A statistical estimation method of S-N curve for aluminum alloys using their static mechanical properties was proposed. Firstly, S-N data series for aluminum alloys were extracted from "Database on Fatigue Strength of Metallic Materials" published by the Society of Materials Science, Japan (JSMS) and semi-logarithmic curve model was applied as mathematical regression model based on the JSMS standard, "Standard Evaluation Method of Fatigue Reliability for Metallic Materials -Standard Regression Method of S-N Curves-". Secondly, correlations between each pair of regression parameters and static mechanical properties were investigated. Using these correlations, S-N curve for aluminum alloys could be predicted easily from the static mechanical properties. Moreover, using (1) the distribution of regression parameter D and (2) the distribution of fatigue strength at 107 cycles, the percent points for the predicted S-N curve was evaluated. As result, it was confirmed that over 70% of S-N data series of wrought aluminum alloys fall within the range of estimated interval between -3s and +3s, where s means a standard deviation for the parameter of D.
This study proposes an anomaly detection method for bridges using Bayesian inference, aiming at efficient inspection based on vibration monitoring. In the proposed method, firstly a posterior distribution of the parameters composing multivariate auto-regressive model is acquired from a bridge under healthy condition by means of Bayesian inference. Secondly, based on the posterior distribution representing vibration of the healthy bridge, a Bayes factor is calculated to detect change in the modal properties caused by damage. To investigate feasibility of the proposed method for damage detection, this study utilized data from a field experiment on an actual steel truss bridge whose truss member was artificially severed. The proposed method detected two different damage levels successfully. A damage indicator previously investigated by the authors is also evaluated with respect to the experimental data, and compared with the proposed method.
In recent years, now words "resilience engineering" paid attention to by many people. The function (four capability: responding, monitoring, anticipating, and learning) is needed for resilience engineering, and then quantitative evaluation becomes important to measure its effect. However, the definition of resilience response is difficult, therefore the establishment of quantitative evaluation method is difficult. In this study purpose, we reproduce resilience response using participatory evacuation simulation. And, We try quantitative evaluation using the evacuation reliability evaluation method. Specifically, targeted for the office floor, The human evacuation behavior at the time of the accident equipped with resilience response ability is assumed and the quantitative value of the resilience response is considered using refuge completion time.
It is necessary to examine the establishment of new evacuation spot so as to minimize the human toll of flooding occurred by a storm surge. Thus, to begin with, two types of evacuation simulations which reflect the result of a storm surge analysis are conducted; one is conducted under the current evacuation planning and the other is done under the combination plan of an additional evacuation spots and the current plan. Secondly, the effect of the additional evacuation spots and the amount of time required for an evacuation completion are seized, and the proper location of an evacuation spot and the reasonable evacuation route are discussed. The additional evacuation spot removes the jam of agents around the evacuation spot and encourage the quick escape from their house to the evacuation spots around which the flooding occurs. Thereby, the completion rate of evacuation under the combination plan increases by 20% compared to that under the current evacuation plan, and 90% of agents could finish evacuating in a final stage. Therefore, it is found that the additional evacuation spot with considering the flooding occurred by a storm surge has a major effect on an evacuation behavior.
Tozai line is the metro rail system serving the urban areas in Tokyo. It was built in 1960s and a construction method, PCT girder bridges is one of the most majority designs still in use through this rail system. In order to identify risk factors and determine appropriate ways to control the hazards, risk assessment for PC Bridge has to be conducted during maintenance activities. In this study, during the stage of construction, two main sources in risk analysis which cause a great failure or decline are insufficient PC grout filling and breaking of the PC steel member, respectively. On the other hand, according to the results of general inspection used in risk analysis, it reveals that although no severe deterioration occurred and the risk of present load-bearing capacity is low, the third-party disasters still retain risks. Therefore, the study reports herein attempt to address risk assessment process to evaluate hazards for PC bridges. Furthermore, considering the risks during the construction stage and the maintenance period, the former issue is evaluated by PC grouted filling condition; whereas the latter is judged by engineers to determine the proper protective approaches to that risks. Finally, by adopting the numerical analysis associated with above issues, the relationship between any changes in appearance and load-bearing capacity for PC bridges are assessed.
