Automotive Composites Require Specialized Quality Control and Inspection Standards (Part 2)

Posted on 4/4/2019 10:36:16 AM By ASC

From Part 1 (located HERE)
The i3 already demonstrates this with a honeycomb structure to absorb impacts, braided carbon fiber, and a foam core. Soon, fiber-metal laminates like glass laminate aluminum reinforced epoxy or GLARE, already used in aerospace applications, are likely to be used in cars too, adding to the complexity of quality control and testing tasks.

Part 2...

Non-destructive testing (NDT) methods in current use include:

Visual inspection: cracks, delamination, impact damage

Optical Coherence Tomography: voids, cracks, delamination

Microscopy: cracks, voids, delamination, broken fibers

Tap test: delamination or cracking

Acoustic emissions testing:fiber breaks, cracks, delamination

Ultrasonic testing: voids, foreign objects, delamination, cracks

X-ray radiography: fiber alignment, splitting fibers, cracks, foreign objects

X-ray computed microtomography: micro cracks, cracks, and voids

Infrared thermography: inclusions, delamination, foreign objects, cracks, voids, impact damage

Not all testing methods are suitable for all situations and challenges will include:

  • The need for training NDT personnel in the testing of multiple materials including metals, a variety of composites, and adhesives.
  • NDT of high attenuation materials remains a challenge as does detecting faults in composite structures consisting of multiple layers.
  • Physical access can also present problems and some composites are not suitable for immersion, eliminating ultrasonic testing as an option.
  • The non-conductive nature of composites will eliminate the use of eddy sensors, electromagnetic probes, or electromagnetic acoustic transducers used in testing metal alloys.

So far, ultrasonic testing seems to hold the most promise since it can be used on metals and composites and picks up a wide range of flaws. Infrared imaging or thermal pulse thermography proves useful in tracing cracks and in monitoring curing while digital radiography will create images of internal structures, helping testers to spot defects. Raman spectroscopy is particularly helpful and can spot stress in carbon fiber or graphene as well as faults in resins, polymers, and films. The equipment can be used to see if resins properly coat fibers and how they cure.

It is noted that while standards for non-destructive testing of composites do exist, further development of standards will be necessary before composites can enjoy wider-spread adoption. Proving equivalence and performance appear to be the primary goals when considering new materials, but standardization of materials and the methods used to test them will be important for the future of composites in motoring.

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