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This study aims at experimentally revealing the effect of accumulated damages in supporting porous components on loosening behaviour using Infrared thermography(IR) and Acoustic emission(AE). Aseptic loosening is occurred due to degradation of fixing force of acetabular cups by biological effects or mechanical loading. However, effects of mechanical loading on loosening behaviors have not been observed yet. An integrated assembly of hip joint components, which is composed of stems and acetabular cups was set in distilled water in order to apply cyclic load in vitro. We developed the simulation system of loosening behaviour of acetabular cups by cyclic loading using cantilever. Damage evaluations on interface between the acetabular cup, HAp coating and supporting porous components (we call it " simulated bone ", which has similar Young ’ s modulus and density for those of cancellous bone) using AE. Additionally inelastic damage behaviour in simulated bone was simultaneously observed using IR. IR could successfully observed dissipation energy by inelastic damage accumulated during cyclic loading, which indicate its fatigue strength within shorter cyclic loading. Cyclic loading test for 1 million revealed that both lateral and angular displacement of the acetabular cup can be associated with the progress of damages in delamination of Hap coating or inelastic compression of simulated bone Loosening mechanism of the acetabular cup by cyclic loading can be considered by the contribution of both damages at the interface and in the simulated bone.

While several metallic implants with bioactive coatings have been developed thus far for treating bone deformations or deterioration, a multifunctional coating with the desired mechanical and antibacterial properties has not been demonstrated. This study aimed to reveal the effect of the composition of hydroxyapatite (HAp)/gray titania coatings on the mechanical and antibacterial properties for biomedical applications. Suspension plasma spray (SPS) aided successful deposition of HAp/gray titania coatings on the surface of titanium substrates. The microstructure of coatings with different compositions was then characterized using scanning electron microscopy, X-ray diffraction, and Raman spectroscopy to identify the crystal structure. All results consistently demonstrated that SPS could transform Ti2O3 into TiO2 with mixed Magneli phases, such as Ti4O7 and Ti3O5, which could typically demonstrate photocatalytic activity. Hardness, Young's modulus, and interfacial strength of composite coatings commonly increased with an increase in the weight percentage of TiO2. A multi-modal damage assessment combining acoustic emission (AE), infrared ray camera (IR), and digital-image-correlation (DIC) was performed to monitor the damage process of HAp composite coating, which successfully revealed initiations of microcracks and nonlinear deformation at interface until fracture. Antibacterial test performed for examining the cytotoxic effects against E. coli under LED light irradiation conditions revealed that SPS HAp/gray titania coating could significantly enhance the antibacterial properties. Enhanced antibacterial properties can be attributed to an increase in the number of Magneli phases and better bacterial adhesion was attributed to hydrophilic properties conferred by submicron-sized particles. Hence, SPS can help fabricate visible light-responsive antibacterial coating, which can be used for medical devices.

In order to achieve recent weight reduction for transport equipment, it is necessary to replace steel with nonferrous materials not only for structural parts but also for joining elements such as bolts and nuts. Fatigue strength of high strength steel bolts has rarely been influenced by clamp force which acts as mean stress to the bolts because of shakedown caused by local plastic deformation at the first thread root. However the effects of clamp force on fatigue strengths for aluminum alloy bolts have not been sufficiently revealed yet. In this study, fatigue tests and elasto-plastic analysis for aluminum alloy A5056 and A6056 bolts have been conducted to reveal the influence of clamp force on fatigue strength. Hexagon head bolts made of aluminum alloy A5056 and A6056 were used. For the internal thread parts for the A5056 bolts, A5056 nuts were used. For the internal screw parts for the A6056 bolts, machined nuts made of die cast material ADC12 considering actual usage were used. Results showed that the fatigue strength for A5056 bolts decreased with an increase in the mean load. Although the fatigue strength for A6056 bolts decreased with an increase in the mean load if the mean load was lower than 6 kN, the fatigue strength for A6056 bolts did not decrease if the mean load was greater than 6 kN. Results of elasto-plastic analyses showed that the causes, that the behaviors of these fatigue strengths were different, were reduction of mean stress due to local plastic deformation at the root of the first thread so-called shakedown. This result indicates that we can tighten A6056 bolts with high clamp force although cannot tighten A5056 bolts with high clamp force.

