Weibull Statistical Method Research Articles

Ballistic Performance, Thermal and Chemical Characterization of Ubim Fiber (Geonoma baculifera) Reinforced Epoxy Matrix Composites.

The search for unexplored natural materials as an alternative to synthetic components has driven the development of novel polymeric composites reinforced with environmentally-friendly materials. Natural lignocellulosic fibers (NLFs) have been highlighted as potential reinforcement in composite materials for engineering applications. In this work, a less known Amazonian fiber, the ubim fiber (Geonoma baculifera), is investigated as a possible reinforcement in epoxy composites and was, for the first time, thermally characterized by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). Additionally, its chemical structure was elucidated by Fourier transform infrared spectroscopy (FTIR). Ballistic tests were also performed against the threat of a 7.62 mm high-speed lead projectile. The results were statistically analyzed by the Weibull statistical analysis method. FTIR analysis showed the functional groups normally found for NLFs highly rich in cellulose, hemicellulose, and lignin. The TGA/DTG results showed the onset of thermal degradation for the composites (325~335 °C), which represents better thermal stability than isolated ubim fiber (259 °C), but slightly lower than that of pure epoxy (352 °C). The DSC results of the composites indicate endothermic peaks between 54 and 56 °C, and for the ubim fibers, at 71 °C. Ballistic tests revealed higher energy absorption in composites with lower fiber content due to the more intense action of the brittle fracture mechanisms of the epoxy resin, which tended to dissipate more energy. These failure mechanisms revealed the presence of river marks, cracks, and broken fibers with a detachment interface. These results may contribute to the production of ubim fiber-reinforced composites in engineering applications, such as ballistic armors.

Mechanical properties and crack evolution of SCC with macro-crack under freeze-thaw cycles

Freeze-thaw cycles (FTC) is a main reason of concrete deterioration in cold area. In actual practical project, concrete structure often works with macro-cracks (MC). In order to understand the damage change and crack propagation evolution of concrete with MC under FTC, this paper investigated the stress-strain curve of self-compacting concrete (SCC) with MC and the propagation evolution of MC under FTC through hydraulic servo test system and laser 3D scanner respectively. The damage constitutive model of SCC with MC was established based on Weibull statistical distribution method. The variation characteristics of SCC damage variables and the mechanism of propagation and evolution of MC were analyzed. Results showed that under FTC, the existence of MC accelerated the deterioration of SCC, and the peak stress and elastic modulus of SCC containing MC rapidly decreased, while the peak strain increased significantly. The damage variables of SCC with MC showed a monotone S-curve increase, and the scale parameter a increased and the shape parameter b decreased exponentially. Under FCT, the damage rate of SCC with MC was higher than that of the non-crack group. Due to the MC in concrete be the first close during compression, the peak damage rate of SCC with MC was lower than that of the non-crack group under uniaxial compression, but the corresponding peak strain increased remarkably. The morphology changes of MC were significant with the increase of FTC. The repeated crystallization pressure of the FTC on the MC led to the stress concentration at the crack tip, resulting in the MC extending along the length. Crystallization pressure also caused the effect of frost swelling and denudation on the inner wall of the MC, leading to a highly significant increase in the width and area of the MC. Therefore, more attention should be paid to the width and area changes of concrete with MC in practical projects.

Evaluation of the density, mechanical, thermal and chemical properties of babassu fibers (Attalea speciosa.) for potential composite reinforcement

The properties of babassu (Attalea speciosa.) fiber was for the first time investigated for potential engineering application such as reinforcement for matrix composites. The diameter distribution of babassu fibers was analyzed and found to be associated with significant variation in fiber density and mechanical properties. Additionally, thermogravimetric and Fourier transform infrared spectrometry (FTIR) analyses were performed. The studied Weibull statistical method was used to analyze the acquired data. The surface morphology of the fibers was studied by scanning electron microscopy. From the diameter ranges, it was possible to confirm that the thinner fibers have higher values of density and mechanical properties, which was attributed to their lower presence of defects. The diameter range was found between of 0.18 and 0.47 mm, and the corresponding densities were 0.79 and 0.27 g/cm³ respectively. Furthermore, the maximum tensile strength found was 100.76 MPa with an elastic modulus of 6.33 GPa and an elongation of 2.98%. Thermogravimetric analyses revealed a three-step mass loss, the main one being the second where the fiber loses 69% of the mass at a temperature of 382 °C. The FTIR analysis showed a similarity with the bands generally found in the literature for natural lignocellulosic fibers.

