Computer simulation of the Charpy V-Notch toughness test

We calculated the impact of a striker with the ASTM Type A Charpy V-Notch specimen. We used an elastic-plastic constitutive law with J₂-flow theory and isotropic hardening to model A-533 Grade B class 1 steel at 100°C. Large strain and rotation are accounted for. We found that the notch stress-strain state was independent of the three-point loading type (round- or flat-tip striker or pressure push) and was most strongly correlated with notch-opening displacement. The dynamic stress-strain state at the time of fracture initiation was obtained by comparing the calculated deformed shape with that obtained in interrupted Charpy-V-notch tests where cracking had started. This time agreed with a computed prediction of fracture initiation obtained using a computer model of material damage. Cracking starts at the notch at about 40% of the maximum load found in an instrumented Charpy test. We have also calculated the distribution and partition of specimen energy. Adiabatic heating and strain rate are discussed.     

Analysis of the Charpy V-notch test for welds

The ductile–brittle transition for a weld is investigated by numerical analyses of Charpy impact specimens. The material response is characterized by an elastic–viscoplastic constitutive relation for a porous plastic solid, with adiabatic heating due to plastic dissipation and the resulting thermal softening accounted for. The onset of cleavage is taken to occur when a critical value of the maximum principal stress is attained. The effect of weld strength undermatch or overmatch is investigated for a comparison material, and analyses are also carried out based on experimentally determined flow strength variations in a weldment in a HY100 steel. The predicted work to fracture shows a strong sensitivity to the location of the notch relative to the weld, with the most brittle behavior for a notch close to the narrow heat affected zone. The analyses illustrate the strong dependence of the transition temperature on stress triaxiality.     

Fracture mechanics considerations in the Charpy impact test

Instrumentation of the Charpy impact test permits an analysis of the data in terms of linear elastic fraeture mechanics. Measurements of time to fracture are converted to estimated crack opening displacements at fracture and thus to values of the fracture toughness parameter KC. The variation of these values with temperature shows a transition which is interpreted as a change from plane strain to plane stress fracture.An expression is derived which relates the critical cleavage stress and the plane strain fracture toughness (K_IC) and allows this latter quantity to be calculated from dynamic stress measurements in those Charpy tests which give fractures at conditions where general yield just occurs. It is noted that the values of K_IC so obtained are significantly lower than the values obtained from time-to-fracture measurements, and the differences are discussed. It is concluded that the K_IC values obtained from the stress measurements are of more general interest, and the uncertainties involved in these estimates are outlined.

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Zusammenfassung Infolge der Instrumentierung der Charpy-Kerbschlagprufüng können die gelieferten Daten durch linear-elastische Bruchmechanik analysiert werden. Messwerte der vorm Bruchvorkommen ablaufenden Zell werden zu geschätzten Rissöffnungswerten (crack opening displacements) beim Bruch, also zu Werten des Bruchwiderstandsparameters KC, umgerechnet. Die Temperaturabhägig dieser Werte zeigt einen Übergang, der nach der Deutung der Autoren einer Änderung der Bruchweise entspricht (zweiachsige Spannung wird zu zweiachsiger Verformung).Ein Ausdruck wird abgeleitet, der die kritische Trennbruchspannung und den der zweiachsige Verzerrung entsprechenden Bruchwiderstand (K_IC) in Wechselbeziehung bring und die Berechnung dieses letzten aus dynanamischen Spannungswerten bei jinen Charpy-Prüfungen ermöglicht, bei denen der Bruch gerade bei der Einstellung des weitverbreiteten Fliessens vorkommt. Es wird bemerkt, dass die so erhaltenen K_IC-Werte bedeutend niedriger sind als die, die aus Zeit zum Bruch Messwerten erhalten werden. Die Unterschiede werden besprochen. Es wird beschlossen, dass die aus den Spannungsmessungen bestimmten K_IC-Werte von weiterem Interesse sind, and die mit diesen geschätzten Werten verbundenen Unsicherheiten werden kurz beschrieben.

