Process Induced Warpage: Prediction, Measurement, Control

Composite component distortion during manufacture is a critical problem for the industry. This area of research continues to be a prime focus area for the Composite Materials, Manufacture and Structures Laboratory researchers. The early cartoon that follows suggests the type of distortion that might occur in a composite leading edge during manufacture. In general this type of distortion has been attributed to the in-plane/out-of-plane anisotropy of laminated composites.


Thus, the common result of distortion during manufacture is that the composite part no longer has the exact shape of the tooling on which it was produced. To measure and predict this distortion, angle bracket specimens have been utilized. The distortion of a carbon fiber/epoxy composite angle can be seen in the following picture. This distortion is often on the order of 1-2 degrees.


To measure the distortion of this angle bracket we could simply measure the room temperature shape; however, it has become obvious that more than one component of distortion exists. Due to the anisotropy, the angle bracket distorts in response to both temperature change (thermoelastic) and to other changes such as cure shrinkage (non-thermoelastic). Thus, we have developed testing techniques which allow both angle brackets and “flat” panels to be measured over a range of temperatures. This allows us to determine the distorted shapes and the relative change in shape with temperature. Further, this also allows us to separate the thermoelastic component of distortion from the non-thermoelastic component. In angle bracket testing, a laser is used to measure changes in specimen included angle. The specimens are in a temperature controlled chamber. For “flat” panels a probe maps the panel contour at varying temperatures.


Since the degree of anisotropy in a laminate varies with many factors, tests of a number of composite variables can be accomplished. The following chart shows the effect of different stacking sequences on the thermoelastic and non-thermoelastic distortion of angle brackets. These results can also now be modeled and quite accurately predicted.


However, the composite distortion problem becomes much more complex than just anisotropy when trying to precisely predict detailed shapes. Effects of microstructure on the ultimate shape have been studied. Changes in volume fraction through the thickness of the laminate, as well as manufacturing defects can all affect the distorted shape. This portion of the effort uses computer image analysis to quantify the defects in the composite and LASER angle measurement to determine relationships between shape and temperature. Specimen shapes are measured at temperatures from room temperature to 200C to determine the thermal response. The ultimate goal is to be able to design and manufacture net-shape composite components which are shape correct and shape stable in the service environment.


Related Publications

Journal Articles

  • Radford, D.W., “Balancing Mechanisms of Distortion to Yield Distortion Free/Shape Stable Composites”, Journal of Reinforced Plastics and Composites, Vol. 29, No.12, 2010, pp. 1875-1892. doi:10.1177/0731684409340707
  • Radford, D.W. and Rennick, T.S., “Separating Sources of Manufacturing Distortion in Laminated Composites”, Journal of Reinforced Plastics and Composites, Vol.19, No.8, 2000, pp.621-641
  • Goetschel, D.B. and Radford, D.W., “Analytical Development of Through-Thickness Properties of Composite Laminates”, Journal of Advanced Materials, Vol. 28, No.4, July 1997, pp.37-46.
  • Radford, D.W., “Volume Fraction Gradient Induced Warpage in Curved Composite Plates”, Composites Engineering, Vol. 5, No.7, 1995, pp.923-934.
  • Radford, D.W., “Cure Shrinkage Induced Warpage in Flat Uni-Axial Composites”, Journal of Composites Technology & Research, JCTRER, Vol. 15, No.4, Winter 1993, pp. 290-296.
  • Radford, D.W. and Diefendorf, R.J., “Shape Instabilities in Composites Resulting from Laminate Anisotropy”, Journal of Reinforced Plastics and Composites, Vol 12, No.1, January 1993, pp.58 – 75.
  • Radford, D.W., Winckler, S.J., and Diefendorf, R.J., “Asymmetric Composites”, Kovové Materiàly (Metallic Materials), Vol.26, No.2, 1988, pp.209 – 213.

Conference Proceedings

  • Pansare, Niraj P. and Radford, D.W., “Part-Tool Interaction Induced Distortion on Flat Tooling Plates”, 36th International SAMPE Technical Conference, SanDiego, CA, Nov. 15 – 18, 2004.
  • Kamonpet, Patrapon and Radford, D.W., “The Effect of Physical Part Constraint on Manufacturing Distortion”, 36th International SAMPE Technical Conference, SanDiego, CA, Nov. 15 – 18, 2004.
  • Radford, D.W. and Fu, S., “A Route To Shape Correct/Shape Stable Laminates”, ICCM14, San Diego, CA, July 2003.
  • Melo, J.D.D. and Radford, D.W., “Modeling Manufacturing Distortion in Flat, Symmetric, Composite Laminates”, 31st International SAMPE Technical Conference, Chicago, IL, Oct. 26 – 30, 1999.
  • Fu, S. and Radford, D.W., “Effects of Lamination Angle on the 3-D Thermal Expansion Coefficients”, 31st International SAMPE Technical Conference, Chicago, IL, Oct. 26 – 30, 1999.
  • Radford, D.W., Fu, S., Derringer, D., and Davis, J.D., “Measurement of Manufacturing Distortion in Flat Composite Laminates”, ICCM-12, Paris, France, July 6 – 9, 1999.
  • Radford, D.W. and Rennick, T.S., “Determination of Manufacturing Distortion in Laminated Composite Components”, ICCM-11, Gold Coast, Australia, July 14 – 18, 1997.
  • Rennick, T.S. and Radford, D.W., “Components of Manufacturing Distortion in Carbon Fiber/Epoxy Angle Brackets”, 28th International SAMPE Technical Conference, Seattle, WA, Nov. 4 – 7, 1996.
  • Diefendorf, R.J., Radford, D.W., and Winckler, S.J., “Asymmetric Composites – Hygrothermal Stability of Flat Plates”, Verbundwerk, 91 – 3rd International Conference on Reinforced Materials and Composite Technologies, Weisbaden, Germany, October 1991.
  • Radford, D.W., “Manufacturing Warpage in Flat Uni-axial Composite Laminates”, 5th Technical Conference – Composite Materials in Transition, American Society for Composites, East Lansing, MI., June 1990, (Technomic Publishing Co.).
  • Radford, D.W., “A Technique for Measuring the Through-Thickness Properties of Laminated Composite Materials”, Industry-University Advanced Materials Conference II, Materials Research Society, Denver, CO., March 1989.
  • Radford, D.W. and Diefendorf, R.J., “Shape Instabilities in Composites Resulting from Laminate Anisotropy”, 4th Japan-United States Conference on Composite Materials, Washington, DC., June 1988, (Technomic Pulishing Co.).

Related Theses

  • Rennick, T.S., “Manufacturing Distortion in Composites”, MS Thesis, Colorado State University, Fall 1999.