Evaluation of the Wind Power Potential in the Northeast of Chad

Chad has done the study and development of renewable resources a priority in its energy mix. Wind energy is one of the renewable sources that can help Chad to develop rural areas and preserve the environment. This study presents from data obtained from NASA, the wind characteristics in Amdjarass, and Fada over thirty (30) years. The wind distribution density and energy potential at different heights were evaluated using the Weibull statistical analysis method. The aim of this paper is to evaluate the wind energy potential of two important sites in Chad. The study shows that over the 30 years, the mean annual wind speeds vary randomly between 4.7 m/s and 5.4 m/s over an average period of 2 years. Eight months of good average wind speeds were recorded, ranging from 5.01 m/s to 6.31 m/s at Amdjarass and 4.92 m/s to 5.70 m/s at Fada. The 04 months of low velocities observed are in the range of 3.211 m/s - 4.064 m/s at Amdjarass and 3.504 m/s - 4.516 m/s at Fada. The power density varies between 21.53 W/m2 and 111.89 W/m2 in Amdjarass, while in Fada, it varies from 19.85 W/m2 to 86.92 W/m2.

WIND ENERGY POTENTIAL IN YOBE, NORTHEASTERN NIGERIA: AN AIDED TECHNIQUE THROUGH GEOGRAPHIC INFORMATION SYSTEM AND REMOTE SENSING

The role of wind energy and other renewable energy sources in combating climate change cannot be overemphasized. Many countries including Nigeria have so far implemented policy measures to promote renewable energy. Moreover, the most important step to be taken in order to effectively harness renewable energy is to estimate their potentials in terms of viability and sustainability. This study was focused on evaluate the wind energy potential zones in Yobe State, northeast Nigeria, using integrated multiple criteria decision-making analysis (MCDA), Geographical Information System and Remote Sensing (GIS-RS), and Analytic Hierarchy Process (AHP) methods. Weibull distribution statistical method was applied to validate the GIS-RS based analysis. The study revealed a wind speed variation ranged from 1.48 to 7.15 m/s and an average annual wind power density of about 80 W/m2. About 90 % of study area has about 90 % wind power density of about 85 W/m2 and below while the remaining 10 % is covered by wind power density ranged between 85 and 616.89 W/m2. The results of the study showed that the area is viable for wind power generation and distribution. Furthermore, the wind energy resource will yield favorable economic gain for the study area. Thus the study concluded that Yobe is a suitable area for wind power generation both at medium scale generation, and standalone connection system.

Experimental and statistical investigation on the wear and hardness behaviour of multiwalled carbon nanotubes reinforced copper nanocomposites

In this experimental work the two parameter Weibull distribution statistical method is used to investigate the effect of fabrication process on the wear and hardness properties of multiwalled carbon nanotubes reinforced copper nanocomposites (MWCNTs/Cu). The MWCNTs/Cu nanocomposites are fabricated by the powder metallurgy processing route in two ways (i) MWCNTs/Cu nanocomposites without hot pressing (NHP-MWCNTs/Cu) and (ii) MWCNTs/Cu nanocomposites with hot pressing (HP-MWCNTs/Cu). The MWCNTs doping weight percentage (wt.%) include 0.0 (Pure copper), 0.5, 1.0 and 1.5. The MWCNTs/Cu nanocomposites are subjected to hardness and wear tests using micro-Vickers hardness tester and rotating type pin-on-disc tribometer, respectively. From the experimental results it is found that the MWNTs/Cu nanocomposites have higher hardness and lower wear rate than the pure Cu. Further, the HP-MWCNTs/Cu nanocomposites showed higher hardness and lower wear rate than the NHP-MWCNTs/C nanocomposites. From statistical analysis it is found that the HP-MWCTs/Cu nanocomposites showed more reliable and repeatable experimental data than the NHP-MWCNTs/Cu nanocomposites. Statistical analysis showed that the effectiveness of MWCNTs doping on the wear rate of Cu is more effective at lower sliding speed. Finally, it is observed form the statistical analysis that both theoretical and experimental results of hardness and wear tests showed good correlation.

