scholarly journals Tensile Properties, Fracture Mechanics Properties and Toughening Mechanisms of Epoxy Systems Modified with Soft Block Copolymers, Rigid TiO2 Nanoparticles and Their Hybrids

2018 ◽  
Vol 2 (4) ◽  
pp. 72 ◽  
Author(s):  
Ankur Bajpai ◽  
Arun Alapati ◽  
Andreas Klingler ◽  
Bernd Wetzel
Keyword(s):  
Fracture Toughness ◽  
Tensile Strength ◽  
Block Copolymers ◽  
Fracture Mechanics ◽  
Fracture Energy ◽  
Tio2 Nanoparticles ◽  
Plastic Zone Size ◽  
Hybrid Nanocomposites ◽  
Tensile Fracture ◽  
Toughening Mechanisms

The effect of the hybridization of a triblock copolymer and a rigid TiO2 nanofiller on the tensile, fracture mechanics and thermo-mechanical properties of bisphenol F based epoxy resin were studied. The self-assembling block copolymer, constituted of a center block of poly (butyl acrylate) and two side blocks of poly (methyl) methacrylate-co-polar co-monomer was used as a soft filler, and TiO2 nanoparticles were employed as rigid modifiers. Toughening solely by block copolymers (BCP’s) led to the highest fracture toughness and fracture energy in the study, KIc = 2.18 MPa·m1/2 and GIc = 1.58 kJ/m2. This corresponds to a 4- and 16-fold improvement, respectively, over the neat reference epoxy system. However, a reduction of 15% of the tensile strength was observed. The hybrid nanocomposites, containing the same absolute amounts of modifiers, showed a maximum value of KIc = 1.72 MPa·m1/2 and GIc = 0.90 kJ/m2. Yet, only a minor reduction of 4% of the tensile strength was observed. The fracture toughness and fracture energy were co-related to the plastic zone size for all the modified systems. Finally, the analysis of the fracture surfaces revealed the toughening mechanisms of the nanocomposites.

scholarly journals Effect of Different Types of Block Copolymers on Morphology, Mechanical Properties, and Fracture Mechanisms of Bisphenol-F Based Epoxy System

2019 ◽  
Vol 3 (3) ◽  
pp. 68 ◽  
Author(s):  
Bajpai ◽  
Wetzel
Keyword(s):  
Mechanical Properties ◽  
Fracture Toughness ◽  
Tensile Strength ◽  
Block Copolymers ◽  
Fracture Energy ◽  
Plastic Zone Size ◽  
Fracture Mechanisms ◽  
Epoxy System ◽  
Bisphenol F ◽  
Different Types

The effect of adding different types of soft block copolymer on the tensile properties, fracture mechanic properties, and thermo-mechanical properties of bisphenol F based epoxy resin were studied. Two different self-assembling block copolymers, (a) constituting of a center block of poly (butyl acrylate) and two side blocks of poly (methyl) methacrylate-co-polar co-monomer (BCP 1) and (b) poly(ethylene oxide)-b-poly(butylene oxide) (PEO-PBO) diblock copolymer (BCP 2), were used with an epoxy-hardener system. The maximum fracture toughness and fracture energy were measured as KIc = 2.75 MPa·m1/2 and GIc = 2.37 kJ/m2 for the 10 wt % of BCP 1 modified system, which were 366% and 2270% higher in comparison to reference epoxy system, and a 63% reduction in tensile strength was also observed. Similarly, for BCP2 modified systems, the maximum value of KIc = 1.65 MPa·m1/2 and GIc = 1.10 kJ/m2 was obtained for epoxy modified with 12 wt % of BCP2 and a reduction of 32% in tensile strength. The fracture toughness and fracture energy were co-related to the plastic zone size for all the modified systems. Finally, the analysis of the fracture surfaces revealed the toughening micro-mechanisms of the nanocomposites.

