Change In Fracture Mode Research Articles

Experimental and Numerical Simulation Research on Micro-Gears Fabrication by Laser Shock Punching Process

The aim of this paper is to fabricate micro-gears via laser shock punching with Spitlight 2000 Nd-YAG Laser, and to discuss effects of process parameters namely laser energy, soft punch properties and blank-holder on the quality of micro-gears deeply. Results show that dimensional accuracy is the best shocked at 1690 mJ. Tensile fracture instead of shear fracture is the main fracture mode under low laser energy. The soft punch might cause damage to punching quality when too high energy is employed. Appropriate thickness and hardness of soft punch is necessary. Silica gel with 200 µm in thickness is beneficial to not only homogenize energy but also propagate the shock wave. Polyurethane films need more energy than silica gel with the same thickness. In addition, blank-holders with different weight levels are used. A heavier blank-holder is more beneficial to improve the cutting quality. Furthermore, the simulation is conducted to reveal typical stages and the different deformation behavior under high and low pulse energy. The simulation results show that the fracture mode changes under lower energy.

Oxidation Assisted Intergranular Cracking in Alloy 718: Effects of Strain Rate and Temperature

Alloy 718 is the most widely used superalloy in industry due to its excellent mechanical properties, as well as its oxidation and corrosion resistance over a wide range of temperatures and solicitation modes. Nevertheless, it is a well-known fact that this alloy is sensitive to oxidation assisted intergranular cracking under loading in the temperature range encountered in service. The mechanisms resulting in such degradation are not well-understood, but it has been well established that a relation exists between a change in fracture mode and the apparition of plastic instability phenomena over a wide range of temperatures. Quantification and characterization of the damaging process provide important information leading to a better understanding of the degradation mechanisms involved in the oxidation assisted intergranular cracking of this alloy. These observations allow various domains to be defined in the strain rate - temperature plane, where the damaging process characteristics are different: a high strain rate / low temperature domain in which instabilities occur and where the fracture mode is systematically transgranular ductile, an intermediary domain where numerous intergranular crack initiations can be observed, and a slow strain rate / high temperature domain where crack propagation is enhanced. These results lead to the proposal of consistent scenarii to explain grain boundary opening due to applied intergranular normal stress and critical decohesion stress changes.

Research on fatigue crack propagation of micro-alloyed steel by acoustic emission

This study focused on fatigue crack propagation of Q345 steel in tests using acoustic emission technique. The fatigue tests of the Q345 steel plate specimens were monitored with acoustic emission, and acoustic emission amplitude, energy and counts were obtained. According to the acoustic emission features, the fatigue crack growth was divided into three parts: primary stage (amplitude of 42–51 dB and energy of 1–10 V μs), steady stage (amplitude of 42–73 dB and energy of 1–80 V μs) and rapid growth stage (amplitude of 42–84 dB and energy of 1–170 V μs). The results showed that acoustic emission could be used as a non-destructive testing method to monitor and analyse the fatigue deformation of micro-alloyed steels because acoustic emission is relatively sensitive to fracture mode changes.

Effect of Mo and Cu on stress corrosion cracking of ferritic stainless steel in chloride media

Stress corrosion cracking behaviour of ferritic stainless steels with copper and molybdenum additions in 42 wt-% boiling magnesium chloride at 143 ± 1°C has been determined. The nature of the corrosion products was analysed by X-ray photoelectron spectroscopy (XPS). XPS results show that the presence of Fe(0), Cr(0) and Mo(0) unoxidised states on the crack tips of (copper+molybdenum) addition ferritic stainless steel cannot form the stable passive film and causes the further corrosion in the chloride solution. The addition of both copper and molybdenum to 19% Cr ferritic stainless steel causes stress corrosion cracking. The susceptibility to stress corrosion cracking increases with the growth of ε-copper precipitates, and the fracture mode changes from transgranular to intergranular with the increasing aging time. Stress corrosion cracking initiates from pitting of ε-copper phases, then propagates to molybdenum atoms, and finally propagates to the other ε-copper precipitations perpendicular to the direction of maximum strain.

