Mechanical Fatigue Tests Research Articles

Durability Characterization of Active Fiber Composite Actuators for Helicopter Rotor Blade Applications

Theprimary objective of this work was to characterize the long-term durability performance of the Active Fiber Composite (AFC) actuator material system for the Boeing Active Material Rotor (AMR) blade application. The AFCs were a new structural actuator system consisting of piezoceramic fibers embedded in an epoxy matrix and sandwiched between interdigitated electrodes. These actuators were integrated directly into the blade spar as active plies within the composite structure to perform structural actuation for helicopter vibration control. Therefore, it was necessary to conduct extensive electromechanical material characterization to evaluate AFCs both as actuators and as structural components of the blade. The long-term durability characterization tests designed to extract important electromechanical properties were electrical fatigue tests and mechanical fatigue tests. This paper presents the test results as well as the comprehensive testing process developed to evaluate the relevant AFC durability properties. The durability tests conducted under simulated electromechanical loading conditions expected on AFCs during the blade operation provided an invaluable insight into the behavior of the AFCs under dynamic loading environment. The results from this comprehensive durability characterization of the AFC material system supported the design and operation of the Boeing AMR blade scheduled for wind tunnel tests.

An experimental characterization of the acoustic fatigue endurance of GLARE and comparison with that of CFRP

GLARE is a new aerospace structural material composed of alternating, bonded layers of aluminium alloy and glass fibre reinforced plastic. The results of an experimental study are presented here concerning mechanical fatigue testing of GLARE structural specimens in conditions relevant to the acoustic fatigue problem. Endurance testing of 35 GLARE Tee-coupons under simulated random acoustic loading has been carried out and resonance frequency, damping loss factor, and strain response of the specimens have been experimentally determined. CFRP specimens have also been tested to provide a benchmark against which to compare the properties of GLARE. FE analysis of the coupons has also been carried out to support the experimental work and the theoretical results have been compared with the experimental data. Damage mechanisms have been observed and fatigue data established. Using these experimental data, surface strain versus number of cycles to failure curves have been established. In particular, this work has assessed the behaviour of GLARE in bending and has highlighted the importance of the lay-up sequence for the “fibre bridging effect” on crack propagation to be effective.

Low Cycle Fatigue Testing of Ball Grid Array Solder Joints under Mixed-Mode Loading Conditions

To give a proper and accurate estimation of the fatigue life of ball grid array (BGA) solder joints, a mechanical fatigue test method under mixed-mode loading is proposed. Experiments were conducted with 63Sn∕37Pb and Sn∕3.5Ag∕0.75Cu solder joints in room temperature. The mechanical low cycle fatigue tests were performed under several loading angles. The loading angle is controlled by several grips which have specific surface angle to the loading direction. Constant displacement controlled tests are performed using a micro-mechanical test apparatus. It was found that the normal deformation significantly affects the fatigue life of the solder joint. Throughout the whole test conditions at room temperature, Sn∕3.5Ag∕0.75Cu solder alloy had longer fatigue life than 63Sn∕37Pb alloy. Failure patterns of the fatigue tests were observed and discussed. A morrow energy model was examined and found to be a proper low cycle fatigue model for solder joints under mixed mode loading condition.

Effect of silver content on the shear fatigue properties of Sn-Ag-Cu flip-chip interconnects

The mechanical shear fatigue test has been performed to study the effect of silver content on the fatigue properties of Sn-xAg-0.5Cu (x=1, 2, 3, and 4) for flip-chip interconnections. The strength of the solder alloy increases with increasing silver content, preventing shear plastic deformation of the solder bump. The flip-chip joints made using higher silver content solder, such as 3%Ag and 4%Ag, exhibit longer fatigue life for all conditions. The fatigue ductility of the solder decreases with an increase in the silver content. The fatigue endurance of 1%Ag solder is superior to other solders over the plastic strain range of 3%, even though the strength of the solder is the lowest in the solders tested. Based on this study, the 3Ag solder may exhibit good fatigue performance for all conditions, and the 1Ag solder is optimum for severe strain conditions.

