Sharif Digital Repository

Fracture tests on Sn93Pb37 solder joints in a double cantilever beam (DCB) configuration were performed at two different strain rates of 10−5 and 0.03 s−1 under mode I loading conditions. In each case, the critical strain energy release rate for crack initiation, Jci, was obtained. Effects of storing specimens at a constant temperature of 75 °C and cyclic temperature varying between 32 and 75 °C were examined at these strain rates. In the strain rate of 0.03 s−1, storing samples in a constant or cyclic temperature caused the fracture energy to decrease significantly with respect to the specimens maintained in ambient temperature. The significant reduction in fracture energy by placing the... 

Finding the optimized set of manufacturing parameters to produce strong solder-copper connections requires investigating the main and interaction effects of processing variables on the joint strength and microstructure. In this study, solder joint specimens were prepared at different levels of cooling rate, time above liquidus (TAL), and soldering temperature. Mode I fracture experiments were designed and performed at a strain rate of 0.5 s−1. The fracture load remained constant from the cooling rate of 0.1 to 1.4 °C/s and then decreased by almost 34% with further increase in the cooling rate to 34 °C/s. Increasing TAL from 60 to 120 s reduced the fracture load by almost 27%, while it was... 

This study investigated the mode I fracture behavior of double cantilever beam (DCB) epoxy adhesive joints with similar adherends on the both sides (i.e., aluminum-aluminum or copper-copper) at different strain rates; i.e., quasi-static (∼10−3 s−1), low (∼7 s−1) and intermediate (∼14 s−1) rates. The fracture energy of the DCB joint in Al-adhesive-Al specimens decreased (i.e., by ∼62%, p = 0.0013) with an increase in the applied strain rate from quasi-static to low values, while it remained almost unchanged with further increase of stain rate to intermediate range (p > 0.05). For Cu-adhesive-Cu cases, however, the fracture energy was found to be almost insensitive to the applied strain rate... 

Although the anterior cruciate ligament (ACL) reconstruction using interference screw is a well-accepted surgical procedure, patients still suffer graft failure in the initial rehabilitation phase. Graft fixation stability of a newly designed anatomical hybrid thread tapered interference screw (AHTTIS) was compared with a conventional standard one (CSIS) by conducting in-vitro mechanical tests. According to the CSIS manufacturer's instruction, eight tapered bone tunnels, matching AHTTIS geometry, and eight straight cylindrical tunnels were drilled in artificial bone blocks. Bovine tendon grafts were fixed using AHTTIS and CSIS in their corresponding bone tunnels. Each graft was subjected to... 

Rod-shaped samples of maraging steel were additively fabricated in vertical and horizontal directions using laser powder bed fusion technique. The samples were first aged at 490 °C for 6 h and then subjected to dynamic compressive tests using Split Hopkinson Pressure Bar apparatus. The dynamic compression tests were conducted on vertical samples at strain rates of 190, 460, 810, 1100, 1300 s−1. However, the high strain rate tests were performed at strain rates of 120, 615, 745, 890, 2200 s−1 on horizontal samples. After applying the compressive impact loads on the samples, it was found that although horizontally built samples exhibit higher dynamic strength, vertically built samples show... 

Background and Objective: The present article has simulated to investigate the efficient hemodynamic parameters, the drug persistence, and drug distribution on an abdominal aortic aneurysm. Methods: Blood as a non-Newtonian fluid enters the artery acting as a real pulse waveform; its behavior is dependent on hematocrit and strain rate. In this simulation of computational fluid dynamic, magnetic nanoparticles of iron oxide which were in advance coated with the drug, are injected into the artery during a cardiac cycle. A two-phase model was applied to investigate the distribution of these carriers. Results: The results are presented for different hematocrits and the nanoparticle diameter. It... 

