A unified numerical framework for modeling interactive failure modes in a single edge notched laminated composite under tension

Interlaminar fracture in polymer matrix composite (PMC) laminates, often called delamination, is defined as an out-of-plane discontinuity between two adjacent plies of a laminate. Intralaminar cracks are defined as in-plane discontinuities that advance through the entire laminate thickness in the direction parallel to the fiber direction. These failure modes are competing with each other and one failure mode often initiates other failure mode, resulting in very complicated interactive failure mechanisms. In this presentation, the interactive failure mechanisms between the intralaminar and interlaminar fracture modes are characterized using finite element analysis with single edge notch tension (SENT) tests. Three major intralaminar failure mechanisms, which are distinct from the microdamage mode, are considered: transverse (Mode I) matrix cracking, shear (Mode II) matrix cracking, and axial (Mode I) fiber fracture. These in-plane damage, once initiated, can trigger other failure mechanisms such as delamination and/or act as delamination migration pathways between adjacent interfaces, leading to the further growth of the delamination. In this presentation, a unified numerical framework is developed to account for these various failure modes to study the interactive failure mechanisms in a single edge notched laminate composite. In plane failure modes are modeled using Enhanced Shapery Theory (EST) and delamination is modeled by Discrete Cohesive Zone Method (DCZM) From the finite element analysis, delamination triggered by in plane damage is observed and changes in load distribution as a ply in the laminated composite loses a load carrying capability one by one are detected. FEA results are compared against experimental data. The stress-strain response obtained from FEA agrees well with test results and the detailed failure progression is also accurately captured from FEA

A Predictive Model for the Compressive Strength of 3D Woven Textile Composites

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/106436/1/AIAA2013-1727.pd

Effect of fiber distributions on the mechanical performance of CMC materials: Virtual manufacturing and testing approach

Ceramic matrix composites (CMCs) exhibit superior thermal stability in an elevated temperature environment and thus are considered as a promising candidate material for gas turbine applications in the field of power generation industry. CMCs also have a higher fracture resistance than conventional technical ceramics owing to the coated ceramic fibers embedded in the matrix. However, the complex heterogeneous microstructure results in complicated damage and failure behavior at the fiber length scale, which appears non-linear stress-strain response at the macro length scale. When a crack is initiated in the matrix phase, the crack grows very rapidly since the ceramic matrix is a brittle material. However, the rapid crack propagation is restrained when the crack tip reaches the ductile coating interface. This fracture process occurring inside the CMC material results in a highly complicated post-peak response and makes its fracture toughness comparable to that of metals. The post-peak response is greatly influenced by local topology of fibers situated inside the composite material and thus the fracture toughness of a CMC may vary locally due to the irregular distribution of fibers. In the present study, the effect of fiber distributions on the post-peak response and the corresponding mechanical performance of a CMC material is closely investigated by utilizing representative volume elements (RVEs) with various fiber distributions. Two-dimensional square RVE enclosing randomly distributed circular fibers with coating layers is considered to represent the microstructure of a long-fiber-reinforced CMC material. Random, yet realistic distribution of fibers is achieved through the virtual force dispersion (VFD) algorithm. The present VFD algorithm arranges fibers with coating layers after the fibers are randomly seeded into a square RVE. Fibers should be rearranged after the random seed, since overlapped regions between fibers are unavoidable during the initial distribution process. The VFD algorithm assumes that fibers are connected through virtual springs, which provide repulsive forces between them. The VFD algorithm finds an equilibrium state in which the springs are completely relaxed and there exists no repulsive force in the system. In this manner, various RVEs with different fiber distributions are easily created for the next step of analysis. Please click Additional Files below to see the full abstract

Progressive Failure Analysis Method of a Pi Joint with Uncertainties in Fracture Properties

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/97058/1/AIAA2012-1544.pd

Static and Dynamic Response of a Sandwich Structure Under Axial Compression.

