Dynamic Fracture Toughness Tests Research Articles

Dynamic Fracture Strength and Toughness of Continuous Alumina Fiber–Reinforced Glass Matrix Composites at Elevated Temperature

An instrumented drop-weight test rig was used in the investigation of the dynamic fracture strength and toughness tests of continuous alumina fiber reinforced glass matrix composites, which were carried out at room and elevated temperatures using charpy-type specimen configuration, and with fiber orientation perpendicular (0°) and parallel (90°) to impact load direction. Increasing test temperatures, the results show a dependency of dynamic flexural strength, toughness, and impact energy for unidirectional 0°and 90°fiber orientation Al2O3-borosilicate composite up to 950°C, whereas the Al2O3-96% silica composites showed little or no dependency on increasing test temperatures, before dropping off at temperatures higher than 750°C. This type of behavior for Al2O3-borosilicate composite could be due to the suppression of matrix microcracking as temperature increases due to increased plasticity of the matrix, resulting in increased dynamic flexural strength and toughness values. Scanning electron microscope (SEM) investigations of fractured surfaces show that there are two identifiable major damage modes: fibrous at room temperature, as in Al2O3-borosilicate composites, where weaker fiber-matrix interfacial bond exists, due to the difference in thermal mismatch at room temperature resulting in reduced fiber-matrix bond strength, matrix microcracking and apparent fiber debonding occurring during the dynamic flexure and toughness tests, resulting in longer fiber pullout; nonfibrous at high temperatures, as in Al2O3-96% silica composites, this occurs as temperature increases, the thermal mismatch between fiber-matrix decreases leading to an increase in fiber-matrix interfacial bonding and thus increasing tendency to embrittlement. This resulted in changing failure mechanisms from fibrous at room temperature to nonfibrous at higher temperatures. The important variables of this test were discussed and its usefulness in comparing dynamic flexural, toughness, and impact resistant ceramic matrix composite (CMC) materials are demonstrated.

Dynamic Fracture Toughness of Porous Ceramics

The paper presents experimental results of static (KIc) and dynamic (KId) fracture toughness testing. The tests were performed for two kinds of porous ceramics with various porosity fraction. The influence of porosity content, as well as loading rate on fracture toughness of alumina (Al2O3) and magnesia (MgO) as analyzed. It was found that an increase of initial porosity reduces values of both static and dynamic fracture characteristics. However, values of KId were much higher than KIc for both kinds of tested materials. In case of Al2O3, they were approximately three times higher, whereas in case of MgO—five to seven times higher depending on the porosity content.

Irradiation embrittlement characterization of the EUROFER 97 material

The paper summarizes original results of irradiation embrittlement study of EUROFER 97 material that has been proposed as one candidate of structural materials for future fusion energy systems and GEN IV. Test specimens were manufactured from base metal as well as from weld metal and tested in initial unirradiated condition and also after neutron irradiation. Irradiation embrittlement was characterized by testing of toughness properties at transition temperature region – static fracture toughness and dynamic fracture toughness properties, all in sub-size three-point bend specimens (27 × 4 × 3 mm 3). Testing and evaluation was performed in accordance with ASTM and ESIS standards, fracture toughness K JC and K Jd data were also evaluated with the “Master curve” approach. Moreover, J– R dependencies were determined and analyzed. The paper compares unirradiated and irradiated properties as well as changes in transition temperature shifts of these material parameters. Discussion about the correlation between static and dynamic properties is also given. Results from irradiation of EUROFER 97 show that this steel – base metal as well as weld metal – is suitable as a structural material for reactor pressure vessels of innovative nuclear systems – fusion energy systems and GEN IV. Transition temperature shifts after neutron irradiation by 2.5 dpa dose show a good agreement in the case of EUROFER 97 base material for both static and dynamic fracture toughness tests. From the results it can be concluded that there is a low sensitivity of weld metal to neutron irradiation embrittlement in comparison with EUROFER 97 base metal.

