What are your Strengths…”Specific” that is?
When your being interviewed for a job be prepared to answer a classic interview question regarding your strengths. This is an invitation to talk about your skills…perhaps its analytical thinking; or, maybe organization…wait-just-a-minute, ahh...wrong topic! The strength I am referring to matters when one is considering the strength of a material. So, do you know, or did you ever consider “Specific Strength” when deciding what material to use in a design? No…well, you should have! You may have a good design; but, is it the best design…. If not, consider adding Specific Strength to your decision matrix before making that all too critical material choice.
Specific Strength Calculate Breaking Length
Got Shear Lock?
Funny…I was at the barber the other day and he kept complaining about his shears locking up…pesky scissors keep jamming on me he said! Well…obviously this is nothing but banal witticism, because that’s surely not what this article is about. I draw your attention to an experience I had regarding a fabric drapeability study that I performed inorder to evaluate fabric compliance over non-developable tool geometry…huh…bear with me. First the basics, when draping a composite fabric (or tape) over a tool, particularly a tool with compound curvatures, it is incumbent upon the designer to check for wrinkling and/or bridging in the fabric; especially near a radius or doubly curved surfaces. Fabric distortions of this type are clearly undesirable, and often yield poor laminate performance in terms of stiffness and lower than expected margins.
shear-lock fabric draping
Did you check for Pull-through?
Not surprisingly over my career…I’ve seen it once and I continue to see it again and again and again…a failure to check a fastened joint for pull-through. What is seemingly a simple stress check is often overlooked. This tip provides a quick method to check for pull-through failure anytime...but hopefully you check during the preliminary phase of the design before a failure or a messy redesign is required. A check that readily ascertains whether a composite joint is thick enough, or possesses the minimum inter-laminar shear strength needed to prevent a pull-through failure is discussed in this article.
pull-through protruding fastener failure
Are you Balanced or Unbalanced?
So how do we know that we have an unbalanced laminate in the first place? Moreover, if you end up with an unbalanced layup, what are the implications? Good questions to have answers to before signing-off on that laminate design.
Firstly, a perfunctory definition is in order regarding a balanced laminate. A designer will need to ensure that for every -α ply there is a +α ply (with the same material and thickness) somewhere within stacking sequence irrespective of location. Examples of balanced laminates are: [0/30/-30/0] or [45/-45/0/0]. An unbalanced laminate is: [0/30/30/0]...notice that the negative 30-degree ply is no longer present. Now maybe you desire an unbalanced laminate or maybe it’s simply unavoidable but in a majority of design cases this layup scheme should be avoided at all costs. Why? Well, perhaps you have already surmised, this layup scheme has adverse implications, one of them significant…the often dreaded and undesirable in-plane extension-shear coupling.
unbalanced shear plate laminate extension coupling balanced