Fatigue design of weld part in non-combustible magnesium alloy has been studied. Specimens for fatigue test were produced by TIG welding with different welding conditions. According to result of fatigue strength tests, all weld specimens tested in the present study were broken at the weld prat, and a weld defect was found as a fatigue fracture origin. Fatigue life was well arranged by effective stress intensity factor calculated with a size of weld defect played as a fracture origin and applied stress. Therefore, it is speculated that fatigue strength of weld part is depending on a size of weld defect and threshold stress intensity factor at the weld part. Size of weld defect and value of threshold stress intensity factor possibly changed by welding condition. Therefore, relationship between heat input during welding process and threshold stress intensity factor was studied by conducting fatigue crack growth test at the weld part. The value of threshold stress intensity factor range increased with increase in heat input of welding process. However, values for threshold stress intensity factor range almost coincided when the crack growth curves were arranged by effective stress intensity factor range. Difference in threshold stress intensity factor range due to difference in heat input of welding process was mainly induced by change in crack closure effect. It is proposed that effect of crack closure depending on mechanical property of weld part should be taken into account on fatigue design of weld part in non-combustible magnesium alloy.

Plates of AL6XN super-austenitic stainless steel with a single-V groove preparation were gas metal arc welded (GMAW) with and without electromagnetic interaction of low intensity (EMILI) during welding using an ER-NiCrMo3 filler wire and 97% Ar + 3% N2 as shielding gas. The fatigue behavior of the welded joints was evaluated under constant stress amplitude (Δσ/2) between 135 and 170 MPa (R = 0.1) and uniaxial load. The Wohler diagram indicated that for stress amplitude of 170 MPa, 4.19 × 105 and 2.96 × 105 cycles were required for failure without and with EMILI, respectively, whereas for 135, 140, and 145 MPa, 1 × 107 cycles were reached without failure. Welding with EMILI was found to have a positive effect nearby fatigue limit. Observation of the fractures indicates that failures started on the surface of the specimens in the weld metal (WM) due to the stress concentration induced by the abundant presence of precipitates located along the interdendritic spaces in this zone of the welded joint. These particles acted as crack-nucleating agents and then the crack propagated throughout the WM. Fractography revealed brittle fracture associated to cleavage.

This study aims at observing the effect of Mg concentration on the interfacial strength and corrosion fatigue behavior of Al-Mg coating layers on structural steel (SS400) substrates. Al-Mg coating has been applied to components of bridges as sacrifice coating layers. Although Al or Al-Mg coating layers are typically applied to the components located in severely corrosive environment, a mechanism behind the effective protection provided by increasing the concentration of Mg has not yet been clarified. The interfacial strength test using four-point bending revealed that a Al-Mg coating layer of higher Mg concentration showed a higher interfacial strength only before immersion in 3.5-wt% NaCl aq.. After immersion in 3.5-wt% NaCl aq. for 30 days, such the difference in interfacial strength was lost due to rapid dissolution of Mg in the coating layers. As regards the fatigue crack growth behavior, the Al-Mg coating with higher Mg concentration exhibited a lower resistance to vertical crack propagation and interfacial delamination. A fracture mechanics model, which includes both effects of corrosion and delamination/cracking was proposed. Numerical simulation based on the fracture mechanics model successfully predicted exposure lives of substrates due to fatigue failure of the Al-Mg coating layers. These results could provide a selection policy for Al-Mg coating layers in which a loading level and the severity of corrosive environment were considered.

In this study, austenitic stainless steel 316L and titanium alloy (ASTM grade 5) were welded together by micro-resistance spot welding at different combinations of welding parameters and by using specifically designed electrode geometry. The welded joints were subjected to tensile shear strength test in order to determine the strength of the welded zones. In addition, micro-hardness and microstructural examinations of the fracture mode (failure analysis) were carried out in order to examine the influence of welding parameters on the welded joints. The results showed that using a combination of 2.0 kN welding current, 100 ms welding time, and 241 N welding force yield the highest load value, 378.25 N by using full factorial design of experiment (DOE). Welding current is the most significant parameter which is obtained through analysis of variance (ANOVA). However, the increase in welding current should be controlled to avoid weld metal expulsion. The microstructure of these resistance-welded metals are detailed and investigated by using SEM and EDS mapping analysis. Based on the SEM observations, columnar dendritic structures can be seen at the fusion zone (FZ) of the welded nugget.