Mechanisms of tetraneedlelike ZnO whiskers reinforced forsterite/bioglass scaffolds

Tetraneedlelike ZnO whiskers (T-ZnOw) reinforced forsterite/bioglass scaffolds were achieved using selective laser sintering. The effects of T-ZnOw on the mechanical properties and on microstructure of the scaffolds were studied. The optimum compressive strength and fracture toughness were 59.17±2.07MPa and 2.61±0.09MPam1/2 respectively when T-ZnOw was 3wt.%, which were about 155.26% and 141.08% that of the T-ZnOw free scaffold. The strengthening mechanisms were ascribed to the unique tetraneedlelike structure of T-ZnOw and the corresponding stress transfer. The toughening mechanisms were characterized by crack deflection, crack bridging, crack tip, T-ZnOw pull out and the change of fracture mode. In addition, cell culture test illustrated that T-ZnOw improved the adhesion and spread of MG-63 cells. The study indicated that the reinforced forsterite/bioglass scaffolds have a great potential for load-bearing applications.

Microstructure and properties of ultrafine WC–Co–VC cemented carbides with different Co contents

Ultrafine WC–Co–VC cemented carbides are used extensively in a variety of industrial environments due to their excellent mechanical properties and outstanding wear resistance. Co content affects the service performance of the cemented carbides. In the present study, the influences of Co content on microstructure, physical, and mechanical properties were investigated systematically. Ultrafine WC–Co–VC cemented carbides with Co content varying from 4 wt% and 7 wt% and assistance of VC (0.35 wt%) as inhibitor of WC grain growth were prepared. The physical and mechanical properties were tested and the microstructure characteristics were observed by optical microscope (OM) and scanning electron microscopy (SEM). From the results, it is found that with Co content increasing, both the cobalt magnetism and bending strength increase, while the coercive force, Rockwell hardness, density, and abrasive wear resistance decrease. In addition, the OM and SEM results show that the increase of Co content in WC–Co–VC cemented carbides tends to reduce the quantity and size of micro-pores, and make the fracture mode change from brittle fracture to ductile fracture.

Studying on High Temperature Thermoplastic of High Carbon Steel

High temperature thermoplastic of 50Mn2V casting slab was tested by Gleeble-1500 thermal simulator machine. The morphology, microstructure and composition of fracture surfacewere observed and analyzed by optical microscope (OM), scanning electron microscope (SEM) and energy dispersive spectrometer (EDS).The results show that, there are two brittle temperature zones of 50Mn2V casting slab at the temperature of 600~950°C and 1300~1465°C, respectively, The section shrinkaging rate is less than 60%. The fracture mode changes from mixed one dominated by intergranular to toughness transgranular one with the increase of temperature at the range of 600~1250°C. However, the fracture is along with the solid-liquid phase at the range of 1300°C~ melting point.

Sintering behavior and mechanical properties of WC–Al2O3 composites prepared by spark plasma sintering (SPS)

The sintering behavior of WC–Al2O3 composites prepared via spark plasma sintering (SPS) was investigated. The initial WC–Al2O3 nanocomposite powders were prepared via metal organic chemical vapor deposition in a spouted bed followed by carburization process. Then the nanocomposite powders were densified via SPS at 1400°C. The mechanical properties of sintered disks such as hardness and toughness were analyzed. The WC–Al2O3 composites show maximum toughness of 6.1MPa·m1/2 and hardness value of 24GPa, which are higher than those of monolithic alumina. Microstructure observations indicate that WC nanoparticles are dispersed within the alumina matrix which limit the grain growth of alumina matrix. The fracture mode changes from intergranular in the case of monolithic Al2O3 to transgranular mode for nanocomposites to reinforce their mechanical properties.