scholarly journals An experimental method to determine the intralaminar fracture toughness of high-strength carbon-fibre reinforced composite aerostructures

2018 ◽  
Vol 122 (1255) ◽  
pp. 1352-1370 ◽  
Author(s):  
H. Liu ◽  
B.G. Falzon ◽  
G. Catalanotti ◽  
W. Tan
Keyword(s):  
Fracture Toughness ◽  
Tensile Strength ◽  
Crack Tip ◽  
Damage Mechanism ◽  
Calibration Method ◽  
Compact Tension ◽  
Tensile Fracture ◽  
High Tensile Strength ◽  
Physical Test ◽  
Area Method

ABSTRACTCarbon fibres with high tensile strength are being increasingly utilised in the manufacture of advanced composite aerostructures. A Modified Compact Tension (MCT) specimen is often deployed to measure the longitudinal intralaminar fracture toughness but a high tensile strength often leads to premature damage away from the crack tip. We present an approach whereby the MCT specimen is supported by external fixtures to prevent premature damage. In addition, we have developed a novel measurement technique, based on the fibre failure strain and C-scanning, to determine the crack length in the presence of surface sublaminate delamination which masks the crack tip location. A set of cross-ply specimens, with a ((90/0)s)4 layup, were manufactured from an IMS60/epoxy composite system Two different data reduction schemes, compliance calibration and the area method, are used to determine the fibre-dominated initiation and propagation intralaminar fracture toughness values. Propagation values of fracture toughness were measured at 774.9 ± 5.2% kJ/m2 and 768.5 ± 4.1% kJ/m2, when using the compliance calibration method and the area method, respectively. Scanning Electron Microscopy (SEM) is carried out on the fracture surface to obtain insight into the damage mechanism of high-tensile-strength fibre-reinforced unidirectional composites. The measured tensile fracture toughness value is used in a fully validated computational model to simulate the physical test.

scholarly journals Measurement of fracture energy of concrete at high strain rates

2018 ◽  
Vol 183 ◽  
pp. 02065
Author(s):  
V. Rey-de-Pedraza ◽  
F. Gálvez ◽  
D. Cendón Franco
Keyword(s):  
Tensile Strength ◽  
Fracture Energy ◽  
Dynamic Fracture ◽  
Dynamic Properties ◽  
Hopkinson Bar ◽  
Experimental Information ◽  
Tensile Fracture ◽  
Strain Rates ◽  
Dynamic Tensile Strength ◽  
Conventional Concrete

The Hopkinson Bar has been widely used by many researchers for the analysis of dynamic properties of different brittle materials and, due to its great interest, for the study of concrete. In concrete structures subjected to high velocity impacts, initial compression pulses travel through the material leading to tensile stresses when they reach a free surface. These tensile efforts are the main cause of concrete fracture due to its low tensile strength compared to the compressive one. This is the reason why dynamic tests in concrete are becoming of great interest and are mostly focused in obtaining tensile fracture properties. Apart form the dynamic tensile strength, which has been widely studied by many authors in the last decades, the dynamic fracture energy presents an increased difficulty and so not too much experimental information can be found in literature. Moreover, up to date there is not a clear methodology proposed in order to obtain this parameter in an accurate way. In this work a new methodology for measuring the dynamic fracture energy is proposed by using the Hopkinson Bar technique. Initial tests for a conventional concrete have been carried out and the results for the dynamic fracture energy of concrete at different strain rates are presented.

