Materials and Structures

Composite Materials Manufacturing and Characterization Laboratory
L. R. Dharani and K. Chandrashekhara

The facilities available for manufacturing and characterization in the area of composite materials are quite extensive and cover almost all facets. Major laboratory equipment available for manufacturing and characterization of composite materials are described briefly below.

Manufacturing of polymer matrix composites: A laboratory scale pultrusion machine is available to manufacture polymer matrix composites having constant cross-sections. Pultrusion is a low cost automated process. In pultrusion, the fibers are continuously impregnated and pulled through a heated die, where they are shaped and cured. A computer controlled, three-axis filament winding machine is available to make shapes through surfaces of revolution such as pipes and cylinders. In filament winding, continuous reinforcements, such as roving are wound onto a mandrel until the surface is covered and the required thickness is achieved. To fabricate composite panels, hot presses are available.

Ceramic composite materials fabrication: Ceramic processing facilities include equipment for synthesizing and forming ceramics and ceramic matrix composites, e.g., tape casting and pressure casting equipment; fiber lay-up equipment for forming fiber reinforced composites; hot press (10 ton) for operation up to 2500oC in vacuum/inert atmosphere, and up to 1800oC in oxidizing atmosphere (Thermal Technology); sintering furnace for operation up to 2500oC in vacuum/inert atmosphere, and up to 1850oC in oxidizing atmosphere (Thermal Technology). This facility is located in the Graduate Center for Materials Research Center (MRC).

Room and high temperature mechanical testing. This facility consists of an MTS 810 material test system with a 22 kip fatigue rated load frame, tensile test module, cyclic function generator and data acquisition system. An environmental chamber (BEMCO) that fits between the MTS loading columns is used for environmental tests on composites. A Fatigue Dynamics, Inc. fatigue machine, in which direct stress and combined tests can be performed, is part of this facility. In high air temperature testing of ceramics and ceramic composites up to 1400oC, is being done using an Instron 4204 microprocessor-controlled 11 kip test system, located in the MRC. For creep testing, an ATS 2430 Lever Arm Tester located in the MRC is available.

Acoustic emission analyzer: The LOCAN 420 D Workstation is an acoustic emission analyzer package made by Physical Acoustics Corporation, Princeton, NJ. Piezoelectric resonant sensors are used to transduce stress waves made through flaw movement or formation in materials testing. The characteristics of these waves are then recorded by the system at a very high rate. Some of these classical wave parameters are amplitude, average frequency, rise time, energy, duration, counts, etc. This PC-based parallel processing architecture can simultaneously record classical acoustic emission feature extraction (ICC Independent Channel Controller) and pure waveform digitization (Transient Recorder Analyzer) in real time. Damage initiation (micro cracking), delamination, fiber breakage, matrix cracking, fiber slippage and crack coalescence can all be captured while acquiring parametric data such as displacement, load and strain. Major advantages of acoustic emission testing include real time non-intrusive damage detection and the unimportance of specimen geometry.

Low velocity impact testing: A gas gun consisting of a high pressure chamber with a 3/8-inch diameter and a 6-foot long tube is available for shooting projectiles, at low velocities, directed towards a composite target. A drop-test tower is also available. These facilities have been used to study the low velocity impact damage in laminated composites.

Modal testing. This facility consists of an HP35665A spectrum analyzer and STAR modal software. Test facilities are available for characterization of the dynamic mechanical properties (stiffness and damping) of composite structures.

Laser-based shearography. Electronic shearography is used to investigate the extent of non-visible damages in composite structures. This facility consists of a SC-400 shearography laser/camera and an IP-4200 image processor manufactured by Laser Technology, Inc. Shearography is a wide-field inspection technique which images internal defects of composite materials as concentrations of surface strain due to applied stresses. This facility is located in the Intelligence Systems Center (ISC).

Friction and wear testing. The resistance to wear and friction stability of brake lining composites can be characterized using a Chase machine provided by Link Engineering, Detroit, MI. This machine allows the determination of wear and friction of materials at various sliding speeds, drum temperature and environment, and is equipped with a computer for test control and data acquisition. The machine has been programmed to conduct standard tests such as SAE J661a.

Students enrolled in AE 282 - Experimental Methods in Aerospace Engineering I, utilize this laboratory to conduct experiments on aerospace structures.