David J. Green
Professor of Ceramic Science and Engineering
B.Sc. (Liverpool), M.S., Ph.D. (McMaster)

* DETAILED BIOGRAPHIC INFORMATION 

* TEACHING ACTIVITIES

* RESEARCH ACTIVITIES 

 


 

Teaching Activities :

MATSE 414                                 Mechanical Properties of Ceramics.               Detailed Information  

MATSE 436                                 Mechanical Properties of Materials               Detailed Information              

MATSE 466                                 Ceramic Laboratory I.                                   Detailed information

MATSE 545                                 Mechanical Properties of Brittle Materials

MATSE 509                                  Composites

MATSE 563 (E MCH   534)        Failure Mechanisms in Materials                   Detailed information

MATSE 564 (E MCH   535)        Deformation Mechanisms in Materials          Detailed information


 
 

Research Activities :

FRACTURE OF BRITTLE MATERIALS

             Optical micrograph showing cracks arrested in a glass surface as it is being stressed

Ceramic materials are usually brittle, breaking in a catastrophic manner. Indeed, this behavior often limits the use of ceramics in both structural and non-structural applications. The low amount of energy involved in breaking these materials is a result of their low toughness. In recent years, however, various mechanisms have been identified for increasing the fracture resistance (toughness) of these brittle materials. For example, improvements in fracture resistance have involved the addition of particles, platelets, whiskers, or fibers to a material.  Manipulation of residual stresses and structure at various scale levels has also proved to be a useful approach.

This methodology has been very successful and, in some material systems, increases in toughness by an order of magnitude have been obtained.  In all these developments, the use of a materials science methodology has been critical philosophy in making the advances. This approach emphasizes the relationships between processing, structure, and mechanical behavior as a way to understand a material, and to identify processing techniques for improving properties.  The research in my group utilizes this philosophy and it is aimed at improving the reliability of ceramics and glasses for technological applications. For example, recent research has also led to a process that strengthens glass and stops cracks as the glass is being bent.  This leads to a strong glass with a very narrow distribution of strengths.

SEE A MOVIE THAT SHOWS CRACKS ARRESTING IN THE SURFACE OF GLASS
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STRESS IN THE DENSIFICATION OF POWDER COMPACTS

                            Picture showing distortio during firing


                            Photograph showing the disortion of a bi-layer during firing

There is a renewed interest in the ability to co-fire layered and integrated structures as a result of new applications or unusual properties for such structures. For example, in the area of structural ceramics, it has been shown that delamination in ceramic hybrid laminates could be used to increase the work of fracture. It has also been suggested that laminates could be tailored to induce stable crack growth, crack arrest and threshold strengths by using differences in the elastic, fracture toughness and thermal expansion properties between the layers. Based on economic considerations, co-firing is an attractive approach for producing these structural laminates.

Layered structures are also of great importance in electronic applications of ceramics and co-firing is often used to produce these devices. Multilayer capacitors are a well-established example of this technology. In this industrial arena, there is a continuous drive for miniaturization and improved reliability, especially with the move to high frequency applications. Other applications that use co-fired layered structures include gas sensors, solid oxide fuel cells and electronic packages. In this last example, there is a strong interest in the use of low-temperatures co-fired ceramics (LTCC), especially in the push for wireless applications. LTCC are commercially available as green tapes that are used to fabricate the electronic package. The tapes are co-fired with the imprinted metallic conductors. A complex three-dimensional circuit can be designed by stacking the LTCC layers and allowing the circuitry to feed through and between the layers. The intent in this technology is also to integrate other electronic components into the final package.  LTCC-based packages are clearly more complex material systems than laminates with continuous layers but many of the scientific issues in the co-firing process are similar. In the co-firing of layered structures, compatibility stresses arise as a result of differences in the shrinkage behavior between the layers. These stresses may arise because of differences in the densification rate during sintering (constrained sintering) and differences in thermal contraction during cooling after densification. The strain incompatibility between the layers leads to internal stresses and distortion. The aim of our current research is to establish the scientific and experimental methodology that is used to quantify these processes, such that material systems can be designed that avoid damage and distortion.

SEE A MOVIE THAT SHOWS A BI-LAYER SPECIMEN UNDERGOING DISTORTION DURING SINTERING
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SEE A MOVIE THAT SHOWS CERAMIC SPECIMENS UNDERGOING CREEP AT HIGH TEMPERATURE
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