Accepted Manuscripts

Bensingh Dhas, Md. Masiur Rahaman, Kiran Akella, D Roy and J.N. Reddy
J. Appl. Mech   doi: 10.1115/1.4038506
A phase field damage model for orthotropic materials is proposed and used to simulate delamination of orthotropic laminated composites. Using the deviatoric and hydrostatic tensile components of the stress tensor for elastic orthotropic materials, a degraded elastic free energy that can accommodate damage is derived. The governing equations follow from the principle of virtual power and the resulting damage model, by its construction, conforms with the physical relevant condition of no matter interpenetration along the crack faces. The model also dispenses with the traction separation law, an extraneous hypothesis conventionally brought in to model the inter-laminar zones. The efficacy of the model is assessed through numerical simulations and experimental validation against planar modes of delamination in composite laminates.
Jia-Liang Le, Jan Elias, Anna Gorgogianni, Joshua Vievering and Josef Kveton
J. Appl. Mech   doi: 10.1115/1.4038496
This paper investigates the effect of strain rate on the scaling behavior of dynamic tensile strength of quasibrittle structures. The theoretical framework is anchored by a rate-dependent finite weakest-link model. The model involves a rate-dependent length scale, which captures the transition from localized damage to diffused damage with an increasing strain rate. As a result, the model predicts a rate and size dependent probability distribution of the nominal tensile strength. The transitional behavior of the strength distribution directly leads to the rate and size effects on the mean value and the standard deviation of the tensile strength. The model is verified by a series of stochastic discrete element simulations of dynamic fracture of aluminum nitride specimens. The simulations involve a set of geometrically similar specimens of various sizes subjected to a number of different strain rates. Both random microstructure geometry and fracture properties are considered in the simulations. The simulated damage pattern indicates that an increase in the strain rate results in a more diffusive cracking pattern, which supports the theoretical formulation. The simulated rate and size effects on the mean and standard deviation of the nominal tensile strength agree well with the predictions by the rate-dependent finite weakest-link model.
Shoujing Zheng and Zishun Liu
J. Appl. Mech   doi: 10.1115/1.4038497
Temperature sensitive hydrogel is blessed with outstanding properties which may be utilized for innovative appliance. However, this is not achievable if the phase transition property of it is not well understood. Under certain mechanical constraint or temperature stimuli, the hydrogel shows the phase transition, a very special phenomenon that has been study for decades. Those studies has cumulated many qualitative conclusions, yet the quantitative ones are still evasive. Using Dynamic Mechanical Analysis, we have conducted experiments to quantitatively investigate this peculiar behaviour. It is evident that the higher the temperature stimuli applied to hydrogel, the higher the stress which triggers phase transition. Based on the experimental results, a decision rule which predicts the stress triggering phase transition is proposed. Furthermore, theoretical study has also been carried out to study this phase transition phenomenon. With a proper fitting parameter and a transformation from referential state to free swelling state, we can compare the theoretical prediction of the stress-stretch curve with results from experiments. Besides experimental observations and theoretical analyses, another feature of this paper is to provide a numerical method to study phase transition under mechanical constraints.
Technical Brief  
Robert L. Jackson
J. Appl. Mech   doi: 10.1115/1.4038495
The indentation of flat surfaces deforming in the plastic regime by various geometries has been well studied. However, there is relatively little work investigating cylinders indenting plastically deforming surfaces. This work presents a simple solution to a cylindrical rigid frictionless punch indenting a half-space considering only perfectly plastic deformation. This is achieved using an adjusted slip line theory. In addition, volume conservation and pileup and sink-in are neglected, but the model can be corrected to account for it. The results agree very well with elastic-plastic finite element predictions for an example using typical steel properties. The agreement does diminish for very large deformations but is still within 5% at a contact radius to cylinder radius ratio of 0.78. A method for accounting for strain hardening is also proposed by using an effective yield strength.
Wei Wang and Xinming Qiu
J. Appl. Mech   doi: 10.1115/1.4038470
In the analysis of Origami structures, the deformation of shells usually couples with the rotation of creases, which leads to the difficulty of solving high order differential equations. In this study, firstly the deformation of creased shell is solved analytically. Then, an approximation method named virtual crease method (VCM) is employed, where virtual creases are used to approximate the deformation of shells, then a complex structure can be simplified into rigid shells connected by real and virtual creases. Then VCM is used to analyze the large deflection of shells as well as the bi-stable states of Origami structures, such as single creased shell and cell of Miura-Ori. Compared with experiment results, the deformed states given by VCM are quite accurate. Therefore, this generalized method may have potential applications in the analysis of Origami structures.
TOPICS: Shells, Deformation, Differential equations, Approximation, Deflection, Rotation
Leichuan Tan, Deli Gao and Jinhui Zhou
J. Appl. Mech   doi: 10.1115/1.4038424
Buckled drillstring is easily existed in extended-reach drilling (ERD) engineering, causing casing wear more severe. However, the effect of the buckled drillstring on casing wear prediction is going unheeded in long-term studies. To solve the issue, this paper proposes a new model, named as circumferential casing wear depth (CCWD) model based on the energy principle and the more complicated geometry relationship than that in casing wear groove depth (CWGD) model. Meanwhile, sensitivity analysis of parameters clearly describes the changing trends among them. With the established composite wear models, the change of casing wear depth versus drilling footage under different composite wear cases is also discussed. The results show that, the severe casing wear may occur if there is the buckled drillstring; due to the greater contact force and more sophisticated wear shape than those under non-buckling condition, a shorter drilling footage could make a larger calculation error when only CWGD model is used. In the case study, the method of the inversion of casing wear factor from the drilled well can be used to predict the well whose structure resembles it; the revised coefficient, the maximum risky casing wear depth can be evaluated for each wellbore section to avoid drilling engineering failure. The new model provides a practical method to improve the prediction accuracy of casing wear in ERD. Neglecting the effect of the buckled drillstring will make the prediction underestimated and a great economic loss, which is significant for ERD.
TOPICS: Wear, Drill strings, Drilling, Composite materials, Buckling, Errors, Failure, Geometry, Sensitivity analysis, Shapes

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