جستجوی مقالات مرتبط با کلیدواژه "shear- lag model" در نشریات گروه "مکانیک"

Bone is a mineralized biological tissue whose main components are enormously different from the mechanical aspect. Some of bone diseases like osteoporosis are due to mutations in bone structure at nano scale, while their clinical symptoms usually appear at macro scale. Therefore, the evaluation of bone at micro and nano scales is important and the obtained results could be used in fabricating the implant materials, scaffolds and bone grafting. In current study, the finite element modeling is performed to evaluate the mechanical properties and structural behavior of bone at nano scale and cohesive element with different mechanical properties is applied. After its verification, the stress distribution and elastic properties are compared with analytical Shear- Lag model. Limited studies are available on strain ratio in previous research and it is presented for different cohesive elements in current study. The influence of mineral volume fraction and mechanical properties of collagen is investigated. The comparison between FE models and the other ones demonstrate an excellent agreement. The collagen- HA interface with unknown mechanical properties is the most important parameter in mineralized collagen fibril and by analyzing different parameters in current research, the thick layer of water with Van der Waals interaction and Viscous shear is determined as the most probable cohesive layer. The result of parametric studies indicates the significant effect of non linear collagen on the model behavior. In order to decrease the cost of investigation in 3D models, the proposed unit cell with periodic boundary conditions could be employed.

In this paper, the stress concentration around a hole in the single layer composite materials with long fibers is examined. The single layer has an infinite length, limited with and instant thickness and is loaded by a constant tension force p at infinity. The width of the lamina is considered to be finite and bears a hole as a defect. Due to presence of excessive shear stress in the matrix bays bounding the hole, a yielded zone of size is developed around the hole. Shear lag model (SLM) is used to drive the displacement and stress fields. The resulting equations are solved analytically based on boundary conditions and continuity in governing equations. Finally, the stress concentrations around the hole are calculated using a computer code. It is shown that the volume fractions of the fiber and matrix, as well as length of the plastic zone, have considerable effect on the stress concentrations within the lamina. Moreover, the number of broken fibers, the total number of fibers and the hole deformation seem to have considerable effect on hole stress concentrations. It is shown the stress concentration coefficient decreases with the increase of the plastic zone length. Also, the stress concentration factor increases in the elastic case with the increase of the volume fraction but in the plastic case at first it increases and then decreases with the increase of the volumes fraction.

In the present study, using a precise shear lag parameter in an extended shear lag model, by considering the effects of out of plane shear stresses, the stress fields distribution as well as strain fields and displacement distributions will be obtained for a typical [0m/90n]s cross ply composite laminate containing a specified matrix cracking density. Then, the stiffness degradation due to existence of matrix cracking in these cross-ply composite laminates will be evaluated and specific damage parameters, which affect the stiffness matrix of composite ply, will be defined. Furthermore, using the concept of fracture mechanics by applying two different criteria including the maximum stress and strain energy release rate, the matrix cracking initiation and evolution as well as induced delamination propagation will be studied. Finally, a closed form relation will be presented which predicts the evolution of matrix cracking under uniaxial loading conditions in cross-ply composite laminates. At last, the obtained results by present study will be compared with available semi-analytical and experimental results. The obtained results reveal that the proposed closed form relations by the authors have a less difference with experimental results in comparison with the previous semi analytic results.