In order to clarify influence of hydrogen on fracture behavior of clinched joint, we performed tensile shear tests and fracture analyses. As verification tests, a hardness test, tensile tests with plate specimens and hydrogen concentration measurement were conducted. The tensile shear tests were conducted with and without hydrogen charging, respectively. The tensile shear test results showed that the maximum load and fracture displacement of the hydrogen-charged specimen were smaller than that of the noncharged specimen. The fracture analyses clarified that macroscopically fracture surface of the joint part on the hydrogen-charged specimen did not deform much, but microscopically showed large dimples with high aspect ratio. Fracture analysis results indicated that a crack growth on the joint part was assisted by hydrogen-enhanced void nucleation, growth and coalescence and hydrogen-enhanced localized plasticity. The hardness of the joint part was higher than that of the material before the joining process. On the tensile test, the maximum load and fracture displacement were not changed by hydrogen charging. The hydrogen concentration measurement showed that the joint was charged with 1 ppm hydrogen. These results show that work hardening and stress concentration have an important role on hydrogen embrittlement on clinched joints.
Valve is a critical device to control fluid flow as an in-plant installation. However, much accidents due to an out-of-control valve have been reported in the past. One reason that the valve will become out-of-control is a Fixation-damage due to corrosion. It is important to evaluate the structural integrity of valve installed in plants because a fixation-damage causes serious accidents. For the purpose of developing a structural integrity monitoring system of valve, this study attempts to classify structural integrity of valve from vibration image data by using deep convolution neural network. First attempt is made to investigate the relationship between vibration characteristics of the valve with fixed-damage due to corrosion and torque to open/close the valve. Second attempt is made to make training data sets from the torque and the image data of vibration frequency of valve and train deep convolution neural network. Finally, it is demonstrated whether the structural integrity of the valve can be classified by using the trained deep convolution neural network.
Kriging, which uses theory of conditional Gaussian random field, has been widely used in geotechnical problems. Least square method and L2 norm plays an important role in the method. The concept of sparse modeling attracts much attention from various fields. It is reported that it is successfully applied to many problems in various fields such as signal processing, image processing, machine learning and so on. The representative formulation LASSO uses L1 norm instead of L2 norm in the formulation. After illustrating the concept and formulation of sparse modeling, application to evaluation of soil property from limited number of boring data is discussed. One dimensional and two dimensional cases are indicated with assumption of sparsity in first-order and second-order differentiation space. In one dimensional case, both assumptions, which are sparsity in first-order and second-order differentiation, give reasonable distribution. In two-dimensional case, however, the assumption of sparsity in first-order differentiation gives unnatural distribution in the numerical examples. In the evaluation of spatial distribution of geotechnical problems, assumption of sparsity in second-order differentiation space seems reasonable.
Maintenance problem for infrastructures such as bridge, road, airport, etc., attracts keen interest in modern Japan. We have to cope with repair and maintenance for infrastructures with limited financial resources. In airport pavements, repair works are restricted by daily flight operation, so that efficient maintenance planning is required. In this paper, we try to model deterioration of an existing airport runway, which is composed of 100 units. PRI (Pavement Rehabilitation Index) for each unit is obtained by 3 to 8 times of inspection during around 28 years. PRI is an index to provide an objective evaluation of pavement surface condition, with criteria determined for judging the need for rehabilitation work on runway, taxiway, and apron pavements. Many researches and practitioners use PRI for airport pavement maintenance in Japan. The spatial distribution of deterioration in airfield pavement is not discussed in many previous studies. This study discusses deterioration curve for each unit and feature of spatial distribution. The distribution of deterioration based on PRI and the probability of exceedance of each PRI criteria in future are estimated by the proposed method.
In order to predict the thermal expansion coefficient (TEC), quasiharmonic approximation based on the ab initio electronic structure calculation is an effective and conventional scheme. However, it is known that the deviation due to anharmonic effect arises at high temperature. Although Molecular Dynamics (MD) naturally includes the anharmonic effect, classical MD is lacking in accuracy because of its empirical interatomic potential and ab initio MD is not applicable because of its high computational cost. In this paper, we have proposed a new hybrid method using ab initio electronic structure calculation and classical molecular dynamics for calculating TEC of alloys at high temperature. Our method is non-empirical, highly accurate and computationally inexpensive. The method consists of three steps. Firstly, various snapshots of the atomic coordination at a certain temperature are sampled by classical MD. Secondly, physical properties of each snapshot are calculated by ab initio electronic structure calculation. Finally, by analyzing them statistically, the equilibrium volume is computed. TEC is obtained by repeating these steps at different temperatures. We have calculated the TECs of Al, Ni3Al, and NiAl. Results show good agreements with experimental results. Our method enables us to improve the conventional quasiharmonic approximation and obtain accurate TEC at high temperature through the incorporation of anharmonic effect.
