Jenn-Ming Yang

Atmospheric pressure plasma effects on the adhesive bonding properties of stainless steel and epoxy composites

An atmospheric pressure helium and oxygen plasma has been used for the surface preparation of 410 stainless steel and carbon-fiber epoxy laminates prior to bonding to themselves or to each other. Lap shear results for stainless steel coupons and carbon-fiber epoxy laminates demonstrated an 80% and a 150% increase in bond strength, respectively, after plasma activation. Following 7 days of aging, wedge crack extension tests revealed a crack extension length of 7.0u2009mm and 2.5u2009mm for the untreated and plasma-activated steel. The untreated stainless steel had 30% cohesive failure compared to 97% for steel activated with the plasma. Surface analysis by X-ray photoelectron spectroscopy showed that carbonaceous contamination was removed by plasma treatment, and specific functional groups, e.g. carboxylic acids, were formed on the surface. These functional groups promoted strong chemical bonding to the epoxy film adhesive. Atmospheric pressure plasmas are an attractive alternative to abrasion techniques for surface preparation prior to bonding.

Three-dimensional progressive failure analysis of bolted titanium-graphite fiber metal laminate joints

This article presents experimental and numerical results regarding the bolt bearing strength of titanium—graphite (TiGr) fiber metal laminate joints as a function of joint geometry, in particular the edge—distance ratio. The measured strength values are used to examine the influence of the laminate constituent materials and optimize the joint geometry. Additionally, a finite element model of the bolt bearing test procedure is introduced; incorporating a three-dimensional progressive failure constitutive model for the fiber-reinforced composite layers. Model validation is accomplished through comparison with experimentally obtained TiGr joint bearing results in terms of loading history, measured strength, and deformed sample geometry.

Chemically Bonded Phosphate Ceramic Composites

Chemically Bonded Ceramics (CBCs) have been extensively used many applications. These include: radiation shielding systems, nuclear waste solidification and encapsulation; high temperature structural applications; composites and biomedical applications. The objective of this chapter is to present the science, manufacturing and mechanical properties of the Wollastonite (CaSiO3) based Chemically Bonded Phosphate Ceramics (Wo-CBPCs) composites, Fig. 1. In general, the CBPCs belong to the broader field of Chemically Bonded Ceramics (Della Roy, 1987; Jeong & Wagh, 2002; Wagh, 2004) where the name CBPC refers to ceramic materials that reach their final mechanical properties by chemical reactions at low temperatures (typically less than 300 C) instead of the high temperature processing (by thermal diffusion or melting) as is normally done in traditional ceramics and cements. The Wo-CBPCs are composite materials themselves, they belong to Chemical Bonded Ceramics (CBCs) consolidated by an acid base reaction (Wilson & Nicholson, 1993). Wo-CBPCs are multiphase materials with silica, Wollastonite and brushite grains in a matrix of amorphous calcium phosphates. Reinfocing materials such as graphite nanoplateles, glass fibers and carbon fibers have been successfully incorporated into – CBPCs, realizing high performance composites.

Multiscale modeling of metal-composite interfaces in titanium-graphite fiber metal laminates part II: Continuum scale

This study presents a multiscale numerical framework designed to predict the nonlinear constitutive behavior of metal-composite interfaces in titanium-graphite fiber metal laminates. Molecular-level property predictions derived in a separate analysis are used to parameterize a finite element model of the interface by means of a traction-separation constitutive law. Additional continuum-level energy dissipation and progressive failure phenomena are implemented into commercial finite element software through a user-defined material subroutine. Results obtained from this multiscale interface model are compared against experimental measurements of titanium-graphite fiber metal laminates in a short-beam shear loading configuration. The model predictive accuracy and its application to other bonded metal-composite systems are subsequently discussed.

Poly-dicyclopentadiene-wollastonite composites toward structural applications

Poly-dicyclopentadiene matrix composites with different concentrations of mineral wollastonite particles (CaSiO3) were fabricated with possible applications as high volume structural materials. This represents a significant reduction in costs. A planetary Thinky mixer was used to initially mix the resin with the curing agent, followed by incorporating grubbs catalyst. Finally, the product was mixed together with different loading of the particles. The microstructure and compositions were identified by scanning electron microscopy and X-ray diffraction. Particles were found to be homogeneously distributed over the polymer matrix. Quartz was found as a byproduct of the calcium dissolution in the resin. The thermo-mechanical behavior was evaluated by compression, curing, dynamic mechanical analyzer and thermo-gravimetric analysis. For all wollastonite loadings it was found that compression strength was over 100u2009MPa. Wollastonite was found to decelerate the curing of the resin by the release of calcium ions that enhanced the exothermic reaction.