Impact Bending Tests Research Articles

Using Subsize Impact Bend Specimens for Estimation of Irradiation and Re-Irradiation Embrittlement of VVER RPV Steels

Abstract Results of impact bend tests of subsize Charpy V-notch-type (CVN) specimens are used in Russia for monitoring both re-irradiation embrittlement of the first generation of VVER-440 (including VVER-440/179 and VVER-440/230, i.e., projects B-179 and B-230) reactor pressure vessel (RPV) steels and irradiation embrittlement of VVER-440/213 RPV steels. For the first generation of VVER-440 RPVs, no surveillance program was foreseen and only subsize specimens (5 by 5 by 27.5 mm and 3 by 4 by 27 mm) can be manufactured from samples taken from the inner surface of the RPV for radiation embrittlement monitoring. For VVER-440/213 RPVs, 80 % of the surveillance specimens are irradiated with a lead factor greater than 20. Only four specimens of base metal and four specimen halves of weld seam material are irradiated with a lead factor less than 3. Taking into account that full-size (10 by 10 by 55 mm) CVN specimens were used in surveillance programs, using subsize specimens enables to solve the flux effect problem for VVER-440/213 RPV beltline materials and ensure representativity of surveillance programs. Application of subsize specimens for the estimation of radiation embrittlement requires developing a correlation between transition temperature values evaluated using test results of standard (full-size) and subsize CVN specimens. Such a correlation is discussed.

Static and low-velocity impact behavior of sandwich beams with closed-cell aluminum-foam core in three-point bending

In this paper, the response and failure of sandwich beams with aluminum-foam core are investigated. Quasi-static and low-velocity impact bending tests are carried out for sandwich beams with aluminum-foam core. The deformation and failure behavior is explored. It is found that the failure mode and the load history predicted by a modified Gibson's model agree well with the quasi-static experimental data. The failure modes and crash processes of beams under impact loading are similar to those under quasi-static loading, but the force-displacement history is very different. Hence the quasi-static model can also predict the initial dynamic failure modes of sandwich beams when the impact velocity is lower than 5 m/s.

Explosion Bulge Test of High Srength Low Alloy Steel PFS-700 in Air and Underwater

Explosion Bulge Test in air has been carried out in order to evaluate base metal and weldment of pre-heating free steel, PFS-700 which was developed for using in submarine, destroyer and aircraft carrier and specified as Korean military specification, KDS-9515-3001. PFS-700 steel has good weldability so that it can be welded without pre-heating before welding. 1.4wt.% of Copper is added to compensate for the decrease of strength due to the decrease of Carbon in PFS-700. Usually, PFS-700 is aged at the temperature of about 650°C for the combination of strength and toughness. PFS-700 of the thickness of 25mm aged at 650°C was used for explosion bulge test. Underwater weapon system demands to conduct this test for the security of weld structures, and test method and procedure are specified in the military specification, MIL-STD-4139(SH). PFS-700 was explosion bulge tested as specified in this spec. Mechanical tests such as tensile test, CVN impact test, dynamic tear test and bend test are conducted from the specimens taken from prolonged EBT specimen and compared with the properties specified in KDS-9515-3001. EBT results show that PFS-700 welded with the welding material of spoorlarc-120 has over the thickness reduction of 14% without propagation of crack to the hole-down area.

Processing of fine-grained W materials without detrimental phases and their mechanical properties at 200–432 K

Low-temperature ductility improvements of tungsten (W) materials with microstructures of fine grains and fine transition metal–carbide dispersoids require sufficient reductions for consolidates that are free from detrimental dispersoids of the W 2C phase. In this paper the cause of the occurrence of the detrimental W 2C phase is studied and an appropriate processing method for its prevention and nearly full densification of mechanically alloyed powder is shown. By applying the method W–0.3 wt%Ti–0.006 wt%C (W–0.3TiC–0.006C) specimens with a negligible amount of the W 2C phase and reductions up to 78% were prepared. It is found that W–0.3TiC–0.006C exhibits an appreciable ductility even at room temperature by three-point bend impact tests and static tensile tests, with the ductile-to-brittle transition temperature of around 260 K. The observed ductility is likely due to elongated, very thin grain structures of the material. For further ductility improvements, control of oxygen impurities to suppress decarburization during sintering and assure appropriate amounts of (Ti,W)C dispersoids is required.

