Fracture Toughness Of Ceramic Composites Research Articles

Improved fracture resistance and toughening mechanisms of GNPs reinforced ceramic composites

The R-curve behavior and toughening mechanisms of graphene nano-platelets (GNPs) reinforced ceramic composites are investigated. A toughening model is developed with the consideration of interface debonding, crack bridging and pull-out of GNPs, which can be used to quantify the contribution of different mechanisms to the improved toughness of ceramic composites. The theoretical results agree well with the experimental data when GNPs homogeneously dispersed in ceramic matrix. All prepared GNPs/ceramic composites exhibit a raising R-curve behavior owing to the toughening mechanisms induced by GNPs, and the curve becomes steeper with increasing GNPs content, indicating that the fracture resistance and flaw tolerance are improved. The dominant toughening mechanism is GNPs pull-out, which is followed by crack bridging and interface debonding. Furthermore, the analytical model suggests that improving GNPs properties, interfacial sheer strength and reducing GNPs thickness can improve the fracture toughness of ceramic composites.

Mechanical properties and microstructure of spark plasma sintered Al2O3-SiCw-Si3N4 composite ceramic tool materials

In this study, Al2O3-SiCw-Si3N4-based ceramic tool materials were fabricated by spark plasma sintering technique. The impact of sintering temperature on mechanical properties and local microstructure was thoroughly investigated. Moreover, detailed comparison was performed between spark plasma sintering and early hot-pressing sintering methods. Evolution law and mechanism of high-temperature mechanical properties were also investigated. Composites with higher density and enhanced mechanical properties were obtained by spark plasma sintering at temperature of 1500 °C, which was 100 °C lower than hot-pressing temperature. The cross-interlocking structure of generated β-Sialon particles and silicon carbide (SiC) whiskers could effectively improve mechanical properties of material configuration. Moreover, Vickers hardness and fracture toughness of ceramic composites decreased by elevating temperature (20–1000 °C); however, following percentages at 1000 °C were still maintained with respect to values at room temperature, i.e., 67 and 51%. This effect is attributed to existence of Sialon phase, healing of partial cracks, as well as manifestation of whisker pullout process. As a result, decreased attenuation rate under high-temperature conditions of respective mechanical properties was observed. Our approach provides useful insights into potential fabrication of novel material configurations with relatively low thermal budget and enhanced mechanical performance.

Моделирование влияния агломерации графена на механические свойства керамических композитов с графеном

A model is proposed that describes the porosity, hardness, and fracture toughness of ceramic composites with agglomerates of graphene platelets. The model assumes that the agglomeration of graphene platelets occurs during the hot pressing of such composites, and pores are formed around the agglomerates. Within the model, the dependences of porosity, hardness, and fracture toughness of ceramic/graphene composites on the volume fraction of graphene are calculated. It is shown that the formation of pores explains the experimentally observed drop in the hardness and fracture toughness of composites for the volume fraction of graphene exceeding a critical value. The results of the model agree with the experimental data for the composites Al2O3-WC-TiC-Gr.

Effect of ZrC and ZrO2 Additions on the Microstructure and Properties of ZrB2–SiC Ceramics

We have studied the effect of ZrC and ZrO2 additions on the microstructure and properties of ceramic composites based on ZrB2???5% SiC, produced by pressure-sintering mechanically activated powders at a temperature of 1600??C. The results demonstrate that the addition of ZrO2 increases the density, hardness, and fracture toughness of ceramic composites based on ZrB2???5% SiC. In particular, the KIc of the ZrB2???5% SiC ceramic is 4.6 ?? 0.3 MPa m1/2 and that of the composite containing 20% ZrO2 is 7.3 ?? 0.4 MPa m1/2.

Experimental and Numerical Investigation of Dynamic Fracture Toughness of Ceramic Composites

This study focusses on the experimental and numerical investigation of the continuous carbon fiber-reinforced silicon carbide (SiC), and silicon nitride (Si3N4) matrix composites. A testing procedure has been designed to study the Charpy impact testing system. The dynamic elastic-plastic fracture toughness (JdSiC=11.88kJ/m2 and JdSi3N4=1.77kJ/m2) as well as the dynamic stress intensity factors (kdSiC=36.88 MPaem2and JdSi3N4=22.03 MPaem2) have been evaluated. Further on, a good agreement between finite element results and experimental findings was found.

