Structures and Materials Commons^™

The Formulation And Computation Of The Nonlocal J-Integral In Bond-Based Peridynamics, Wenke Hu, Youn Doh Ha, Florin Bobaru, Stewart A. Silling

Florin Bobaru Ph.D.

This work presents a rigorous derivation for the formulation of the J-integral in bond-based peridynamics using the crack infinitesimal virtual extension approach. We give a detailed description of an algorithm for computing this nonlocal version of the J-integral.We present convergence studies (m-convergence and δ-convergence) for two different geometries: a single edge-notch configuration and a double edge-notch sample.We compare the results with results based on the classical J-integral and obtained from FEM calculations that employ special elements near the crack tip.We identify the size of the nonlocal region for which the peridynamic J-integral value is near the classical FEM solutions.We discuss …

The Meaning, Selection, And Use Of The Peridynamic Horizon And Its Relation To Crack Branching In Brittle Materials, Florin Bobaru, Wenke Hu

Florin Bobaru Ph.D.

This note discusses the peridynamic horizon (the nonlocal region around a material point), its role, and practical use in modeling. The objective is to eliminate some misunderstandings and misconceptions regarding the peridynamic horizon. An example of crack branching in a nominally brittle material (homalite) is addressed and we show that crack branching takes place without wave interaction. We explain under what conditions the crack propagation speed depends on the horizon size and the role of incident stress waves on this speed.

Peridynamic Model For Dynamic Fracture In Unidirectional Fiber-Reinforced Composites, Wenke Hu, Youn Doh Ha, Florin Bobaru

Florin Bobaru Ph.D.

We propose a computational method for a homogenized peridynamics description of fiber-reinforced composites and we use it to simulate dynamic brittle fracture and damage in these materials. With this model we analyze the dynamic effects induced by different types of dynamic loading on the fracture and damage behavior of unidirectional fiber-reinforced composites. In contrast to the results expected from quasi-static loading, the simulations show that dynamic conditions can lead to co-existence of and transitions between fracture modes; matrix shattering can happen before a splitting crack propagates. We observe matrix–fiber splitting fracture, matrix cracking, and crack migration in the matrix, including …

Crack Nucleation In A Peridynamic Solid, S. Silling, O. Weckner, E. Askari, Florin Bobaru

Florin Bobaru Ph.D.

A condition for the emergence of a discontinuity in an elastic peridynamic body is proposed, resulting in a material stability condition for crack nucleation. The condition is derived by determining whether a small discontinuity in displacement, superposed on a possibly large deformation, grows over time. Stability is shown to be determined by the sign of the eigenvalues of a tensor field that depends only on the linearized material properties. This condition for nucleation of a discontinuity in displacement can be interpreted in terms of the dynamic stability of plane waves with very short wavelength. A numerical example illustrates that cracks …

Studies Of Dynamic Crack Propagation And Crack Branching With Peridynamics, Youn Doh Ha Ph.D., Florin Bobaru Ph.D.

Florin Bobaru Ph.D.

In this paper we discuss the peridynamic analysis of dynamic crack branching in brittle materials and show results of convergence studies under uniform grid refinement (m-convergence) and under decreasing the peridynamic horizon (δ-convergence). Comparisons with experimentally obtained values are made for the crack-tip propagation speed with three different peridynamic horizons.We also analyze the influence of the particular shape of themicro-modulus function and of different materials (Duran 50 glass and soda-lime glass) on the crack propagation behavior. We show that the peridynamic solution for this problem captures all the main features, observed experimentally, of dynamic crack propagation and branching, as well …

Open Beyond Orbit: Using The Designs From The Open Prototype For Educational Nanosats Outside Of Earth Orbit, Jeremy Straub

Jeremy Straub

This paper presents an overview of the Open Prototype for Educational NanoSats (OPEN) and its prospective use in interplanetary missions. OPEN is framework to facilitate the low-cost creation of CubeSat-class spacecraft via using publically available (provided by the OPEN project) de- signs, software, fabrication instructions and test plans. The base open configuration is designed to be able to be produced with a parts budget of under $5,000. Despite this low cost, it is a very ro- bust spacecraft (with capabilities meeting or exceeding many of the vendor-kit solutions which cost eight-or-more times this amount).

Two approaches for using the OPEN …

Work To-Date On Mechanical Design For An Open Hardware Spacecraft, Jacob Brewer, Brian Badders, Josh Berk, Jeremy Straub

Jeremy Straub

The OpenOrbiter CubeSat seeks to demonstrate the designs created for the Open Prototype for Educational NanoSats (OPEN) initiative. OPEN provides a set of freely available design documents that can be utilized by educational and research teams worldwide. The OPEN structure implements a different strategy than most other CubeSats, allowing it to maximize the use of the overhang space (an area of space between the supports for the frame rails and the wall in the PPOD deployer). It also provides a location for payload components or a propellant tank at the spacecraft’s center of mass. This design is enabled by a …

Stemsat: An Iss Cubesat Program Based On Spare Parts, Anders Nervold, Josh Berk, Jeremy Straub

Jeremy Straub

With the national government’s focus on driving STEM-education, it is important to provide hands-on ave-nues where students can engage with, and accumulate ex-perience working directly with projects within their fields of interest. The Student Technology Emersion Satellite (STEMSat), provides an avenue for students to become in-volved in CubeSat design and development with only mi-nor hardware and monetary resources, and without being dependent on a launch.

STEMSats are CubeSat satellites that are created from spare parts, residual tools and equipment, obsolete mate-rials, and other types of trash aboard the ISS. A list of all the excess items available for such a …

The Open Prototype For Educational Nanosats: Fixing The Other Side Of The Small Satellite Cost Equation, Josh Berk, Jeremy Straub, David Whalen

Jeremy Straub

Government supported nano-satellite launch programs and emerging commercial small satellite launch services are reducing the cost of access to space for educational and other CubeSat projects. The cost and complexity of designing and building these satellites remains a vexing complication for many would be CubeSat aspirants. The Open Prototype for Educational NanoSats (OPEN), a proposed nano-satellite development platform, is described in this paper. OPEN endeavors to reduce the costs and risks associated with educational, government and commercial nano-satellite development. OPEN provides free and publicly available plans for building, testing and operating a versatile, low-cost satellite, based on the standardized CubeSat …

Blended Isogeometric Shells, D. J. Benson, S. Hartmann, Y. Bazilevs, Ming-Chen Hsu, T.J.R. Hughes

Ming-Chen Hsu

We propose a new isogeometric shell formulation that blends Kirchhoff–Love theory with Reissner–Mindlin theory. This enables us to reduce the size of equation systems by eliminating rotational degrees of freedom while simultaneously providing a general and effective treatment of kinematic constraints engendered by shell intersections, folds, boundary conditions, the merging of NURBS patches, etc. We illustrate the blended theory’s performance on a series of test problems.