The fatigue strengths at 1000 °C of layered W-Re/TZM, bulk W-Re and bulk TZM for x-ray target materials were successfully evaluated under load-controlled four-point bending by introducing a fatigue failure criterion as two-times increase of initial compliance. The obtained fatigue strengths at 1000 °C for layered W-Re/TZM and bulk W-Re were similar and 280 MPa and 290 MPa at 106 cycles, respectively, while that of bulk TZM was 200 MPa. During fatigue loading at 1000 °C, dominant fatigue damage would be multiple intergranular crack nucleation and propagation, which would induce the increase of compliance. The reasonability of the fatigue failure criterion was confirmed by the fatigue process observations and the results of room temperature fatigue tests of the specimens tested at 1000 °C up to the cycles corresponding to the fatigue failure criterion. Keywords: Fatigue strength, High temperature, Fatigue damage, Microstructure-property relationship, Refractory materials

An observation system of loosening behavior of an acetabular cup by interfacial dam ages induced by cyclic loading was successfully developed. The purpose of this study was to investigate the effects of inplane cup angles, which changed the distance between position of screw holes and loading points, to the loosening behavior of the acetabular cup. Recently artificial hip joint is widely used to replace in human in order to reduce the pain in patients Revision cases of acetabular cups have been increased due to loosening. Loosening was considered to be caused by infection or osteolysis . However, in the long-term use of total hip joints, loosening without infections, called “aseptic loosening,” is a major cause of revisions. However, the mechanism of progression of aseptic loosening is still unclear. One of the unrevealed factor is interfacial damages by loading, and then it should be investigated an experimental system which can exclude the effects of infections. A cyclic loading system using a fatigue testing machine to an assembly of a stem, a femoral head, a liner and a acetabular cup was designed. The acetabular cup coated by plasma-sprayed hydroxyaptite (HAp) to simulate practical fixation condition of cementless bonding of the acetabular cup to surrounding acetabulum. AE (Acoustic Emission) sensor system was subsequently attached on the bottom of the acetabular cup to observe damages at the interface between the embedded acetabular cup with simulated bone during the cyclic loading. Interfacial damages were intermittently observed at the edge of the acetabular cup during cyclic loading tests and those frequency were varied by changing an inplane cup angles. SEM(Scanning Electron Microscope) observed significant delamination of HAp coating after the cyclic loading, which attributed to the rotational displacement of the acetabular cup. Furthermore, observed values of the rotational displacement of the acetabular cup were compatible with those observed in normal patient of THA(Total Hip Arthroplasty). The result demonstrated that loosening behavior of the acetabular cup can be occurred only by mechanical damages such as delamination of HAp coating , wear or damages in simulated bone, which enlightened the importance of mechanical factors in practical loosening behavior of aceptic loosening.

The purpose of this study is to evaluate interfacial strength of plasma-sprayed HAp coating by using more general adhesives. Plasma-sprayed HAp coating has been applied to bond bones with the surfaces of artificial hip joints. However, HAp coating is subjected to crack or delamination by mechanical loading. Conventional standard codes for measurement of interfacial strength of calcium phosphate coating determine the use of a specific adhesive irrationally. Our group previously proposed pre-immersion treatment process in preparation of interfacial testing specimens in order to obtain valid value of interfacial strength. However, the type of the adhesive was for medical purpose and not general one. To widen applicability of the proposed method, a selection policy of adhesive is indispensable. Metal Lock Y610 (ML adhesive) was selected as one of general adhesives. Interfacial strength tests by using ML adhesive were conducted. The results of interfacial strength test were compatible with the one reported by previous study, which suggest that the selection of general type of adhesive was successful. Raman spectroscopy analyses were also conducted to confirm a suppressed infiltration of ML adhesives.