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Résumé À force d'instrumenter Fessay Charpy du dureté au choc on se met en position de faire l'analyse des résultats qu'il fournit en utilisant le méchanique linéar—elastique de la rupture. De la valeur du temps avant la rupture se laisse calculer approximativement l'ouverture du dout de la fissure (crack opening displacement) au moment de la rupture et de la valeur du paramètre de la résistance à la rupture, K_C. La dépendence de cette valeur de la température montre une transition considérée comme changement du mode de la rupture de deformation planaire en contrainte planaire.On développe une expression qui met en corrélation la contrainte critique du clivage et la résistance à la rupture dans les conditions de la déformation planaire et permet le calcul de cette quantité au moyen du mesurage de la contrainte dynamique dans les essais Charpy où la rupture se produit lors de l'écoulement général. On remarque que les valeurs de K_IC ainsi obtenues sont d'une manière significative inférieures à celles que l'on obtient du temps avant la rupture, et les différences sont discutées. Il est conclu que les valeurs de K_IC que l'on obtien en mesurant la contrainte sont d'un interêt plus général et les incertitudes qu'entraînent ces calculs approximatifs sont brièvement décrites.

     

Progress and development in the instrumented Charpy impact test

Toughness is the most important characteristics for structural component materials and has been evaluated widely by Charpy impact test. Charpy test has been presented firstly in 1901, and instrumentation to record load history during impact has been attempted since 1920's. Various methods to estimate quantitative fracture toughness values under dynamic loading condition have been presented. In the development of fracture mechanics, one of the authors has successfully developed the new dynamic fracture toughness testing and evaluation system using the instrumented Charpy impact test, which is called “CAI system”. This paper introduces history of instrumented Charpy impact test and CAI system. Moreover, instrumented impact testing method on brittle materials is also mentioned. Worldwide standard on dynamic fracture toughness evaluation by the instrumented impact testing is highly expected to be established.     

Estimation of ASTM E-1921 reference temperature from Charpy tests: Charpy energy-fracture toughness correlation method

In this paper, some of the older and newer Charpy-fracture toughness correlations have been examined and new correlations have been developed for predicting the ASTM E-1921 standard reference temperature, T₀. The results have been applied to some selected new steels and compared with measured T₀, where available. It is found that the predicted reference temperature from the new procedure gives reliable and acceptably conservative engineering estimate of T₀. Predicted values of reference temperatures under dynamic conditions from these T₀ using Wallin’s strain rate shift equation agree well with measured dynamic values for a few steels giving added support to the new procedure.     

Specimen loading determined by displacement measurement in instrumented Charpy impact test

An experimental method based on the specimen displacement measurement with a commercially available laser sensor is proposed in order to determine the actual specimen loading in instrumented impact test. The prediction resulting from this approach is compared with results deduced from dynamic analysis of impact tests with mass-spring model.     

Charpy impact test on A508-3 steel after neutron irradiation

Reactor pressure vessel (RPV) is the critical un-changeable component of the reactor during its service lifetime, which prevents the radioactive leak of the nuclear power plant core. The irradiation test (about 10 × 10¹⁹ cm^− 2, E > 1 MeV) in research reactor of the pressure vessel material was carried out, and the charpy impact test has been carried out before and after the neutron irradiation. Analysis of the impact energy and the fracture morphology has been done to estimate the embrittlement due to neutron irradiation. It shows that the main effects of neutron irradiation to fracture are the crack initiation and stable expansion process. And there also are a small amount of intergranular fracture in the unstable crack expansion after neutron irradiated which aware us pay more attention to the increasing intergranular fracture behavior of higher neutron fluence level after 60a nuclear power plant operation.     

The Charpy impact properties of beryllium

Notched and unnotched Charpy impact measurements have been made on two grades of hot pressed beryllium over a range of densities between 80% and 100% theoretical density. The beneficial effect of ≈ 5–10% porosity on notched impact properties is demonstrated and the effects of annealing out machine-induced surface stresses is shown. In unnotched specimens this annealing leads to an increase of a factor of six in absorbed energy. Possible reasons for this phenomenon are discussed.     

Analysis of impact properties of A533 steel for nuclear reactor pressure vessel by instrumented Charpy test

Instrumented Charpy impact test can become more useful by connecting the digital memory and microcomputer, where yield load (P_y), maximum load (P_m), premaximum load energy (E_i) and post-maximum load one (E_p) are automatically and rapidly analyzed. In such analysis, cyclic oscillations in a load signal are corrected and smoothened by using a method of moving averages (the nonrecursive low pass digital filter). Dynamic J_1c value (J_1d) of A533 steel can be measured in a fatigue precracked type Charpy specimen, provided that a true deflection of specimen and a true crack initiation point in the load-deflection curve are known. For this purpose, elastic compliance values of the testing machine and the specimen are measured dynamically by the elastic low blow test to correct the apparent deflection. Crack initiation point, on the other hand, is detected by the plastic low blow test. It is shown that the crack initiation in the fatigue pre-cracked specimen of this material occurs prior to the maximum load, and that the relation between crack initiation energy (E_Δα) and pre-maximum load energy (E_i) is $\text{E}{}_{\mathrm{\Delta \alpha }}\text{E}{}_{\mathrm{i}}\text{? 0.8}$.     

