Impact Bending Tests Research Articles

Features of the fracture of specimens of low-carbon steels under impact and static loading conditions

1. Use of the relative length of a stable cracklc/b, where b is specimen width, is proposed for evaluation of the fracture resistance of a steel and determination of the critical defect size. 2. 09G2S steel has higher impact strength and crack resistance and a lower ductile-to-brittle transition temperature but a greater anisotropy of properties than 20 steel. 3. In fractures of specimens of 20 and 09G2S steels at temperatures of the ductile-to-brittle transition in impact bend and static tensile tests zones of drawing out (Θ1) and of shear (Θ2) and separation (Θ3) fracture were observed. Their total is the zone of stable crack growth (lc). The ductile-to-brittle transition temperature of 20 steel determined from the fibrous constituent in the fracture (F=50%) is practically independent of notch sharpness of the specimens used.

Correlation between fracture toughness and fatigue crack growth thresholds in RIM polyamide block copolymers filled with milled glass fibres

The fracture and fatigue behaviours of reaction injection moulded (RIM) polyamide block copolymers (NBC) without and with milled glass fibres (GF) were studied using the fracture mechanics concept at ambient temperature. The static fracture toughness determined according to the ASTM E 399 standard ( K Q) aand its maximum value computed from the maximum load ( K Q,max) decreased with increasing polyol (soft segment) content and proved to be unaffected by GF filling. Increasing the deformation rate, including high-speed impact bending tests, resulted in higher fracture toughness ( K d) values, closely matched to K Q,max. The resistance to fatigue crack propagation (FCP) deteriorated with increasing soft segment and GF filler content. This was explained by differences in the molecular build-up and porosity of the NBC and related composites caused by moulding. The lower and upper bounds of the stable FCP range were found at K Q and K Q,max, respectively.

Determination of ?true? specific characteristics of fracture toughness of specimens in dynamic and static tests

A method is proposed for determining “true’ specific fracture toughness characteristics of solids in dynamic and static tests in which the fracture toughness characteristics are calculated using a new parameter, i.e., the true (real) area of the fracture surface instead of the extensively used section of fracture resistance. Using as an example the results of impact bend tests on steel 45 specimens in two conditions, it is shown that the determination of the true values of KCU makes it possible to reduce greatly their scatter and obtain information expressing more accurately the structure and the properties of the material.

Dynamic fracture mechanics of a RIM polyamide block copolymer reinforced with glass strand mat

The fracture behavior of a reaction injection molded (RIM) polyamide block copolymer reinforced with randomly arranged continuous glass fiber bundles (glass mats) was studied under dynamic loading conditions at T=RT and T=-40 °C. Dynamic fracture toughness, Kd, and fracture energy, Gd, values were derived from instrumented high-speed impact bending tests carried out on Charpy and Izod specimens of different size and notching direction, respectively. It was established that fracture mechanics data depend on the ligament width of the specimens. It was shown how the “inherent” flaws caused by machining and molding can be determined. Failure mode of the composites was characterized by fractography and possible failure events were summarized. Recommendations were given for further material improvements.

Relationships Between the Results of Nail Impact Bend Tests and Selected Nail Material Properties

Abstract Selection criteria for nails vary significantly. Some fastener specifications contain criteria based on hardness tests; others are based on yield strength or the results of impact bend tests (MIBANT). Selection may also be based on the carbon content or SAE class of the nail wire. To assist the specifier in the nail selection process, the relationship was studied between the MIBANT angle, an apparent flexural yield strength, the hardness, and the carbon content of nails. Carbon content was found to have a small influence on the mechanical properties of non-hardened nails. Because of apparent variations in work hardening during wire drawing and nail manufacture, carbon content is not a reliable criterion for the selection of non-hardened steel nails. Conversely, carbon content significantly influences the properties of hardened steel nails when the steel carbon content is greater than 0.10%. MIBANT angle, Vickers hardness number, and flexural yield strength are highly correlated for lowcarbon steel nails. Empirical relationships between these properties are presented. MIBANT angle was found to be a better indicator of the flexural yield strength of nails than Vickers hardness number.

Impact bending fatigue and impact response behavior of a nuclear-grade graphite beam

Repeated impact bending tests have been carried out on a fine-grained Isotropic graphite for HTTR under constant energy condition. Each specimen whose length differed was centrally impacted by an instrumented pendulum. The simple one-dimensional model taking the Hertzian contact stiffnesss into consideration has been applied to evaluate the relationship between the maximum stress of specimen generated by impact, the impact force, and the impact energy. It has been confirmed that the endurance curves in terms of impact energy are dependent on the length of the specimen, but the one in terms of the evaluated maximum stress is independent of that, and the strength of graphite is lower in impact fatigue than in nonimpact fatigue.