The texture, microstructure, and mechanical properties of severely deformed aluminum subjected to friction stir processing (FSP) with SiC nanoparticles under ambient and cryogenic temperatures are comprehensively investigated. Even one pass of FSP in the ambient temperature results in the formation of quite large grain structure with random texture in the heat affected zone (HAZ). It suggests the occurrence of static recrystallization and subsequent grain growth because of the appreciable strain stored within the base metal. One FSP pass under condition of cryogenic temperature causes to the development of bimodal grain size distribution in HAZ, including the elongated grains with interior subgrains and very large grains as a result of texture-induced abnormal grain growth. Large grains with random texture are formed throughout HAZ during further FSP passes. In the stir zone where SiC nanoparticles are dispersed during FSP in the ambient temperature, fine grain structure with the shear texture components of C and A 1 ∗ is obtained through the geometrically dynamic recrystallization mechanism. When FSP is performed in the cryogenic temperature, the grain size of stir zone is decreased because of the increased cooling rate. Although the shear texture components developed in the stir zone are the same at both mentioned processing conditions, the texture strength is less in the case of cryogenic temperature, suggesting the contribution of additional grain formation mechanism, namely discontinuous dynamic recrystallization. This mechanism gives rise to the formation of randomly oriented grains. The nano-indentation test results confirm that FSP under cryogenic temperature improves the mechanical properties not only in the stir zone, but also in HAZ.

The elastic-plastic fracture toughness JIC of two titanium-zirconium-molybdenum (TZM) alloys with different kinds of grain boundary particles was estimated at elevated temperatures using the convenient JIC test method with a suitable depth of side-groove for determining the JIC at the maximum load point. It was found that the convenient JIC test method can be successfully applied to evaluate high temperature fracture toughness at least up to 1200 °C. The JIC values at temperatures ranged from 800 °C to 1200 °C were almost constant regardless of temperature, while the JIC values of the TZM with carbide particles were higher than those of the TZM with oxide particles. The TZM with different forging rates showed similar JIC values, which suggested the effect of forging rate would be not significant at high temperatures.

Formation behavior of bubbles and its effect on strength in PET/SUS304 dissimilar materials laser spot lap joint was studied. Surface of SUS304 was irradiated through transparent PET with fiber laser. Static and cyclic contact force was applied at the welding region during the joining process. Strength of the joint was evaluated by conducting tensile shear test. The formation behavior of bubbles inside PET nearby the interface changed with change in condition of contact force. In case of applying lower static contact force, welded area and failure load of the joint increased with increase in contact force. This result might be due to flow of molten PET by applying compressive force. On the other hand, when higher static contact force was applied, welded area and failure load of the joint decreased, because suppress of the flowing for molten and softened PET occurred. The joint joined with applying cyclic contact force showed lower values of welded area and failure load compared to the joint joined with applying the same maximum static contact force. According to fracture surface observation, crack mainly passed through bubbles to failure in all joints. Apparent strength was calculated by failure load and welded area obtained. The strength of the joint decreased with increase in bubbles density, except the joint joined without contact force. In case of joint joined without contact force, large bubbles were formed and decreased strength. Bubble size formed was small when contact force was applied. Density of bubbles affected strength of the joint and changed by applying contact force, particularly that decreased by applying cyclic contact force. It is considered that applying the contact force is an effective way to control formation behavior of bubbles and results in improvement for reliability of the dissimilar material joint between plastic and metallic materials.

A strain gage method has been developed for determining the generalized stress intensity factors (GSIFs) of sharp V-notched plates subjected to transverse bending. The study is based on Mindlin’s theory of plate bending. The bisector of the notch opening angle is inclined to the edge of the plate, and the mixed mode loading is created simultaneously. The singular strain fields around the notch tip including the non-singular terms are derived in terms of the GSIFs. These strain fields of dominant terms do not coincide with those of the plane problem. The crack strain fields, however, are coincident with those of the plane problem, if we take a limiting value in the notch strain fields obtained. In order to separate the mixed-mode GSIFs, two strain gages with five element grids are severally positioned along the two lines extending from the bisector of the notch, and a simple procedure to determine the GSIFs for each mode is presented. Experiments on the specimens in strip form with various notch opening angles and inclination angles as well as an inclined crack in rectangular plates are carried out to compare with the results of finite element analyses according to Mindlin’s plate theory. It is shown that the reasonable agreement is obtained between them.

