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C T Sun - One of the best experts on this subject based on the ideXlab platform.

  • A method for testing interlaminar dynamic Fracture Toughness of polymeric composites
    Composites Part B: Engineering, 2004
    Co-Authors: C T Sun, C. Han
    Abstract:

    Static and dynamic Mode I delamination Fracture in two polymeric fiber composites was studied using a WIF test method. The dynamic test was conducted on a Split Hopkinson Pressure Bar apparatus. Crack speeds up to 1000 m/s were achieved. Dynamic Fracture and crack propagation were modeled by the finite element method. Dynamic initiation Fracture Toughness of S2/8552 and IM7/977-3 composites were obtained. The dynamic Fracture Toughness of IM7/977-3 associated with the high speed propagating crack was extracted from the finite element simulation based on the measured data. It was found that the dynamic Fracture Toughness of the delamination crack propagating at a speed up to 1000 m/s approximately equals the Static Fracture Toughness.

  • Dynamic delamination Fracture Toughness in unidirectional polymeric composites
    Composites Science and Technology, 2001
    Co-Authors: J. L. Tsai, C Guo, C T Sun
    Abstract:

    A modified end-notched flexure (ENF) specimen was used to determine Mode-II-dominated dynamic delamination Fracture Toughness of fiber composites at high crack propagation speeds. A strip of FM-73 adhesive film was placed at the tip of the interlaminar crack created during laminate lay-up. This adhesive film with its greater Toughness delayed the onset of crack extension and produced crack propagation at high speeds. Dynamic delamination experiments were performed on these ENF specimens made of unidirectional S2/8553 glass/epoxy and AS4/3501-6 carbon/epoxy composites. Crack speed was measured by means of conductive aluminum lines created by the vapor deposition technique. A finite-element numerical simulation based on the measured crack speed history was performed and the dynamic energy release rate calculated. The results showed that the dynamic Fracture Toughness is basically equal to the Static Fracture Toughness and is not significantly affected by crack speeds up to 1100 m/s.

Shojiro Ochiai - One of the best experts on this subject based on the ideXlab platform.

  • shape effect of ultrafine grained structure on Static Fracture Toughness in low alloy steel
    Science and Technology of Advanced Materials, 2012
    Co-Authors: Tadanobu Inoue, Yuuji Kimura, Shojiro Ochiai
    Abstract:

    A 0.4C-2Si-1Cr-1Mo steel with an ultrafine elongated grain (UFEG) structure and an ultrafine equiaxed grain (UFG) structure was fabricated by multipass caliber rolling at 773 K and subsequent annealing at 973 K. A Static three-point bending test was conducted at ambient temperature and at 77 K. The strength-Toughness balance of the developed steels was markedly better than that of conventionally quenched and tempered steel with a martensitic structure. In particular, the Static Fracture Toughness of the UFEG steel, having a yield strength of 1.86 GPa at ambient temperature, was improved by more than 40 times compared with conventional steel having a yield strength of 1.51 GPa. Furthermore, even at 77 K, the Fracture Toughness of the UFEG steel was about eight times higher than that of the conventional and UFG steels, despite the high strength of the UFEG steel (2.26 GPa). The UFG steel exhibited brittle Fracture behavior at 77 K, as did the conventional steel, and no dimple structure was observed on the Fracture surface. Therefore, it is difficult to improve the low-temperature Toughness of the UFG steel by grain refinement only. The shape of crystal grains plays an important role in delamination toughening, as do their refinement and orientation.

  • Static Fracture Toughness of fail-safe steel
    Scripta Materialia, 2011
    Co-Authors: Tadanobu Inoue, Yuuji Kimura, Shojiro Ochiai
    Abstract:

    A 1800 MPa class steel with ultrafine elongated grain structures was fabricated by multi-pass caliber rolling and a Static three-point bending test was conducted. The strength–Toughness balance of the developed steel was remarkably improved compared with conventionally quenched and tempered steel with a martensitic structure. The Static Fracture Toughness of the developed steel was about 40 times higher than that of the conventional steel. The microstructural design that improves the Toughness in ultrahigh-strength steels is clarified.

Naveed A Siddiqui - One of the best experts on this subject based on the ideXlab platform.

  • mode i interlaminar Fracture behavior and mechanical properties of cfrps with nanoclay filled epoxy matrix
    Composites Part A-applied Science and Manufacturing, 2007
    Co-Authors: Christopher Ky Leung, Naveed A Siddiqui, Arshad Munir
    Abstract:

    Abstract The mechanical properties and Fracture behavior of nanocomposites and carbon fiber composites (CFRPs) containing organoclay in the epoxy matrix have been investigated. Morphological studies using TEM and XRD revealed that the clay particles within the epoxy resin were intercalated or orderly exfoliated. The organoclay brought about a significant improvement in flexural modulus, especially in the first few wt% of loading, and the improvement of flexural modulus was at the expense of a reduction in flexural strength. The quasi-Static Fracture Toughness increased, whereas the impact Fracture Toughness dropped sharply with increasing the clay content. Flexural properties of CFRPs containing organoclay modified epoxy matrix generally followed the trend similar to the epoxy nanocomposite although the variation was much smaller for the CFRPs. Both the initiation and propagation values of mode I interlaminar Fracture Toughness of CFRP composites increased with increasing clay concentration. In particular, the propagation Fracture Toughness almost doubled with 7 wt% clay loading. A strong correlation was established between the Fracture Toughness of organoclay-modified epoxy matrix and the CFRP composite interlaminar Fracture Toughness.

