TOUGHENING OF BORON CARBIDE COMPOSITES BY HIERARCHICAL MICROSTRUCTURING

2021 ◽  
Author(s):  
JINGYAO DAI ◽  
EVAN PINEDA ◽  
BRETT BEDNARCYK ◽  
JOGENDER SINGH ◽  
NAMIKO YAMAMOTO
Keyword(s):  
Fracture Toughness ◽  
Boron Carbide ◽  
Bending Test ◽  
Toughening Mechanisms ◽  
Hierarchical Microstructure ◽  
Micro Scale ◽  
Four Point Bending ◽  
Micromechanics Modeling ◽  
Toughness Enhancement ◽  
Micro Indentation

Due to a unique combination of properties including high hardness, low density, chemical and thermal stability, semi-conductivity, and high neutron absorption, boron carbide (B C) is a potential candidate for various applications involving extreme environment. However, B C’s current application is limited because of its low fracture toughness. In this study, a hierarchical microstructure design with features including TiB grains and graphite platelets was used to toughen B C by simultaneously utilizing multiple toughening mechanisms including crack deflection, bridging, and micro-crack toughening. Using field-assisted sintering technology (FAST), B C composites with dense and hierarchical microstructure were fabricated. Previously, the fracture toughness of fabricated B C composites was measured at micro-scale using micro- indentation to have up to 56% improvement. In this work, the B C composites’ fracture toughness was characterized at macro-scale using four-point bending methods and compared with previous results obtained at micro-scale. Micromechanics modeling of fracture behaviors for B C-TiB composites was also performed to evaluate the contributions from experimentally observed toughening mechanisms. From four-point bending tests, B C composites reinforced with both TiB grains (~15 vol%) and graphite platelets (~8.7 vol%) exhibited the highest fracture toughness enhancement from 2.38 to 3.65 MPa·m1/2. The measured values were lower than those obtained using micro- indentation but maintained the general trends. The discrepancy between the indentation and four-point bending test results originated from the complex deformation behaviors triggered by the high contact load during indentation tests. Through micromechanics modeling, introduced thermal residual stress due to thermal expansion mismatch between B C and TiB , and weak interphases at B C-TiB boundaries were identified as the main causes for experimentally observed toughness enhancement. These results proved the effectiveness of hierarchical microstructure designs for B4C toughening and can provide reference for the future design of B4C composites with optimized microstructures for further fracture toughness enhancement.

scholarly journals Tomographic investigation of the fracture toughness of the quasi-brittle specimens subjected to four-point bending test

2018 ◽  
Vol 13 ◽  
pp. 1967-1970 ◽  
Author(s):  
Daniel Vavřík ◽  
Pavel Beneš ◽  
Tomáš Fíla ◽  
Petr Koudelka ◽  
Ivana Kumpová ◽  
...  
Keyword(s):  
Fracture Toughness ◽  
Bending Test ◽  
Four Point Bending ◽  
Four Point Bending Test

Strength and Toughness of Graphite Materials for Solid Rocket Motor

2004 ◽  
Vol 449-452 ◽  
pp. 709-712
Author(s):  
Shoichi Nambu ◽  
Manabu Enoki
Keyword(s):  
Mechanical Properties ◽  
Fracture Toughness ◽  
Crack Propagation ◽  
Fracture Probability ◽  
Bending Test ◽  
Fracture Toughness Test ◽  
Solid Rocket Motor ◽  
Four Point Bending ◽  
Toughness Test ◽  
Solid Rocket

It was pointed out that one of the causes of recent failure to launch rocket was due to the fracture of nozzle throat insert made of graphite materials. The relationship between mechanical properties and microfracture process in graphite was not enough analyzed. To ensure the reliability of such aerospace equipment, we considered the necessity of assurance by non-destructive evaluation, evaluation of mechanical property for graphite material and design based on fracture probability. In this study, four-point bending test and fracture toughness test were used to evaluate mechanical properties. Mean strength, Weibull parameters, and R-curve for crack propagation were estimated. AE measurement during tests was performed in order to obtain location and stress of microfracture. AE results were analyzed by stochastic process theory. The result of AE demonstrates that microfracture process during bending test is divided into three stages. AE behavior in fracture toughness test was also closely related to crack propagation.