In this study, the influence of temperature on serrated flow behavior, strain rate sensitivity (SRS) and effective activation volume in a Ti-based bulk metallic glass (BMG) bent at different strain rates has been investigated. Results reveal that the fundamental origin of shear deformation is related to the time-dependent structural relaxations, which occur during deformation at special temperatures and strain rates. Furthermore, the localized structural relaxation processes at intermediate temperatures cause an inelastic shuffling within cages and mitigate the activation of STZs. The main reason of negative SRS at intermediate temperatures is due to the insufficient time for structural... 

In this research, the dynamic behavior of serrated flows observed in the flexural stress-deflection curves during three-point bending (3 PB) tests on Zr-, Ti- and La-based bulk metallic glasses (BMGs) is statistically analyzed. Furthermore, the effect of strain rate on the serrations is studied. Based on the ductility of alloy, two distinct types of dynamics are detected. For more ductile alloys (Zr- and Ti-based BMGs) the stress drop magnitude of serrations obeys a power-law distribution of shear avalanches, which is an indicator of the self-organized critical (SOC) state in dynamics. In this case, the size of avalanches has no characteristic scale. In contrast, the size of serrations... 

In this study, the influence of temperature on serrated flow behavior, strain rate sensitivity (SRS) and effective activation volume in a Ti-based bulk metallic glass (BMG) bent at different strain rates has been investigated. Results reveal that the fundamental origin of shear deformation is related to the time-dependent structural relaxations, which occur during deformation at special temperatures and strain rates. Furthermore, the localized structural relaxation processes at intermediate temperatures cause an inelastic shuffling within cages and mitigate the activation of STZs. The main reason of negative SRS at intermediate temperatures is due to the insufficient time for structural... 

LDL concentration is believed to be responsible for plaque formation that leads to atherosclerotic cardiovascular disease. We conducted this study to investigate the effects of hematocrits and LDL diameters on LDL concentration on the wall of an abdominal aortic aneurysm (AAA). The blood flow was considered to be a pulsatile and non-Newtonian flow whose viscosity was a function of hematocrits and strain rate. Lumen, Brownian, and thermophoresis diffusions were analyzed in LDL concentration. The results demonstrated that adding thermophoresis diffusion increases LDL concentration. Moreover, among three types of LDLs, including small LDLs, intermediate LDLs, and large LDLs, small LDLs were the... 

LDL concentration is believed to be responsible for plaque formation that leads to atherosclerotic cardiovascular disease. We conducted this study to investigate the effects of hematocrits and LDL diameters on LDL concentration on the wall of an abdominal aortic aneurysm (AAA). The blood flow was considered to be a pulsatile and non-Newtonian flow whose viscosity was a function of hematocrits and strain rate. Lumen, Brownian, and thermophoresis diffusions were analyzed in LDL concentration. The results demonstrated that adding thermophoresis diffusion increases LDL concentration. Moreover, among three types of LDLs, including small LDLs, intermediate LDLs, and large LDLs, small LDLs were the... 

Double cantilever beam (DCB) specimens were prepared according to standard surface mount technology (SMT). The samples were stored inside an environmental chamber at two different relative humidity values (i.e. 40 or 100%) for either 2 or 4 h. Then they were aged at 25 °C, 75 °C or 125℃ for the same time. Finally, after being cooled to room temperature, fracture tests were performed under mode-I loading conditions at a strain rate of 0.03 s−1 at room temperature. Storage time did not have a significant effect on the fracture behavior. The fracture load and energy of the solder joints decreased significantly when the temperature was increased from 25 to 75℃. By further increase in the... 

The aim of this study is to investigate the role of the temperature, stress, and rhenium (Re) on the γ/γ' interfacial misfit dislocation network and mechanical response of Ni-based single crystal superalloys. After aging at elevated temperatures, mismatch between the two phases results in an interfacial dislocation network to relieve the coherency stress. Molecular dynamics (MD) simulations have been performed to study the properties of the (100), (110), and (111) phase interface crystallographic directions. Increasing temperature disperses the atomic potential energy at the interface diminishing the strength and stability of the networks. In the case of loading, when a constant strain rate... 

