CharacterizationThe thermo-viscoela

Characterization

The thermo-viscoelastic properties of the neat epoxy resins and composites were measured with a dynamic viscoelastometer (UBM, Rheogel-E4000) using a non-resonance tensile method. The dynamic complex moduli of the specimens for tensile oscillation with a frequency of 10 Hz were measured at 1 K intervals ranging from 223 to 493 K. The heating rate was 1 K/min. The glass transition temperatures of the composites and the neat epoxy resins were determined at peaks of the maximum tan 8 of their loss moduli. The cross-linking density of the composites and the neat epoxy resins were calculated from the dynamic storage moduli in a rubbery state according to [28, 33]

E' = 3nRT, (1)

where T and R are the absolute temperature and gas constant [=8.3145 J/(mol K)]. The cross-linking densities in the composites were assumed to be the same as those of the neat epoxy resins with the same EEWRs [28] because the EEWRs are concerned with the chemical reactions of the epoxide resin and the curing agent. The results for the glass transition temperatures, [T.sub.g], and the cross-linking densities, n, are listed in Table 1 [30, 32]. The cross-linking densities of the neat epoxy resins and the matrix resins of the composites ranged from 2740 to 490 mol/[m.sup.3].

Experimental procedure

Single-edge-notched bending test was performed at room temperature to measure the mode I fracture toughnesses of the neat epoxy resins and the composites in terms of the critical stress intensity factor, KIC, according to ASTM standard D5045-99. The specimens had a length of 100 mm, a height of 20 mm, and a width of 5 mm. The length of pre-crack at the middle point of the specimen and span length between the supports corresponded to 10 and 60 mm, respectively. A constant deflection rate of 50 jim/s was applied at the loading point, and the load was recorded using a universal materials testing machine (Shimadzu, AGS-J). The fracture toughness was calculated as

[MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII], (2)

where [alpha] = a/W. [P.sub.max], B, L, W, and a correspond to the maximum load, width, span length, height, and pre-crack length of the specimens.

The fracture surface of the neat epoxy resins and the composites were observed 2 mm from the pre-crack tip after the fracture tests with a scanning electron microscope (SEM) (Keyence, VE-8800).

Experimental results

Load-deflection curves

Figure 1 plots typical load-deflection curves for the neat epoxy resins, and the composites were measured with single edge-notched bending tests. Every specimen had a linear load-deflection relation until brittle fractures occurred regardless of the EEWRs. We, therefore, applied Eq. 1 on the basis of linear elastic fracture mechanics to determine the fracture toughness of the neat epoxy resins and composites. The average values for fracture toughnesses were evaluated with their standard deviations from more than five experimental results.

[FIGURE 1 OMITTED]

Fracture surfaces

The fracture surfaces of specimens observed by SEM after the single-edge-notched bending tests are shown in Fig. 2. Because the particles on the fracture surfaces were found to be surrounded by the matrix resins, namely interphase regions [16, 18], it could be concluded that cracks propagated in the matrix resins, regardless of cross-linking densities. The state was the same as the fracture surfaces in Adachi et al. [16, 18] and those after bending tests in Umboh et al. [32]. Therefore, the properties of matrixes near particles, which would be dependent on the interaction between the particles and matrixes, were important to take into consideration the fractures in the specimens.

Fracture toughness and bending strength

Figure 3 plots the fracture toughness and bending strength for neat epoxy resins and composites. The open circles and triangles are averages of the bending strength and fracture toughness calculated from more than five experimental results. The error bars indicate the standard deviations for the experiment data, and the solid lines are the fitting curves.

[FIGURE 2 OMITTED]

Within the cross-linking density decreasing from stoichiometric condition (2740 mol/[m.sup.3]) to 1500 mol/[m.sup.3] in Fig. 3a, the fracture toughness of the neat epoxy resins suddenly increased and reached 1.7 [MPam.sup.1/2], whereas the bending strength was constant at 150 MPa, which was approximately the same as that for the stoichiometrically cured epoxy resin. Below the cross-linking density of 1500 mol/[m.sup.3], the fracture toughness moderately decreased, although the bending strengths suddenly decreased from 150 to 100 MPa.