In the present study, fatigue crack growth tests of Pb-containing [Sn-37Pb (wt.%)] and Pb-free [Sn-3.0Ag-0.5Cu (wt.%)] solders were performed under cycle/time-dependent step loading at a constant J-integral range (ΔJ). The C* parameter was also estimated for discussing time-dependent crack growth behavior. The experimental results indicated that acceleration of the crack growth rate at the beginning of the second loading step was induced when the C* value for the first loading step was high, regardless of time- or cycle-dependent crack growth and for both Sn-37Pb and Sn-3.0Ag-0.5Cu solders. The length of the acceleration region of the crack growth rate for both solders was in good agreement with the creep damage zone size estimated by the creep zone model proposed by Riedel and Rice.

Dissimilar materials laser spot joining between polyethylene terephthalate (PET) and aluminum alloy (A5052) was studied by using pulse YAG laser. The results showed that it was possible to make a joint in a wide range of heat input. Molten pool was formed at the interface of A5052 and depth of molten pool increased with increase in heat input. Tensile shear test was carried out to evaluate strength of the joints. The result showed that tensile shear strength increased with increase in the heat input when the molten pool filled with molten or softened PET. On the other hand, instability of joining state inside the molten pool might induce variation in the strength. FEM analysis was carried out to investigate effect of molten pool shape on the strength. The result showed that molten pool radius did not significantly affect tensile shear strength. In contrast, the joint strength increased with increase in the molten pool depth as observed in result of the experiment. It is proposed that taking into account the mechanical effect such as molten pool shape is an important approach to improve the joining strength under tensile shear loading.

In the present study, scatter behavior of fatigue limit for the die-cast magnesium alloy AM60B was investigated. Twelve fatigue limits were determined based on S-N curves obtained according to the standard fatigue test methods. The scatter of fatigue limit for the die-cast AM60B was large compared to the extruded AZ61: the values of Weibull modulus and COV were 16 and 6.8, respectively, for the die-cast material, whereas those for the extruded one were 159 and 0.7. The COV value of 0.7 for the extruded AZ61 meant that only 0.7% of scatter from the mean value was included in the fatigue limit determined based on the S- N curve. This COV value was comparable to that of 0.6 for the tensile strength of the same material. Therefore, the fatigue limit for the extruded material has small enough scatter to be considered as the material property similar to the tensile strength that can be determined from the average value of 2-3 samples.

Overall fatigue strengths and hardness distributions of the aluminum alloy similar and dissimilar friction stir welding (FSW) joints were determined. The local fatigue strengths as well as local tensile strengths were also obtained by using small round bar specimens extracted from specific locations, such as the stir zone, heat affected zone, and base metal. It was found from the results that fatigue fracture of the FSW joint plate specimen occurred at the location of the lowest local fatigue strength as well as the lowest hardness, regardless of microstructural evolution. To estimate the fatigue strengths of aluminum alloy FSW joints from the hardness measurements, the relationship between fatigue strength and hardness for aluminum alloys was investigated based on the present experimental results and the available wide range of data from the references. It was found as: σa (R = −1) = 1.68 HV (σa is in MPa and HV has no unit). It was also confirmed that the estimated fatigue strengths were in good agreement with the experimental results for aluminum alloy FSW joints.

The joining of lead-free Sn-3.0Ag-0.5Cu (SAC305) solder alloy to metal substrate with the addition of a porous Cu interlayer was investigated. Two types of porous Cu interlayers, namely 15 ppi—pore per inch (P15) and 25 ppi (P25) were sandwiched in between SAC305/Cu substrate. The soldering process was carried out at soldering time of 60, 180, and 300 s at three temperature levels of 267, 287, and 307 °C. The joint strength was evaluated by tensile testing. The highest strength for solder joints with addition of P25 and P15 porous Cu was 51 MPa (at 180 s and 307 °C) and 54 MPa (at 300 s and 307 °C ), respectively. The fractography of the solder joint was analyzed by optical microscope (OM) and scanning electron microscopy (SEM). The results showed that the propagation of fracture during tensile tests for solder with a porous Cu interlayer occurred in three regions: (i) SAC305/Cu interface; (ii) inside SAC305 solder alloy; and (iii) inside porous Cu. Energy dispersive X-ray spectroscopy (EDX) was used to identify intermetallic phases. Cu6Sn5 phase with scallop-liked morphology was observed at the interface of the SAC305/Cu substrate. In contrast, the scallop-liked intermetallic phase together with more uniform but a less defined scallop-liked phase was observed at the interface of porous Cu and solder alloy.