Mechanical performance and fracture behavior of Fe41Co7Cr15Mo14Y2C15B6 bulk metallic glass

The mechanical properties of a new Fe41Co7Cr15Mo14Y2C15B6 bulk glassy alloy were studied by impact bending, compression, and hardness tests carried out at room temperature. The compressive fracture strength, elastic strain to fracture, Young’s modulus and Vickers hardness were measured to be 3.5 GPa, 1.5%, 265 GPa, and 1253 kg mm−2, respectively. The fracture mode of the glassy alloy under uniaxial compression is different from those of other bulk metallic glasses in that this fracture mode causes the samples to be broken, in an exploding manner, into a large number of micrometer-scale pieces. The fracture mechanisms of this bulk glassy alloy under bending and uniaxial compression are discussed based on the observation of the fracture surfaces. Vickers indentation tests indicate that the structure of the glassy ingot may be inhomogeneous.

Development of ultra-fine grained V–W–Y alloys with superior mechanical properties by effective usage of WC debris introduced during mechanical alloying

Mechanical alloying (MA) is a very effective means for microstructural control. However, MA inevitably accompanies contamination with impurities arising from milling vessels and balls. In this study effective usage of MA processed powders containing WC debris introduced from WC/Co vessels and balls is attempted to develop ultra-fine grained V–W–Y alloys with superior mechanical properties. V–8.4W–1.4Y and V–2.9W–1.6Y (mass%) alloys were fabricated by powder metallurgical methods utilizing MA, HIP and various thermo-mechanical treatments and then subjected to three-point bend impact and static tensile tests. It is shown that the post-HIP thermomechanical treatments lead to significant improvement in the ductility of the alloys: V–8.4W–1.4Y decarburized at 1573 K possesses a grain size of approximately 400 nm and exhibits full bend at 173 K and tensile yield stress of 540 MPa and uniform elongation of 13% at room temperature. Effects of WC debris on the mechanical properties and microstructures in the alloys are discussed.

Interrelationship between the severity of heat treatments and sieve fractions after impact ball milling: a mechanical test for quality control of thermally modified wood

Abstract Thermal modification processes improve the durability and dimensional stability of wood, but strength properties, especially dynamic ones, are compromised. Results from standard dynamic strength testing, such as impact bending tests, suffer from high variability and therefore require a high number of replicates. To overcome this, a new test method named high-energy multiple impact (HEMI) was developed by investigating heat-treated Picea abies Karst., Abies alba Mill. and untreated Robinia pseudoacacia L. The method is based on crushing small specimens by thousands of impacts from pounding steel balls in a heavy vibratory mill. The level of destruction was determined by sieving and analyzing the size distribution of the fragments. We calculated the resistance to impact milling (RIM) based on the mass of the size fractions. RIM shows a linear correlation with the intensity of the thermal treatment. The HEMI test method has the following advantages: small number of specimens, short time for specimen preparation, small variances, and high reproducibility of results.

EXPERIMENTAL STUDY ON MECHANICAL PROPERTIES OF WELDED JOINT USING VIBRATORY CONDITIONING TECHNOLOGY

The vibratory welding conditioning process is investigated in the electroslag welding of blast furnace steel. The metallographs show that a refined joint is produced. The residual stress, side bend property, tension and impact tests are carried out in different vibratory conditions (0g, 0.3g and 0.6g). The results of the test have fully proved that vibratory conditioning technology can effectively reduce residual stress and improve the comprehensive properties of weld joints. Especially, in the 0.6g vibratory condition, the qualification rate of side bend performance is up to 100%. The impact values at two vibratory accelerations (0.3g and 0.6g) are compared and the changing mechanism is discussed. The internal friction test indicates that the internal friction SKK (Snoek-Ke-Koster) peak of the weld metal has good correlation with the impact value of the weld.