An investigation on tensile and fatigue properties of cast Al-7Si-1.5Cu alloy applied in cylinder head considering size effect phenomenon

The cylinder head is one of the most critical diesel engine components. Under service conditions, different loads are exerted on the cylinder head, leading to the failure of various degrees at different positions of the cylinder head. In this study, the differences in mechanical properties at the different positions of the cylinder head are investigated by sampling specimens, metallography measurement, tensile and fatigue tests, and fracture surface analysis. Meanwhile, the Weibull statistical distribution method is used to analyze the size effect of the specimen. The results show that the microstructure features of the cylinder head exhibit high spatial heterogeneity. The mechanical properties are affected by microstructure features. The tensile properties of the top plate are optimum, followed by the flame plate, and the connecting wall has the worst properties. The difference in tensile properties at different positions is mainly affected by the grain and eutectic structure. In the same position, the tensile and fatigue properties of standard specimens are better than small specimens. The porosity is the critical parameter determining the tensile and fatigue properties of the different specimens. In addition, based on the statistical analysis of mechanical properties, the relationship of mechanical properties between the standard and small specimens was established. Through the established relationship, the mechanical properties of small specimens can be used to predict the mechanical properties of standard specimens, and the predicted value is in good agreement with the experimental data.

Shear performance of MWCNTs modified single-lap joints of glass/epoxy laminates

In this experimental work, the single lap joint (SLJ) adhesive strength of glass fibre reinforced epoxy (GFRP) composites was investigated under quasi-static tensile loading. The adhesive used was 'Araldite® adhesives-2015 (AA)'. Further, the functionalized multiwall carbon nanotubes (s-MWCNTs) were used to modify the AA. The s-MWCNTs were mixed in AA through the ultrasonication method at six weight ratios, i.e. 0, 0.25, 0.5, 0.75, 1 and 1.25 wt. %. Experimental results showed that among different weight fractions of s-MWCNTs modified AA, the 1 wt. % of s-MWCNTs reinforcement yielded a maximum bond strength and slip. The two-parameter Weibull statistical method proved that the results for increasing s-MWCNTs in AA were reliable up to 1 wt. % s-MWCNTs doping. Strain-field analysis at bond-edge by using digital image correlation (DIC) technique showed a significant variation with s-MWCNTs reinforcement in strain distributions at bonded edge-section. Fracture behaviour analysis at the macroscopic and microscopic proved that with the rise in uniformly distributed s-MWCNTs, bridging (or interlocking mechanism) occurs, which hindered the bond failure. Further, above the optimized value of s-MWCNTs reinforcement, i.e. 1.25 wt. % of s-MWCNTs in AA; an agglomeration of s-MWCNTs took place, reducing the bond performance.

Crystalline and amorphous PEO based ceramic coatings on AA6061: Nanoindentation and corrosion studies

Present study reports the detailed nanomechanical and corrosion behaviours of crystalline and amorphous plasma electrolytic oxidation (PEO) coatings developed on Aluminium alloy-6061. The concentration of sodium silicate in the electrolyte is tailored to achieve crystalline and amorphous natures of the PEO coatings. X-ray diffraction (XRD), scanning electron microscopy (SEM) and nanoprofilometry techniques are utilized to investigate microstructural and morphological properties of the PEO coatings. XRD studies confirmed that crystalline ceramic phases are obtained at lower silicate concentration while amorphous nature occurred for comparatively higher concentration of silicate in the electrolyte. Nanoindentation technique is utilized to study the mechanical properties such as hardness (H) and Young's modulus (E) of the PEO coatings. The scatter of the data is treated with well-established Weibull statistical method. Finally, in depth corrosion behaviour of the coatings are investigated by electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization techniques. Amorphous coatings exhibited superior mechanical properties compared to the crystalline coatings. This is possibly linked with the presence of aluminosilicate phases and difference in silicon content in the coatings. However, as expected crystalline PEO coatings offer better corrosion resistance than the amorphous coatings and this behaviour is explained in terms of porosity contents of the coatings.