Loading Rate Effect on the Master Curve Reference Temperature, T, for the A533 B Material

Abstract The National Institute for Nuclear Research in Mexico participated in the international research project “Master Curve Approach to Monitor the Fracture Toughness of Reactor Pressure Vessel in Nuclear Power Plants” coordinated by the International Atomic Energy Agency (IAEA), where the loading rate effect on the Master Curve reference temperature, T0, was investigated. The experimental program consisted in quasi-static and dynamic fracture toughness testing of precracked Charpy specimens on the IAEA reference reactor pressure vessel steel Japanese reference quality (JRQ) (A533 Grade B Class 1), which was analyzed with the Master Curve methodology. The tests were carried out in displacement control at two temperatures, −70 and −60°C, and at three load rates, dK/dt=0.1, 1, and 10 MPa√m/s. The determined reference temperatures, T0 (0.1 MPa√m/s)=−73.6±6.4°C, T0 (1 MPa√m/s)=−63.3±5.4°C, and T0 (10 MPa√m/s)=−50.3±5°C, are similar to those obtained by other laboratories [IAEA Second Meeting on Master Curve to Monitor the Fracture Toughness of RPVs in NPPs, November 2006, Dresden, Germany]. The shift in T0 within the quasi-static loading rate interval (0.1–2 MPa√m/s) recommended by ASTM E1921-05 [“Standard Test Method for Determination of Reference Temperature, T0, for Ferritic Steels in the Transistion Range,” Annual Book of ASTM Standards, Vol. 03.01, ASTM International, West Conshohocken, PA.] is 14.4°C and the shift in T0 between decades of dK/dt on logarithmic scale is 11°C. The empirical relation proposed by Wallin [“Effect of Strain Rate on the Fracture Toughness Reference Temperature T0 for Ferritic Steels,” Recent Advances in Fracture, R. K. Mahidhara et al., Eds., The Minerals, Metals and Materials Society, 1997, pp. 171–182] predicts very well the shift in T0 in the quasi-static loading regime (0.1–2 MPa√m/s). This work provides experimental support to limit the quasi-static loading rate interval in ASTM E1921.

Hydrothermal ageing of radiation cured epoxy resin-polyether sulfone blends as matrices for structural composites

The hydrothermal ageing of epoxy–thermoplastic blends, used as matrices for carbon fibre composites, cured by electron beam, has been studied. Two different thermoplastic percentages have been adopted. A suitable choice of both curing process and formulation parameters allows to carry out irradiation at mild temperature with several advantages, coming from a “non thermal” process, for both the final properties of the materials and the environment. Nevertheless the occurring of vitrification phenomena needs the use of a short thermal treatment after irradiation on the already solid materials, in order to complete the cure reactions. Radiation cured epoxy based matrices have been subjected to a thermal and moisture absorption ageing treatment and its influence on the thermal and mechanical properties has been investigated through dynamic mechanical thermal analysis and fracture toughness tests. The results have been interpreted on the basis of the different curing degree reached by the investigated systems and in the light of their morphological structures. Plasticization, thermal curing and degradation reactions occur in different extent depending on the kind of the material. In particular, for fracture properties, a better resistance to ageing is shown by the system at higher thermoplastic concentration.

Large scale testing and statistical analysis of dynamic fracture toughness of ductile cast iron

The present paper deals with the experimental determination and statistical analysis of dynamic fracture toughness values of ductile cast iron. K Id data from 140 mm thick single edge bend specimens of two dynamic fracture toughness test series on ductile cast iron from heavy-walled castings were analysed. At first, the statistical analysis of data at −40 °C was done based on ASME Code Case N-670 using a two-parameter Weibull distribution function. Weibull analyses of three samples covering different pearlite contents (⩽4%, ⩽9%, ⩽20%) were performed and characteristics of the distribution functions as well as two-sided confidence intervals were calculated. The calculated characteristics show that K Id of ductile cast iron decreases with increasing pearlite content. In a second step, the applicability of the Master curve procedure according to ASTM E 1921 to ductile cast iron materials was investigated and it was formally used for statistical analysis of ductile cast iron dynamic fracture toughness data. Although the Master curve method was originally introduced for static fracture toughness data of ferritic steels, the successful individual analyses performed here support the engineering way taken to apply the method to ductile cast iron materials too. The results of both methods, the Master curve procedure and the ASME Code Case N-670, show acceptable congruity. At the same time, it is concluded from the present study that further investigations and experiments are required to improve precision and for verification before the results could be applied within component safety analyses.

