Comparing Test Methods for the Intra-ply Shear Properties of Uncured Prepreg Tapes

Abstract

To achieve cost-efficient manufacturing and a high part quality in Thermoset Automated Fiber Placement (TS-AFP), knowledge about the interaction between material and process parameters is of special interest. Material properties of prepregs are well known at the cured state of the resin. However, there are no standardized test procedures for the mechanical behavior of the uncured prepreg tapes. To investigate the intra-ply shear deformation behavior of uncured unidirectional prepreg tapes, we compared several measurement procedures and conducted experiments for rheometer based tests using 8552/AS4 material. We identified a rotational parallel platens rheometer test method and a torsion bar rheometer test method to be suitable. Experiments using both methods revealed that the Torsion Bar Test has a higher repeatability and the analysis is less complex. Furthermore, first results show that changes in material properties caused by aging can be analyzed using this method. In the future,we will use the Torsion Bar Test to characterize changes in deformation behavior due to material aging as well as material modifications. By this, we will be able to provide data for the material modeling thus enabling the prediction of lay-up defects such as buckling due to steering.

Quantifying the Influence of Out-Time on Prepreg Material Properties and Out-Of-Plane Steering Defects During Automated Fiber Placement

“…For the other experiments, specimens were cut from a wider roll. Wherever we needed multi-layer specimens (E 2 and G 12 measurements), we used a preparation method from previous investigations (Heller et al, 2020a): we compacted large layers applying vacuum at room temperature for 35 min followed by cutting the layers into the specimen size using an NC cutting machine. To measure the influence of controlled out-time conditions on the properties, the material was kept in controlled temperature and humidity conditions at 21 °C and 40% RH and tests were conducted at the aforementioned outtimes t out -1, 5, 10, and 15 days.…”

“…We considered peel tests as a complementary test method to the probe tack test method since peel tests allow for a better relation to the peel mechanisms in automated lay-up processes (Crossley et al, 2012). In a previous publication (Heller et al, 2020b), we presented a novel peel tack test for prepreg tapes which is incorporated in a standalone test bench-see Figure 3. Since specimen preparation and peel test are decoupled, the influence of the lay-up rate on tack can be measured independently of the peel rate.…”

“…The second mechanical property which is an input parameter for AFP defect prediction models and is affected by out-time is the in-plane shear modulus G 12 . Based on a previous comparison of test methods (Heller et al, 2020a), we selected the torsion bar test for the characterization of G 12 .…”

A Peel Test Method to Characterise the Decay Law of Prepreg Tape Tack at Different Temperatures

“…Consequently, researchers have investigated the changes in prepreg during storage to determine whether their processability remains sufficient for production. Presently, the primary test methods include dielectric analysis [19,20], differential scanning calorimetry (DSC) [21,22], dynamic mechanical analysis (DMA) [23], spectroscopic analysis [24], and rheometry [8,25]. However, the physical and chemical studies' findings may not be perfectly predictable due to the prepreg's mixture nature and imperfect resin dispersion at the microscopic scale.…”

A Study on the In-Plane Shear-after-Impact Properties of CFRP Composite Laminates

“…Some of the most well-known test methods are Iosipescu shear (ASTM D 5379), ±45° tension shear (ASTM D 3518), two-rail and three-rail shear (ASTM D 4255), double-notched shear (ASTM D 3846), V-Notched Beam (ASTM D5379), torsion of a thin tube (ASTM D 5448), torsion of a solid rod (ASTM E 143), V-notched rail shear (ASTM 7078), picture frame shear (ASTM D 8067), and so on. These in-plane shear test methods are applied and discussed in many studies [ 16 , 17 , 18 , 19 , 20 , 21 ], in addition to these, the Arcan and modified Arcan test methods were also applied by some scholars to obtain the in-plane pure shear properties of the composite materials [ 22 , 23 , 24 , 25 ]. However, most of these above-mentioned methods are limited to the specimen geometry, layups and shear stress area.…”