Before now, several estimation methods of total strain-fatigue life curve (Δεt-Nf curve) formulated by mechanical properties have been proposed. In these estimation methods, Universal slopes method, Modified universal slopes method and Medians method can be utilized effectively for preliminary fatigue design. However, it appears that the validity of three estimation methods about copper and copper alloys has been not investigated. Accordingly, in this report, actual fatigue life (Nf) of copper and copper alloys were compared to predicted fatigue life (Np) obtained by each three estimation methods in order to investigate their validity. The conclusions are obtained as follows : (1) Equation approximated on Medians method by strain controlled fatigue test results of copper and copper alloys was suggested as follows. Δεt=(2.70σB/E)Nf-0.0805+0.543Nf-0.529 (2) Precision of Np obtained by Universal slopes method was the worst in three estimation methods. In addition, this Np was non-conservative prediction under 104cycles and conservative prediction over 105cycles. Consequently, It is decided that Universal slopes method was not practical for preliminary fatigue design. (3) Precision of Np obtained by Modified universal slopes method was better than one of Np obtained by Medians method. But, the advantages and disadvantages of two estimation methods could not be judged, because precisions of two may be change according to increase of experimental results. At the present time, It is thought that there is no difference of a practical use for preliminary fatigue design between Modified universal slopes method and Medians method.
Torsional fatigue tests were conducted for circumferentially notched bars of carbon steel (JIS SGV410) under cyclic torsion without static tension (case A) and with static tension (case B). The direct electrical potential method was used to monitor the initiation and propagation of cracks from the notch root. For both cases A and B, the lives of crack initiation, Nc , and propagation, Np , decreased with increasing stress concentration. The ratio of Nc to the total life, Nf , was smaller for sharper notches under lower stress amplitudes, and was larger when the static tension was superposed. The fatigue fracture surfaces under high stress amplitudes for case A was flat with rubbing marks, and that under low stress amplitudes was factory-roof shaped. The electrical potential change in one cycle indicated the contacts of fracture surfaces, which will cause the retardation of crack propagation. For case B, the fatigue fracture surfaces became flatter, and no evident retardation was observed in crack propagation. Contrary to the case of austenitic stainless steel (JIS SUS316L), the amount of crack retardation due to fracture surface contact in SGV410 was much smaller and the notch-strengthening did not take place. The difference in the crack propagation path at the notch root is responsible for the amount of crack surface contact, resulting in notch-weakening for SGV410 and notch-strengthening for SUS316L steel for case A.
In this study, tensile and fatigue tests were performed to evaluate the fatigue limit of lamellar pearlitic steel used for manufacturing railroad rail. The fatigue ratio of lamellar pearlitic steel was lower than that of general steels, the reason for which is unknown. Fatigue cracks initiated in pearlitic steel at a very early stage of the fatigue test. Then, it was speculated that the steel should be treated as that with initial defects. In order to determine the initial defect size in the ultra-low cycle fatigue test, tensile tests were performed. The tensile test results clarified that the crack initiation size depends on the crystal structure. In order to predict the fatigue limit of the pearlitic steel, the prediction method proposed by Murakami was applied to the steel. The measured defect sizes were applied to the prediction method, and fatigue tests were performed. The predicted fatigue limit and the test results were in good agreement. In addition, in order to evaluate the crystal structure at the location of the fatigue crack initiation, electron backscatter diffraction pattern (EBSD) analyses were performed. The analysis results revealed that the crack initiation depends on the pearlite block. Then, we concluded that the fatigue limit of pearlitic steel can be predicted by Murakami's method and the defect size is pearlite block size. Then, decreasing the pearlite block size would cause an improvement in the fatigue limit of the pearlitic steel.
The effects of the strain-induced martensitic transformation on the fatigue behavior of type 304 stainless steel were studied. Rotating bending fatigue tests have been performed in laboratory air and in 3%NaCl solution using specimens subjected to tensile-prestrains at ambient temperature and -25°C. Martensitic transformation occurred more remarkably at -25°C than at ambient temperature. In laboratory air, the fatigue strengths of the prestrained specimens increased with increasing prestrain and the specimens subjected to the same prestrains at each temperature exhibited similar fatigue strength in spite of the different amount of martensitic phase. This indicated that the increase in fatigue strength of the prestrained specimens was primarily attributed to work hardening. In 3%NaCl solution, the fatigue strengths of the prestrained specimens at -25°C decreased significantly compared with those in laboratory air. EBSD analysis revealed that the strain-induced martensitic transformation took place within slip bands and corrosion pits were observed at the crack initiation site in the large prestrained specimens. Based on these results, it was confirmed that the strain-induced martensitic transformation exerted large influence on the fatigue behavior in 3%NaCl solution.
