• Journal of the Korean Ceramic Society
• /
• v.34 no.11
• /
• pp.1129-1138
• /
• 1997

Al2O3/20 vol%YAG composite containing equiaxed grains and Al2O3/20 vol%LaAl11O18 composite containing elongated grains were fabricated using Al2O3-Y2O3 composition and Al2O3-La2O3 composition, respectively, by hot-pressing. In order to investigate the influence of microstructural control of second phase on toughening effect of toughened ceramic composites, AE (acoustic emission) measurements have been coupled with fracture toughness experiments(SENB and SEPB method). A separation of the fracture toughness and analysis of toughening mechanism was possible using the AE technique. The fracture toughness of hot-pressed materials was estimated to be 3.2 MPam0.5 for monolithic alumina, 4.7 MPam0.5 for Al2O3/20 vol%YAG composite and 6.2 MPam0.5 for Al2O3/20 vol%LaAl11O18 composite. In monolithic Al2O3, toughening does not occur as a result of either microcracking or grain bridging, whereas, composites exhibit toughening effects by both microcracking in the frontal zone and gain bridging in the wake zone, resulting in an improvement of fracture toughness as compared with monolithic Al2O3. The fracture toughness of Al2O3/20 vol%LaAl11O18 composite is higher than that of Al2O3/20 vol%YAG composite. It may be attributed to the elongated microstructure of Al2O3/20 vol%LaAl11O18 composite, resulting relatively greater bridging effect.

• Polymer(Korea)
• /
• v.31 no.2
• /
• pp.123-129
• /
• 2007

Toughening mechanisms and mechanical properties of three different polyolefin-based composite systems we studied using the tensile, Izod impact and double-notch lout-point-bending (DN-4PB) test, which is well known be an effective tool for probing the failure mechanism (s) around the subcritically propagated crack tip. Microscopy observations such as optical microscopy and transmission electron microscopy were carried out lot the test samples. A detailed investigation clearly shows that a variety of toughening mechanisms, i.e., shear yielding, craze, particle-matrix debonding, rubber particle cavitation, crack deflection and bifurcation, are observed around crack tip damage zone. These toughening mechanisms are responsible for the observed, improved fracture toughness. Based on this study, DN-4PB technique is sufficient to obtain the information needed to describe the fracture behavior of polyolefin-based composites as well as their corresponding toughening mechanisms.

• Proceedings of the Korean Society For Composite Materials Conference
• /
• 2001.05a
• /
• pp.106-109
• /
• 2001

In this work, we investigate the toughening mechanism of the rubber-modified epoxy resin. The fracture toughness($K_{IC}$) is measured using CT specimens for three kinds of rubber-modified epoxy resin with different rubber content. The damage zone and rubber particles around a crack tip of a damaged specimen just before fracture are observed by a polarization microscope and an atomic force microscope(AFM). Both the fracture energy($G_{IC}$) and the size of damage zone increase with the rubber content below l5wt%. The size of the rubber particles can be qualitatively correlated with the $G_{IC}$ and the size of damage zone. The cavitation of the rubber particles inside the damage zone is observed, which is expected to be main toughening mechanism by rubber particles. the stress which causes the cavitation of rubber particles is estimated by the Dugdale model.

• Journal of the Korean Ceramic Society
• /
• v.35 no.12
• /
• pp.1266-1273
• /
• 1998

Al2O3/(5~20vol%)LaAl11O18 composites in which the second phase was dispersed with a elongated grain shape were fabricated using Al2O3 and La2O3 composition by hot-pressing. In order investigate the in-fluence of LaAl11O18 on the toughening of LaAl11O18 on the toughening of Al2O3 matrix composites AE(acoustic emission) analysis was con-ducted together with an evaluation of fracture toughness using of SEPB technique. The degree of AE events occurred in composites were more than those in monolithic alumina. The occurrences of AE event increased with increasing the amount of LaAl11O18 phase in the Al2O3/LaAl11O18 composite is two times higher compared to monolithic alu-mina. The main toughening mechanism was attributed to the bridging of LaAl11O18 grains at tip of pro-pagating crack.

• Journal of the Korean Ceramic Society
• /
• v.33 no.4
• /
• pp.464-470
• /
• 1996

Toughening mechanism of boron carbide ceramics by the addition of titanium boride was investigated. Speci-men was prepared by hot pressing of boron carbide with upto 30vol% of titanium boride particulates. Toughness of boron carbide ceramics was increased from 4.7 MPa m1/2 to 6.3 MPa m1/2 with 15 vol% TiB2 addition. But further increase of TiB2 content results in slow decrease of toughness. From microstructure evaluation and crack propagation behavior it is concluded that the major toughening mechanism is crack deflection pheno-mena.

