudinal (L-), flexural (F-) and torsional (T-) modes which are consistent with Lamb waves and shear-horizontal (SH) mode waves. The L- and F-modes of the cylindrical waves have characteristics which are asymptotic to Lamb waves and to waves in a solid cylinder. Experimentally, wide-band cylindrical waves in aluminum pipes were generated using a laser-ultrasonic method. Wavelet transform of the cylindrical wave signals was utilized for time-frequency analysis in order to compare them with the theoretical dispersion curves. For the L(0, 1), F(1, 1), F(2, 1), L(0, 2), F(1, 2) and F(2, 2) modes of the cylindrical waves, which were efficiently excited, theoretical and experimental dispersion curves agree with each other.

Internal stresses due to an oblate spheroidal inclusion: Misfit, inhomogeneity and plastic deformation effects☆

Abstract Internal stress in and around an oblate spheroidal inclusion is evaluated by using Eshelby theory. We consider three different sources of internal stress as a function of the aspect ratio and elastic moduli ratio; these are 1. (1) misfit effect, 2. (2) inhomogeneity effect 3. (3) plastic deformation effect. The misfit effect arises from the difference of thermal expansion coefficients of the matrix and inclusion. Normal stresses within the inclusion (or the principal stresses), maximum shear stress inside the inclusion, total strain energy and the normal stress at the matrix-inclusion boundary are determined. The inhomogeneity effect arises from the difference of the elastic moduli of the matrix and inclusion, which perturbs otherwise uniform applied stress. The direction of applied stress is parallel to the axis of revolution of the inclusion. Normal stresses within the inclusion and at the matrix-inclusion boundary are obtained. Plastic deformation of the matrix in the presence of a plastically non-deformable inclusion produces internal stresses, as shown by Ashby and by Tanaka and Mori. The approach developed by Tanaka and Mori is extended here to evaluate the internal stresses for the inclusion geometries appropriate to the analysis of technically important cases. The results of the present calculations in limiting cases agree with previously published calculations. Implications of the results are discussed in connection with several experimental studies.

The strain energy of a spheroidal inclusion and its application to b.c.c.-h.c.p. martensitic transformation☆

The strain energy of a spheroidal inclusion was evaluated exactly using the Eshelby theory. Numerical results for an oblate spheroid are presented in a parametric form in terms of the transformation strain tensor. Using atomistic transformation mechanisms, the transformation strain was determined for b.c.c.-h.c.p. martensitic transformation in Ti and its alloys. The lattice correspondence satisfied the Burgers relationship and the ca-ratio in the product phase was taken as 1.586. The habit plane was predicted on on the basis of the strain energy minimization principle. Results of the calculation indicate that the strain energy is minimized when the morphology of h.c.p. Ti martensite is a thin disc-shaped inclusion lying on a plane close to (11 X)B, where X is equal to 1.2–1.3. This habit plane is in excellent agreement with experimental observations. The present approach is discussed in detail and compared with the crystallographic theory based on the invariant plane strain hypothesis.

Stress concentration due to an oblate spheroidal inclusion

Abstract The stress concentration of an oblate spheroidal inclusion parallel to the stress and deformation axis is obtained by using Eshelbys theory. This is complementary to our previous study, in which stress concentration is analyzed for an oblate spheroidal inclusion normal to the stress and deformation axis. Effects of the elastic stiffness and the aspect ratio of the inclusion on the stress concentration are examined in detail. The internal stresses inside the inclusion, and at the matrix-inclusion boundary, are calculated considering inhomogeneity and plastic deformation effects. Stress concentrations at graphite flakes and nodules in cast iron are discussed.

Anisotropic mechanical and acoustic emission behavior of A533B steels

Abstract Acoustic emission characteristics of ASTM A533B steels were determined during tensile and fracture testing. Two different heats of thick plates were employed, and the orientation dependence of acoustic emission and mechanical behavior were studied in tensile tests and slow bend Charpy fracture tests. The types of acoustic emission signals, acoustic emission event counts, signal levels and amplitude distribution analysis were investigated. Three distinct types of acoustic emission signals were identified. One is the continuous type due to plastic deformation of the ferrite matrix. Two others are burst emissions, one of which has the characteristic Weibull function as its amplitude distribution and is attributed to the debonding of manganese sulfide inclusions. The other has a power law amplitude distribution which has often been reported in the literature. The exact origin(s) of this emission need(s) to be clarified. In this paper we describe a detailed study establishing the inclusion debonding to be the primary source of acoustic emission during the ductile fracture of A533B steels. This study further suggests that most burst-type acoustic emission in typical structural steels results from non-metallic inclusions in these materials.