Assessment of an instrumented Charpy impact machine

The dynamic responses of the standard Charpy impact machine were studied experimentally using strain gauges and accelerometer attached to the striker and the rotary position sensor fixed at the rotating axis and numerically with the finite element analysis. The fracture propagation was simulated with the cellular automata finite element approach developed earlier. A series of low velocity as well as full capacity Charpy tests were analysed. It was found that the strain gauge signal recorded close to the tup edge and the acceleration recorded at the back of the striker do not match. The energy calculated with the strain gauge data agrees well with the dial reading, while the energy calculated with the accelerometer signal is never near it. Frequencies close to the first natural \hbox{frequency} of the Charpy sample have high modal magnitudes in the acceleration signal but are effectively damped in the strain gauge response. Vibrations of the striker arm have highest modal magnitudes in the rotary position sensor. A low-pass filter is used to obtain the striker movements. The finite element analysis partly supports the experimental observations but also suggests that acceleration at the tup edge suffers higher oscillations than strain.     

Direct evidence for dislocation-free zone in Fe–5% Si fractured by Charpy impact test

Defect structure in the subsurface region below a fracture surface of an Fe–5% Si specimen that had been fractured by a Charpy impact test at 77 K was examined by transmission electron microscopy. The specimen was fabricated by a focused ion beam technique to enable analysis of areas that had been carefully selected on the basis of observation. Near the nucleation site of the crack, many dislocations were observed just beneath the fracture surface. Far away from the nucleation site, no dislocations at all were observed in the subsurface region of the fracture surface. Between these two extreme positions, a dislocation-free zone was observed.     

Evaluation of dynamic fracture toughness KId by Hopkinson pressure bar loaded instrumented Charpy impact test

A novel method for measuring the dynamic fracture toughness, K_Id, using a Hopkinson pressure bar loaded instrumented Charpy impact test is presented in this paper. The stress intensity factor dynamic response curve (K_I(t)−t) for a fatigue-precracked Charpy specimen is evaluated by means of an approximate formula. The onset time of crack initiation is experimentally detected using the strain gauge method. The value of K_Id is determined from the critical dynamic stress intensity factor at crack initiation. A K_Id value for a high-strength steel is obtained using this method at a stress-intensity-factor rate () greater than 10⁶ MPa .     

Superplastic deformation of sheet test pieces machined from Ti-6Al-4V bar

Sheet tensile test pieces were machined in three orientations from edge textured Ti-6Al-4V bar and tested at temperatures in the range 800 to 975‡ C and at strain rates of 3 × 10⁻⁴ and 1.5×10⁻³ sec⁻¹. Bands of contiguous alpha grains aligned in the rolling direction caused local variations in the flow stress, strain to necking, strain rate sensitivity, plastic strain ratio values and surface roughness. Texture effects were only detected at the lowest test temperature (800‡C) and highest strain rate (1.5×10⁻³ sec⁻¹).     

Numerical simulation of the Charpy impact testing

This paper deals with the dynamic effects understanding of the impact three point testing. In the first step, the transverse vibrations of the discretized simply supported beam are investigated and compared to the open literature. In the second step, a modal analysis is performed on the specimen-tup mechanical system. A linear contact stiffness at the impact point is introduced.     

复印机典型能耗测试结果的不确定度分析

测量结果的质量直接影响产品品质的评价。测量不确定度是衡量测量结果质量的重要参数,ISO/IEC 17025规定:校准、检测实验室必须建立并实施测量不确定度的评估程序,以评价测试结果的准确性和可靠性。复印机的典型能耗(TEC)是衡量复印机能效的重要特征指标之一,其测量值是评价复印机典型能源消耗等级的重要依据之一。本文采用GB 21521-2008《复印机能效限定值及能效等级》中规定的试验方法,测量复印机的典型能耗,对测量结果的不确定度进行分析。     

The lower critical field Hc1 of V3Si

The temperature dependence of the lower critical field H_c1 of V₃Si single crystals was investigated. Measurements were carried out using an alternating field method. Superposition of a small alternating field onto an outer magnetic field arising linearly in time makes it possible to detect flux changes in hard superconductors with a high degree of sensitivity.