Epoxy resin Flexural test

Evans et al. [43] carried out 4 MeV electron irradiations of 14 different epoxy resins at 77 K which were selected from a large number of resin systems after screening tests on thermal shock at cryogenic temperatures [44]. The results of flexural tests show that most of these irradiated resins possess only moderate resistance to radiation. Takamura and Kato [45] tried to irradiate the bisphenol-A type epoxy resins with various hardeners at 5 K in a fission reactor and reported that the compressive strength of these epoxy resins decreased sharply after a combined neutron and y-ray irradiation equivalent to a dose of about 107 Gy. 

Epon 828 resins, which are based on diglycidyl ether of bisphenol A filled with 40wt.% Si02, were irradiated at 4.9 K and tested at 77 K after being warmed up to room temperature. The flexural and compressive strengths of the filled epoxy resins were found to be little affected by a y-ray dose of 2 x 107 Gy, but to deteriorate significantly after exposure to 1 x 108 Gy [49],... 

In this study. Macro-defect-free cements were produced by addition of two different epoxy resins, and their strength and durability properties were investigated from mechanical, structural and morphological point of view by using biaxial flexural strength test, contact angle measurements and atomic force microscopy (AFM). 

Davies et al. [64] studied the influence of water absorption on the interlaminar shear strength and end notch flexure (ENF mode II shear) fracture toughness of quasi-unidirectional (88% 0°, 12% 90°) E-glass fibres in DGEBA epoxy resin cured with an amine hardener. Laminates were immersed in (a) distilled water and (b) the Atlantic Ocean ( at Boca Raton, Florida) for up to 8 months at temperatures of 20°C, 50°C and 70°C. Sea water was more slowly absorbed than distilled water. This observation has frequently been made and it provides some reassurance that laboratory tests using distilled water are useful, if slightly cautious, estimates of behaviour in the ocean. 

Plasma treatment with benzene monomer, with pyridine monomer as well as with aniline monomer led to an improvement of interlaminar shear strength of 5 to 12 % in epoxy resin composites. The highest improvement in ILSS tests on epoxy composites was achieved by treatment of the fibres in a benzene/argon/air plasma. This treatment led also to better values of 38 % in flexural strength and the edge fibre elongation increased to 41 %. The reason for the improvement of the fibre matrix adhesion lies... 

Flexural strain reflects the flexibility of a material. Highly flexible resins like rubbery epoxy, polyurethane, and modified resins do not break even after a large deflection determination of ultimate flexural strength is impractical for them. The relevance of mechanical tests depends on the form in which the material is going to be used. If a material is to be used as a beam, then a flexural test is more relevant than a tensile test. 

Loos and co-workers [64] studied the effect of CNT on the mechanical and viscoelastic properties of epoxy matrices. Bisphenol A based epoxy resin nanocomposites were prepared with various small proportions of single-walled carbon nanotubes (SWCNT) and then investigated using acetone as a diluent to reduce the resin viscosity, and the products after removal of the solvent were characterised by FT-IR, Raman spectroscopy, thermogravimetric analysis (TGA), DSC, DMA, tensile, compression, flexural and impact testing, and SEM of the fracture surfaces. The effects of small amounts of SWCNT on mechanical and viscoelastic properties of the nanocomposites are discussed in terms of structural changes in the epoxy matrix. 

Figure 8. Fracture surface of neat epoxy resin from flexural testing. Brittle fracture with smooth areas. ...

Mechanical testing was performed on epoxy resin toughened by incorporation of up to 17 vol% of PEI.1 The dynamic mechanical tests were carried out in DMTA at 10 Hz, in a single cantilever bending mode at r = -80 to 300°C. The flexural properties at 23°C were carried... 

Heat resistance is an important characteristic of the bond. The strength of typical abrasive stmctures is tested at RT and at 300°C. Flexural strengths are between 24.1 and 34.4 MPa (3500—5000 psi). An unmodified phenoHc resin bond loses about one-third of its room temperature strength at 298°C. Novolak phenoHc resins are used almost exclusively because these offer heat resistance and because the moisture given off during the cure of resole resins results in undesirable porosity. Some novolaks modified with epoxy or poly(vinyl butyral) resin are used for softer grinding action. 

A thermosetting resin containing approximately 40% of cardanol by weight has been synthesized by adding an epoxy monomer and an acid-based catalyst to a resole compound (Maffezzoli et al., 2004). This last was manufactured through a polycondensation reaction between cardanol and formaldehyde in the presence of a basic catalyst. The formulation characterized by adequate properties and curing temperatures was reinforced with natural fibers (i.e. short ramie, flax, hemp fibers and a jute fabric) to obtain samples which were then tested both in tensile and in flexural configurations. 

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