In this study, fracture healing was simulated by the CA method, which is one of the discrete computation methods. First, the state of a cell was defined as “bone”, “cartilage” or “fibrous connective tissue” and a set of local rules was constructed referring to the fuzzy logic model for sheep metatarsal. The simulation results obtained by the CA method agreed well with the ones in the previous research and the experimental data. As a result, it was concluded that the CA simulation model proposed in this study is a suitable model for describing fracture healing. Next, modifying the parameters of local rules, fracture healing of human bone was simulated. On the basis of the simulation results obtained under various conditions of external fixation, it was concluded that an optimal set of stopper gap and initial gap conditions may exist because they have a close relationship to each other.
The authors developed a fractal branch and bound method for optimization of stacking sequences of laminated composites to maximize buckling load of composite structures. The method demands an approximation of a design space with a response surface comprising quadratic polynomials for pruning branches of stacking sequences. Approximation of the objective function with quadratic polynomials has been confirmed for buckling load maximizations and panel-flutter-speed-limit maximizations using lamination parameters as predictors. Flutter speed maximization of composite delta wing is employed in this study as an example of stacking-sequence optimization using the fractal branch and bound method. This paper describes the theoretical background of the fractal branch and bound method. Then approximations are performed using quadratic polynomials with lamination parameters as predictors. Subsequently, we investigated effectiveness of this method for supersonic flutter of a composite delta wing. Results indicate that the method was applied successfully; a practical optimal stacking-sequence was obtained using modified response surfaces.
The effect of moisture absorption on the static and fatigue properties for plain-woven CF/epoxy composites (plain-woven CFRP) was examined when the humidity condition changed at the following stages; mixing of epoxy resin with hardener, laminating of carbon fabrics with epoxy resin, storage before testing and static and fatigue testing. At each stage, the materials were exposed to either completely dry nitrogen gas to isolate the materials from moisture or the laboratory atmosphere. The experimental results showed that the tensile strength and fatigue life of plain-woven CFRP were significantly improved when the materials were protected from moisture absorption at the mixing and laminating stages. This protection improved the resistance of crack growth and interfacial shearing strength at the fiber/matrix interface. Such improvement contributes to the enhancement of the tensile strength and fatigue life of plain-woven CFRP.
Real-time Scheduling has been recognized as the central function in an Advanced Planning and Scheduling (APS) environment. The present study proposes a hybrid approach of utilizing the Lagrangean Relaxation method and due-date buffer in order to realize the real-time scheduling function. A penalty cost is calculated from a relevant due-date buffer is incorporated into the normal Lagrangean Relaxation method by two approaches. The implicit approach is to adopt the penalty cost in the dispatching rule of the list scheduling, and the explicit approach is to adopt the penalty cost in the objective function of the Lagrangean Relaxation method. The proposed approaches are compared to the original methods by various experiments adopting different features and scales of the workshops. Based on the experiment results, the effectiveness of the proposed approaches is verified and a feasible experimental method by which to decide the best due-date buffer size is presented.
This paper deals with coordinating delivery schedules and inventory replenishments in a supply chain operated under Vendor Managed Inventory (VMI) system. We propose a new model of Vendor Managed Inventory Routing (VMIR) based on the existing Period Traveling Salesman Problem (PTSP) model. The proposed model will be referred to as the Integrated Inventory and Period Traveling Salesman Problem (IPTSP). In the IPTSP, the delivery frequency is treated as a decision variable instead of a given parameter. We formulate the problem and develop a heuristic approach to solve it. We put emphasis on the procedure for seeking the best delivery frequency for retailers called “delivery consolidation”. Assuming that each retailer is initially visited every day during the m-day period, the procedure tries to consolidate the current deliveries in order to make a trade-off between traveling costs and inventory holding costs in order to minimize system-wide costs. The numerical experiment results show that by treating the delivery frequency as a decision variable some benefits can be produced.
We discuss the cryogenic damage and fracture behaviors of G-11 woven glass-epoxy laminates. In conjunction with the cryogenic fracture toughness test, a finite element analysis was conducted to predict the fracture and deformation for models of the compact tension (CT) specimens. Effective elastic moduli were determined under the assumption of uniform strain inside the representative volume element. Hoffman’s criterion was selected as the criterion for fiber-dominated failure, and matrix cracking was detected by the maximum strain criterion. The virtual crack extension method was adopted to calculate strain energy release rate which leads to determination of stress intensity factor. In order to verify the model, correlations between experimental and analytical results were made, in terms of the load-displacement response and the extent of damage growth. Reasonable agreements between the calculations and the experimental data were achieved.
Ellipsoidal inclusions can be regarded as a general model of defects in structures because they cover a lot of particular cases, such as line, circular and spherical defects. This paper deals with three-dimensional stress analysis for ellipsoidal inclusions in a bimaterial body under tension. The problem is formulated as a system of singular equations with Cauchy-type or logarithmic-type singularities, where unknowns are densities of body forces distributed in the r- and z-directions in bimaterial bodies having the same elastic constants of those of the given problem. In order to satisfy the boundary conditions along the ellipsoidal boundary, four types of fundamental density functions proposed in the previous paper are applied. Then the body force densities are approximated as a linear combination of fundamental density functions and polynomials. The present method is found to yield rapidly converging numerical results for stress distribution along the boundaries of both the matrix and inclusion even when the inclusion is very close to the bimaterial interface. Then, the effect of bimaterial surface on the stress concentration factor is discussed with varying the distance from bimaterial interface, shape ratio, and elastic modulus ratio.
The phenomenon of fatigue failure due to In-line flow-induced vibration has been investigated. In the experimental program an induced-vibration experimental set-up involving water flow was developed. This apparatus was used to produce fatigue failure resulting from In-line flow-induced vibration. The fatigue specimens were made of a medium carbon steel. A small hole was drilled into the specimen surface to localize the fatigue cracking process. A strain histogram recorder (Mini Rainflow Corder, MRC) was used to acquire the service strain histogram and also to detect any variations in natural frequency. The cumulative fatigue damage, D, as defined by the Modified Miner Rule, was determined by using the strain histogram of the early portion of the test record. The value of D was almost unity in the case of In-line vibration. In contrast, the value of D obtained in a previous investigation for the case of the Cross-flow vibration ranged approximately from 0.2 to 0.8.