In this study, the effects of CeO2 nanoparticle addition on tensile strength and formation of interfacial intermetallic compound layer for lead-free Sn-3.5Ag-0.7Cu solder joint were investigated. The results showed that the thickness of intermetallic layer was decreased with increasing weight percentages of CeO2 reinforcements, and the growth of the intermetallic layer was remarkably suppressed during isothermal aging at 150 °C. It was also found that the tensile strength of the solder joint gradually increased with the addition of CeO2 particles, reached to the maximum value at 0.5 wt% CeO2 and then decreased drastically with further increase in CeO2 content. Microstructural investigation of 1 wt% CeO2 reinforced solder joint revealed that due to particle pushing under the influence of interfacial tension between the particles and the matrix, the brittle cluster-like regions with high concentration of CeO2 particles were formed inside the joint. These brittle clusters act as preferential site for crack initiation during tensile test which would degrade the tensile strength. Hence, based on the results obtained in this study, addition of CeO2 particles up to 0.5 wt% provide an optimized solder joint with improved strength together with suppressed intermetallic growth and long-term reliability.

Scatter behavior of fatigue life in a die-cast AM60B magnesium alloy was investigated. For comparison, those in a rolled AM60B alloy and a die-cast A365-T5 aluminum alloy were also studied. Scatter behavior of pore size was also investigated to discuss about dominant factors for fatigue life scatter in the die-cast materials. Three-parameter Weibull function was suitable to explain the scatter behavior of both fatigue life and pore size. The scatter of fatigue life in the die-cast AM60B alloy was almost comparable to that in the die-cast A365-T5 alloy, while it was significantly large compared to that in the rolled AM60B alloy. Scatter behavior of pore size observed on the specimen cross-section was comparable to that of fatigue life. Therefore, the scatter behavior of fatigue life can be estimated, if the scatter behavior of pore size on the cross section of specimen would be evaluated, as proposed in the present study.

High-density, ultrasmall-pitch electronic applications require miniaturized solder bumps with improved thermomechanical performance. In addition, novel techniques which are able to precisely characterize these solder bumps are needed. One approach to meeting both of these requirements is to make use of recently developed nanocomposite solders with enhanced creep resistance, and to characterize these solders using a nanoindentation technique. In the present study, the creep behavior of ceria-reinforced nanocomposite solder foils fabricated by the accumulative roll-bonding process was characterized using a depth-sensing nanoindentation technique. It was found that the creep resistance of the composites increased with increasing volume fraction of CeO2 reinforcement, and it was deduced that the creep deformation of this nanocomposite proceeded by deformation of the matrix, with the role of the reinforcement being to increase the creep resistance by reducing the effective stress acting on the matrix. The values of the creep exponent suggested that the dominant creep deformation mechanisms involved were diffusion creep and grain boundary sliding.

As one of the key technologies for high performance electronic devices, composite solders have been recently developed to improve thermal and mechanical properties of solder joints. In this study, accumulative roll bonding process was used as an effective alternative method for manufacturing high-strength, finely dispersed, void-free and highly uniform Sn–Ag–Cu/CeO2 nanocomposite solders. Microstructural investigation of nanocomposite solders revealed that homogenous distribution of CeO2 nanoparticle has been achieved and the eutectic as-cast morphology of the solder changed to recrystallized fine grained structure. As a result of severe plastic deformation during rolling, brittle and elongated intermetallics crushed into fine particles with an average diameter of a few hundred nanometers and dispersed uniformly in the solder matrix. Mechanical test results showed that the microhardness, 0.2% yield stress, and ultimate tensile strength of the composite solder increased with addition of CeO2 nanoparticles, while the ductility of the composite was decreased.