Choosing the place for cutting specimens for impact bending tests of reinforcing steel

Results of impact bending tests of specimens of various types and cutting variants are presented. The type of specimen for impact bending testing of hot-rolled reinforcing steel, the place for its cutting from the reinforcement, and the location of the notch are suggested. The expediency of the choice is substantiated. The possibility of the use in Mongolian standards of recommendations accepted in international practice for other steels is considered.

Fatigue Strength of BGA Type Solder Joints between Package and Printed Wiring Board of Portable Device

Solder joints between a package and a printed wiring board (PWB) of a portable electronic device sustain heat cycling as a result of power on-off operations, cyclic bending by key pad operation, and impact bending by dropping. Therefore, heat cycling, cyclic bending, and cyclic impact bending tests were conducted on the ball grid array solder joints between a chip scale package and a PWB. The evaluated solders were Sn-3Ag-0.5Cu and Sn-37Pb. The tests showed that the life cycles of the Sn-3Ag-0.5Cu solder joints for the heat cycling and cyclic bending tests were approximately twice those of the Sn-37Pb solder joints. For the cyclic impact bending test, however, the life cycle of the Sn-3Ag-0.5Cu joint under large strain was smaller than that of the Sn-37Pb solder joint because of interfacial crack growth between the solder and the PWB. Finally, fatigue lives of the joints were compared with crack initiation and failure lives of plain specimens by calculating local strain ranges in the joints by elastic-plastic finite element analysis.

Numerical Analysis of the Three Point Bend Impact Test for Polymers

The three point bend impact test is analysed by employing the finite volume method. Numerical modelling was necessary to enhance understanding of the test and to obtain dynamic correction functions, which are convenient to calculate K and G from measured time to fracture. A simple model of the three point bend test and a more sophisticated model, which included contact effects, were analysed. A good fit with experiments was found when using the contact model. The anvils were found to be important only at a late stage in the test. Several test parameters were varied to investigate their influence on the dynamic correction function. The contact stiffness was found to have an important influence on the shape of the dynamic correction function. Due to the nonlinear contact stiffness the impact velocity also affects the dynamic correction function. For a polymer specimen and a steel striker the specimen width and the specimen material were found to have only a small influence on the dynamic correction function. The dynamic correction function for G was found to exhibit higher oscillations than the dynamic correction function for Kas expected, and hence the former is a more sensitive parameter.

Radiation embrittlement behavior of fine-grained molybdenum alloy with 0.2 wt%TiC addition

In order to elucidate the effects of pre-irradiation microstructures and irradiation conditions on radiation embrittlement and radiation-induced ductilization (RIDU), fine-grained Mo–0.2 wt%TiC specimens with high and low reduction rates in plastic working, which are designated as MTC-02H and MTC-02L, respectively, were prepared by powder metallurgical methods. The specimens were neutron irradiated to 0.1–0.15 dpa with controlled 1-cycle and 4-cycle heating between 573 and 773 K, and 473 and 673 K, respectively, in JMTR. Vickers microhardness and three-point bending impact tests and TEM microstructural examinations were made. The degree of radiation embrittlement, assessed by DBTT shift due to irradiation, was strongly dependent on the reduction rate and cycle number. The 4-cycle irradiation suppressed the radiation embrittlement compared with the 1-cycle irradiation, and the suppression was much more significant in MTC-02L than in MTC-02H. The observed behavior is discussed in connection with RIDU and microstructural evolution caused by the 4-cycle irradiation.

Pedestrian lower limb injury criteria evaluation

In the field of pedestrian injury biomechanics, knees and lower legs are highly recruited during crash situations, leading to joint damage and bones failures. This paper shows how numerical simulation can be used to complete injury mechanism analysis and then to postulate on a knee injury criteria in lateral impact. It focuses on relationships between ultimate lateral bending and shearing at the knee level and potential ligament damage, based on subsystem experimental tests. These ultimate knee lateral bendings and shearings for potential failure of ligaments (posterior cruciate, medial collateral, cruciates and tibial collateral) were estimated at 16° and 15 mm in pure lateral shearing and bending impact tests respectively. Then this methodology was applied on a full test of pedestrian impact.