This paper presents the results of a study of the notch effect in low cycle fatigue of Mod.9Cr-1Mo steel under multiaxial loading. Tension-torsion multiaxial low cycle fatigue tests were carried out at room temperature using three types of circumferential notched specimens and crack initiation, propagation and failure lives were experimentally obtained. Two proportional and nine nonproportional strain paths were used in low cycle fatigue tests. The crack initiation and failure lives decreased with the elastic stress concentration factor but the crack propagation lives slightly decreased with the elastic stress concentration factor in push-pull low cycle fatigue. The superposition of torsion straining on push-pull loading reduced the crack initiation, propagation and failure lives but they little decreased with elastic stress concentration factor. The crack initiation, propagation and failure lives in nonproportional loading were smaller than those in proportional loading but showed smaller reduction with the elastic stress concentration factor. Finite element analysis was carried out for evaluating the local strain at the notch root using elastic linear plastic model. Von Mises equivalent strain, path strain and nonproportional strain ranges conservatively estimated the crack initiation and failure lives of the notched specimens. The most suitable parameter for evaluating the crack initiation and failure lives was von Mises equivalent strain range.
Fatigue fracture occurs frequently in very high cycle regime for surface strengthened steels. In this case, fatigue cracks initiate from defects such as non-metallic inclusions existing at the interior of specimens and then the cracks grow to become fish-eyes which can be clearly observed on the fracture surfaces. In this study, the shape of fish-eye was analyzed quantitatively and the relationships between the shape of fish-eye and mechanical conditions such as applied stress and residual stress were discussed. The value of γs/γc was paid an attention to describe the shape of fish-eye, where γs and γc are distances from the origin to the edges of the fish-eye in the directions of the surface and the interior, respectively. Amounts of crack growth in both directions were evaluated by the Paris law, where stress intensity factors were estimated using finite element method under an assumption of a through crack in a plane strain state. The values of γs/γc obtained by the present analyses coincided with experimental data obtained for shot-peened spring steel under various conditions of fatigue tests. These results mean that the shape of fish-eye indicates the background of the fatigue fracture.
To integrate RC slabs and UFC panels into a single piece construction, the UFC panels were placed in the longitudinal direction of bridges, steel bars were arranged on the UFC panels, and concrete was cast on the panels. In this case,lap joints need to be installed between the UFC panels with a core of φ30mm in every 300mm distance away from each others. To evaluate the load-carrying capacity of RC slabs using UFC panels with lap joints, the authors conducted tests of specimens with the following three types of lap joints under running loads. The first type was concrete-injected into the cores. The second type was UFC cylinders inserted into the cores. The third type was steel round bars inserted into the cores.As a result, the load-carrying capacities of RC slabs using UFC panels with the lap joints of concrete-injected cores, the UFC cylinders and steel round bars were 1.24, 1.31 and 1.46 times larger than ordinary RC slabs, respectively. Moreover, the fatigue resistance results evaluated by looking at the equivalent cyclic frequency with fatigue test under running wheel load, the specimens with three types of lap joints had also been evaluated by the fatigue resistance. Furthermore, the proposed lap joints structure's week points and usage had also been evaluated in this paper.
This study was conducted to grasp the possibilities of a method for determining alkali-aggregate reaction rapidly, through the use of potential difference between two aqueous solutions separated by a cation exchange membrane. The rhyolite powder (75∼150μm) was used in the test samples. The membrane potential according to the equation for theory (Goldman equation) was calculated by substitution of the analysis value of Na, K and Si concentrations at aqueous electrolyte solutions. The results obtained were as follows : (1) The potential difference was measured with “Positive (+)” and “Negative (-)” values at testing periods of 3∼15minutes, by the use of “Innocuous” and “Deleterious” powder interpreted according to ASR chemical method (JIS A 1145), respectively. (2) The potential difference was highly correlated with Rc/Sc ratio tested to ASR chemical method. (3) The membrane potential according to the theory equation was calculated for “Positive (+)” and “Negative (-)” value, respectively, as in the case of the potential difference by the membrane. (4) From these results, it was recognized that the method of test for alkali-aggregate reaction by electrochemical technique was able to judge rapidly, and held great promise at the site of mine.