In Fig. 3b, the fracture toughness of the composites drastically increased and reached 2.3 [MPam.sup.1/2], which was 30 % more than that for the stoichiometrically cured composites. After that, the fracture toughness reduced below that for the stoichiometrically cured neat epoxy resins. The bending strength was constant from the stoichiom

Hasil (Bahasa Indonesia) 1:

CharacterizationThe thermo-viscoelastic properties of the neat epoxy resins and composites were measured with a dynamic viscoelastometer (UBM, Rheogel-E4000) using a non-resonance tensile method. The dynamic complex moduli of the specimens for tensile oscillation with a frequency of 10 Hz were measured at 1 K intervals ranging from 223 to 493 K. The heating rate was 1 K/min. The glass transition temperatures of the composites and the neat epoxy resins were determined at peaks of the maximum tan 8 of their loss moduli. The cross-linking density of the composites and the neat epoxy resins were calculated from the dynamic storage moduli in a rubbery state according to [28, 33]E' = 3nRT, (1)where T and R are the absolute temperature and gas constant [=8.3145 J/(mol K)]. The cross-linking densities in the composites were assumed to be the same as those of the neat epoxy resins with the same EEWRs [28] because the EEWRs are concerned with the chemical reactions of the epoxide resin and the curing agent. The results for the glass transition temperatures, [T.sub.g], and the cross-linking densities, n, are listed in Table 1 [30, 32]. The cross-linking densities of the neat epoxy resins and the matrix resins of the composites ranged from 2740 to 490 mol/[m.sup.3].Experimental procedureSingle-edge-notched bending test was performed at room temperature to measure the mode I fracture toughnesses of the neat epoxy resins and the composites in terms of the critical stress intensity factor, KIC, according to ASTM standard D5045-99. The specimens had a length of 100 mm, a height of 20 mm, and a width of 5 mm. The length of pre-crack at the middle point of the specimen and span length between the supports corresponded to 10 and 60 mm, respectively. A constant deflection rate of 50 jim/s was applied at the loading point, and the load was recorded using a universal materials testing machine (Shimadzu, AGS-J). The fracture toughness was calculated as[MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII], (2)where [alpha] = a/W. [P.sub.max], B, L, W, and a correspond to the maximum load, width, span length, height, and pre-crack length of the specimens.The fracture surface of the neat epoxy resins and the composites were observed 2 mm from the pre-crack tip after the fracture tests with a scanning electron microscope (SEM) (Keyence, VE-8800).Experimental resultsLoad-deflection curvesGambar 1 Plot kurva beban-defleksi khas untuk resin epoxy rapi, dan komposit diukur dengan satu berkumai tepi membungkuk tes. Spesimen setiap memiliki hubungan linear beban-defleksi sampai patah tulang rapuh terjadi tanpa EEWRs. Kami, oleh karena itu, diterapkan EQ 1 berdasarkan mekanika fraktur elastis linier untuk menentukan ketangguhan fraktur resin epoxy rapi dan komposit. Nilai rata-rata untuk fraktur toughnesses dievaluasi dengan deviasi standar mereka dari lebih dari lima hasil percobaan.[GAMBAR 1 DIHILANGKAN]Permukaan patahFraktur permukaan spesimen yang diamati oleh SEM setelah tes membungkuk tunggal-tepi-berkumai ditampilkan dalam Fig. 2. Karena partikel-partikel pada permukaan fraktur ditemukan dikelilingi oleh resin matriks, yaitu interphase daerah [16, 18], dapat disimpulkan bahwa retakan disebarkan dalam resin matriks, terlepas dari pembentukan ikatan Hotel kepadatan pertautan di peta silang. Negara adalah sama seperti permukaan patah di Adachi et al. [16, 18] dan orang-orang setelah membungkuk tes di Umboh et al. [32]. Oleh karena itu, sifat-sifat matriks dekat partikel, yang akan tergantung pada interaksi antara partikel dan matriks, adalah penting untuk mempertimbangkan patah tulang pada spesimen.Fraktur ketangguhan dan kekuatan lenturGambar 3 plot fraktur ketangguhan dan kekuatan yang membungkuk untuk resin epoxy rapi dan komposit. Lingkaran terbuka dan segitiga yang rata-rata membungkuk kekuatan dan fraktur ketangguhan dihitung dari hasil percobaan lebih dari lima. Error Bar menunjukkan deviasi standar untuk data percobaan, dan garis yang solid yang pas kurva.[GAMBAR 2 DIHILANGKAN]Dalam kepadatan cross-linking menurun dari kondisi stoikiometri (2740 mol/[m.sup.3]) untuk 1500 mol/[m.sup.3] di Gambar 3a, ketangguhan fraktur resin epoxy rapi tiba-tiba meningkat dan mencapai 1,7 [MPam.sup.1/2], sedangkan kekuatan membungkuk konstan pada 150 MPa, yang kira-kira sama untuk resin epoksi stoichiometrically sembuh. Di bawah cross-linking kepadatan 1500 mol/[m.sup.3], ketangguhan fraktur cukup menurun, meskipun kekuatan membungkuk tiba-tiba menurun dari 150 menjadi 100 MPa.Dalam gambar 3b, ketangguhan fraktur komposit secara drastis meningkat dan mencapai 2.3 [MPam.sup.1/2], yang adalah 30% lebih dari itu untuk komposit stoichiometrically sembuh. Setelah itu, ketangguhan fraktur berkurang di bawah resin epoxy rapi stoichiometrically sembuh. Kekuatan membungkuk adalah konstan dari stoichiom