Manufacturing Technology: Composites Resins

Flashcards covering the fundamentals, chemical reactions, cure stages, selection factors, and characterization techniques for composite resins as discussed in the lecture.

Thermoplastics

Matrices with essentially linear chains held together largely by entanglement.

Thermosets

Matrices where the whole block of resin may effectively be a single three-dimensional molecule; they start with relatively low viscosity and building molecule size through cure reactions.

Condensation Reaction

A chemical reaction occurring in phenolic and polyimide resins where a molecule of water is spat out for each bond produced.

Free Radical Reaction

A reaction used in polyester and vinyl ester resins where a catalyst generates free radicals that catalyze the opening of double bonds leading to cross-link formation.

Ring Opening Reaction

A two-step reaction occurring in epoxy and bismaleimide resins consisting of a ring opening reaction followed by a cross-linking reaction.

Gelation

The point during the cure of a resin when the first chain forms across the whole sample and all flow stops.

Vitrification point

A stage in the cure process after which resin shrinkage is very small but leads to locked-in stress.

Moisture Pick-up Sweeling

The process where resins pick up moisture from the atmosphere and swell, offsetting some of the locked-in stresses from cure shrinkage.

Resin Modulus Requirement

The matrix resin generally needs a Young’s modulus of above $3\,GPa$ to provide good compressive properties in laminates.

FST (Fire, Smoke, and Toxicity)

Selection criteria for aircraft interiors requiring resins that resist ignition and do not produce toxics; phenolic resins are the normal choice as they char rather than burn.

Exotherm

Heat generation on cure which can result in centerline temperatures more than $50^\circ C$ above the tool temperature in thick laminates.

Shop life (Out time)

The time a preimpregnated material can spend at room temperature prior to cure without degrading performance.

Qualification

The non-technical aerospace selection criterion involving a process that can cost >$1\,million$ and take up to $7$ years to generate allowable properties for a new resin.

Binders

Materials used in resin infusion processes to stabilize individual preforms and hold together the assembly, available as powders, fibrils, tacky threads/films, or sprays.

Darcy's Law

An equation used to approximate gross resin flow: $V = \frac{K}{\eta} \times \frac{dp}{dx}$, where $V$ is flow front velocity, $K$ is permeability, $\eta$ is viscosity, and $dp/dx$ is the pressure gradient.

Permeability ($K$)

A property of reinforcements typically ranging from $1 \times 10^{-9}\,m^2$ (low $V_f\%$ random reinforcements) to $1 \times 10^{-11}\,m^2$ (high $V_f\%$ unidirectional reinforcements).

Viscosity vs. Temperature Relationship

In the absence of cure reactions, viscosity falls as temperature rises, modeled as $\eta = \eta_0 e^{-a(T-T_0)}$.

TGA (Thermal Gravimetric Analysis)

A quality assurance technique that monitors weight changes in a sample as a function of temperature to determine volatiles, resin, fiber, and inorganic residue content.

DSC (Differential Scanning Calorimetry)

A characterization technique measuring the rate of heat evolution ($dH/dt$) or enthalpy absorption of a specimen relative to a reference.

TMA (Thermal Mechanical Analysis)

A technique used to study thermal transition behavior (e.g., $T_g$) by measuring the thermal expansion and contraction of specimens.

DMA (Dynamic Mechanical Analysis)

A technique that measures the rheological response of resins (storage modulus, loss modulus, complex viscosity, and tan delta) as a function of frequency, temperature, or state of cure.

DDA (Dynamic Dielectric Analysis)

A technique using electrical measurements (dielectric constant, dissipation factor, capacitance, or conductance) to monitor flow and curing characteristics.