This paper describes the creep characteristics of three kinds of electrolytic copper thin films. Tensile creep and creep rupture tests were performed using three kinds of electrolytic copper thin films with 30mm gage length, 5mm width and 12μm thickness at 353K, 373K, 398K and 423K. The electrolytic copper plating thin films were direct current thin films (DC), periodic reverse pulse thin films (PL) and via fill thin films (VF). The DC and VF showed the same creep rupture lifetimes which were longer than those of the PL. Clear transient and steady creep stages were found in these kinds of the thin films but no acceleration creep stage was found. The minimum creep strain rates of the PL were faster than those of the DC and VF, which corresponded well with the creep rupture lifetimes. The thin film that yielded the faster creep strain rate had the shorter creep rupture lifetime. The relationship between the minimum creep strain rates and rupture lifetimes was well expressed by the Monkman-Grant equation. This implies that the creep rupture lifetime was mainly controlled by the creep deformation rate so that the thin film that has slower creep strain rate is preferable to use in electric devices because it has a stronger creep resistance. The creep rupture lifetimes at different temperatures were well correlated with the Larson-Miller parameter for each film. The correlation indicates that the temperature acceleration testing is performable to obtain the longer creep rupture lifetimes from the relatively shorter creep testing.
The dynamic friction coefficients of the commercial aluminum alloys (A2014, A2024 and A6061) and a superplastic IN9021 alloy were measured by ring-compression tests in a temperature range from 573 to 753K and a stain rate range from 1.0 × 10-2 to 4.0 × 100s-1. In general the friction coefficients (m values) increase slightly with increasing the compressive strains even under the well-lubricated test conditions. The m values of the Al-Cu based alloys, including A2014, A2024 and IN9021, were almost same at 0.2∼0.4 at the temperatures below 723K, but increased rapidly at the temperatures above 723K. On the other hand those of A6061 were almost constant at about 0.4 at the temperatures below 753K. The analysis based on the constitutive equation with consideration of the effect from an existence of the particles indicated that the dominant deformation mechanisms under the investigated conditions were dislocation creep for A2014, and were superplasticity for IN9021 except for the test condition at 573K with 1.0 × 10-1s-1. The m values of the IN9021 were lower than those of A2014, even if the flow stresses of IN9021 were higher than those of A2014. So it was concluded that the m value under a superplasticity region was lower than that under a dislocation creep region. It suggested that the superplastic forming had more benefits for the engineering applications.
Glass-like carbon (GC) is expected as a die material for press molding of glass micro optical devices. However, the mechanical and thermal properties are not enough to use as precision mold die. So, GC composites reinforced by vapor grown carbon fiber (GC/VGCF composites) were developed to improve the properties. The GC/VGCF composites achieved high thermal conductivity and bending strength, and the decreased linear expansion coefficient and good mold releasability. However, surface roughness of the GC/VGCF composites after focused ion beam (FIB) etching increased up to 50nm, when VGCF of 28vol% was added.
A novel solidifying composite material based on hydrophilic polyurethane (abbreviated as W-OH) is used as a sustainable sand-fixing material. The objective of this study was to investigate the actual function of desertification control using W-OH to fix sand from the Qinghai Lake basin. In the first experiment, the effects of sand fixing and resistance of wind/sand erosion were studied by wind tunnel testing. The wind/sand erosion modulus was measured and studied by setting the wind-sand flow velocity to 10m/s, 15m/s, 20m/s or 25m/s and the direction to 0°, 30° or 60°, respectively. A field demonstration was constructed in the Qinghai Lake basin to investigate the actual effects on sand fixation outdoors. The results of wind tunnel testing showed that W-OH can well fix the sand of the Qinghai Lake basin. The sand-fixing layer formed by a W-OH concentration of 3% remained intact under the action of a 25-m/s wind and sand flow. W-OH concentrations of 4% and 5% showed excellent resistance to wind/sand erosion. In the demonstration, the area without W-OH treatment had an amount of 15g/m2/h of windblown sand on average, and the area tacked with a W-OH concentration of 2% showed a reduced amount of windblown sand. However, the area was still seriously damaged by wind/sand erosion. The area treated with a W-OH concentration of 3% showed good resistance to wind/sand erosion without any damage during a 49-day test.
This paper describes the application of Taguchi experimental design to a nano-structure film. An L9 orthogonal array and a molecular dynamics simulation were used to design a metal film made up of eight atomic layers so that the metal film was made to have strong adhesion to a wholly aromatic polyester resin. By carrying out sensitivity analysis with the orthogonal array, among four metal-film factors (the short-side and long-side lattice mismatches with the resin Δa and Δb, surface energy G, and cohesive energy H of an atomic-layer laminated metal film), the mismatches were found to be the most dominant factors in the adhesion strength. The author also found that reducing the mismatches and increasing the surface energy and cohesive energy are effective in increasing the adhesion strength and the signal-to-noise ratio. Molecular simulations showed that a copper/ruthenium/cobalt-laminated film is an appropriate structure that has strong adhesion to the polyester resin.