Strengthening of Gadolinia-Doped Ceria (Ce0.80Gd0.20O2-δ) Thick Ceramic Membranes with Co-Doping of 1 mol% CuO

Nano-sized Ce0.79Gd0.2Cu0.01O2-δ (CGCO) and Ce0.80Gd0.2O2-δ (CGO) powders were synthesized via a facile PVA-assisted combustion method. Full densification can be achieved at much lower temperature (950°C) with minor CuO doping (1 mol%, CGCO) as compared with CGO (1400°C); meanwhile, mechanical strength can be enhanced with CuO co-doping. The CGCO sintered at 1100°C possesses a relative density of 98.80% and biaxial flexural strength of 302 ± 35 MPa, which is higher than those of CGO sintered at 1400°C (96.43%, 250 ± 39 MPa). A tentative microstructural analysis indicates that this strength enhancement can be attributed to a change in fracture mode from partial to complete transgranule dominant.

Assessment of mechanical reliability of surface mounted capacitor by an accelerated shear fatigue test technique

In this study mechanical reliability of Sn3.5Ag0.75Cu solder joints in SMD capacitors has been investigated. Tensile response of the solder joint with respect to thicknesses and aging conditions was studied by using Cu/SnAgCu/Cu model samples. Isothermal lifetime curves of SMD devices subjected to high strain vibrational loading were obtained by using an ultrasonic fatigue testing set-up. Mechanical reliability and the failure modes of solder joints in the SMD capacitors were found to be highly dependent on the microstructure of the solder and the intermetallic compound layer and the testing temperature. Testing at elevated temperature resulted in a clear change of crack path and fracture mode of the solder joints.

Sn-Ag-Cu-In 4원계 무연솔더 조인트의 고속 전단 특성

본 연구에서는 고속 전단시험의 변형속도를 500 mm/s로 설정한 상태에서 Sn-Ag-Cu계(Sn-1.0wt.%Ag-0.5Cu 및 Sn-4.0Ag-0.5Cu)뿐만이 아니라 4종의 4원계 Sn-Ag-Cu-In 조성(Sn-1.0Ag-0.5Cu-1.0In, Sn-1.2Ag-0.5Cu-0.4In, Sn-1.2Ag-0.5Cu-0.6In, Sn-1.2Ag-0.7Cu-0.4In)을 포함하는 무연 솔더 접합부의 솔더링 직후 및 시효 시간에 따른 파면 생성결과, 접합강도 및 접합부 파괴에너지값의 변화를 측정, 비교해 보았다. 그 결과, 리플로우 솔더링 직후 및 <TEX>$125^{\circ}C$</TEX>에서의 500 시간 시효까지 주로 연성 파괴모드 및 준연성 파괴모드가 관찰되었으며, 준연성 파괴모드의 발생 빈도를 분석할 때 고속 전단조건에서 상용 무연 솔더 조성인 Sn-3.0Ag-0.5Cu 이상의 연성파괴 특성을 나타내는 것으로 파악되었다. 또한 4원계 무연 솔더 조인트는 평균적으로 Sn-Ag-Cu계 조성 수준의 파단에너지값을 나타내었는데, 약 100 시간의 시효 후 최고의 파단에너지값이 관찰되었으나 500 시간의 시효 후에는 파단에너지값의 확연한 감소가 관찰되어 500 시간의 시효시점부터 솔더 접합 계면부의 신뢰성 감소가 가속화되는 경향을 관찰할 수 있었다. With Pb-free solder joints containing Sn-Ag-Cu-based ternary alloys (Sn-1.0 wt.%Ag-0.5Cu and Sn-4.0Ag-0.5Cu) and Sn-Ag-Cu-In-based quaternary alloys (Sn-1.0Ag-0.5Cu-1.0In, Sn-1.2Ag-0.5Cu-0.4In, Sn-1.2Ag-0.5Cu-0.6In, and Sn-1.2Ag-0.7Cu-0.4In), fracture-mode change, shear strengths, and fracture energies were observed and measured under a high-speed shear test of 500 mm/s. The samples in each composition were prepared with as-reflowed ones or solid-aged ones at <TEX>$125^{\circ}C$</TEX> to 500 h. As a result, it was observed that ductile or quasi-ductile fracture modes occurs in the most of Sn-Ag-Cu-In samples. The happening frequency of a quasi-ductile fracture mode showed that the Sn-Ag-Cu-In joints possessed ductile fracture properties more than that of Sn-3.0Ag-0.5Cu in the high-speed shear condition. Moreover, the Sn-Ag-Cu-In joints presented averagely fracture energies similar to those of Sn-Ag-Cu joints. While maximum values in the fracture energies were measured after the solid aging for 100 h, clear decreases in the fracture energies were observed after the solid aging for 500 h. This result indicated that reliability degradation of the Sn-Ag-Cu-In solder joints might accelerate from about that time.