Continuum Damage Modeling for Dynamic Fracture Toughness of Metal Matrix Composites

Short fiber reinforced metal-matrix composites (MMCs) have widely adopted as structural materials and many experimental researches have been performed to study fracture toughness of it. Fracture toughness is often referred as the plane strain(maximum constraint) fracture toughness KIc determined by the well-established standard test method, such as ASTM E399. But the application for dynamic fracture toughness KId has not been popular yet, because of reliance in capturing the crack propagating time. This paper deals with dynamic fracture toughness testing and simulation using finite element method to evaluate fracture behaviors of MMCs manufactured by squeeze casting process when material combination is varied with the type of reinforcement (appearance, size), volume fraction and combination of reinforcements, and the matrix alloy. The instrumented Charphy impact test was used for KId determination and continuum damage model embedded in commercial FE program is used to investigate the dynamic fracture toughness with the influence of elasto-visco-plastic constitutive relation of quasi-brittle fracture that is typical examples of ceramics and some fibre reinforced composites. With Compared results between experimental method and FE simulation, the determination process for KId is presented. FE simulation coupled with continuum damage model is emphasized single shot simulation can predict the dynamic fracture toughness, KId and real time evolution of that directly.

Applicability of Sub-Size Charpy Specimens to Transition Behaviour of RPV Materials

The advancement of proper methodology to determination of VVER reactor pressure vessel (RPV) materials transition behaviour has been followed. The project included selection of proper specimen geometries (standard 10x10x55 mm, sub-size 3x4x27 mm and 5x5x27.5 mm Charpy-V samples) and impact as well as dynamic fracture toughness testing. All the fundamental criterions have been applied to consider an applicability of small-sized specimens to Cr-Mo-V and Cr-Ni-Mo-V steel radiation embrittlement studies. Selected specimen geometries have been found to be fully valid for impact and dynamic fracture data and capable for prediction of standard specimen behaviour from the small specimens. Within testing of irradiated materials, it has been found not fully validity of all the compared transition temperatures.

Effect of Heat Treatment on Mechanical and Fracture Properties of Poly (lactic acid)/Poly (butylene succinate) Blends

Poly (lactic acid) /Poly (butylene succinate) (PLA/PBSU) polymer blends were fabricated to improve the fracture and biodegradable properties. Heat treatments were conducted on the specimens to improve the reduction in stiffness due to blending. The effects of heat treatment on the mechanical and fracture properties were discussed with the results of dynamic mechanical tests and fracture toughness tests, respectively. Storage modulus increased with increasing PLA contents. Heat treatments also improved the modulus because of the crystallization. The critical energy release rate, Jcr and the fracture energy, Jf, however, decreased with heat treatment. Excessive contents of PLA or PBSU significantly decreased Jcr and Jf.

2003 電子スペックルパターン干渉法を用いた破壊靭性値測定に関する研究(G03-1 測定・検出・評価技術(1),G03 材料力学)

In this study, a plastic zone at a crack tip vicinity of specimens was visualized with electronic speckle pattern interferometry (ESPI). And dynamic fracture toughness value of a specimen with a crack was easily obtained by measuring the visualized plastic zone dimension. It was found by previous our research to be able to obtain the dimension of plastic zone at crack tip vicinity in statically and to decide the fracture toughness value by using the dimension. In this report, ESPI was applied to the dynamic fracture toughness test, and the result was shown. Then preliminary experiments using a new visualization method with ESPI to observe the plastic zone have been employed and the result is also presented. Additionally, a new Measuring method of fracture toughness value is showed in this paper.

Application of the Normalization Method to Dynamic Fracture Toughness Testing of Alloy 718

Abstract The fracture toughness and tensile properties of Alloy 718 were measured at quasi-static and dynamic loading rates for two different heat treatments and two product forms. Two different methods for conducting the dynamic tests were investigated; one involving interrupted tests and the other utilizing a single impact. The interrupted test method used multiple impacts with displacement limits to enable measurement of crack lengths at intermediate points. The normalization method was used to generate tearing resistance curves for the dynamic tests following the guidelines in ASTM Standard Test Method for measurement of Fracture Toughness (E 1820). The analysis pointed out the importance of obtaining a good measurement of load, displacement, and crack length at the point of maximum displacement (the anchor point). As the amount of ductile crack extension increased, the uncertainty in the plasticity function fit also increased. Methods to improve the fit were investigated, including the addition of anchor points from multiple tests, and use of a tangency point to estimate initiation. The resulting curves are compared to ascertain the variability obtained from nominally identical specimens, and to evaluate the effect of loading rate on the plasticity function. The normalization tearing resistance curves are compared with curves generated from the interrupted tests using compliance measurements during unloads to determine crack extension. Good agreement was obtained between the two methods of measuring tearing resistance, thereby validating the normalization analysis. The tests showed that multiple impacts drive down the tearing resistance, which may be significant in applications where a dynamic event causes load fluctuation.