Effects of size and shape on the crushing strength of coral sand particles under diametral compression test

As a brittle material, coral sand particles are characterized by their irregular shape, complex internal structure, and high strength variability. This study used the Weibull statistical method to analyze the crushing strength of single coral sand particle. In this study, the diametral compression test was conducted on 200 coral sand particles that were divided into two groups according to their equancy (E = I/L*S/I, where L, I, and S represent particles’ long axis, intermediate axis, and short axis, respectively.) Based on the resulting force-displacement curves, four types of particle breakage are summarized. Based on the resulting survival probability curves, an inverse correlation between size and strength of coral sand particles is pointed out. Moreover, those particles’ circularity values (C, a parameter to describe the form and roughness of the particle) were obtained through image processing and analysis. Based on the analysis of the circularity-strength relationship of those particles, with the help of the Weibull statistical method, a positive correlation between circularity and strength of coral sand particles is found. Finally, this paper introduces parameter equancy to analyze the relationship between equancy and strength of the concerned particles, and by applying the Weibull statistical method, a positive correlation between equancy and strength of those particles is found.

Electrical Insulation Characteristics of LN2/CF4 Mixture at Cryogenic Temperatures

High-temperature superconducting (HTS) power equipment and tests at present require operating temperatures higher than the liquid nitrogen (LN2). LN2 is an important cryogenic refrigerant and liquid insulation material, which is widely used in HTS equipment. Although pressurized LN2 can achieve temperatures higher than 77 K, it requires the use of sealed pressure vessels. Thus, a liquid cryogen that can offer temperatures higher than LN2 at atmospheric pressure, excellent electrical insulation performance, and high thermal conductivity has to be explored. Tetrafluoromethane (CF4) is another cryogenic refrigerant and electrical insulation material. The mixture of LN2 and liquid CF4 has excellent thermal properties. When mixed in appropriate proportions, it has a melting point of 50 K and a boiling point of 145 K. The LN2/CF4 mixture is used in the insulating layer of the superconducting energy pipeline to provide a low-temperature environment (85–100 K) for the HTS dc cable. However, the insulation characteristics of the LN2/CF4 mixture at cryogenic temperatures have not been studied, quantitatively. In this article, a test platform is developed to measure the breakdown voltage of the liquid mixture. The dc breakdown voltages of LN2/CF4 liquid mixture under varying mixing proportions are obtained at cryogenic temperature. The insulation failure probability is estimated using a two-parameter Weibull statistical method. The results reveal that the breakdown strength of the LN2/CF4 mixture is lower than that of pure LN2. As the proportion of CF4 increases, the breakdown field strength of liquid mixture first decreases and then increases. When the mole fraction of CF4 is 60%, the average breakdown strength decreases to the lowest value (14.07 kV/mm), about half of that of pure LN2 (28.26 kV/mm). The results of this article can provide a reference for the applications of LN2/CF4 liquid mixture in HTS power equipment and a scheme to expand the working temperature range of superconducting applications.

Mechanical and microstructural properties of ultra-translucent dental zirconia ceramic stabilized with 5 mol% yttria

Monolithic dental prostheses fabricated from 3 mol.% yttria-stabilized zirconia (3YZ) are becoming increasingly popular. Recently, 5 mol.% yttria-stabilized zirconia (5YZ) which significantly improves the translucency of 3YZ has been prepared. However, its mechanical and microstructural properties, especially those affected by low-temperature degradation (LTD), have not been fully elucidated yet. The objective of the present study was to establish the relationship between the flexural strength of 5YZ with or without autoclave-induced LTD and its microstructural properties. For this purpose, a total of 320 bar-shaped specimens were cut from 5YZ and 3YZ blocks, and half of the specimens in each group were autoclaved at 134 °C for 50 h. Their flexural strengths were determined by conducting three-point bending tests, and the obtained results were analyzed by the Weibull statistical method. Grain sizes and crystalline structures of the specimens were analyzed by scanning electron microscopy (SEM) and X-ray diffraction, respectively. Additionally, the LTD-induced phase transformation was examined by Raman microscopy and cross-sectional surface analysis. The characteristic strengths of 5YZ and 3YZ were approximately 620 and 950 MPa, respectively, and 5YZ was found to be more resistant to LTD in terms of phase transformation than 3YZ. However, a low amount of the monoclinic phase was detected even in 5YZ after 50 h of autoclaving, which significantly decreased its flexural strength and reliability. The results of SEM analysis revealed that 5YZ was composed of two distinct regions: a dominant matrix with large grains (median size: 0.8 μm) and scattered areas with small grains (median size: 0.4 μm). Phase transformation analysis and fractography data indicated that the small-grain region was strongly affected by LTD and likely represented a fracture origin. The described properties should be considered during the clinical application of monolithic 5YZ dental prostheses.

Blind Image Quality Assessment of Natural Scenes Based on Entropy Differences in the DCT Domain.