Fabrication and mechanical properties of silicon carbide–aluminum oxynitride nanocomposites

Although aluminum oxynitride (AlON) has been considered as an ideal candidate ceramic material due to high rigidity, good chemical stability, superior corrosion and wear resistance, it has relatively low flexural strength and poor fracture toughness. The aim of this investigation was to develop silicon carbide (SiC) nano-particulate reinforced AlON composites via a change of SiC content. The processing and mechanical behavior of SiC–AlON composites was investigated. The addition of SiC nano-particles resulted in a change of fracture mode from intergranular cracking to combined cracking in the composites due to the pinning effect of SiC nano-particles positioned at grain boundaries or triple junctions of micro-sized AlON particles. With increasing amount of SiC nano-particles up to 8wt%, a reduction of porosity and grain size was observed in the composite. Meanwhile, the hardness, Young׳s modulus, flexural strength and fracture toughness all increased moderately. When the addition of SiC nano-particles reached up to 12wt%, however, the agglomerates of SiC nano-particles were occurred and the relative density decreased obviously, resulting in the decrease of the hardness, Young׳s modulus, flexural strength and fracture toughness. By evaluating the effect of the additive concentration, on the mechanical properties of the AlON matrix, it is confirmed that the optimal SiC addition is 8wt%.

Fracture toughness of aluminum nitride ceramics at cryogenic temperatures

We reported, for the first time, the fracture toughness of aluminum nitride ceramics at cryogenic temperatures. The fracture toughness increased from 3.98±0.19 to 4.59±0.28MPam1/2 with the decreasing temperature from 293 to 77K. Increasing fraction of transgranular fracture (from 7.3% at 293K to 14.5% at 77K) was proposed as a governing mechanism for toughness improvement at cryogenic temperatures based on the experimental observations. The effect of residual stresses on crack propagation was theoretically analyzed, considering energy release rates of intergranular and transgranular fractures. The variation of crack paths would contribute to the change of fracture modes and fracture toughness at cryogenic temperatures.

Rhenium Effect in Irradiated Mo-Re Alloys and Welds

The mechanical properties and microstructure of Mo-Re alloys and welds were examined after low- and high-temperature irradiation focusing on the effects of Re concentration, phase stability, microstructural changes and impurity redistribution. Ductility improvement and fracture mode changes from intergranular to transgranular are clearly observed in Mo-Re alloys with an increase in Re content. Neutron irradiation causes hardening of the matrix and concurrently reduces its ductility. The hardening effect is rather limited and unstable after low-temperature irradiation because of the lack of ductility. The damaging effect of neutrons is smaller and hardening of the matrix is more pronounced after high-temperature irradiation. Intensification of homogeneous nucleation of Re-rich phases throughout the bulk is observed after high-temperature irradiation in all of the Mo-Re alloys studied. As a result, the microstructure and strength of all parts of as-irradiated welds equalize and show approximately the same level of strength.