Effect of Stepped Aging Treatment on Microstructure and Properties of AA7085 Aluminum Alloy

2011 ◽  
Vol 228-229 ◽  
pp. 968-974 ◽  
Author(s):  
Chun Mei Li ◽  
Zhi Qian Chen ◽  
Su Min Zeng ◽  
Nan Pu Cheng ◽  
Quan Li ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Mechanical Properties ◽  
Heat Treatment ◽  
Electrical Conductivity ◽  
Fracture Toughness ◽  
Tensile Strength ◽  
Aging Treatment ◽  
Tensile Fracture ◽  
X Ray ◽  
Thermodynamic Factors

The effect of stepped aging treatment including two-stepped retrogression aging and retrogression reaging treatment on the mechanical properties, electrical conductivity and the microstructure of AA7085 has been investigated. Electron microscopy observations were used to analyze the microstructures and tensile fracture surfaces of AA7085 processed via various treatment schedules. Besides, X-ray diffractometer and differential scanning calorimeter were used to explore the thermodynamic factors of heat treatment. Through the investigation of the effect of the retrogression time on the properties and microstructure of AA7085, the optimized retrogression time was confirmed. The results of comparing retrogression aging and retrogression reaging treatment showed that through RRA treatment, higher conductivity and fracture toughness were gained. Through the optimized RRA treatment based on appropriate retrogression time, the tensile strength, elongation, fracture toughness and conductivity of AA7085 were raised to 660MPa, 12%,36.6MPa•m1/2and 38.1%IACS.

Experimental Research on Size Effect of Mode II Fracture Toughness of Concrete

2013 ◽  
Vol 438-439 ◽  
pp. 229-234
Author(s):  
Shao Wei Hu ◽  
Liang Hu
Keyword(s):  
Fracture Toughness ◽  
Fracture Mechanics ◽  
Size Effect ◽  
Fracture Energy ◽  
Experimental Research ◽  
Shear Fracture ◽  
Concrete Strength ◽  
Displacement Curve ◽  
Fracture Parameters ◽  
Mode Ii Fracture Toughness

Based on specimen size, which is the main reason of the shear fracture toughness of concrete, experimental research was carried out by 5 groups including 40 symmetrically loading specimens with different length and height. Through load and crack tip sliding displacement curve P-CTSD, load and strain curve P-ε and load and time curve P-t, the effects of length and height of specimens to shear fracture toughness were studied. Specimen stability is strengthened with increasing of length and weakened with increasing of height. Size effect of fracture toughness is weakened with increasing of length, is strengthened with the increasing of height. Fracture toughness increases with the increasing of length, decreases with the increasing of height. Research Background The size effect exists in parameters of concrete, such as concrete strength, modulus of elasticity, fracture toughness, fracture energy and so on [1-. In 1961, the theory of fracture mechanics was applied to concrete structure for the first time by Kaplan [. A vast majority of research work about concrete fracture mechanics was carried out by international scholars [6-. As the development of fracture theory of concrete, the size effect of fracture parameters became the focal point in theory study. Karihaloo [ pointed out that the size effect of concrete strength strengthens with the increasing of components size, however, the size effect weakens when crack length decreased relative to the size of specimens. Hu [3, 10, 11] accounted for the size effect by applying the theory of boundary effect and carried out the concept of local fracture energy which changes with width of fracture process zone. Based on the fictitious crack model, an analytical method [12, 13] for predicting the effective fracture toughness of concrete of three-point bending notched beams is proposed and the effects of initial seam height ratio and height on fracture parameters were carried out by Wu and Xu. At present, research on shear fracture toughness of concrete is immature and there are almost no papers about the size effect of shear fracture toughness of concrete. Aiming at the issue, this paper conducts a study on the size effect of shear fracture toughness of concrete by using symmetrically single-edge notched specimen.

Effect of tensile strength of rock on tensile fracture toughness using experimental test and PFC2D simulation

2016 ◽  
Vol 52 (4) ◽  
pp. 647-661 ◽  
Author(s):  
H. Haeri ◽  
V. Sarfarazi ◽  
A. Hedayat ◽  
A. Tabaroei
Keyword(s):  
Fracture Toughness ◽  
Tensile Strength ◽  
Experimental Test ◽  
Tensile Fracture