Effects of Sintering Temperature and Excess Zr on Mechanical Properties of Reactive Hot-Pressed ZrB2-ZrCx-Zr Cermets

2016 ◽  
Vol 697 ◽  
pp. 633-638 ◽  
Author(s):  
S.Q. Guo
Keyword(s):  
Mechanical Properties ◽  
Fracture Toughness ◽  
Sintering Temperature ◽  
Bending Test ◽  
Cracking Behavior ◽  
Propagation Behavior ◽  
Four Point Bending ◽  
Different Temperatures ◽  
Four Point Bending Test ◽  
Reactive Hot Pressing

In this study, a series of ZrB2-ZrCx-Zr cermets were prepared by reactive hot-pressing of Zr + B4C powder mixtures at different temperatures between 1400°C and 1900°C. The microstructure of the resulting cermets was characterized by field emission scanning electron microscopy. The strength and fracture toughness of the cermets were measured by four-point bending test at room temperature. The results showed that the strength and fracture toughness dependend on the amount of excess Zr and sintering temperature as well. In addition, the crack propagation behavior of the cermets was examined under indent cracking. The cracks induced by indenter directly propagated in the samples with less than 16 vol% Zr. For comparison, the multiple cracking behavior was observed for the samples with equal to or greater than 16% Zr. Furthermore, the effects of compositions and sintering temperatures on the microstructure and the mechanical properties of the cermets were discussed.

scholarly journals Ensuring Accurate Results in Fracture Mechanics Four-Point Bending Interface Characterization

2021 ◽  
pp. 149-158
Author(s):  
Jefferson Talledo
Keyword(s):  
Fracture Toughness ◽  
Fracture Mechanics ◽  
Bending Test ◽  
Interface Fracture ◽  
Test Problems ◽  
Experimental Setup ◽  
Interface Characterization ◽  
Four Point Bending ◽  
Four Point Bending Test ◽  
Semiconductor Packages

Interface adhesion tests are conducted to obtain a quantitative value of the adhesion strength or interface fracture toughness to forecast initiation and propagation of interface delamination failures in semiconductor packages. One of the common methods of fracture mechanics interface characterization is the four-point bending test. Problems with the experimental setup would result in having inaccurate results. In this study, different issues with the four-point bending test using mold/copper bi-material beam with notch were addressed. It was shown that incorrect anvil alignment and centering could give inaccurate fracture toughness results. The distance between anvil supports and the depth of the notch is also very important. From the study, it can be concluded that issues with experimental setup and the test sample must be addressed to ensure accurate results from four-point bending interface characterization.

Influence of Confinement on Ceramic’s Mechanical Properties

2016 ◽  
Vol 848 ◽  
pp. 249-255
Author(s):  
Xiao Cong Hang ◽  
Yun Kai Li
Keyword(s):  
Mechanical Properties ◽  
Fracture Toughness ◽  
Boron Carbide ◽  
Fracture Process ◽  
Hot Spot ◽  
Efficiency Factor ◽  
Bending Test ◽  
Depth Of Penetration ◽  
Constraint Force ◽  
Three Point Bending

The wide use of ceramic material in engineering is restricted by its brittleness, so the strengthening and toughening of ceramics is always a hot spot of research in material area. And in general, the modification of ceramics is achieved by changing its internal microstructure. In this paper the influence of confinement on the mechanical properties of ceramics and the specific use of this method were investigated. Firstly, the influence of confinement on ceramic’s fracture process was analyzed in theory. Then the three-point bending test was conducted using two types of ceramics, viz. Zirconia and Alumina. The experimental results showed that the fracturing load of zirconia increased from 4.3298 to 5.4639KN as the confinement was increased from 0 to 150MPa, 26.19% increase was found in the confined specimen. The same trend was observed in alumina, whose fracturing load increased from 3.0446 to 5.0259KN as the confinement was increased from 0 to 150MPa, 65.07% increase was found. After that, a series of ballistic experiments were performed. The target in this experiment was boron carbide ceramic, and it was confined by 45 steel. The results showed that with the constraint force was bigger, the ballistic efficiency factor was better and the depth of penetration was smaller. In other words, the confinement can increase the defensible performance of the target. In summary, the ceramic’s fracture toughness, defensible performance and ballistic efficiency factor can be increased by adding confinement to it.

scholarly journals Brittle material strength and fracture toughness estimation from four-point bending test

2021 ◽  
Author(s):  
Aurélien Doitrand ◽  
Ronan Henry ◽  
Sylvain Meille
Keyword(s):  
Fracture Toughness ◽  
Tensile Strength ◽  
Characteristic Length ◽  
Bending Test ◽  
Material Strength ◽  
Material Characteristic ◽  
Flexural Stress ◽  
Bending Tests ◽  
Four Point Bending ◽  
Specimen Height

The failure stress under four-point bending cannot be considered as an intrinsic material property because of the well-known size effect of increasing maximum flexural stress with decreasing specimen size. In this work, four-point bending tests are analyzed with the coupled criterion for different sample sizes. The maximum flexural stress only tends towards the material tensile strength provided the specimen height is large enough as compared to the material characteristic length. In that case, failure is mainly driven by a stress criterion. Failure of smaller specimens is driven both by energy and stress conditions, thus depending on the material tensile strength and fracture toughness. Regardless of the material mechanical properties, we show that the variation of the ratio of maximum flexural stress to strength as a function of the ratio of specimen height to material characteristic length follows a master curve, for which we propose an analytical expression. Based on this relation, we propose a procedure for the post-processing of four-point bending tests that allows determining both the material tensile strength and fracture toughness. The procedure is illustrated based on four-point bending experiments on three gypsum at different porosity fractions.

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