Effect of strain rate on tensile and work hardening properties for Al-Zn magnesium alloys

The effect of strain rate on the mechanical behaviour of Al-Zn magnesium alloys was examined at room temperature under tensile loading with wide range of strain rate. Quasi static tensile test was performed in four different strain rates to obtain their effect on tensile properties, work hardening rate, strain hardening exponent and strength coefficient using a round shape tensile sample. Two types of Al-Zn magnesium alloys were used in this research study, i.e., AZ31 and AZ61 magnesium alloys. The yield stress and tensile strength of AZ31 were found to be strain rate dependent but not for AZ61. The elongations of AZ31 were approximately about 15% for all strain rate levels but for AZ61 the elongations were slightly decreased with increasing strain rate. For all strain rate levels, the work hardening rate of AZ61 was found to be higher compared to that of AZ31. The strain hardening exponent was decreased with increasing strain rate. In contrast, the strength coefficient was increased with increasing strain rate for both alloys. The change in fracture mode as observed from the fracture surface implies that the fracture mechanisms in AZ31 change as the strain rate increases.

&lt;i&gt;In-Situ&lt;/i&gt; Study on Deformation Behavior of ZK60 Alloy Processed by Cyclic Extrusion and Compression

The effects of cyclic extrusion and compression (CEC) on the deformation behavior and failure of ZK60 alloy were examined using in-situ scanning electron microscope (SEM) uniaxial tensile testing at room temperature. Fracture surface was analyzed by SEM. Result shows that the tensile elongation of the extruded ZK60 alloy is obviously increased by CEC deformation. The change in fracture modes has been attributed to the suppression of twinning and the activation of non-basal slips due to the grain refinement and texture modification induced by CEC deformation. [doi:10.2320/matertrans.MC201405]

PCB Photo-lithography 공정에 사용되는 Photo-resist인 Dry Film에 대한 물의 확산 침투 현상평가

본 연구에서는 ATR-FTIR (Attenuated Total Reflectance-Fourier Transfer Infrared)기법을 이용하여 PCB 회로형성에 사용하는 아크릴레이트 계열의 포토레지스트 드라이필름(Dry film)의 흡습 특성을 평가하였다. 또한 습도 변화에 따른 드라이필름의 파단면을 관찰하여 습도에 따라 고분자의 파단특성이 달라지는 것으로 확인하였으며, 정량적인 분석방법으로써 흡습에 따른 무게 변화 및 ATR-FTIR을 이용한 흡광도 변화를 통하여 확산계수를 계산하였다. 실험 결과 주변환경의 온도와 습도가 높아질수록 상온에서 취성과 연성의 중간 정도의 특성을 나타내던 드라이필름이 연성으로 전이되는 사실을 확인할 수 있었고, 온도와 습도가 낮을 경우엔 취성의 특성을 나타냄을 알 수 있었다. 이를 통해 PCB 회로형성 공정의 온 습도 환경 조건을 항상 일정하게 유지해야 일정한 품질을 유지할 수 있다는 사실을 알 수 있었다. 본 연구에서 사용된 흡습특성 평가법인 ATR-FTIR방법의 타당성을 확보하기 위해, 기존에 많이 사용하는 무게 변화법을 통한 고분자-물 확산계수와 ATR-FTIR을 이용한 값을 상호 비교하였다. ATR-FTIR을 이용한 방법은 무게변화법과 동일한 수준의 정확도를 가질 뿐만 아니라 흡습 및 탈습 과정에서 고분자 구조가 어떻게 변화하는지를 평가할 수 있어 가장 적합한 방법으로 판단된다. In this study, we have evaluated the water absorption phenomenon of photoresist dry film, which is commonly used to build circuits on PCB (Printed Circuit Board) by photolithography, by using ATR-FTIR (Attenuated Total Reflectance-Fourier Transform Infrared). We have firstly observed significant change in fracture mode of dry film with respect to temperature and humidity, which we assumed the material transition from ductile to brittle. Secondly, we have established the process of absorption test for determining the diffusion coefficients of water into the dry film both with gravimeter and ATR-FTIR. We have successfully calculated the diffusion coefficients for each environmental conditions from the results which we achieved by gravimeter and ATR-FTIR. Compared to the gravimeter which is a conventional method for absorption test, the ATR-FTIR method in this study has been found to be very easy to use and have the same accuracy as gravimeter. Moreover, we are expecting to use the ATR-FTIR as an appropriate method to study the absorption phenomena related to any kinds of solvent and polymer system.