Blind/no-reference image quality assessment is performed to accurately evaluate the perceptual quality of a distorted image without prior information from a reference image. In this paper, an effective blind image quality assessment approach based on entropy differences in the discrete cosine transform domain for natural images is proposed. Information entropy is an effective measure of the amount of information in an image. We find the discrete cosine transform coefficient distribution of distorted natural images shows a pulse-shape phenomenon, which directly affects the differences of entropy. Then, a Weibull model is used to fit the distributions of natural and distorted images. This is because the Weibull model sufficiently approximates the pulse-shape phenomenon as well as the sharp-peak and heavy-tail phenomena of natural scene statistics rules. Four features that are related to entropy differences and human visual system are extracted from the Weibull model for three scaling images. Image quality is assessed by the support vector regression method based on the extracted features. This blind Weibull statistics algorithm is thoroughly evaluated using three widely used databases: LIVE, TID2008, and CSIQ. The experimental results show that the performance of the proposed blind Weibull statistics method is highly consistent with that of human visual perception and greater than that of the state-of-the-art blind and full-reference image quality assessment methods in most cases.

Techno-economic Analysis of Wind Turbines in Algeria

AbstractIn this study, the wind energy potential and the unit energy cost related to six wind turbines in the city of Illizi in Southeast of Algeria are investigated. The hourly measured data (wind, pressure and temperature) observed during the period 2005–2014 at meteorological station in Illizi were used. An analysis of the collected data using the Weibull statistical method was made. The preliminary results were used to evaluate the power density in this region. Moreover, technical data of six chosen wind turbine models were analyzed to select the best appropriate turbine according to the techno economic analysis. The annual energy output of the selected wind turbines was calculated and the energy cost for each model was evaluated using two different methods. Input parameters affecting the cost, return on investment and payback period are also studied. For the 1MW wind turbine which, according to the economic analysis, is found to be the most suitable for this region, the cost of energy per kWh varies between 0.0388$ and 0.0634$ with PVC method and in range of 0.0878$ to 0.1142$ with LCOE method.

Effect of Double Oxide Film Defects on Mechanical Properties of As-Cast C95800 Alloy

The morphology of double oxide film defects and their influence on the tensile mechanical properties of a commercial Cu–Al (C95800) alloy were investigated in this study. Plane castings were produced with two types of pouring systems, and their tensile properties were measured and then analyzed by means of Weibull statistics method. The fracture surfaces of the tensile specimens were examined using scanning electron microscopy equipped with energy-dispersive spectroscopy. A large amount of double oxide film defects were observed on the tensile fractured specimens of the top-filled plane castings, and their chemical composition is identified to be Al2O3. Weibull statistics analyses showed that the double oxide film defects significantly reduce mechanical properties of the castings investigated. Furthermore, the ultimate tensile strength is more obviously deteriorated by double oxide film defects than elongation.

Failure analysis of transformer liquid — solid insulation system under selective environmental conditions using Weibull statistics method

Abstract The failure free operation of transformers is a main factor on economic and safety aspects as per the industrial consumer's point of view. Basically, the transformer is one of the prime equipment in power system network because of its unkind operating condition at different circumstances like higher operating temperature, overloading and continuous operation under uneven outdoor environmental conditions. Above said operating conditions lead to unpredicted failure in the transformer and this directly has an effect on reliability of the power system network. This work aims to investigate the failure rate of transformer liquid insulation (LI)–solid insulation (SI) system at various selective environmental conditions, by considering relative humidity of the air as a frequently variable environmental factor. For investigation, mineral oil (MO) and natural ester like sunflower oil (SFO) and rapeseed oil (RSO) are chosen as the LI system and Kraft paper is chosen as the SI system. The humidified samples are aged at 140 °C up to 1000 h at closed condition. Critical parameters of both LI and SI are periodically measured at an interval of 200 h. Weibull distribution statistics method is used to predict the failure rate of the insulation system with respect to time and relative humidity of the air. From the analysis, it is inferred that the degradation rate of the transformer LI–SI increases with an increase in relative humidity of the air. It is also noted that the LI-MO degrades rapidly when compared with other natural esters.