Dynamic Fracture Toughness Testing for Welding Part of Nuclear Piping Using Normalization Data Reduction Technique

In this study, we performed the static test of nuclear piping materials by the unloading compliance method and the normalization data reduction technique and obtained two fracture resistance curves (J-R curves). The two curves were similar, which proves that the normalization data reduction technique can be adopted in the static test. Then we performed the dynamic fracture toughness test for welding part of nuclear piping. The J-R curves were obtained from the dynamic test by the normalization data reduction technique and were compared to those of the static test results.

Determination of Dynamic Fracture Toughness Using Strain Measurement

By contrast with static fracture toughness determination, the methodology for dynamic fracture toughness characterization is not yet standardized and appropriate approaches must be devised. The accurate determination of the dynamic stress intensity factors must take into account inertial effects. Most methods for dynamic fracture toughness measurement are experimentally complex. However, dynamic fracture toughness determination using strain measurement is extremely attractive in terms of experimental simplicity. In this study, dynamic fracture toughness tests using strain measurement are performed. High rate tension and charpy impact tests are carried out for titanium alloy, maraging steel and Al alloys. In the case of evaluating the dynamic fracture toughness using high rate tension and charpy impact tests, load or energy methods are used commonly. The consideration about inertial effects is essential, because load or energy methods are influenced by inertia. In contrast, if the position for optimum response of strain is provided, dynamic fracture toughness evaluation using strain near crack tip is more accurate. To obtain the position for optimum response of strain, a number of gages were attached at angles of 60°. Reliability for experimental results is evaluated by Weibull analysis. The method presented in this paper is easy to implement in a laboratory and it provides accurate results compared to results from load or energy methods influenced by inertia.

Fabrication, characterization, and dynamic behavior of polyester/TiO 2 nanocomposites

Unsaturated polyester resin specimens embedded with small loadings of 36 nm average diameter TiO 2 particles were fabricated using a direct ultrasonification method to study the effects of nanosized particles on nanocomposite bulk mechanical properties. The ultrasonification method employed produced nanocomposites with excellent particle dispersion as verified by transmission electron microscopy (TEM). Quasi-static fracture toughness, tension, and compression testing was carried out. The presence of the particles had the greatest effect on fracture toughness; negligible influence was observed in the remaining quasi-static properties. Scanning electron microscopy (SEM) of fracture surfaces was carried out to identify toughening mechanisms. The inadequacy of the bond between the filler and the matrix and the presence of minor particle agglomerations in specimens containing higher volume fractions of particles were believed to be responsible for a consistent decrease in property values beyond a volume fraction of 1 vol.%. Dynamic fracture toughness testing was carried out, and an increase in dynamic fracture toughness relative to quasi-static fracture toughness was observed. High strain rate testing conducted using a split Hopkinson pressure bar (SHPB) apparatus revealed a moderate stiffening effect with increasing particle volume fraction, although no marked effect was observed on the ultimate strength.

Dynamic fracture toughness test and master curve method analysis of IAEA JRQ material

IAEA conducted a round-robin fracture test program to test and verify the Master Curve method. One of the materials selected for the round-robin is a A-533B1 plate designated as reference material JRQ. Unnotched Charpy-size specimens were fabricated and distributed to a number of testing laboratories. The three US Owners Groups received specimens for both Charpy impact and three-point bending tests to establish fracture toughness master curves. The B&W Owners Group elected to perform a dynamic fracture toughness test under a high loading rate using the JRQ specimens. The master curve method was successfully applied to numerous fracture toughness data sets of pressure vessel steels. Joyce [Small Specimens Test Technique, ASTM STP 1329, 1997, ASTM] applied this method to high loading rate fracture toughness data for A-515 steel and showed the applicability of this approach to dynamic fracture toughness data. This paper presents the data and the resulting reference temperature shift in the Master Curves from static to dynamic fracture data. Based on earlier PTS analyses performed in 1985, an appropriate T 0 shift value is selected for nuclear power plant applications. This shift in T 0 is compared with the temperature shift between K Ic and K Ia curves in ASME Boiler and Pressure Vessel Code.