Guo Qiao Lai - One of the best experts on this subject based on the ideXlab platform.

  • grafting of epoxy chains onto graphene oxide for epoxy composites with improved mechanical and thermal properties
    Carbon, 2014
    Co-Authors: Yanjun Jean Wan, Yi Bao Li, Lian Bin Wu, Dong Yan, Longcheng Tang, Jian Xiong Jiang, Li-xiu Gong, Guo Qiao Lai
    Abstract:

    Abstract Epoxy composites filled with both graphene oxide (GO) and diglycidyl ether of bisphenol-A functionalized GO (DGEBA–f–GO) sheets were prepared at different filler loading levels. The correlations between surface modification, morphology, dispersion/exfoliation and interfacial interaction of sheets and the corresponding mechanical and thermal properties of the composites were systematically investigated. The surface functionalization of DGEBA layer was found to effectively improve the compatibility and dispersion of GO sheets in epoxy matrix. The tensile test indicated that the DGEBA–f–GO/epoxy composites showed higher tensile modulus and strength than either the neat epoxy or the GO/epoxy composites. For epoxy composite with 0.25 wt% DGEBA–f–GO, the tensile modulus and strength increased from 3.15 ± 0.11 to 3.56 ± 0.08 GPa (∼13%) and 52.98 ± 5.82 to 92.94 ± 5.03 MPa (∼75%), respectively, compared to the neat epoxy resin. Furthermore, enhanced quasi-Static Fracture Toughness ( K IC ) was measured in case of the surface functionalization. The GO and DGEBA–f–GO at 0.25 wt% loading produced ∼26% and ∼41% improvements in K IC values of epoxy composites, respectively. Fracture surface analysis revealed improved interfacial interaction between DGEBA–f–GO and matrix. Moreover, increased glass transition temperature and thermal stability of the DGEBA–f–GO/epoxy composites were also observed in the dynamic mechanical properties and thermo-gravimetric analysis compared to those of the GO/epoxy composites.

  • the effect of graphene dispersion on the mechanical properties of graphene epoxy composites
    Carbon, 2013
    Co-Authors: Longcheng Tang, Yanjun Jean Wan, Yi Bao Li, Lian Bin Wu, Dong Yan, Jian Xiong Jiang, Yong Bing Pei, Li Zhao, Guo Qiao Lai
    Abstract:

    Abstract The effect of dispersion state of graphene on mechanical properties of graphene/epoxy composites was investigated. The graphene sheets were exfoliated from graphite oxide (GO) via thermal reduction (thermally reduced GO, RGO). Different dispersions of RGO sheets were prepared with and without ball mill mixing. It was found that the composites with highly dispersed RGO showed higher glass transition temperature (Tg) and strength than those with poorly dispersed RGO, although no significant differences in both the tensile and flexural moduli are caused by the different dispersion levels. In particular, the Tg was increased by nearly 11 °C with the addition of 0.2 wt.% well dispersed RGO to epoxy. As expected, the highly dispersed RGO also produced one or two orders of magnitude higher electrical conductivity than the corresponding poorly dispersed RGO. Furthermore, an improved quasi-Static Fracture Toughness (KIC) was measured in the case of good dispersion. The poorly and highly dispersed RGO at 0.2 wt.% loading resulted in about 24% and 52% improvement in KIC of cured epoxy thermosets, respectively. RGO sheets were observed to bridge the micro-crack and debond/delaminate during Fracture process due to the poor filler/matrix and filler/filler interface, which should be the key elements of the toughening effect.

C. Han - One of the best experts on this subject based on the ideXlab platform.

  • A method for testing interlaminar dynamic Fracture Toughness of polymeric composites
    Composites Part B: Engineering, 2004
    Co-Authors: C T Sun, C. Han
    Abstract:

    Static and dynamic Mode I delamination Fracture in two polymeric fiber composites was studied using a WIF test method. The dynamic test was conducted on a Split Hopkinson Pressure Bar apparatus. Crack speeds up to 1000 m/s were achieved. Dynamic Fracture and crack propagation were modeled by the finite element method. Dynamic initiation Fracture Toughness of S2/8552 and IM7/977-3 composites were obtained. The dynamic Fracture Toughness of IM7/977-3 associated with the high speed propagating crack was extracted from the finite element simulation based on the measured data. It was found that the dynamic Fracture Toughness of the delamination crack propagating at a speed up to 1000 m/s approximately equals the Static Fracture Toughness.