The broad scala of aspects involved in fatigue predictions for practical purposes is outlined. Special aspects of aircraft fatigue predictions are indicated. Results of some recent investigations are summarized, which are related to crack closure of part through cracks, fatigue crack growth prediction models for variable-amplitude loading, and the significance of fractographic observations for the verification of prediction models. Another solution of the aircraft fatigue problem is offered by recently developed materials (ARALL and GLARE). These laminates are built up from thin Al-alloy sheets and unidirectional fiber prepregs. The high fatigue crack growth resistance of the new materials is discussed.

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One-dimensional, generalized thermoelasticity is presented based on Lord and Shulman's theory and Green and Lindsay's theory. The former theory involves one relaxation time of the thermoelastic process and the latter involves two relaxation times. These theories have been developed in an attempt to eliminate the paradox of the infinite velocity of thermoelastic propagation inherent in the classical dynamically coupled theory. A formulation of generalized thermoelasticity which combines both generalized theories is derived. The generalized thermoelastic problems in an infinite solid cylinder are analyzed by means of a Laplace transform technique. The numerical calculations for displacement, temperature and stress under the generalized formulation are carried out and compared with the results under the classical formulation.

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The present paper describes the theoretical aspects of the renewal and a change of coordinate system in finite deformation. The proposed renewal method is accomplished through mathematically equivalent transformation of the fundamental work equations derived from the total Lagrangian approach. Since no subsidiary condition is imposed on the transformation, it is proven that the variational principle and the constitutive equation can be treated as an independent problem. Discussed are the relative advantages of the total or updated Lagrangian approaches as well as the Green or Jaumann rate constitutive equations from the viewpoint of numerical analysis. Attention is also focused on the work theorems and the constitutive equation to ensure objective numerical integration under the change of frame.

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The theoretical prediction of the forming limit (strain) diagram (FLD), or the forming limit strains of sheet metals by the author's method is reviewed, giving some new and useful information. J₂-Gotoh's corner theory; (or MG-) (J2G) constitutive equation previously proposed by the author is used, together with the localized necking condition as the failure condition. Theoretical FLD nets of sheet metals subjected to various proportional loadings are illustrated with the n-value orρ-value as the parameter for the convenience of determining the most appropriate value ofρ(the material constant involved in the J2G). Furthermore, discussions onρ-and n-values and on the material properties of the prestrained sheet are given. The secondary-FLD and the sheet thickness effects on the forming limit strains are also discussed.

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In bar rolling, a bar is usually formed by applying front and back tensions; thus, it is important to analyze the effects of the front and back tensions on the rolling properties. Futhermore, it is also important for precise rolling to confirm the control equation coefficients, that is, the ratios of the variations of the rolling properties, such as the width spread, forward slip, load and torque, to the changes of the tensions. In this paper, the analysis was performed by the energy method using the finite-element division, which we proposed previously. First, the effects of the tensions on the rolling properties were proved reasonable by the comparison with the experimental formulas. Next, the control equation coefficients for the torque were obtained approximately using the results obtained when no tension was applied. Finally, it was found that as the roll radius increases, the control equation coefficients for all of the rolling properties decrease.

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To measure the flow stress of metals under forming conditions, i.e. at large strains, high strain rates and elevated temperatures, a method based on the ring compression test is proposed. In this method, a ring-shaped specimen is compressed between two flat tools with and without lubrication. The coefficient of friction between the specimen and the tools is determined from the change in inner diameter, and then the load and reduction in height measured in the test are converted into the average flow stress and average equivalent strain by taking the friction into account. The calibration curves for determining the coefficient of friction, the average equivalent strain and the average flow stress are derived from the results of rigid-plastic finite element calculation. This method is simple to carry out and does not require control of friction during compression. Ring compression tests for certain kinds of lubricants, materials and strain rates are carried out. The method is confirmed to provide flow curves within an error of 5%, and is effective especially for measuring the flow stress of heat-resistant materials such as Ti alloys and Ni base superalloys which are formed at elevated temperatures. As an example, the flow curves of Ti-6Al-4V alloy measured by the proposed method are demonstrated.

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This paper considers the possibility of identifying unknown applied loads when a structure has an optimal shape for the loads. First, a shape-optimization problem is solved for given forces by the inverse-variational-shape-determination method. The optimality in the method is the uniformity of the strain energy densities calculated on the surface of the structure for assumed loads. Second, the true loads are searched for by minimizing the variance of the strain energy densities from several points on the surface with respect to unknown load parameters.

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In a previous paper, we presented a new adhesive-strength evaluation method which uses two stress-singularity parameters. Here this method is applied to single-lap joints which are generally used as adhesive-strength test specimens. Using this method, the relationships between adhesive-strength to lap length, adhesive layer thickness, substrate thickness, and bonding edge angle, are analyzed. The analytical results coincide well with the estimated results based on maximum stresses in adhesive layers.

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The prediction method for analyzing the crack opening area of a pipe is essential for leak-before-break evaluation. Several theoretical approaches are proposed for predicting crack opening areas. One approach is the Tada and Paris formula, developed based on the linear elastic fracture mechanics. Another is the engineering approach developed by German and Kumar. Round-robin analyses for crack opening areas are performed using these two methods. The pipe analyzed is a 6-inch-diameter Type 304 stainless steel pipe with a circumferential through-wall crack. The applied load is bending moment. The crack opening areas calculated by Tada and Paris method coincided among the four participants. However, the areas using German and Kumar method were quite different. It is concluded that in the present situation, Tada and Paris method is suitable for a leak-before-break standard to predict the crack opening area. In addition, material properties used in the calculation of the standard are discussed compared with the results of the pipe bending experiment.

