Best of the Net: Data

Introduction

One of the most popular pages on the Composites site is the Material Data page. As someone who designs composite structures, I understand that finding material properties is one of the most difficult tasks an engineer faces. The Internet has improved the situation, but there's still a ways to go.

The Data page doesn't actually list data: instead, it points you to sources of data on the 'net. This review will help you find those pages which are worth a visit.

Criteria

To be "Best of the Net," a site must first have good, original content which is related to composite materials. In general, I look for material which is useful and which may not be found in other locations.

If a site's material is good, I then evaluate it as a Web site. The material should be presented in a nice format, contain few errors, and be easy to browse. Graphics, especially large ones, should be kept to a minimum and only used where necessary or appropriate.

Specific things I look for in a good data site include: a wide range of materials; full sets of material properties; references to data sources or statistical bases; and easy navigation or search functions.

Vendor Sites

Several vendors provide online properties for their materials. These pages are usually online versions of the vendor datasheets. That means the quality of the data is acceptable for preliminary design or material selection, but it should not be used for final or critical designs.

Anything less than a full set of datasheets is unacceptable--there is no excuse for not putting them online. Putting a PDF document online takes very little effort. Anything beyond the standard datasheet would be nice, but unfortunately most vendors have trouble meeting just that minimum.

Hexcel provides a table of properties for continuous fibers, as well as downloads of more detailed data sheets. Downloadable datasheets are also available for chopped fibers.

Notably absent from this list is Cytec Fiberite. They have an excellent printed catalog with fiber, resin, and prepreg properties, but their Web sites are notable for their lack of data.

Although I've included it in the Vendors category, Owens Corning has one of the better overall data sites. Although the focus is on fiberglass composites, other materials are included for comparison. You can look at simple tables of physical, mechanical, or electrical properties, and these tables also include a detailed description of chemical resistance. You can also generate custom tables by selecting materials and properties.

Matroc Materials provides a good set of data tables for their ceramics. Composite engineers might not find this table too useful, but prepreg and resin vendors should use this page as an example of what they should include on their own sites.

Some of the plastics vendors provide selection guides. These usually aren't directly applicable to composites, but I find them useful simply because I'm less familiar with unreinforced plastics and molding compounds.

Endura Plastics has a table of thermoplastics with general descriptions, brand names, and typical properties. The same table can be found on Actech's Web site. (Endura has a copyright notice, so I assume they are the original author.) Tri-Star Plastics has a similar page, organized a bit differently and with more properties (though many are marked N/A). Plastics USA has the most complete and best organized set of pages among the plastics vendors.

Miscellaneous Sites

There are a wide variety of data sites which don't fit into a specific category. These site include small tables of data collected from the literature, and tables for specialty applications.

A table of ceramic properties doesn't give references, but at least it warns you to verify the data before using it.

ATHAS has a large database of polymer molecular properties (mostly thermal properties). This site would most likely be of interest to chemists of chemical engineers.

The table of engineering material properties has an eclectic selection of materials including metals, plastics, gases, and liquids, organized by type of property.

For an extensive collection of thermal data, including a absorptivities, emissivities, conductivity, specifc heat and more, visit the Thermal Connection.

Commercial Databases

The distinction between database sites and some of the miscellaneous sites may not always be clear. In general, the database sites should be searchable (not just simple tables), contain a wide variety of materials, and show the basis or source for the properties.

I don't have access to any of the commercial databases. I will mention them here, but I can't evaluate their quality.

The IDES Prospector databases (online and desktop versions) provide data on plastics. There are no sample pages, but you can view a list of properties in the database, with the test method used for each property.

The CRDA Handbooks are published by Purdue Univsersity. The handbooks are only available in printed form, and they mainly cover metals and alloys. One book, however, covers the techniques and data of composite failure analysis.

NASA Database

NASA does a great job of putting its databases online. Quality of the data is generally high, though quality of the online implementations varies from site to site. These are very useful databases, but too specialized to qualify for a "Best of the Net" award.

The available databases are indexed by NASA. Links are not provided to the databases themselves, but contact information is given. (As I find the databases, I am creating links to them on the Data page.)

When designing a spacecraft, materials must often meet a maximum outgassing requirement. The Volatile Condensable Materials site is a browsable database of material outgassing data.

For material used in thermal protection systems, the TPSX databases provide thermal properties. The downloadable database allows you to add your own materials; the online database is browsable by type of material.

The LDEF Database contains the data from the Long Duration Exposure Facility (LDEF) experiment. LDEF was a satellite which carried several trays of materials experiments into orbit. It was retrieved after several years, and the trays were examined for the effects of the LEO environment on the materials. Most of the data and many reports are available online.

Free Databases

The one reference which has the potential to be most useful to composites engineers is MIL-HDBK-17. This is a printed database of composite properties developed in the aerospace industry. All properties included in the database have a statistical basis. The current working draft is available in PDF format. Unfortunately, very few materials have been entered into the book (I have yet to actually use it for any real work).

Probably the most comprehensive and free database is the MatWeb database. It currently contains over 12,000 materials, and more are being added. The main search page allows you to search by material type and property range. There is also an index that you can browse by material type, and a simple keyword search engine.

At the moment, the database mainly has metals and polymers. Some composites are represented, particularly carbon fibers and fiber filled molding compounds. These materials can be found by browsing under polymers.

The data on this site comes from manufacturer data sheets. This means that they are typical properties, not suitable as design allowables. Also, the data for composites is generally not as complete as printed datasheets: only a few properties are given, and they appear to be in the fiber direction only.

Best of the Net

Selecting just one Data site as "Best of the Net" was a tougher call than I thought it would be. MIL-HDBK-17 is the obvious choice for a composites site--it has the properties needed for most designs, and presents them with a statistical basis--but there are hardly any materials in the book yet.

The NASA Databases are a great resource for spacecraft design, and the properties are backed up by references and raw data. Unfortunately, the basic properties needed for structural analysis are not included.

The award for the best online source of material properties goes to the MatWeb database. It covers not only plastics, but also metals and fibers, and there is an active effort to add more materials to the database.

For composites, MatWeb doesn't provide enough properties for even a preliminary design effort. Neither, however, do any of the other databases. Because most composite structures use other materials, this site should still make a good reference for composite engineers.