Abstract
The effects of the addition of an aromatic hyperbranched polyester (AHBP) on thermal, mechanical, and fracture toughness properties of a thermosetting resin system were investigated. AHBP filler, synthesized by using a bulk poly-condensation reaction, reveals a glassy state at room temperature. Indeed, according to differential scanning calorimetry measurements, the glass transition temperature (Tg) of AHBP is 95 °C. Three different adduct weight percentages were employed to manufacture the AHBP/epoxy samples, respectively, 0.1, 1, and 5 wt%. Dynamical Mechanical Analysis tests revealed that the addition of AHBP induces a negligible variation in terms of conservative modulus, whereas a slight Tg reduction of about 4 °C was observed at 5 wt% of filler content. Fracture toughness results showed an improvement of both critical stress intensity factor (+18%) and critical strain energy release rate (+83%) by adding 5 wt% of AHBP compared to the neat epoxy matrix. Static and dynamic compression tests covering strain rates ranging from 0.0008 to 1000 s−1 revealed a pronounced strain rate sensitivity for all AHBP/epoxy systems. The AHBP composites all showed an increase of the true peak yield compressive strength with the best improvement associated with the sample with 0.1 wt% of AHBP.
Highlights
Epoxy resins are widely used in different application fields such as aerospace [1], electronics [2], and structures [3,4] because of their low specific weight compared to metals, good mechanical properties, and high corrosion resistance
The engineering and true digital image correlation (DIC) strains were calculated from the developed full displacement field as average strain in an area of astprpairnoxmiFamenigadaust(urecer)lye3ds.e3,(t.ara5e)ils×Dopyf3ent.c5hateimmvsiepmcllyci2.toHomnopprtekhsiensissoounnrtfpearscetesssaoumfretphbleeargsaeseomtmuppelteru,ysf,eo(dbllf)oopwritcihtnuegrdetyhonefatmrheeifcemcroeSamnntcuepeferaeBlcstbisuoiaortrenadntesdsatmsH.pelnesc,ky
The need to use a high Tg polymer as toughener for epoxy resin system has driven the choice toward aromatic hyperbranched polyester (AHBP)
Summary
Epoxy resins are widely used in different application fields such as aerospace [1] (matrix in composites), electronics [2] (high-performance protective coatings), and structures [3,4] (anti-corrosive coatings and structural adhesives) because of their low specific weight compared to metals, good mechanical properties, and high corrosion resistance. The digital image correlation (DIC) technique was used to obtain full-field strain measurements locally on the surface of the samples To this purpose, two high-speed cameras positioned under a certain angle were used to record the geometry and boundary conditions were used as for the dynamic tests. Three different quasi-static testing speeds of 0.2, 2, and 20 mm/min were imposed to the sample For both reference quasi-static and high strain rate compression tests, the recorded DIC images were processed using the commercial digital image correlation software MatchID to obtain the local strains after testing. Three different quasi-stSatteicetlebsatirng speeds of 0.2, 2, and 20 mm/min were imposed to the sample For both reference quasi-static and high strain rate compression tests, the recorded DIC images were processed using the coSmammperlecial digital image correlation software MatchID to obtain the local strains after testing. The engineering and true DIC strains were calculated from the developed full displacement field as average strain in an area of astprpairnoxmiFamenigadaust(urecer)lye3ds.e3,(t.ara5e)ils×Dopyf3ent.c5hateimmvsiepmcllyci2.toHomnopprtekhsiensissoounnrtfpearscetesssaoumfretphbleeargsaeseomtmuppelteru,ysf,eo(dbllf)oopwritcihtnuegrdetyhonefatmrheeifcemcroeSamnntcuepeferaeBlcstbisuoiaortrenadntesdsatmsH.pelnesc,ky
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