차체 구조용 에폭시 접착제의 접합부 특성에 미치는 Zirconate 첨가효과

The effect of zirconate having - NH functional group on the T-peel and lap shear strength of <TEX>$CaCO_3$</TEX> containing structural epoxy adhesive for car body assembly was investigated. Curing behavior of epoxy adhesive samples were investigated by differential scanning calorimeter (DSC) techniques. The addition of zirconate up to 7.5 phr did not affect the curing mechanism of epoxy adhesive. While the small amount of zirconate addition less than 1.1 phr increased the cross-linking density, the excess addition of zirconate resulted in the increase of uncross-linked impurity. From the increase of T-peel and lap shear strength and the change of fracture mode from the adhesive failure to the mixed one, it was considered that the small addition of zirconate was effective in improving the adhesion strength of epoxy adhesive to the adherend and inorganic filler surfaces. The formation of uncross-linked impurity with the excess addition of zirconate was considered to decrease the joint strength by decreasing the cohesive strength of the cured epoxy.

Oxidation behavior and effect of oxidation on microstructure and tensile properties of Ti–5Al–5Mo–5V–1Cr–1Fe alloy

Abstract In this study, both oxidation behavior and tensile properties of Ti–5Al–5Mo–5V–1Cr–1Fe alloy are investigated in air between 100 °C and 1000 °C. X-ray diffraction and light optical microscope are used to characterize the phase composition and morphology of oxide layers, respectively. The mixed oxide layer consists of the white TiO 2 , the golden TiO and blue Ti 2 O 3 , with white TiO 2 being the dominant oxide phase. These colored titanium oxides result in different colors on the surface of the specimens. The oxidation has a significant effect on the tensile properties of the alloy. Both adherent oxide layer and stable microstructure of adequate equiaxed α phase within a fine β transformed matrix are primarily responsible for a good combination of strength and ductility below 750 °C. However, as the alloy oxidized above 750 °C, both strength and ductility decrease dramatically due to the formation of defective oxide layer and coarsed β grains. An reliable oxidation model is proposed to predict the thickness of the oxide layer after taking the spalled oxide layer thickness into account. Moreover, the spallation of oxide layer leads to a fracture mode change from ductile fracture in specimens with dense oxide layer to a mixture of ductile fracture and brittle intercrystalline fracture in specimens with defective oxide layer.

Cyclic deformation and lifetime of Alloy 617B during isothermal low cycle fatigue

Isothermal low cycle fatigue tests are carried out on the nickel-base Alloy617B in the solution-annealed, stabilized and long-term aged conditions at temperatures between room temperature and 900°C. In addition, fatigue microcrack growth is measured using the replica technique. Transmission electron microscopy studies suggest that the observed differences in cyclic hardening between the different heat treatments result from the precipitation of fine carbides. Scanning electron microscope observations indicate a change in fracture mode for the solution-annealed and long-term aged material with temperature. The Chaboche model is able to describe the time and temperature dependent cyclic plasticity of the three material conditions. The measured lifetimes and crack growth rates can be described using a fracture mechanics based lifetime model. However, the data for room temperature and for temperatures above 400°C fall into two different scatter bands due to differences in crack growth rates.