Kirigami is a traditional art of papercraft, which makes 3 dimensional structure from 2 dimensional sheet. Recentyears, the mathematical foundations of kirigami and origami have been developed as well as the practical applications.In this research, we analyze the out-of-plane deformation of kirigami structure under tensile force, and investigate themechanism of the deformation based on the beam theory. We simulate the process from in-plane deformation to out-ofplanedeformation using molecular dynamics, and discuss the effect of geometry parameters on stability.
Asphaltene adsorption on silica surface plays an important role in wettability alternation in an oil reservoir and the durability of asphalt pavement. In this study, we investigated the relationship between asphaltene structure and adsorption characteristics via potential of mean force (PMF) by molecular dynamics simulation. We prepared six types of asphaltene molecules, and studied the adsorption Gibbs free energy on two different silica surfaces (e.g., hydrophilic and hydrophobic silica). In total, twelve PMFs between a single asphaltene molecule and silica were calculated. On both hydrophilic and hydrophobic silica surfaces, the calculated adsorption Gibbs free energy of asphaltene with a hydroxyl terminal was larger than the similar types of asphaltene without hydroxyl terminals because of hydrogen bonding between a hydroxyl terminal and silica surfaces. The adsorption Gibbs free energy of asphaltene with larger aromaticity was also large, while those of asphaltene with less aromaticity and no alkyl chain were small. Moreover, for all asphaltene molecules, the calculated adsorption Gibbs free energy is significantly larger for hydrophobic surface than hydrophilic one (by 8-54 kJ/mol). The underlying mechanism can be ascribed to the polarity difference of those two surface structures. This study shows a quantitative evaluation of the adsorption characteristics in different types of asphaltene and mineral surfaces.
In this study, we perform molecular dynamics simulations to investigate plastic deformation modes of a magnesium (Mg) nanotwinned structure. Periodic units including (1011) twin boundaries (TBs) are analyzed using an embedded atom method potential. Equal spaces between the TBs are assumed at the initial state and the space is parametrized in the range between about 5 nm and 30 nm. It is found that plastic deformation is triggered by the slip along a (1011) twinning plane near a TB, and that this event induces two different deformation modes depending on the space, i.e., the migration of the TBs and the evolution of double twinning, which leads to void nucleation and polycrystallization. The plastic deformation provided by the two different modes is quantitatively verified from geometric analysis. As the space decreases, the migration of the TBs is superior to the evolution of double twinning.
Discontinuous propagation of a crack tip in heterogeneous media is characterized by a power-law distribution, but discontinuity of crack propagation in homogeneous media is still unclear. In this study, we investigate the discontinuous features of the mode-I crack propagation in single crystals by performing molecular dynamics simulations of uniaxial tensile deformation for a two-dimensional single crystal model with an open cleavage. Temporal dynamics of the crack propagation is extracted by locating the position of the crack tip in the model. In the simulations, discontinuous crack propagation, go-stop motions of crack propagation, has been observed. The displacement of the crack seems to follow an exponential distribution depending on the temperature rather than power-law distributions. The observation indicates that the discontinuous behavior is due to dislocation emissions; a crack propagation started by increasing of local stress due to external loading stops by decreasing of the stress due to dislocation emission from the crack tip. This picture directly provides an exponential distribution consistent with the observed statistical feature.
In this study, the grafting modes of the silane coupling agent (3-aminopropyltriethoxysilane; APTMS) that modifies the silica surface were analyzed by considering the chemical adsorption onto the surface and the self-condensation of the APTMS molecules. First-principles electronic state calculations were performed to evaluate the difference in energy among a variety of molecular forms of APTMS, which were supposed to arise from the surface adsorption of an APTMS molecule and the oligomer formation of APTMS molecules. The APTMS monomer exhibited an energetically stable structure via strong interactions of its OH groups and NH2 group with the OH groups on the silica surface. Furthermore, there was a possibility that an APTMS molecule can be covalently bonded by mono- and di-grafting with the silica substrate. In addition, we found that the APTMS undergoes condensation reaction between the molecules with forming an extended-chain type di- to tetramer, a cyclic tetramer, and a larger branched oligomer. Such oligomer formation was energetically favorable compared to the chemisorption onto the silica surface. The finding provides an insight for understanding the atomic details of network structures of silane coupling agent molecules in the interfacial region of composite materials.