High cycle fatigue of a die cast AZ91E-T4 magnesium alloy

This study reveals the micro-mechanisms of fatigue crack nucleation and growth in a commercial high-pressure die cast automotive AZ91E-T4 Mg component. Mechanical fatigue tests were conducted under R=−1 conditions on specimens machined at different locations in the casting at total strain amplitudes ranging from 0.02% to 0.5%. Fracture surfaces of specimens that failed in the high cycle fatigue regime with lives spanning two orders of magnitude were examined using a scanning electron microscope. The difference in lives for the Mg specimens was primarily attributed to a drastic difference in nucleation site sizes, which ranged from several hundred μm’s to several mm’s. A secondary effect may include the influence of average secondary dendrite arm spacing and average grain size. At low crack tip driving forces ( K max<3.5 MPa m ) intact particles and boundaries act as barriers to fatigue crack propagation, and consequently the cracks tended to avoid the interdendritic regions and progress through the cells, leaving a fine striated pattern in this single-phase region. At high driving forces ( K max>3.5 MPa m ) fractured particles and boundary decohesion created weak paths for fatigue crack propagation, and consequently the cracks followed the interdendritic regions, leaving serrated markings as the crack progressed through this heterogeneous region. The ramifications of the results on future modeling efforts are discussed in detail.

機械的疲労試験によるSn-3.OAg-0.5Cuはんだ接合部の相成長変化(J01-1 はんだ接続信頼性,J01 エレクトロニクス実装における熱制御および信頼性評価)

This paper describes phase growth of Sn-3.OAg-0.5Cu solder joints by a mechanical fatigue test. A lap joint type shear specimen was used to evaluate the influence of temperature and strain on the phase growth of solder joints. The fatigue test was carried out under constant temperature condition. Nonperiodically the specimen was taken out from the chamber and the micro structure of the solder joint was observed by the scanning electron microscope (SEM). Consequently, in Ag_3Sn phase growth proceeds so that the average phase size to the 4th power is proportional to the number of cycles, and is mainly induced by strain rather than thermal equilibrium.

超硬合金の繰返し熱衝撃下のき裂進展特性 : 機械的繰返し荷重との比較(S10-2 実験,S10 熱応力と強度評価)

超硬合金の繰返し熱衝撃下のき裂進展特性 : 機械的繰返し荷重との比較(S10-2 実験,S10 熱応力と強度評価)

Evaluation of long-term durability in high temperature resistant CFRP laminates under thermal fatigue loading

Thermal fatigue tests were conducted on high temperature resistant carbon fiber reinforced plastics cross-ply laminates to evaluate microscopic damage progress which affects macroscopic mechanical behavior of the laminates. Materials system used were thermoplastic polyetheretherketone based, AS4/PEEK and thermoset bismaleimide based, G40-800/5260. Several types of laminate configuration were used to clarify the effect of ply thickness on microscopic damage progress. Microscopic damages were observed using optical microscopy and soft X-ray radiography. Energy release rate associated with transverse cracking was calculated using variational analysis. The modified Paris law was used to predict transverse cracking. From comparison to mechanical fatigue test results, it is clarified that transverse crack accumulation rate was larger under thermal fatigue loading at same energy release rate range due to the dependence of the fracture toughness on temperature.

OS10W0196 Fatigue strength evaluation for Sn-Zn-Bi and Sn-Zn lead-free solder joints

In this paper, the authors have investigated mechanical fatigue strength of lead-free solder joints. The use of Sn-Zn-Bi and Sn-Zn solder is increasing because of the advantage of low cost and low melting point. Therefore, it is important to ensure the fatigue strength of Sn-Zn-Bi and Sn-Zn solder joints. In this study, the mechanical fatigue strength of Sn-Zn-Bi and Sn-Zn solder joints has been studied, by using the CSP(Chip Size Package) specimen. In order to investigate the influence of plating treatment on the fatigue strength of the solder joint, the specimens with Ni/Au or Cu plating treatment on Cu-pad were prepared. And these specimens were aged by holding 200, 500, 1000 hours at 85, 125, 150℃, respectively to investigate the influence of the growth of the intermetallic compounds on the fatigue strength. Through a series of isothermal mechanical shear fatigue tests and FEM(Finite Element Method) analysis, it has been found that if the Sn-Zn-Bi and Sn-Zn solder with Ni/Au plating treatment were aged at the temperature above 125℃, the fatigue strength decreased remarkably in comparison with the specimens with Cu plating. By plating with the Ni/Au on the substrate side, the interface in the substrate side was strengthened. But, the interface in the chip side is weakened. It causes the interface fatigue crack between intermetallic compound layer and solder at the chip side, and the decrease of fatigue strength.