新しい衝撃曲げ試験法による動的破壊じん性の評価

A novel impact bend test procedure is described for determining the dynamic fracture-initiation toughness, KId, at a loading rate KI of the order of 106MPa√m/s. The split Hopkinson pressure bar technique was used to measure dynamic loads applied to a fatigue-precracked bend specimen. The dynamic stress intensity factor history for the bend specimen was evaluated by means of a dynamic finite element code. The onset of crack initiation was detected using a strain gage near a crack tip. The KId value was determined from the critical dynamic stress intensity factor at crack initiation. A series of dynamic fracture tests were performed for a Ti-6246 alloy and a 7075-T6 aluminum alloy. The KId values obtained for both the alloys were compared with the corresponding values obtained under quasi-static loading conditions. The fracture surface morphology was examined with the help of a scanning electron microscope to rationalize the apparent differences in the measured fracture-initiation toughness in response to the change in loading rate. Furthermore, the validity of the KId determination was confirmed by measurements of the crack tip plastic zone size in the interior of the fracture specimens based on the microhardness tests.

A simplified method of determining the time dependence of the stress intensity factor in support-free impact bend testing of beam specimens

A simplified method of determining the time dependence of the stress intensity factor in support-free impact bend testing of beam specimens

Special features of fracture of full-profile railroad rails in impact bend testing

1. The work of crack initiation can be determined in the impact tests on the full-profile rail specimens. 2. The energy of fracture of the full-profile rail specimens is greatly scattered as a result of the presence of various external and internal stress raisers formed in the course of testing. 3. We proposed a mechanism of fracture of the-full-profile rail specimens in the impact tests which explain the reduction of the energy capactity of fracture as a result of splitting of part of the rail foot at the saart of the fracture process and the effect of the elastic wave reflected from the surface of the rail head.

A novel impact three-point bend test method for determining dynamic fracture-initiation toughness

A novel impact three-point bend test method has been developed for determining the dynamic fracture-initiation toughness,K Id, over the range of loading rates $$10^5 MPa\sqrt m /s \leqslant K_I \leqslant 10^5 MPa\sqrt m /s$$ . The split-Hopkinson pressure-bar technique is used to measure dynamic loads applied to a bend specimen with a fatigue precrack. The stress-intensity-factor histories for the bend specimen are evaluated by means of a dynamic finite-element technique and the standard formula (ASTM E 399-83) based on the measured dynamic loads. The time of crack initiation is determined using a strain gage mounted near a crack tip. The results for 7075-T6 aluminum alloy and Ti−6A1−2Sn−4Zr−6Mo alloy indicate that the reliableK Id data can only be obtained by evaluation procedures which take the inertial effects into account. It is shown that the novel impact bend test method in conjunction with dynamic finite-element analysis provides an effective means of characterizing the dynamic fracture-toughness parameterK Id.

A method of evaluating the crack resistance of steels from the results of standard tension and impact-bending tests

1. Single relationships linking the minimum level of static crack resistance KIc with the conditional yield point and reduced test temperature Ttest-Td50 are constructed on the basis of experimental results of the testing of steels of different strength and structural state. 2. The curves obtained make it possible to propose a simple method for calculating the minimum guaranteed level of static crack resistance KIc of structural steel on the basis of standard mechanical characteristics of strength (σ0.2) and cold resistance (Td50), which can be used in selecting and working steels and also in optimizing regimes for their smelting and heat treatment. 3. The proposed method, which is used to calculate temperature dependencies of the static crack resistance of steels cast from experimental melts, has made it possible to select the optimal composition of a cold-resistant cast steel for the undercarriage of heavyduty quarry excavators.

Nil-ductility transition temperature of ship plate and its connection with unit crack-propagation work

1. Niobium-bearing steels (15GB and 15G2FB) have the lowest values of NDTT, vandium-and nitrogen-bearing steels (15GAF and 15G2AF) have somewhat higher values, and vanadium-bearing steels (15GF) have the highest values. The NDTT of nickel-bearing quenched-and-tempered steel 10KhSND of category E40 is comparable to that of the normalized niobium-bearing steels. 2. Heat treatment can be regarded as one of the most effective methods of reducing the NDTT, although the opposite may occur — NDTT may be increased — depending on the steel. The change in sulfur content and the morphology of sulfide inclusions which occurs due to out-of-furnace treatment of steel with CS and LSS does not affect the NDTT. 3. The correlation established between the NDTT and the critical temperature Tc. t. f. makes it possible, with a confidence level of 95%, to determine the NDTT from the above-derived regression equation in impact-bending tests of specimens with an induced fatigue crack.

Nature of brittle fracture of structural steels and welded joints in impact bend testing

Nature of brittle fracture of structural steels and welded joints in impact bend testing

Impact bending fatigue behavior of an isotropic nuclear graphite for HTTR.

Repeated impact bending tests were carried out on isotropic nuclear graphites for HTTR. Each specimen whose length differed was centrally impacted by an instrumented pendulum. The simple one-dimensional model taking the Hertzian contact theory into consideration has been applied to evaluate the relationship between the maximum stress of the specimen generated by impact, the impact force and the impact energy. It has been confirmed that the endurance curves in terms of impact energy is dependent on the length of specimen but the one in terms of the evaluated maximum stress is independent of that, and the strength of graphite is lower in impact fatigue than in non-impact fatigue.