５０８３アルミニウム合金Ｏ材の極低温から高温における動的破壊靭性

Effect of temperature on mechanical properties of an 5083 aluminum alloy has been investigated for various testing temperatures from 10 to 773 K. For that purpose, the static tensile, dynamic fracture toughness test and fractography are carried out, and stop block method is employed to characterize fracture behavior at cryogenic temperatures. Mechanical properties such as 0.2% proof stress and ultimate tensile strength increase with decreasing temperature. The high temperature embrittlement, which has been often reported for 5000 series alloys having high Mg content, was not observed in the present study. The dynamic fracture toughness value, Jd, and dynamic crack extension toughness, Tmat, at 20 K are approximately 57% and 74% lower than that at 150 K, respectively. Fracture toughness at cryogenic temperatures shows strong dependence on formation of delamination cracks. The delamination cracks are initiated at grain boundaries. According to a SEM-EDX analysis, Mg is detected adjacent to the delamination cracks. Therefore, it is concluded that the formation of delamination cracks are concerned with β(Al3Mg2) phase at the grain boundaries.

A method for dynamic fracture toughness determination using short beams

This paper deals with dynamic fracture toughness testing of small beam specimens. The need for testing such specimens is often dictated by the characteristic dimensions of the end product. We present a new methodology which combines experimentally determined loads and fracture time, together with a numerical model of the specimen. Calculations are kept to a minimum by virtue of the linearity of the problem. The evolution of the stress intensity factor (SIF) is obtained by convolving the applied load with the calculated specimen response to unit impulse force. The fracture toughness is defined as the value of the SIF at fracture time. The numerical model is first tested by comparing numerical and analytical solutions (Kishimoto et al., 1990) of the impact loaded beam. One point impact experiments were carried out on of commercial tungsten base heavy alloy specimens. The robustness of the method is demonstrated by comparing directly measured stress intensity factors with the results of the hybrid experimental-numerical calculation. The method is simple to implement, computationally inexpensive, and allows testing of large sample sizes, without restriction on the specimen geometry and type of loading.

Toughness and microstructural parameters in thermomechanically processed 2091 Al-Li alloy

The effect of microstructural features on the toughness of 2091 A1-Li alloys processed with various thermomechanical schemes was analyzed. Grain size and the distribution of precipitates were varied by thermomechanical processing. Dynamic fracture toughness tests were done to evaluate the toughness of these materials using a Computer Aided Instrumented testing system. The δ (A13Li) and S’ (Al2CuMg) precipitates, which are primary strengthening precipitates, were confirmed by TEM analysis in the under-aged 2091 Al-Li alloy. From analysis of the relation between toughness and the microstructural factors induced by thermomechanical processing, the toughening of the alloy was found to be associated with the refinement of the subgrains. The strength and toughness parametzrs were well related to subgrain size.

Relationship between fracture toughness and microstructure of Ti–6Al–2Sn–4Zr–2Mo alloy reinforced with TiB particles

Ti–6Al–2Sn–4Zr–2Mo alloy matrix composites reinforced with various volume fractions of TiB particles were fabricated using the blended elemental powder method in the present study. The static and dynamic fracture toughness tests were carried out on the composites at room temperature in order to understand the fracture mechanism. The dynamic fracture toughness value is fairly smaller than the static fracture toughness value. The ratio of dynamic fracture toughness value to static fracture toughness value increases with increasing the volume fraction of TiB particles. The fracture toughness value increases with increasing the degree of crack deflection which is greater under static conditions than under dynamic conditions. The fraction of TiB particles on the fracture surface is greater in the specimen with greater volume fraction of TiB particles, and is greater under dynamic conditions than under static conditions. Since the debonding of TiB particles from the matrix and shearing of TiB particles occurs easily, the fracture toughness value of composites decreases with increasing the volume fraction of TiB particles.

Toughness problems in advanced materials

Toughness is the most important characteristic of structural materials and is widely measured using the Charpy impact test, which was developed at the beginning of twentieth century by the Frenchman Charpy. The author has successfully developed a new dynamic fracture toughness testing and evaluation system using the instrumented Charpy impact test. The new system is called the 'CAI system'. This paper introduces the CAI system. Many advanced materials have been developed since 1980. Apart from cost performance, the most important problem with new materials is in their low fracture toughness. The toughness problems of various advanced structural materials such as ceramics, intermetallics, Al–Li–alloys, Ti alloys, metal matrix composites and austempered ductile iron (ADI) are reviewed based on the author's research.