The temperature‐dependent ballistic performance and the ductile‐to‐brittle transition in polymer networks

Abstract

The temperature dependence of the ballistic impact performance of a series of transparent polymer networks is evaluated. A systematic series of homogeneous epoxy/propyleneoxide-based thermosets, a nanoscale phase-separated epoxy/ dual amine thermoset, and two homogeneous, completely aliphatic materials synthesized via ring-opening metathesis polymerization are examined. The Vogel temperature (T o ) and the Kauzmann temperature (T K ) are critical parameters for scaling the temperature-dependent ballistic impact performance of each class of materials. The ductile-to-brittle transition temperature in a series of propylene-oxide amine-cured epoxies occurs at the material T K , corresponding to a sharp drop in fracture toughness and ballistic impact performance. Two aliphatic, ring-opening metathesis polymerized materials are found to exhibit no clear transition from purely ductile to purely brittle behavior, but the temperature dependence is still scaled to a single curve when normalized by T o . The cooperatively rearranging region (CRR) or the volume of this region is related to the breadth of temperatures over which these materials exhibit purely ductile deformation both quasi-statically and at higher rates. The temperature-dependent performance is discussed in the context of the configurational entropy. The breadth of the ductility window is related to the size of the CRR, calculated from calorimetric measurements at the resin T g .

Transparent, methacrylate‐based polymer networks with controlled crosslinker ductility

“…Shown in Figure 7 are the normalized KE50 values for the TET:MMA networks studied here, as well as ring‐opening metathesis polymerized networks based on dicyclopentadiene (DCPD), and its mixtures with 5‐ethylidine‐2‐norbornene (ENB) and a CL 20 . As with previous studies 35,37–38 , the ballistic performance appears to follow a similar T – T g trend (see Supplemental Information Figure S5). The results are plotted as a function of the DMA‐determined rubbery modulus (Figure 7(a)), as a function of an apparent molecular weight between crosslinks (Equation , Figure 7(b)), and as the volume percentage of the CL (Figure 7(c)).…”

Stimuli‐responsive mechanical properties in polymer glasses: challenges and opportunities for defense applications

“…2, some protection-related applications may require response times approaching impact dwell times, which are of the order of microseconds. 19 Additionally, uncovering a range of stimulated response volumes is needed. The common theme across the literature is to observe centimeter-scale movement or actuation in response to stimuli.…”

“…8,14 Recently, ring-opening metathesis polymers, as exemplified by dicyclopentadiene, have illustrated that the combination of crosslink density, 7 polarity, 15 void space [15][16][17] and chain stiffness 18 within a glass contribute to changes in the polymer dynamics and ultimately the ductility under high-strain-rate deformation, resulting in a unique combination of high T g and high toughness. 19 However, many common toughening techniques ultimately lead to reductions in other desired properties, such as T g , stiffness, yield stress or processability, resulting in a final material that is a balance of properties for a specific application. Alternatively, the use of external stimuli to obtain orthogonal properties on demand in glassy polymers is a potential avenue to obtain performance not found in a single material.…”

Influence of Hydroxyl Group Concentration on Mechanical Properties and Impact Resistance of ROMP Copolymers

“…6 T h i s c o n t e n t i s Additionally, the yield stress should be as high as reasonably possible to increase energy absorption during a high velocity impact event without compromising the K IC . These two critical parameters have further been correlated to nanoscale polymer properties such as the volume of cooperatively rearranging regions (V a ) 14 and the size and number of nanovoids created to accommodate strain in the materials. 5,15,16 Larger V a values are found in polymers that show comparatively large values of configurational entropy, indicating that advantageous local relaxations still occur and ductility is retained even at temperatures well below T g (e.g., T g − 100 °C).…”