Fractal Nature of the Brittle Fracture Surfaces of Metal

We have studied the fracture surfaces of low-alloy low-perlite steel after impact bending tests and of aluminum wire after fatigue failure at different temperatures. We have established that the fracture surfaces after brittle destruction are fractal surfaces. On the basis of the fractal model of a crack and the determined fractal dimensionalities of the boundaries of fracture surfaces, we have evaluated the critical sizes of brittle cracks.

Fatigue Strength of BGA Type Solder Joints between Package and Printed Wiring Board of Portable Device

Solder joints between a package and a printed wiring board (PWB) of a portable electronic device sustain thermal cycling as a result of power on-off, cyclic bending by key pad operation, and impact bending by dropping. Therefore, the authors conducted heat cycling, cyclic bending, and cyclic impact bending tests on the ball grid array solder joints between a chip scale package and a PWB. The evaluated solders were Sn-3 Ag-0.5 Cu and Sn-37 Pb. The tests showed that the life cycles of the Sn-3 Ag-0.5 Cu solder joints for the feat cycling and cyclic bending tests were approximately twice those of the Sn-37 Pb solder joints. On the other hand, in the case of cyclic impact bending test, the life cycle of the Sn-3 Ag-0.5 Cu joint under large strain was smaller than that of the Sn-37 Pb solder joint because of interfacial crack growth between the solder and the PWB. These fatigue lives of the joints were compared with crack initiation and failure lives of plain specimens by calculating local strain ranges in the joints by elastic plastic finite element analysis.

Special Features of Fracture of Steels from Partially-Alloyed Powders

Special features of fracture of structural steels 45N2D2M and 45N4D2M manufactured by pressing with subsequent sintering from partially alloyed iron powders are studied. Impact bending tests of specimens with different levels of retained porosity show two kinds of fracture, i.e., intraparticle cleavage and interparticle dimple fracture. In addition, the surfaces of the “initial” pores come out to the fracture surface. Other conditions being equal, growth in porosity decreases the proportion of the brittle component of fracture and decreases the critical brittle point.

Influence of residuals resulting from scrap use in the electric arc furnace process on the properties of hot-work tool steels

Hot-work tool steels are produced by the electric arc furnace route applying scrap as the main raw material. Besides iron being the most important alloying element for the steel production, a number of generally undesired residual elements are contained in scrap. Due to the continuous scrap recycling, some residuals that normally cannot be removed from the melt such as copper and nickel are in the future expected to enrich in scrap as well as in the steel produced with consequences for the material properties not yet known [1, 2]. To extend the knowledge, it was the objective of a project financially sponsored by the ECSC to determine the impact of scrap use on the properties of hot-work tool steels by investigating the influences of the residuals nickel, copper, phosphorus and aluminum. For the investigation, 13 heats of steel H11 (X38CrMoV5-1) were produced via vacuum induction melting followed by electroslagor vacuum arc remelting. While the alloying elements were kept on a constant level in the admissible range according to German standard (SEL), the residuals were adjusted according to Table I. From the remelted billets with a weight of 1 ton forged bars with a dimension of 90 mm square were produced for the tests. Besides of the working properties, the mechanical properties and the microstructure were investigated. Details concerning the material production and testing are included in [3]. The residual phosphorus was investigated within the scope of 0.002% to 0.021%. It most notably had a deteriorating impact on the mechanical properties, e.g., toughness and ductility. In impact bending tests at room temperature and elevated temperatures, the impact bending energy was reduced with increasing phosphorus content (Fig. 1). The effect was noticed for unnotched and notched specimens likewise. The reason for this behavior most likely is the segregation of phosphorus at grain boundaries and at interfaces between martensite laths and carbides, a phenomenon that has been discussed in connection with the role of phosphorus in temper embrittlement [4]. Segregation of phosphorus leads to a reduction of cohesion in the microstructure and allows easy crack initiation, thus reducing toughness. For the alloys tested, a noticeable reduction of toughness occurred with 0.021% P although the impact bending values were still high enough to meet the demands of various customer specifications. Also, ductility determined in tensile tests at room temperature was reduced with increasing phosphorus content. A content of 0.021% P was found to increase the yield strength by 100 MPa while it did not have a bearing on tensile strength. The effect on yield strength results from the integration of phosphorus atoms in the iron-solid solution and has already been described for engineering steel grades. Due to the different atom radii the crystal lattice is distorted and thus a hardening effect and an influence on yield strength is evoked. The properties determined in creep tests such as creep strength and yield strength were significantly reduced by phosphorus (Fig. 2). This effect on the creep resistance can be explained by time-dependent grain boundary phosphorus segregation reducing toughness. Also it is known that phosphorus accelerates the velocity in primary and secondary creep regions as it facilitates the formation of coarse carbides that reduce creep resistance [5]. The influence of copper was determined for contents between 0.05% and 0.38%. Copper as a residual in steel H11 did not show any effect on the processing properties although this element is always mentioned in connection with defects during casting and hot-forming operations [6]. Obviously, the effects of