In this paper, a comprehensive analytical study is performed to assess the lycopodium-diesel dual-fuel combustion system in counter-flow premixed configuration. The system is modeled as multiple zones that are coupled together via proper boundary and jump conditions on interfaces. According to the respective reaction and transport phenomena in these zones, conservation equations of mass and energy are derived, non-dimensionalized, and solved by Matlab and Mathematica in an analytical way. The porosity of lycopodium particles and the thermal radiation from the reaction zone and the post-flame zones into the preheating zone are considered, in order to improve the realism and accuracy of the... 

The dynamic and static softening phenomena in Al-6Mg alloy were studied through interrupted two-stage hot compression test performed isothermally at 480°C and strain rate range of 0.001-0.1 s-1. The interruptions of 29 and 90 s were considered when the true strain reached 0.5. It was concluded that the effect of static softening on the flow stress was not highlighted by extending the interruption at a constant strain rate. Also, it was exhibited that softening rate highly enhanced with the strain rate decrement at a constant time. Moreover, the static and dynamic recrystallization was revealed as the dominant softening mechanisms at low and high strain rates, respectively  

Abstract High ductility of metals as well as high strength of ceramics has made the metal/ceramic composites an attractive material for many applications requiring high strength to weight ratios. An important issue in using this material is the behavior of the material and its ceramic-metal interface under various loading, especially at high strain rate. To provide a better understanding of the interface conditions, in this work, a molecular dynamics study of the interface behavior in Al/α-Al2O3 composite as the result of tensile and shear loadings is presented. For this purpose, the reactive force field (ReaxFF) potential function is utilized. The effects of... 

In this paper, the dynamic large deformation X-FEM method is presented for modeling the full process of dynamic ductile fracture based on a nonlocal damage visco-plasticity model. The effect of inertia is modeled using an explicit central difference scheme which is enhanced through the use of mass lumping, reduced integration with hourglass control, and numerical damping. The material nonlinearity and the flow stress dependency on strain rate, hardening and temperature are modeled with the Johnson-Cook visco-plastic model. The micro-void nucleation, growth and coalescence are modeled macroscopically with an isotropic damage model. The localization phenomenon due to the damage and thermal... 

It has been shown that FEM simulation of creep deformation of composites is somehow very challenging. The type of FEM model, mesh size, element type, internal defects (such as fibre/matrix debonding), and the type of mathematical creep law all affect the calculation of the creep strain rate. In the present study, the fibre offsetting which happens in the manufacturing phase of composites is added to the simulation. It is shown that this defect at some critical point can affect the calculation of creep deformation. Here, the quantification of this phenomenon is performed using 3-D FEM models. Since it has also been shown that the fibre/matrix debonding affects the creep strain rate, the... 

Double cantilever beam (DCB) specimens of 2.5-mm-long SAC305 solder joints were prepared with thickness of copper adherends varying from 8 to 21 mm each. The specimens were tested under mode I loading conditions (ie, pure opening mode with no shear component of loading) with a strain rate of 0.03 second−1. The measured fracture load was used to calculate the critical strain energy release rate for crack initiation, Jci, in each case. Fracture behaviour showed a significant dependence on the adherend thickness; the Jci and plastic deformation of the solder at crack initiation decreased significantly with increase in adherend thickness. This behaviour was attributed to changes in stress... 

Double cantilever beam (DCB) specimens of 2.5-mm-long SAC305 solder joints were prepared with thickness of copper adherends varying from 8 to 21 mm each. The specimens were tested under mode I loading conditions (ie, pure opening mode with no shear component of loading) with a strain rate of 0.03 second−1. The measured fracture load was used to calculate the critical strain energy release rate for crack initiation, Jci, in each case. Fracture behaviour showed a significant dependence on the adherend thickness; the Jci and plastic deformation of the solder at crack initiation decreased significantly with increase in adherend thickness. This behaviour was attributed to changes in stress...