This thesis is concerned with a combined experimental and theoretical investigation of the static and dynamic response of an axially compressed sandwich structure. For the static response problem of sandwich structures, a two-dimensional mechanical model is developed to predict the global and local buckling of a sandwich beam, using classical elasticity. The face sheet and the core are assumed as linear elastic orthotropic continua in a state of planar deformation. General buckling deformation modes (periodic and non-periodic) of the sandwich beam are considered. On the basis of the model developed here, validation and accuracy of several previous theories are discussed for different geometric and material properties of a sandwich beam. The appropriate incremental stress and conjugate incremental finite strain measure for the instability problem of the sandwich beam, and the corresponding constitutive model are addressed. The formulation used in the commercial finite element package is discussed in relation to the formulation adopted in the theoretical derivation. The Dynamic response problem of a sandwich structure subjected to axial impact by a falling mass is also investigated. The dynamic counterpart of the celebrated Euler buckling problem is formulated first and solved by considering the case of a slender column that is impacted by a falling mass. A new notion, that of the time to buckle is introduced, which is the corresponding critical quantity analogous to the critical load in static Euler buckling. The dynamic bifurcation buckling analysis is extended to thick sandwich structures using an elastic foundation model. A comprehensive set of impact test results of sandwich columns with various configurations are presented. Failure mechanisms and the temporal history of how a sandwich column responds to axial impact are discussed through the experimental results. The experimental results are compared against analytical dynamic buckling studies and finite element based simulation of the impact event.Ph.D.Aerospace EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/61790/1/wooseok_1.pd

DVC analysis of a polymer material subjected to tensile loading with synchrotron radiation tomography

Subsurface deformation behavior of a polymeric material is studied through the digital volume correlation (DVC) technique. Fundamental principles of the DVC technique are presented and the supplemental state-of-the-art algorithmic schemes to improve the efficiency and accuracy of the DVC analysis are also introduced. Tensile tests on an epoxy material are performed in conjunction with synchrotron radiation tomography. In order to create randomly distributed grayscale values in the tomograms for the following image analysis, microscale high-density particles are embedded when the epoxy specimens are fabricated. 3D tomographic images taken at multiple loading steps are utilized for the DVC analysis. The performance of the present DVC analysis is evaluated with the experimental data

Effects of Nonuniform Fiber Geometries on the Microstructural Fracture Behavior of Ceramic Matrix Composites

Microstructural fracture behavior of a ceramic matrix composite (CMC) with nonuniformly distributed fibers is studied in the presentation. A comprehensive numerical analysis package to study the effect of nonuniform fiber dimensions and locations on the microstructural fracture behavior is developed. The package starts with an optimization algorithm for generating representative volume element (RVE) models that are statistically equivalent to experimental measurements. Experimentally measured statistical data are used as constraints while the optimization algorithm is running. Virtual springs are utilized between any adjacent fibers to nonuniformly distribute the coated fibers in the RVE model. The virtual spring with the optimization algorithm can efficiently generate multiple RVEs that are statistically identical to each other. Smeared crack approach (SCA) is implemented to consider the fracture behavior of the CMC material in a mesh-objective manner. The RVEs are subjected to tension as well as the shear loading conditions. SCA is capable of predicting different fracture patterns, uniquely defined by not only the fiber arrangement but also the specific loading type. In addition, global stress-strain curves show that the microstructural fracture behavior of the RVEs is highly dependent on the fiber distributions

Computational modeling of failure in composite structures including uncertainties in material and geometrical properties

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/90654/1/AIAA-2011-1722-752.pd

The Optimal Approach for Laparoscopic Adrenalectomy through Mono Port regarding Left or Right Sides: A Comparative Study

Introduction. Several studies have shown the feasibility and safety of both transperitoneal and posterior retroperitoneal approaches for single incision laparoscopic adrenalectomy, but none have compared the outcomes according to the left- or right-sided location of the adrenal glands. Materials and Methods. From 2009 to 2013, 89 patients who received LAMP (laparoscopic adrenalectomy through mono port) were analyzed. The surgical outcomes attained using the transperitoneal approach (TPA) and posterior retroperitoneal approach (PRA) were analyzed and compared. Results and Discussion. On the right side, no significant differences were found between the LAMP-TPA and LAMP-PRA groups in terms of patient characteristics and clinicopathological data. However, outcomes differed in which LAMP-PRA group had a statistically significant shorter mean operative time (84.13 ± 41.47 min versus 116.84 ± 33.17 min; P=0.038), time of first oral intake (1.00 ± 0.00 days versus 1.21 ± 0.42 days; P=0.042), and length of hospitalization (2.17 ± 0.389 days versus 3.68 ± 1.38 days; P≤0.001), whereas in left-sided adrenalectomies LAMP-TPA had a statistically significant shorter mean operative time (83.85 ± 27.72 min versus 110.95 ± 29.31 min; P=0.002). Conclusions. We report that LAMP-PRA is more appropriate for right-sided laparoscopic adrenalectomies due to anatomical characteristics and better surgical outcomes. For left-sided laparoscopic adrenalectomies, however, we propose LAMP-TPA as a more suitable method