Mechanical Properties of Fine-Grained, Sintered Molybdenum Alloys with Dispersed Particles Developed by Mechanical Alloying

In order to develop Mo alloys with improved mechanical properties of low-temperature toughness and room- and high-temperature strengths without any plastic working after consolidation, fine-grained, particle-dispersed Mo alloys were fabricated by hot isostatic pressing (HIP) or spark plasma sintering (SPS) of mechanically alloyed powders of Mo and 0.8 mol% ZrC or TaC (designated as ZRC08 and TAC08). The fabricated Mo alloys were subjected to high-temperature annealing for 3.6 ks up to 2470 K, three-point impact bending tests at temperatures from 270 to 470 K at 5 m s-1 and static tensile tests at temperatures from 300 to 1970 K at initial strain rates from 4.2 × 10-5 to 8.3 × 10-2 s-1. The fabricated alloys exhibited no significant grain growth even after annealing at 2470 K for 3.6 ks due to the pinning effect of the particles against grain boundary migration. The ductile-to-brittle transition temperatures (DBTT) assessed by impact bending were lower and the tensile strengths up to 1770 K were higher for the fabricated alloys than for recrystallized pure Mo. In particular, HIPed TAC08 was superior in low-temperature toughness having the DBTT lower by 30-40 K than recrystallized Mo-La2O3 (TEM) with an elongated coarse-grained microstructure. HIP- or SPS-treated ZRC08 was superior in room- and high-temperature strengths, respectively. Furthermore, HIPed ZRC08 showed a large elongation of 551% at 1770 K. These excellent mechanical properties of the fabricated Mo alloys were obtained for the first time in the as-consolidated state without subsequent plastic working, and are attributable to fine-grained microstructure and grain-boundary strengthening by the fine particles.

An Analysis for Arrest Toughness of Impact-Induced Delamination in Carbon/Epoxy Laminates

A model is proposed to identify an arrest toughness, which governs a delamination in laminates. Also, a statistical analysis is conducted to identify a variation of arrest toughness due to material nonhomogeneity. To these ends, impact and 3-point bending tests are performed on the Carbon/Epoxy laminates with various thickness. The fracture behavior can be described by a crack arrest concept. The arrest toughness can be evaluated by an elastic work factor. Also, the Weibull distribution is suitable to predict a failure probability for the arrest toughness. Moreover, the variation of toughness increase gradually with the increase of the specimen thickness. This behavior may be attributed to a change of material nonhomogeneity with the specimen thickness.

Impact Resistance of SM Joints Formed With ICA

Isotropic conductive adhesives (ICA) have been considered as replacement materials for lead-tin solder alloys. In this paper, the post-impact shear strength of ICA surface mount (SM) joints was obtained experimentally and compared with that of SM lead-tin joints. The dynamic impact energy was provided in the form of three-point bending on the PCB using equipment called the split Hopkinson bar. Strain rates of over 4000/s were used for the impact bending test. The action of impact bending was used to simulate the effect on the PCB and the interconnection as a result of high energy impact on an electronic equipment. Shear test was then performed to examine the change in strength of the ICA joints as a result of impact damage. It was found that the SM ICA joints failed due to impact at a strain rate just over 4000/s. Microstructural examination carried out using a scanning electron microscope revealed that the interface between the ICA and copper pad on the PCB was the weakest region of the joint.