Influence of radiation damage mechanisms on the load signal and on the transition curve of instrumented impact testing

The irradiation behaviour of various pressure vessel steels was examined by means of instrumented notched bar impact bending tests. The steels were irradiated at different temperatures so that different defect mechanisms became effective. It was possible to identify the defect mechanisms influencing the different ranges of the impact load signal. Three fractions of the impact load signal were identified. The first fraction comprises the impact energy up to the ultimate load point. The next fraction is the impact energy from the ultimate load point to the inflection point of the impact load signal and the third fraction extends from the inflection point to the impact end. It was possible to correlate the influence of the elements copper and nickel with these fractions and with the effect of two defect mechanisms. This was the starting point for a physically substantiated mathematical description of the impact energy as a function of the test temperature.

Strength of an ?-alloy of titanium taking into consideration its hydrogen impregnation

Results are presented of an investigation of the influence of the conditions of conduct of an experiment on the appearance of hydrogen embrittlement of PT-7M ..cap alpha..-titanium alloy hydrogen impregnated to various concentrations. Tensile tests of notched and unnotched specimens, impact bend tests, and static three-point bend tests of specimens with a crack were made in a broad temperature range. To determine the fracture toughness, specimens with a center notch and a fatigue crack recommended for finding the critical stress intensity factors and the critical crack opening were used. Metallography was used to determine the dependence of lamellar titanium hydride formations on hydrogen content. The results of calculation of the critical crack opening made it possible to predict the character of failure of cylindrical thin-walled shells of the alloy. Maximum allowable shell thickness, beyond which brittle fracture occurs, could be established from ductile-to-brittle transition curves. The most sensitive methods for determining a tendency toward hydrogen brittleness were impact strength and fracture toughness tests.

セラミックスの衝撃破壊強度特性と確率論的評価

A new device for impact testing suitable for evaluating ceramic strength was developed and was used in the experiments to develope a unified method for estimating both fast fracture and fatigue strengths. The fracture strength was measured by making 3 point and 4 point impact bending tests for three kinds of sintered Si3N4 specimens. Weibull analysis was performed for all the strength data with our original idea by considering the both effects of applied stress pattern and specimen size. With introduction of the effective hold time teff and the effective volume Veff, the impact strength obtained by each test was expressed commonly as the delayed fracture strength by using the following formula.σf(Nf teff)nf=Dfm√ln(1-Pf)-1/Veffwhere nf is the strength decrement index, Df the strength constant and m the Weibull Modulus.This formula is applicable to the probabilistic estimation of impact strength of ceramics.On the other hand, the strain rate-dependence of impact strength could be estimated by the following formula derived from the above formula.σf=ε1/(1+n){(1+n)EDfn}1/(1+n)m√ln(1-Pf)-1/Veffwhere n is the crack growth rate index (1/nf) and E Youngs modulus.

Influence of long-term thermal ageing on creep-fatigue behaviour of ferritic steels

For the design and to assess the final life span and the potential for life extension of components, such as, e.g. turbine shafts, piping and valve casing and nuclear pressure vessels, which are subjected to temperature and alternating load, data are required on the long time history of the corresponding material. Especially, it is necessary to know about the material alterations and the consequences of the changes in material properties. For turbine application, the creep resistant ferritic 28 CrMoNiV 49 steels (forged) and 13 CrMo 44 (rolled) as well as the creep resistant cast steel GS 17 CrMoV 5 were investigated. Ageing times between t = 1000 h and t = 81000 h were applied at temperatures of 530 °C.and 560 °C. For the nuclear grade RPV steel (forged) 20 MnMoNi 55 (similar to A 508 Cl 3) the ageing time was 30 000 h at 320 °C. The following tests were conducted: mechanical and technological tests (tensile tests, high temperature tests, notch impact bending tests), creep tests and LCF tests. The interpretation of results were supported by extensive metallographical and microstructural investigations. The creep fatigue behaviour of creep resistant steels can be described and explained with the help of these investigations. It can be decided whether it is possible to simulate structural changes in material caused by service load properties, by means of long-term thermal ageing. Furthermore, the microstructural influence was assessed.

Unnotched impact bend test assessment of the degree of gelation in unplasticized poly(vinyl chloride) pipe

AbstractIt is suggested that the unnotched impact test is suitable for quantitative quality control of unplasticized poly(vinyl chloride) pipe. The relative level of processing is assessed by the probability that failure is nucleated at a surface flaw. Tests show that this assessment is very sensitive to the level of processing.

Influence of explosive loading on the micromechanisms of fallure of constructional steels

1. Explosive loading with p=5 and 10 GPa of specimens of St3sp and 20G2S steels leads in subsequent impact bend tests to complication of their fracture relief and to an increase in the degree of microlocal deformation, as the result of which the energy expenditure for the failure process may increase. The increase in relief is caused by complication of the trajectory of the crack, the development of which is a discrete process. The microcracks and then the main crack propagate in jump, the length of which is determined by the specific structure of the material. 2. The combination of explosive loading with subsequent heat treatment substantially increase the brittle fracture resistance of the investigated steels at low temperatures as the result of decreasing localization and more uniform occurrence of deformation and fracture. Explosive and heat treatment provides the optimum mechanical properties of steels [5, 6] and may be used when traditional methods of hardening and thermomechanical treatment are inapplicable.