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Fatigue crack growth rates in the base metal and welds of HT80 steel welded joints were evaluated at temperatures ranging from room temperature down to 93 K. For the welds, the crack growth rates between room temperature and 173 K were dominated by residual stresses rather than temperatures. As temperatures decreased below 123 K, the crack growth rates of the base metal and welds increased markedly because of cyclic cleavage during striation growth. The crack growth rates of the welds were correlated with an effective stress intensity factor range, ΔK_effR, which was estimated by superposition of the respective stress intensity factors for the residual stress fields and for the applied stresses when the crack growth was dominated by striation formation.

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Titanium alloys have nonmagnetic and high strength properties as well as low density. These excellent characteristics are expected to make the alloys candidates for structural materials of cryogenic systems including superconducting machineries. We have been studying on mechanical properties of titanium alloys at cryogenic temperatures. Fatigue tests were carried out for Ti-5Al-2.5Sn and Ti-6Al-4V alloys, both of which had high fracture toughness at low temperatures. Fatigue crack initiation started at the inside of the specimens when tested at lower temperatures and under higher cycles. Neither macroscopic nor microscopic defects were observed at the crack initiation sites.

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The test system was newly developed for precisely evaluating the tensile strength of ceramics at elevated temperatures. Four-point bending and tensile tests were performed on the sintered silicon nitride ceramic in the temperature range from room temperature to 1300°C. The track of ductile fracture was observed on the fracture surface of a tensile specimen tested at temperatures above 11OO°C, suggesting the occurrence of inelastic deformation. The fracture stress of bending specimens was about l.18-1.43 times as large as that of the tensile specimen. The test temperature dependency, however, was very similar in both the fracture stresses in the whole test temperature range. The fracture toughness from tensile and bending specimens were almost the same in the test temperature range from R.T. to about 800°C. The fracture toughness obtained from the chevron-notch-type specimen was almost coincident with that from the Knoop-indented specimen in the temperature range from R.T. to 900°C. However, they manifested some differences in temperatures above this, suggesting the occurrence of adhesion at the crack tip in the Knoop-indented specimen.

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The crack propagation behavior under cyclic load was investigated on two types of sintered Si₃N₄. The main results obtained are as follows. (1) The crack propagation rate was accelerated by cycling the load. As the stress ratio decreased or the test frequency increased, the crack propagation rate increased. (2) If the fracture toughness of a specimen was high, the crack propagation rate was low as compared with that of another specimen with low fracture toughness. (3) Debris of the fractured grains and wear mark were left on the fracture surface under the cyclic loads. (4) By measuring the crack opening displacement, crack closure was observed. The size of the debris (∼1μm) on a fracture surface under cyclic load was nearly equal to the crack opening displacement at no load. It was concluded that the crack closure of sintered Si₃N₄ was induced by debris between the crack surface.

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The theoretical study for quantitative evaluation of material quality by the backscatter of an ultrasonic Gaussian beams has been made. The density and location of flaws, such as microcracks and porosities, can be estimated by the change of electrical power due to the backscatter. The power change is theoretically formulated based on the dynamic reciprocal theorem. Some kinematical postulations are used for simplicity to neglect the multiple scattering effect among the flaws; the characteristic dimension of a contained flaw is very small in comparison to the incident wavelength, and the flaw distribution is sparse. Numerical calculations of the analytical backs-cattering power have been carried out. The power is approximately proportional to the flaw density. The obtained expression is of closed form, and it is easy to calculate the power. Thus, the expression is practical for the quantitative characterization from the backscattering wave data by ultrasonic measurement.

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This paper presents a method to detect damage of metals with no contact using a laser speckle technique. This method is based on observations of the change of the laser speckle pattern depending on the surface roughness and texture change of the material caused by slip bands due to plastic deformation. The laser speckle pattern was analyzed automatically and quantitatively using an image processing system in this experiment. A new parameter, c_k, was derived to statistically express the features of the speckle pattern. It was found that this parameter can express the features of the speckle pattern accurately and has excellent reproducibility. Also, it allows an accurate measurement of plastic strain. The experiment was carried out for cases of both static tensile and fatigue loading using aluminum alloy as the material.

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Although the acoustic emission (AE) method provides useful information on the operating fracture processes of materials, a synthesized evaluation of AE signals using several AE parameters is necessary for composite materials, because AE signals arise from various fracture processes. In this paper, the relationships between several AE parameters and AE original sources were investigated, and fracture mechanisms of carbon fiber reinforced plastics (CFRP) are discussed in terms of observations of fracture surfaces and internal damage of the laminates by a scanning electron microscope (SEM) and a scanning acoustic microscope (SAM), respectively. Synthesized AE signal wave analyses, including the distributions of AE amplitude, AE-event duration, and counts/duration (corresponding to frequency), give us useful and powerful information to analyze the complicated fracture mechanisms of composite materials with. The fracture in tensile tests and cyclic tensile tests of unidirectionally reinforced carbon/epoxy composites goes through fiber/matrix interface debonding and fiber breakage.

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