Hydrogen diffusion in Pd with various H concentrations and Pd-Ag alloys with various Ag and H concentrations is investigated using molecular dynamics simulations. At H concentration of 0.5 in Pd, the miscibility gap caused by the spinodal decomposition is observed. The diffusion coefficient of H in Pd is kept constant at H concentration less than 0.1, then increases with increasing H concentration until the phase transition occurs, and after reaching a maximum it decreases with increasing H concentration. The simulations of varying a temperature predict the activation energy for H diffusion of 0.163 eV at H concentration of 0.05, which agrees well with that reported in the literature, and minimum activation energy of 0.144 eV at H concentration of 0.5. Moreover, our results indicate that the addition of Ag to Pd leads to the dissipation of the miscibility gap. The diffusion coefficient of H in Pd-Ag alloys significantly decreases with increasing Ag concentration. The minimum activation energy for H diffusion in Pd-Ag alloys is estimated to be 0.135 eV when Ag and H concentration are 0.1 and 0.5, respectively.
Various amorphous/crystalline polypropylene (PP) and polyethylene (PE) are pressed under multi layer graphite (MLG) rigid walls and then detached or scratched to evaluate the interfacial strength by molecular dynamics simulation. Not only perfect at MLG surface, but also periodic sine wave surfaces of stacked graphite akes are considered to discuss the effect of surface pattern. PP always show higher strength than PE both in the debonding and shear. The debonding stress shows the highest for the at MLG surface and decreases with narrower surface pattern. The local density at the polymer/MLG interface reveals that the adhesiveness decreases with the smaller surface pattern and leads this tendency. However, crystalline polymers, oriented normal direction to MLG, always show lower strength than the amorphous ones despite of their high density at the interface. This result emphasizes the fact that the interfacial strength is not uniquely decided by the van der Waals energy but also by the morphology of the molecular chains attached to the interface. Observations of chain morphology shows that the random coil PP chains tend to form clusters while the PE chains widely spread in the amorphous block. Thus longer PE chains bridge the surface convex and prevent filling of other chains to the surface concave, resulting in the lower interfacial density and debonding stress. On the other hand, the PP chain clusters cling to the interface with same ratio and the longer chains have massive “anchor part” in the amorphous, showing same interfacial density and higher debonding stress. Contrary to the debonding strength, the shear strength is always zero for the perfect surface and extremely increases with the narrower surface pattern for the crystalline polymers. This result can be simply explained with the difficulty of the conformation change or chain rotation in the straight chain bundle of crystal polymers, and with the gradient of the surface convex that work as barrier against the flow deformation of sandwiched polymers.
Fracture tests for circumferentially through-wall STPG370 cracked pipes were simulated by elastic-plastic ordinary state based peridynamics where work hardening model was newly introduced. Three fracture tests were selected as objects of analysis with different crack angle and test temperature. Load-load point displacement curves were reproduced by the peridynamics while crack extensions were slightly slower than experimental results. Slant crack extension directions of specimens were also well reproduced by the peridynamics analyses.
The annealing effect on dislocation emission from non-equilibrium grain boundaries (NEGBs) is investigated through atomic simulations of bicrystal models in order to consider why bulk nanostructured metals (BNMs) show the unique mechanical property of “hardening by annealing and softening by deformation” reported by Huang et al. (Science, Vol. 312, pp. 249-251 (2006).). NEGBs with extrinsic grain boundary dislocations (EGBDs) in bicrystal models are annealed at different temperatures. The critical resolved shear stresses (CRSS) to dislocation emission from annealed NEGBs are measured by deformation tests at 0.1 K, and we find that the CRSS increases with the annealing temperature. This result shows the same tendency of “hardening by annealing.” Next, we investigate the controlling factors to the annealing dependence of the CRSS by focusing on the annealing effect on the grain boundary energy, atomic free volume and hydrostatic stress field around the EGBDs. As a result, the structural change of the EGBD core by the annealing process is the dominant cause of the annealing dependence of the CRSS to dislocation emission from NEGBs. Our results show that the plastic phenomenon of dislocation emission from grain boundaries is one of the deformation mechanisms that can explain the unique mechanical property of “hardening by annealing and softening by deformation” in BNMs.
Impurity atom distribution and its time evolution in cylindrical nanowire were studied using a diffusion equation based on chemo-mechanical potential, which considered coupling effects between chemical potential (chemical effect) and internal stress (mechanical effect) due to interstitial impurity atoms. We did consider diffusion blocking and nanowire yielding effects when we solved the diffusion equation. The yield criterion was described by comparing local volumetric strain caused by impurity atoms with critical volumetric strain at which the lattice instability appears. Obtained results used the diffusion equation with realistic materials parameters indicate a possibility of nanowire yielding due to interstitial atom diffusion and diffusion slowdown due to the yielding.