On the minimization of strain energy in the martensitic transformation of titanium

Abstract On the basis of Eshelby theory, we have devised a method of predicting various features of martensitic transformation that lead to the minimization of total strain energy. In addition to elastic strain energy considered in previous works, plastic relaxation strain (PRS) concept is introduced in order to relieve the high internal stress due to martensitic transformation. It is postulated that the minimization of the elastic strain energy and the plastic work from the operation of a PRS system dictates the morphology and orientation of a transformation product and the amount and type of the PRS. The theory was applied to the case of martensitic transformation in Ti. In order to reduce the elastic strain energy resulting from transformation, a total of 84 glide and twin systems were evaluated as PRS. For oblate spheroids with aspect ratio less than 0.01, {1011} 〈1012〉 twin, {1011} 〈1123〉 glide and {1122} 〈1123〉 glide or twin systems produced strain energy minima at shear strain of about 2%, although crystal plasticity data of Paton and Backofen rules out the latter twin system. Theoretical prediction on habit plane, shape shear, orientation relationship, the amount and type of PRS, etc. are in excellent agreement with experimental observations.

Relaxation Processes in Metastable Beta Titanium Alloys.

Abstract Extensive observations have been made on an internal friction peak in a series of binary titanium alloys containing Mo and V. The compositions of the alloys ranged from 8 to 16 at.% Mo and from 15 to 50 at.% V, respectively. The peak was observed depending on alloy compositions in temperature ranges of 120°K to 140°K at 104 Hz and 153°K to 210°K at 107 Hz, respectively. In both alloy systems, the peak strength passed through a maximum with increasing alloy content at or near the upper compositional bound for athermal omega formation. The peak persisted well beyond the composition associated with the peak strength maximum, although its strength was greatly diminished. The peak structure was not disturbed by 15 per cent room temperature plastic deformation. The peak strength was severely reduced by annealing in the temperature range of thermal omega precipitation. Activation parameters of Q = 0.2 eV andτ0 = 2 × 10−14 sec were observed for both Ti-10 Mo and Ti-20 V. The results of this work are compared to the properties of a similar internal friction peak reported earlier in Ti and Zr base alloys, and discussed in conjunction with a reciprocal lattice streaking phenomenon also known to occur in these metastable beta titanium alloys. It is suggested that the atomistic mechanism responsible for the internal friction peak is the same “atom shuffle” process proposed by de Fontaine, Paton and Williams to explain reciprocal lattice streaking. Limited observations on a lower temperature relaxation (T ≤ 25°K at 104 Hz) in the Ti-V alloy system are also reported.

Acoustic Emission Behavior of Flawed Unidirectional Carbon Fiber-Epoxy Composites

This paper reports an experimental investigation on mechanical and acoustic emission behavior of specially designed and manufactured carbon fiber epoxy composites. Uni directional composite laminates with various flaw configurations were tested in tension and their mechanical and acoustic emission responses were determined. Fiber fracture, delamination, splitting (or cracking along fibers) and friction of delaminated faces contrib uted to characteristic acoustic emission behavior. These can be discrimination on the basis of peak amplitude and event duration of observed acoustic emission signals. The short duration ( < 100 μs), lower amplitude signals ( < 50 dB) signify carbon fiber fracture, while the medium amplitude signals (50 ∼ 70 dB) with an average event dura tion of —120 μs indicate the initiation and slow growth of delamination. High amplitude events ( > 70 dB) have long ( > 200 μs) event durations and are caused by rapid advances of delamination. Splitting or cracking along the fibers produces low to medium amplitude events with a long event duration ( > 100 μs). This type of acoustic emission signals has overlapping characteristics with those of delamination and needs further delineation of distinguishing parameters. Delaminated samples also emit acoustic emission signals with amplitudes in the range of 40 ∼ 50 dB and event duration of < 150 μs. These appear to arise from the friction of delaminated faces.