Syntactic foam under compressive stress: Comparison of modeling predictions and experimental measurements

Abstract

Syntactic foams are composite materials consisting in the association of hollow particles, called “microspheres” and a polymer matrix. The use of soft shell microspheres confers to the foam interesting properties but in return increases significantly its compressibility. Therefore, understanding and predicting the relationship between pressure and volume change is a crucial issue for the development of this type of material. The present study focuses on a high void fraction syntactic foam made with soft shell polymer microspheres embedded in a polyurethane matrix. Compression tests are performed using a capillary rheometer and a PVT accessory for the hydrostatic compression, and a more conventional apparatus for the confined compression. The experimental results are compared with De Pascalis’s pressure/volume model predictions, using Fok and Allwright’s model to determine the critical buckling pressure of the microspheres. The model proves to be fairly accurate at low pressure and high pressure, despite a notable deviation in the mid-pressure range. The influence of key model parameters such as microsphere size distribution and microsphere and matrix elastic properties is investigated. It is shown that the reinforcement of the matrix seems to be the only efficient way to limit the compressibility of such a syntactic foam.

Physical and mechanical properties of hybridized elastomeric foam based on ethylene-propylene-diene-monomer, multiwall carbon nanotube, and barium titanate

“…Figure 6 and Table 3 present the mechanical properties of the nanocomposite foams, that is, hardness, tensile, and compression results. 46 MWCNT continuously increases the values of tensile and compression strength at different deformations, with tensile strength increases of up to 340% and up to 1138% in compression for foams with 10 phr of MWCNT at 50% strain (normalizing by foam densities, the increases are up to 140% and 576% in tensile and compression, respectively). These increases are much more compared to other EPDM nanocomposites foams.…”

Modeling hysteresis in expanded polystyrene foams under compressive loads using feed-forward neural networks

“…These three stages are ideally represented in Figure 1, but a specific experimental discussion of such phenomenology in an EPS polymer foam can be found in the work by Vaitkus et al, 24 where micrographs show the structural changes of the material at compressive loads for these three stages. Information and descriptions about the phenomenology of polymer foams can be found in the Gibson and Ashby work, 23 and a review of developments in bead foams and novel approaches to model local characteristics in novel foams are reported in the work by Kuhnigk et al 25 and Paget et al 26…”

“…These three stages are ideally represented in Figure 1, but a specific experimental discussion of such phenomenology in an EPS polymer foam can be found in the work by Vaitkus et al, 24 where micrographs show the structural changes of the material at compressive loads for these three stages. Information and descriptions about the phenomenology of polymer foams can be found in the Gibson and Ashby work, 23 and a review of developments in bead foams and novel approaches to model local characteristics in novel foams are reported in the work by Kuhnigk et al 25 and Paget et al 26 The strain energy in compressed EPS polymer foams can be represented by the area under the loading curve similar to that represented in Figure 1; on the other hand, hysteresis is found by the difference between strain energy and the area of the unloading curve as also shown in Figure 1. About this, further formal descriptions of these energy properties are given in the following section.…”

Remarkable response of hollow thermoplastic microspheres-elastomer matrix composites in uniaxial tension

“…They are made of hollow thermoplastics microspheres (HTMs in the following, commercial name Expancel) encapsulating a gas (Curd et al, 2021) that act as fillers in silicone (Shorter, 2014) or polyurethane (Yousaf et al, 2020) elastomer matrix. In a large majority of studies devoted to these materials, the focus is laid on their compressive properties: such experimental results are proposed by Paget et al (2021); Yousaf et al (2020); Smith et al (2021). These investigations being very recent, only few attempts of modelling have been published; roughly speaking authors are trying to account for the (reversible) buckling of the HTMs by different approaches: simple physical models (De Pascalis et al, 2013), numerical or analytical homogenization techniques (Shrimali et al, 2020), or phenomenological compressible constitutive equations (Smith et al, 2021).…”