• Proceedings of the Polymer Society of Korea Conference
• /
• 2006.10a
• /
• pp.290-290
• /
• 2006

The toughening mechanisms of polypropylene (PP) containing 9.2 vol % of calcium carbonate ($CaCO_{3}$) nanoparticles were investigated using optical microscopy and transmission electron microscopy. Double-notch four-point bending (DN-4PB) Charpy impact specimens were utilized to study the fracture mechanism(s) responsible for the observed toughening effect. A detailed investigation reveals that the $CaCO_{3}$ nanoparticles act as stress concentrators to initiate massive crazes, followed by shear banding in PP matrix. These toughening mechanisms are responsible for the observed improved impact strength.

• Korean Journal of Materials Research
• /
• v.9 no.2
• /
• pp.132-138
• /
• 1999

In order to investigate the toughening characteristic by microcrack formation in ceramic composites, $Al_2$O$_3$/(0~20)vol% YAG composites containing equiaxed second grains were fabricated using$ Al_2$$O_3$ during hot-pressing. AE(acoustic emission) measurements have been coupled with fracture toughness experiments of SENB method, to evaluate the microcrack formation and the improvement in fracture toughness of ceramic composites. Formation of microcrack was detected by Ae. The generation of AE events increased with increasing of load when load was applied at specimen. The AE events are generated mainly around at maximum load. Specially, the detected AE evetns of composites are many as compared with monolithic $Al_2$$O_3$. Fracture toughness of composites was improved than that of monolithic alumina. $Al_2$O$_3$/YAG composites exhibit main toughening effects by microcracking, results from mutual coalesence of microcracks being generated under applied load. However, there are few toughening mechanism like microcracking in monolithic alumina.

• Magazine of the Korea Concrete Institute
• /
• v.6 no.6
• /
• pp.151-158
• /
• 1994

In this work, in order to inrprove the flexural strength of hardened portlarid cerncrit paste, mix ing water was reduced to water ccrnent ratio of 0.1 aid water soluble polymer such as hydroxy propyl methyl cellulose was adclelri to the paste to obtain a better dispersion. The paste was kneaded by the twin roll mill for cornpact and homogeneous mixing. The high strength mechanism of the hardened cement paste may be due to the removal of macropores larger than 100${\mu}m$, the reduction of capillary pores acting as the passage of crack propagation, the increase of Young's moculus with iticrease of unhytlratcci cenxxnt ard the incicasc of fracture toughnevs with the crack toughening mechanism (grain bridging, polymer fibril bridging and fritional inter-locking).

• Applied Chemistry for Engineering
• /
• v.5 no.2
• /
• pp.215-222
• /
• 1994

As a toughness modifier for plastics chlorosulfonated polyethylene(CSM) can be used. CSM has a good resistance to oxygen and ozone. CSM has a crosslinkable functional group(sulfonyl chorid) with sulfur and metal oxide. Polyvinylchloride(PVC) is widely used industrial plastics because of its balanced properties and low cost. But it has some disadvantages such as low impact strength, light, ozone and oxygen degradation. In order to improve these properties of PVC, CSM was blended with PVC. The toughening effect appeared at about 10wt% and there is no additional effect above 30wt% of CSM. The weatherability, ozone resistance and mechanical properties of PVC were improved by blending with CSM. The toughening mechanism is studied by SEM.

• The Korean Journal of Ceramics
• /
• v.1 no.4
• /
• pp.197-203
• /
• 1995

Nearly fully dense PZT samples both with tetragonal and with morphotropic phase boundary compositions were prepared by the conventional powder processing and sintering. A micro-indentation technique was used to evaluate the dependence of fracture toughness on remanent polarization, crack length and the direction of crack propagation. The result shows that the toughness increases with the remanent polarization along the poling direction and decreases in the transverse direction. The dependence of toughness on the remanent polarization is neither symmetric nor linear but rather shown to be saturated quickly with the increase in remanent polariztion. R-curve behaviors are observed in both poled and unpoled samples. Sequential SEM and XRD studies on annealed, poled, ground, fractured and etched samples show that domain switching is evident as a viable toughening mechanism but might depend upon the rate of crack propagation. Grain bridging is also observed as one of the active toughening mechanisms.