CompositesWorld
Issue link: https://cw.epubxp.com/i/697353
29 CompositesWorld.com NEWS N E W S N S N E W S E N W S W CFRP Design not stay constant like trace. Trace is analogous to the weight of a laminate. It weighs the same regardless of how we rotate it. How does trace help? Let's imagine, for example, that a change or changes have been made to your CFRP material for a molded part. Tat you will have to run tests to deter- mine what efects those changes might have on its properties is a given. If the trace of the CFRP material doesn't change, you immedi- ately know you're on safe ground. Your prop- erties are unchanged. But what if the trace of the CFRP material with the altered resin is, for example, 10% greater than the trace of a CFRP sample made with the legacy resin? Ten you know immediately that the new version will be 10% lower in deformation, 10% higher in buckling, and the square root of 10% higher in natural frequency for all lami- nates. Tat is how powerful trace is. No other constants can deliver this kind of reliable aid. We need only one test to determine the value of trace (E x /0.88 for the CFRP material). With that trace value, you can, in fact, derive all the constants of all laminates. Trace also can make the coefcients of governing equations for not only deformation, buckling and natural frequency, but also vibra- tion and stress concentrations, such as open- and flled-hole, universal as well. And we can turn this around: Each laminate only needs to be solved once, and the same solution is applicable to all CFRP materials. Te buckling loads, for example, for AS4/MTM45 and IM7/977-3 (in Figs. 1 & 2) difers only by their relative trace values; i.e., the factor is 1.5. Te same ratio would be valid for deformation and defection. For natural frequencies, it would be the square root of 1.5, or 1.22. For stress concentration of an open-hole tension (OHT) or compression (OHC), the factor for [π/4] is 3 for all materials. (For a diferent laminate, such as [0° 5 /±45° 2 /90°], this factor will be diferent, in this case, 3.25.) Tere are supporting data to show that OHT and OHC are more dependent on laminates than materials. Te implications of these universal connections are far-reaching. One of the most important is that for testing. We no longer have to start from scratch with each new material and conduct thousands of hours of coupon tests to establish design allowables. If we have already tested and established the design allowables for one CFRP material, we can, in fact, derive the allowables data for all other CFRP materials, using simple mathematical calculations based on the ratio between the traces of the materials. Our physical testing, then, could be limited to the much less time- and cost-intensive series required for validation of the manufacturing process of the panels and their coupons, and the care in testing and data analysis. Trace sets the standard. We engineers just have to see how well we can do to match the prediction in the fabrication process. Fig. 2 Trace as a constant If we divide those same diagonal values by that material's trace, in all four cases, regardless of the material or laminate, the result is 1. This has proven true with all laminates for all CFRP materials. The implication is clear: Trace is a universal constant, and in carbon fber-reinforced plastics, the fractions of longitudinal, transverse and shear moduli in trace are, likewise, constant. Fig. 3 One plot for all CFRP materials In this sample carpet plot, we get all we need in the laminate stifness. For each material, the diference is merely in the ratio of their traces. That makes the carpet plot for every laminate universal: We can make one carpet plot for all CFRP materials, not one for each material.