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Interlaminar and In-Plane Shear Strength

  • 1.  Interlaminar and In-Plane Shear Strength

    Posted 04-09-2018 13:25
    Edited by Sebastian Kirmse 04-10-2018 13:18

    Hello everyone,

    My name is Sebastian Kirmse. I am a graduate student in Mechanical Engineering and Systems Engineering at the University of South Alabama and am currently working on shear strength testing of CFRP panels reinforced with carbon nanofibers for my Master's Thesis.

    I am planning on performing the following two tests:

    ASTM D2344: "Standard Test Method for Short-Beam Strength of Polymer Matrix Composite Materials and Their Laminates"

    and

    ASTM D3846: "Standard Test Method for In-Plane Shear Strength of Reinforced Plastics".

    Now, looking at the two tests, I got confused about the difference between in-plane shear strength and interlaminar shear strength.

    Also, it seems to me, even though ASTM D3846 is called in-plane shear strength, it is actually an interlaminar shear like ASTM D2344.

    So, my questions are:

    • What is the difference between interlaminar shear and in-plane shear?
    • Are the two tests technically testing the same "property"?
    • Any suggestions, recommendations or pitfalls for the tests?
    • How much does a difference in fiber volume fraction influence the test results?

     

    Let me know if you need any additional information from me in order to be able to answer those questions.

     

    Thank you,

     

    Sebastian Kirmse



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    Sebastian Kirmse
    Graduate Research Assistant
    University of South Alabama
    Mobile, AL
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  • 2.  RE: Interlaminar and In-Plane Shear Strength

    Posted 04-10-2018 12:04

    https://www.compositesworld.com/articles/the-double-notch-shear-test-specimen-for-composite-materials

     

    Jeff Kessler

    Mechanical Engineer/Laboratory Manager

    Composite Mechanics Lab

    Dept. of Mechanical Engineering

    University of Utah

    1495 E. 100 S., MEK 1550

    Salt Lake City, UT 84112

    801-581-4252

     






  • 3.  RE: Interlaminar and In-Plane Shear Strength

    Posted 04-10-2018 12:04

    Dear Sebastian,

    You are correct that D3846 is an interlaminar shear test. Here's a link to a brief article discussing the issue.

    JK

     

    Jeff Kessler

    Mechanical Engineer/Laboratory Manager

    Composite Mechanics Lab

    Dept. of Mechanical Engineering

    University of Utah

    1495 E. 100 S., MEK 1550

    Salt Lake City, UT 84112

    801-581-4252

     






  • 4.  RE: Interlaminar and In-Plane Shear Strength

    Posted 04-11-2018 13:06
    Hello,

    ASTM D2344 is not considered a true shear test any longer.  The terminology for it being a shear test have been removed by the ASTM D30 committee in the last few years.  An alternative test to this would be ASTM D5379 if panels can be made thick enough.

    For in-plane shear on CFRP, the suggested methods for testing are ASTM D3518 and ASTM D7078.  Alternatively, ASTM D5379 can be used as well.  For CFRP tests, usually you are trying to get the shear strength at 5% shear strain or peak stress prior to this point if the sample cannot reach 5% strain.  This is often considered the target value.

    I would look into ASTM D30 standards listings.

    https://www.astm.org/COMMIT/SUBCOMMIT/D30.htm

    ------------------------------
    Kerry Necessary
    Project Engineer
    CTL
    Cincinnati OH
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  • 5.  RE: Interlaminar and In-Plane Shear Strength

    Posted 04-12-2018 11:26
    Edited by Sebastian Kirmse 04-12-2018 11:28
    Thank you, everyone, for the great replies so far! I always enjoy the helpful comments from the SAMPE community!

    The article Jeff recommended is highly interesting and I will definitely take a look at ASTM D30 standards list. Gordon sent me a PM, recommending Donald Adams' book "Experimental Characterization of Advanced Composite Materials".

    Another question I am having is:
    How much does a difference in fiber volume fraction (FVF) influence the test results when comparing materials (especially for shear strength)? I am comparing an unmodified CFRP (Control) with modified CFRPs (CFRPs enhanced with carbon nanofibers (CNFs)). However, it is sometimes difficult to reach the exact same FVF for both CFRPs using a hand-layup approach or a different approach without thickness control. So, I was wondering, what an acceptable range would be? For example, comparing test results of a CFRP with a FVF of 60% with samples that are at 63% or a sample with let's say as high as 70% or as low as 50%. Within what range should the FVF of the test samples be in order to get comparable results?

    Again, thank you, everyone, for your great replies so far and I am looking forward to more insightful feedback!

    ------------------------------
    Sebastian Kirmse
    Graduate Research Assistant
    University of South Alabama
    Mobile, AL
    ------------------------------



  • 6.  RE: Interlaminar and In-Plane Shear Strength

    Posted 05-03-2018 13:31
    Fiber volume fraction and the associated matrix volume fraction and void volume fraction each can affect your results.  You can end up with a specimen that is either nominal, resin rich, or resin deprived.  What range is ideal would be dependent on the fiber/resin system.  Additionally, a high void content cant greatly affect your results.  A high porosity specimen will generally have a very low strength value.

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    Kerry Necessary
    CTL
    Cincinnati OH
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  • 7.  RE: Interlaminar and In-Plane Shear Strength

    Posted 05-24-2018 13:10
    ​Worth sharing whether you are testing uni-directional tape or woven fabric. Industry norm for acceptable FVF deviation for UD is around 3-4%, fabrics is around 5-6%. For eg. if your target pristine UD tape's FVF is 60%, with all the improvements to the matrix through CNF or grapheme or microcapsules have shown a FVF of 57%, compliance engineers can buy-off the FVF results as acceptable.

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    Vijay Sahadevan
    Stress Technical Authority
    GKN Aerospace Services Limited - Building 04H
    Bristol BS34 7QQ
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