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Trace Evidence: Fibers

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olencia
22 diapositives · 311 Views · Oct 03, 2012

Trace Evidence: Fibers. Fabric is the type of material and fibers are the “threads” that make up the fabric Wayne Williams. How are fibers used as evidence?. As with other trace evidence, fibers can be transferred to/from a person or objects linking them to one another.

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Trace Evidence: Fibers
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  1. Trace Evidence: Fibers

  2. Fabric is the type of material and fibers are the “threads” that make up the fabric • Wayne Williams

  3. How are fibers used as evidence? • As with other trace evidence, fibers can be transferred to/from a person or objects linking them to one another.

  4. How long do fibers persist? Most fiber evidence is lost (fall off) a short time after the transfer occurs. The fibers that do remain will be persistent.

  5. Classification Natural • Vegetable • Animal or protein • Mineral Man-Made • Regenerated • Pure Synthetic

  6. Natural Fibers: • Found in nature • Can be artificially colored or treated Cotton Wool Hemp

  7. Plant Fibers Cotton - seed hairs of cotton plant • by far most common fiber(find almost everywhere) Under microscope, fibers resemble twisted ribbon Natural Fibers

  8. Plant Fibers Linen - stem fiber from flax plant Kapok - from seed hairs of kapok plant Other fibers - Manila, hemp, sisal, jute Natural Fibers

  9. Animal Fibers • Wool--animal fiber coming most often from sheep but may be goat (mohair,cashmere), rabbit (angora), camel, mink, beaver Wool Fibers (400X) Natural Fibers

  10. Silk - comes from silkworm Spun as double filament (separated before use) Because of length, doesn’t shed easily Animal Fibers Natural Fibers

  11. Mineral Fibers Asbestos - crystalline material • Used to be used for insulation • Fractures into thin rods that can get into your lungs; can kill you • Not used much anymore Natural Fibers

  12. Manufactured Fibers Regenerated Fibers • Cellulose is dissolved, then resolidified to form the polymer fiber • Can occur in filament or staple form Example:Rayon Man-made Fibers

  13. Synthetic Fibers • Man made • Can also be filament or staple Examples: Nylon and Polyester Man-made Fibers

  14. Synthetic Fibers Acrylics • More common as evidence • Usually in staple form • Staples spun together, similar to wool Man-made Fibers

  15. Threads, Yarn, Rope, Cordage Smallest component is fibers (staple) twisted together to form thread or is a filament. This thread can then be twisted with other threads to form a thicker thread (string, etc.) This thicker cord can then be twisted with other thicker cords, etc.

  16. Filament vs. Staple Filament: Long continuous fiber (like silk) Staple: Filament is cut into smaller pieces; staples are spun together to form thread (like cotton)

  17. Woven Fabric • Woven fabric are made by interlacing warp (lengthwise) and weft (filling) yarns. Warp run the length of the fabric and parallel to the selvage which is the edge of the fabric. Weft cross over and under the warp threads

  18. Woven Fabric • TWILL • Create by passing the warp yarn over one to three weft yarns before going under one • Makes a diagonal weave • Design resembles a stair steps • Denim is the most obvious example

  19. Knitted fabrics are made by interlocking loops into a specific arrangement. Knitted Fabric

  20. Using the evidence • Begin by identifying and comparing class characteristics for unknown sample (evidence) and known sample. Known Unknown

  21. Class characteristics Color: microscopic examination Size: length and width can be measured Shape: cross section is viewed

  22. Man, I was nailed when those forensic guys found fibers from the kid’s math assignment in my teeth.