Impact of carbon nanotube defects on fracture mechanisms in ceramic nanocomposites

Carbon nanotubes (CNTs) can improve the fracture toughness of ceramic composites. It is widely believed that defects in the CNTs will alter key properties that ultimately dictate composite toughening. However, to date there have been no studies that directly correlate these specific properties to controlled defect levels in CNTs. This type of investigation is presented here, using ceramic nanocomposites with a polymer derived ceramic (PDC) matrix, reinforced with multiwalled CNTs. This work includes basic fracture measurements on full composite films, combined with careful testing of individual CNTs embedded in the same PDC matrix. The defect levels in these CNTs were controlled with high energy carbon ions. By using this approach, it was possible to directly correlate defect levels with the interfacial shear strength (IFSS) of the CNT/PDC interface, the CNT fracture strengths, and the pull-out lengths observed after fracture of the full composites. The radiation induced defects led to substantial increases in the IFSS, and only a marginal decrease is observed in the measured fracture strength. Based on this, the shorter pull-out lengths that occurred with higher defect levels were primarily attributed to stronger bonding at the CNT/PDC interface.

A New Method for Determining Strength and Fracture Toughness of Ceramic Materials in Air at 1500-2000 °C

Evaluation of the mechanical properties at ultra-high temperatures for ceramic composites is necessary and important for the safety of designing the ceramic components. In this work, a new and novel test method named as local ultra-high temperature together with applied load method (LUHTAL), was developed to determine the tensile, compressive, bending strength and fracture toughness of ceramic composites. The four point bending load was conducted to measure the bending strength and fracture toughness of ceramic composites after the center of the sample was heated up to about 1500-2000°C by oxygen-assisted spray combustion. To check the availability and reliability for this method, typical ceramic materials including ZrB2/SiC and C/SiC fiber reinforced composite coated with Si, were used as the testing samples. It is indicated that this method is good and feasible for evaluating the mechanical properties of the ceramic composite at ultra-high temperatures in air.

Prediction of fracture toughness of ceramic composites as function of microstructure: I. Numerical simulations

The evaluation of macroscopic material parameters such as fracture toughness as functions of microstructural attributes is a fundamental issue in material science. The task requires the quantification of both microstructure and material response. Currently, no systematic approach other than experiments exists for establishing microstructure–fracture toughness relations for materials. In this paper, we present a multi-scale computational framework based on the cohesive finite element method (CFEM) for predicting fracture toughness of materials as a function of microstructure. This framework provides a means for evaluating fracture toughness through explicit simulation of fracture processes in microstructures. The approach uses the J-integral, allowing fracture toughness to be calculated for microstructures with random heterogeneous phase distributions and fracture processes with arbitrary crack paths or micro-crack patterns. Calculations carried out concern two-phase Al2O3/TiB2 ceramic composites and focus on the effects of constitute behavior, phase morphology, phase distribution, phase size scale, and interphase bonding on fracture toughness. Results show that microstructure and constituent properties can significantly influence fracture behavior and combine to determine the overall fracture toughness through the activation of different fracture mechanisms. In particular, a combination of fine microstructure size scale, rounded reinforcement morphology, appropriately balanced interphase bonding strength and compliance can best promote desirable crack–reinforcement interactions and lead to enhanced fracture toughness.

Microstructural Evaluation of Silicon Carbide Whisker Reinforced Alumina Fabricated with Carbon-Coated Whiskers

The presence of interfacial films at the whisker-matrix interface can significantly influence the fracture toughness of ceramic composites. The film may alter the interface debonding process though changes in either the interfacial fracture energy or the residual stress at the interface. In addition, the films may affect the whisker pullout process through the frictional sliding coefficients or the extent of mechanical interlocking of the interface due to the whisker surface topography.Composites containing ACMC silicon carbide whiskers (SiCw) which had been coated with 5-10 nm of carbon and Tokai whiskers coated with 2 nm of carbon have been examined. High resolution electron microscopy (HREM) images of the interface were obtained with a JEOL 4000EX electron microscope. The whisker geometry used for HREM imaging is described in Reference 2. High spatial resolution (< 2-nm-diameter probe) parallel-collection electron energy loss spectroscopy (PEELS) measurements were obtained with a Philips EM400T/FEG microscope equipped with a Gatan Model 666 spectrometer.