Nanoindentation Assessed Fracture Toughness of Cement Paste

2016 ◽  
Vol 368 ◽  
pp. 186-189 ◽  
Author(s):  
Jiří Němeček ◽  
Vladimír Hrbek
Keyword(s):  
Fracture Toughness ◽  
Fracture Mechanics ◽  
Fracture Energy ◽  
Cement Paste ◽  
Quantitative Data ◽  
Brittle Materials ◽  
Fracture Properties ◽  
Micro Scale ◽  
Energetic Approach

This paper deals with fracture properties of microlevel components of hydrated cementpaste. Determination of fracture energy and fracture toughness for quasi-brittle materials hasbecome a challenge for many years on both macro- and micro-scales. Limited number of quantitative data can be found in the literature for the micro-scale. This work uses energetic approach and decomposition of work of indentation into plastic and other parts. Based on simplified assumptions fracture energy and fracture toughness are calculated for individual microstructural phases of cement paste with the aid of nanoindentation, statistical deconvolution and fracture mechanics.

Evaluation of the Strain-Softening Law of Concrete from the Fracture Test

2012 ◽  
Vol 535-537 ◽  
pp. 1868-1876
Author(s):  
Wai Ching Tang ◽  
Hong Zhi Cui
Keyword(s):  
Experimental Data ◽  
Tensile Strength ◽  
Fracture Energy ◽  
Modulus Of Elasticity ◽  
Strain Softening ◽  
Peak Load ◽  
Strain Curve ◽  
Tensile Fracture ◽  
Stress Strain ◽  
Ordinary Concrete

This paper proposes a method for evaluating the linear stress-strain curve and bilinear stress-COD curve, suggested by Petersson, which can describe the tensile fracture behaviour of ordinary concrete satisfactorily. The two curves can be evaluated once modulus of elasticity (E), tensile strength (ft) and fracture energy (GF) are determined. It is proposed that the same fracture energy test suggested in the RILEM Recommendation be used to evaluate E, ftand GF. Firstly, the fracture energy was as usual evaluated from the area under the load-deflection curve. Secondly, the modulus of elasticity was calculated from the initial compliance in the same curve. Finally, the tensile strength was derived from the peak load. The proposed method was verified using some experimental data available in literature. The calculated values of the modulus of elasticity and the tensile strength were in good agreement with the corresponding experimental data. The method seems to provide a simple and practical way of evaluating the stress-strain and strain-softening curves of ordinary concrete, though further assessment is needed.

Comparison Investigation of Tensile Fracture Properties of Al Alloy at Different Dynamic Loadings

2013 ◽  
Vol 535-536 ◽  
pp. 156-159
Author(s):  
Fang Yun Lu ◽  
Xiao Feng Wang ◽  
Rong Chen ◽  
Xiang Yu Li ◽  
Duo Zhang ◽  
...  
Keyword(s):  
Fracture Toughness ◽  
Tensile Strength ◽  
Tensile Fracture ◽  
Uniaxial Tensile ◽  
Uniaxial Tensile Test ◽  
Al Alloy ◽  
Good Prediction ◽  
Fracture Properties ◽  
Uniaxial Tensile Strength ◽  
Split Hopkinson

Spall Strength, uniaxial tensile strength and fracture toughness, are three typical parameters describing the fracture properties of materials subjected to different loadings. Actually, these three macroscopically parameters are connected to the tensile fracture (Model I) properties, and many papers have been trying to find the intrinsic connection between each other. In this work, ZL205A aluminum is conducted by varies experiments: the spallation test loaded by a light gas gun, the dynamic uniaxial tensile test using the Split Hopkinson Tensile Bars (SHTB), and the dynamic fracture toughness obtained with a three point bending specimen loaded by Split Hopkinson Pressure Bars (SHPB). The three parameters are compared with the view of energy. The results show that the cavity expansion model is successfully used to set up a connection between spallation strength and dynamic uniaxial tensile strength of this material, while the energy release rate or the surface energy can give a good prediction of dynamic tensile strength and fracture toughness.

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