Structural integrity assessment of glass components in Concentrated Solar Power (CSP) systems

Due to the importance of glass components in Concentrated Solar Power (CSP) systems, an integrated assessment procedure conceived to facilitate the design of an intrinsically brittle component, limiting the amount of calculations, is presented. Since the fracture strength of brittle materials depends on the size and distribution of flaws as well as the duration of loading, conventional design approaches are generally very conservative and large safety factors are often used. However, these large safety factors are somewhat arbitrary and not satisfactory, because it is not very clear what the true factor of safety really is. In this paper, it is firstly reviewed and discussed the advanced methods to characterise the strength of glass. Then, based on the Weibull statistical method and the resulting probabilistic theory of the weakest link, a new modelling framework is proposed to consider different possible failure mechanisms (over-loading fracture and stress corrosion induced failure). In this way, the size effect as well as the multi-axial stress effect (including the contact stress between the glass component and the mount assembly) are considered. The integrated assessment procedure for structural glass elements is developed and implemented as a post-process of finite element analysis. The proposed procedure is demonstrated trough an application example: the design of a glass window to be used in a solar furnace reaction chamber.

Corrosion and nanoindentation studies of MAO coatings

Ceramic coatings have been developed on AZ31B Mg alloys by micro arc oxidation (MAO) technique, using a mixture of sodium phosphate and sodium fluoride electrolytes. Further, MAO coatings were sealed by the conventional hot water immersion technique. The coatings were characterised by X-ray diffraction, potentiodynamic polarisation, mechanical as well as optical profilometry and nanoindentation techniques. The results showed that the surface roughness and related parameters were always higher after the corrosion test in comparison to as developed MAO coatings, the corrosion resistance of the sealed MAO coatings were enhanced in comparison to unsealed coatings and the MAO coatings had nanohardness ∼10 times and Young’s modulus about two times as high as those of the AZ31B Mg alloys. Further, the characteristic scatter in the data was treated by the application of Weibull statistical method. These results are discussed in terms changes in microstructure of the MAO coatings, especially after sealing.

Elasto-plastic characteristics and mechanical properties of as-sprayed 8mol% yttria-stabilized zirconia coating under nano-scales measured by nanoindentation

Abstract The elasto-plastic characteristics and mechanical properties of as-received 8 mol% Y 2 O 3 –ZrO 2 (8YSZ) coatings were studied by nanoindentation at ultra-low loads with a Berkovich indenter at room temperature. All experimental data including hardness H and elastic modulus E were analyzed by the Weibull statistical method due to the porous and heterogeneous nature of the tested samples. It was found that the hardness firstly exhibits interesting reverse indentation size effect, and then shows normal indentation size effect within different indentation scales. The average elastic modulus of 8YSZ was estimated as 214.8 ± 13.2 GPa. In order to reveal the elasto-plastic characteristics of 8YSZ at nano-scales, the distribution of resolved shear stresses underneath the indenter tip region was evaluated by Hertzian contact theory when the deformation behavior of 8YSZ changed from fully elastic to elasto-plastic stages. The results shed light on understanding possible foreign object damage mechanisms of thermal barrier coating systems.

Effect of Annealing on Properties of Carbonaceous Materials. Part III: Macro and Microstrengths

Carbonaceous materials including cokes, chars, and pyrolyzed coals were annealed at temperatures ranging from 973 K to 1773 K (700 °C to 1500 °C) in an inert atmosphere. Macro and microstrengths of original and annealed carbonaceous materials were characterized by the tensile strength and fracture toughness. Fracture toughness was determined for inert maceral-derived component (IMDC) and reactive maceral-derived component (RMDC) using ultramicro indentation. Experimental data obtained by tensile tests were processed using the Weibull statistical method to find “inherent” strength. Tensile strength of chars and coals was significantly increased by annealing at temperatures ranging from 973 K to 1373 K (700 °C to 1100 °C); further increase in annealing temperature to 1773 K (1500 °C) increased their tensile strength only slightly. Tensile strength of cokes decreased with the increasing annealing temperature; the major effect was observed in the temperature range from 1573 K to 1773 K (1300 °C to 1500 °C). Fracture toughness of chars and coals was enhanced significantly by heat treatment at temperatures ranging from 973 K to 1373 K (700 °C to 1100 °C) as a result of pyrolysis, while that of cokes increased slightly by heat treatment. Fracture toughness of IMDC was higher than RMDC. Macrostrength of carbonaceous materials was strongly affected by their porosity and microstrength. The effect of pore geometry on macrostrength was marginal. Decreasing the porosity was more effective compared with increasing the microstrength in improving the macrostrength of carbonaceous materials.