Normal failure or risk analyses procedure contains the following steps; 1) modeing process, 2) assessment process of its hazardous extent. 1) Modeling process is the considering procedure that sets the sequence of happening failures or risks. 2) Assessment process is the evaluation procedure that express its hazardous extent quantitatively or qualitatively (probability, seriousness of injury etc.). According to ISO14120 (Risk assessment process), ranking procedure of risks are established. However, there is no logical procedure for 1. Modeling process and these steps still highly depends on designer’s knowledge or experiences of failures and accidents. It is necessary to establish a logical guideline of failure modeling process for fresh designers in order to effectively conduct failure and risk analyses with their acceptable workloads. This study aims at proposing the logical failure modeling process based on the SSM (Stress-strength model) and the normal-state conditions. In the beginning, designers make a stress-strength model of considering components and its “normal condition”. Introducing “deviations” in normal conditions of stress-strength state and surrounding environmental conditions can lead the designers to easily predict failure modes caused by the proposed deviations. Similar steps are applied in the process of considering risk phenomena caused by failure modes. A case study of assessing the safety of micro windmill demonstrated the effectiveness of our proposed procedures.

Spark plasma sintering (SPS) technology was used to determine the appropriate conditions for SPS sintering of commercially pure magnesium as well as the magnesium alloy AZ31. It was found that the sintering temperatures of 585 °C and 552 °C were the most suitable sintering temperatures for the magnesium and the AZ31 alloy, respectively. Magnesium matrix and AZ31 alloy matrix composites reinforced with SiC particles were then successfully fabricated by the SPS method at sintering temperatures of 585 °C and 552 °C, respectively. A uniform distribution of SiC particles was observed along the boundary between matrix particles. The mechanical properties, i.e. hardness and tensile strength increased with increasing SiC content up to 10 wt%. However, when the SiC content was larger than 10 wt%, the tensile strength decreased due to the agglomeration of SiC particles. The agglomeration of SiC particles was found to lead to the degradation of the interfacial bonding strength between matrix and reinforcement.

A new direct joining method for dissimilar materials between a metal and a plastic by using friction stir heating technique is introduced. A5052 and polyethylene terephthalate (PET) were used as materials used in this study. The joining strength was evaluated under tensile shear loading condition. The fracture surface and the cross section of the joined specimens were observed in order to understand characteristics of the joints. The results show that A5052 and PET were successfully welded by the present joining method. Similar strength of the joints was obtained regardless of the joining conditions. Melting and softening behaviors of PET and formation of bubbles observed in welded area might affect the joining strength.

The knowledge of statistic characteristics in mechanical properties is important for designers in order to assess the reliability of structures. Scatter characteristics of fatigue limit, fatigue life and tensile strength for magnesium alloy were investigated in this study. At least 20 specimens were tested to obtain the scatter data of fatigue limit, fatigue life and tensile strength, respectively. The probability distributions of fatigue limit, fatigue life and tensile strength were evaluated by using Normal distribution and Weibull distribution function. The values of the Weibull modulus, m were 159, 10, 175 for fatigue limit, fatigue life and tensile strength, respectively. Therefore, it can be concluded that scatter of fatigue limit is small and almost coincides with that of tensile strength, while scatter of fatigue life is significantly large compared to those of fatigue limit and tensile strength. The large scatter of fatigue life will be due to crack nucleation and small crack growth processes, which strongly depend on local microstructure near the crack nucleation region.

In order to reduce weight of a vehicle, application of light metals has increased. Magnesium alloy is very light and has high specific strength compared to other structural metals. SPR (Self Piercing Rivet) joining has been applied mainly for an aluminum alloy in motor industries. However, application of SPR joining to a magnesium alloy is very limited. In this study, SPR joining was carried out with AM50 magnesium alloy sheets. According to the result of joining experiment, cracking easily occurred at the lower sheet due to poor formability of the alloy. Static and fatigue strength of the joint were evaluated under shear tensile loading condition. The crack introduced in SPR process affects on strength of the joint. As a practical way to solve the problem, adhesive aided SPR joining was proposed. Adhesive was spread on the surface and then SPR joining was conducted before its hardening. The maximum shear tensile load of the joint increased by using an adhesive and was strongly influenced by kind of adhesive used. Fatigue strength also improved by using an adhesive. It is proposed that control for deformation due to SPR process at the edge of the joining area could be effective to improve the strength.