Welded structures are widely used for construction machines, automobiles, railway vehicles, etc. In these structures, the welded parts are generally the weakest points. In particular, the toes of welding and the tops of non-welded portion become causes of fractures because these are stress concentration points. Thus, a method is required for evaluating fatigue life by analyzing these stress concentration points in a lump. In this study, a new evaluation method was developed for welded parts using strain gradient parameters. The conclusions were as follows: (a) Comparing strain approximation equation Δε = Hε/rλε (Δε: Strain range, r: Distance from strain concentration point, Hε: Magnitude of strain concentration, λε: Slope of strain concentration) to the strain distribution of the aluminum alloy specimens calculated by using elasto-plastic analysis, the strain gradient parameters Hε and λε were derived. A fatigue-life surface was derived using the parameters and fatigue life data that were obtained from the fatigue testing of the test specimens. The equation of the surface was logN = －5.2logHε－3.5λε＋21.7. (b) The fatigue life calculated by the fatigue-life surface equation had approximately good agreement with the fatigue life derived in the test.
Intermittent EBSD assessment of creep damage behavior was performed on five kinds of notched specimens of a Ni-base superalloy DS material. As a result, it was found that the fixed area average intra-grain misorientations (GRODave) of the notched damaged material corresponded to the NOD (Notched Opening Displacement). In addition, a misorientation parameter (GRODave/φ0) normalized with the initial notch opening value was able to express creep curves regardless of the notch geometries as well as the RNOD (Relative Notched Opening Displacement). Furthermore, a misorientation parameter (∫GRODext/φ0) normalized with the initial notch opening value after extracting the GROD value exceeding a threshold on the GROD map was proposed. It was concluded that the damage assessment parameter of ∫GRODext/φ0 uniformly allowed creep damage assessment by generally defining the damage evaluation area even for actual components with various stress concentrated areas.
In the automobile industry, CFRTP (Carbon Fiber Reinforced Thermoplastics) are expected to be used because of their superior properties such as high toughness, high productivity and high recycling efficiency. Although the composite materials allow the integral molding of complicated structure, a large number of joints such as bolts and rivets still exist for assembly of the vehicle. These fastening implements cause an increase of the weight and the stress concentration at the holes. In the current aerospace industry, the welding technique for fiber-reinforced thermoplastics by direct resistance heating to metal mesh has been developed and applied. In this process, weight increase due to the use of metal mesh and bonding strength between metal mesh and matrix are issues to be overcome. We have been developing a resistance welding technique in which carbon fiber itself was used for the heating elements. To reduce the bonding area, further improvement of bonding strength is needed. In this study, waterjet surface treatment was applied to CFRTP to improve bonding strength. The influence of scanning direction of waterjet treatment (vertical or parallel to the fiber direction of CFRTP) on the ablation of the CFRTP was analyzed by means of the microscope. Bonding strength evaluated by tensile shear tests was improved under the condition of the waterjet treatment in parallel to the fiber direction.
In recent years, bone tissue engineering, whose basic elements are an appropriate cell source, optimal culture conditions and a biodegradable scaffold, has been getting attention. The scaffold is used as space filling material to work as an extra cellular matrix to organize cells into three dimensional structures. Nanofibers are expected to be used as the scaffold because their small size is close to the structural dimension of the extra cellular matrix of native tissues. Thermoplastic polymers have been spun to nanofibers by the electrospinning method, which applies a high voltage to a polymer solution. Among many thermoplastic polymers, polylactic acid (PLA) is expected to be used for a scaffold because of its biocompatibility, bioabsorbability and mechanical properties. To obtain better affinity properties of a PLA nanofiber scaffold with the bone, compounding with hydroxyapatite nanoparticles (HA), which have the same composition formula with the human bone, had been conducted. HA/PLA composite nanofiber is expected as the scaffold for bone tissue engineering. However, the strength of HA/PLA composite nanofiber is weak because of its low interfacial strength between HA and PLA and the easy aggregation property of HA. In this study, the surface treatment of HA by hot water and silane coupling agent was conducted (HW＋HTS). HA/PLA composite nanofibers were fabricated by electrospinning, and the mechanical properties of its nonwoven fabrics, aligned fabrics and single fibers were evaluated. HW＋HTS treated HA showed high dispersion condition in PLA. While the tensile strength of untreated HA/PLA composite nanofibers was smaller than that of pure PLA nanofibers, HW＋HTS treated HA/PLA composite nanofibers showed almost the same strength of pure PLA nanofibers. By dispersing HA in PLA nanofiber by HW＋HTS treatment, HA/PLA composite nanofiber showed uniform mineralization behavior, which was evaluated using Hanks' Balanced Salt Solution (HBSS).