New test capability probes failure processes in polymer composites. (News Briefs).A new measurement tool for visualizing and quantifying time-dependent failure mechanisms in polymer composites has been developed at NIST (National Institute of Standards & Technology, Washington, DC, www.nist.gov) The standards-defining agency of the U.S. government, formerly the National Bureau of Standards. It is one of three agencies that fall under the Technology Administration (www.technology. . The new test method produces optical images of multi-fiber test specimens as the specimens are deformed under mechanical load. Previous work, based on single-fiber tests, ignored how rupture of one fiber affects the failure of neighboring fibers and provided only limited information regarding the influence of the polymer matrix on mechanical failure. Initial results from the new test apparatus show that the nucleation nu·cle·a·tion n. 1. The beginning of chemical or physical changes at discrete points in a system, such as the formation of crystals in a liquid. 2. The formation of cell nuclei. of critical flaws in unidirectional fibrous composites depends on the time-dependent redistribution of the mechanical stress in the polymer matrix. The behavior of the matrix determines how the rupture of one reinforcement fiber affects the integrity of neighboring fibers. In addition, new information regarding the role of matrix cracks and residual curing stresses on fibrous composite failure behavior has been revealed. A visual representation of the time dependent failure behavior in two-dimensional multi-fiber composites can be found at: http://polymers.msel.nist.gov/researcharea/ multiphase/ project-detail.cfm?PID (1) (Process IDentifier) A temporary number assigned by the operating system to a process or service. (2) (Proportional-Integral-Derivative) The most common control methodology in process control. =56 Knowledge of the time-dependent failure processes in fiber-reinforced composites is critical to their use as structural parts in automotive applications. Automotive design engineers need better tools for predicting and managing how composite parts respond to crashes. To address this need NIST researchers are adapting the object oriented finite element analysis Finite element analysis (FEA) is a computer simulation technique used in engineering analysis. It uses a numerical technique called the finite element method (FEM). There are many finite element software packages, both free and proprietary. (OOF OOF - Object-Oriented Fortran ) program to include viscoelastic Adj. 1. viscoelastic - having viscous as well as elastic properties natural philosophy, physics - the science of matter and energy and their interactions; "his favorite subject was physics" materials. The data from the multi-fiber tests will be used to aid the development of failure models for the new OOF program. CONTACT: Gale Holmes, (301) 975-5280; gale.holmes @nist.gov. |
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