A novel mold design for one-continuous permeability measurement of fiber preforms

Abstract

One-continuous permeability measurement experiments allow measuring permeability of a fiber preform within a range of fiber volume fractions by conducting a single unsaturated (a.k.a. transient) flow experiment on a dry specimen at an initial thickness, and a set of saturated flow experiments on the wetted specimen by varying the thickness of the mold cavity. This approach allows quicker database construction and reduces the effect of inherent variation of fabric structure caused by inconsistent labor on permeability. In this study, the drawbacks of previous mold designs are eliminated by using appropriate sealing, gap thickness adjustment mechanism and features that allow straightforward and reliable manual operation. Experiments for three different fabric types are conducted and the results are discussed. It is mainly observed that the unsaturated permeability is higher than the saturated permeability.

Effect of permeability characterization at different boundary and flow conditions on vacuum infusion process modeling

“…This approach was used and discussed in detail in various studies. 13,21,22 2D radial and unsaturated flow enables measurement of two components of [K] tensor (in both principal directions) at a certain V f in a single experiment as reported in various studies. 20,[23][24][25] This feature makes radial experiments superior to 1D experiments as it is quicker to construct a permeability database.…”

“…The experimental procedures and permeability calculations were widely discussed in the previous studies. 13,14 The most common permeability measurement is conducted on a dry fabric preform under 1D unsaturated flow at a certain V f (i.e., the mold cavity has a constant thickness). Injection boundary condition can be either constant-P or constant-Q.…”

“…Resin flow front is tracked until the mold is completely filled and K is calculated by using either (1) the flow front location versus time data for constant-P case or (2) injection pressure versus time data for constant-Q case. Some studies 13,[15][16][17] reported the following causes of errors in experiments: (i) race-tracking of resin along the preform-mold wall interface (i.e., faster flow along the high-permeable interface than the flow through the bulk fabric preform); (ii) non-uniformity in the fabric structure; (iii) non-repeatable labor (preparation of fabric preform) and (iv) deflection of the mold plates due to the reaction of the compacted fabric preforms and high resin pressure.…”

“…Permeability measurement methods were outlined by Yalcinkaya et al. 13 in an earlier study by grouping them in terms of (i) flow dimension: 1D (linear), two-dimensional (2D) (radial) or three-dimensional (3D); (ii) flow type: unsaturated (transient) or saturated (steady); (iii) injection boundary condition: constant pressure or constant flow rate and (iv) how to schedule experiments: several-separate or one-continuous. The experimental procedures and permeability calculations were widely discussed in the previous studies.…”

Comparison of in-plane resin transfer molding and vacuum-assisted resin transfer molding ‘effective’ permeabilities based on mold filling experiments and simulations

“…For compaction characterization, researchers have used thickness- 16–18 or pressure-controlled compaction experimental setups by either mimicking VARTM process 19–21 or using universal testing machines. 22,23 Permeability characterization has been conducted to determine one component along the flow direction (linear (1D)), 24–27 in-plane components with a radial (2D) geometry 28–31 or to determine in-plane and through-thickness permeabilities separately 32 or simultaneously with 3D flow experiments 33,34 using either the constant pressure or flow rate injection to measure transient or steady permeability values. 24 Permeability also needs to be characterized at more than one fiber volume fraction so the change in permeability can be expressed as a function of fiber volume fraction.…”