On the low cycle fatigue deformation of K40S cobalt-base superalloy at elevated temperature

Low cycle isothermal mechanical fatigue testing K40S cobalt-base superalloy was carried out at 700 and 900 °C with total strain amplitude from ±0.1 to ±1.0 pct. Correlations between microscopic cyclic deformation and cycle stress response with various microstructural phenomena were enabled through scanning electron microscopy (SEM) and transmission electron microscopy (TEM), detailing the deformation substructure and carbide precipitation. The results show that K40S superalloy exhibited cyclic stress response of cyclic hardening at 700 °C, and of initial hardening followed by softening at 900 °C. In addition, at both temperatures, cyclic hardening during cycle deformation increased with increasing strain amplitude, while the fatigue lifetime decreased. The cyclic stress response behavior can be rationalized based on the mechanisms associated with dislocation–dislocation interactions, dislocation–precipitate (M 23C 6) interactions and interactions between solute atoms and dislocations.

Behaviour of an EB-PVD thermal barrier coating system under thermal–mechanical fatigue loading

Thermal–mechanical fatigue (TMF) tests were carried out on specimens made of alloy NiCr22Co12Mo9 which were coated with a LPPS CoNiCrAlY bond-coat (BC) and an electron beam-physical vapour deposition zirconia thermal barrier coating (TBC). The TMF tests simulate the thermally induced loadings at the outer surface of TBC-coated cooled gas turbine blades. In the present paper the cyclic deformation behaviour of the samples is analyzed and a quantitative evaluation of the degradation of the TBC system in two heat treatment states under TMF loadings is given. Segmentation cracks within the TBC as well as fatigue cracks in the BC and in the substrate were observed. Both types of cracks occur predominantly perpendicular to the loading direction. The main reason for this degradation of the TBC system are tensile stresses which are formed at low temperatures (<DBTT). The fatigue crack distribution within the BC and the substrate is mainly influenced by the heat treatment state as well as the applied mechanical strain. A preoxidation treatment before the TMF loading slightly increases the number of lateral cracks at the interface TBC/TGO/BC but does not result in a severe degradation of the TBC system compared to the as-received state. Because of the relatively high mechanical loading of the TBC system which leads to lifetimes of the specimens up to 500 cycles, no wide area spallation or buckling of the TBC was observed.

Progress on design and R&D of ITER FW/blanket

The electromagnetic (EM) load on the first wall (FW) panel during disruptions is reduced by slots penetrating the copper layer and the SS backing plate. The maximum stress in the central beam is within the allowables under the most significant load induced by halo currents. In the recent ITER R&D, full-scale FW panels have been manufactured successfully by hot isostatic pressing (HIP) as the reference method. The shield block cooling scheme consists of front water headers that distribute the coolant in radial channels. The shield block is composed of four flat forged blocks electron-beam (EB) welded together at the rear side. Recently, full-scale shield blocks were fabricated by drilling/machining and plugging/welding of flat forged blocks, and assembled with a FW panel with a central beam. Detailed design has progressed on the blanket attachments. Buckling tests, fatigue tests and dynamic load tests have been performed on the T-alloy flexible support (550 kN). Mechanical and thermal fatigue tests, and electrical tests in a solenoid coil, have been carried out on the electrical connection (280 kA). Feasibility of the blanket sub-components has been demonstrated through the R&D.

A study on μBGA solder joints reliability using lead-free solder materials

In this study, the numerical prediction of the thermal fatigue life of a ,μBGA (Micro Ball Grid Array) solder joint was focused. Numerical method was performed using the three-dimensional finite element analysis for various solder alloys such as Sn- 37%Pb, Sn- 3.5%Ag, Sn- 3.5%Ag-0.7%Cu and Sn-3.5%Ag-3%ln-0.5%Bi during a given thermal cycling. Strain values obtained by the result of mechanical fatigue tests for solder alloys, were used to predict the solder joint fatigue life using the Coffin-Manson equation. The numerical results showed that Sn- 3.5%Ag with the 50-degree ball shape geometry had the longest thermal fatigue life in low cycle fatigue. A practical correlation for the prediction of the thermal fatigue life was also suggested by using the dimensionless variable ??. Additionally Sn-3.5Ag-0.75Cu and Sn-2.0Ag-0.5Cu-2.0Bi were applied to 6×8μBGA obtained from the 63Sn-37Pb Solder. This 6×8μBGA were tested at different aging conditions at 130℃,150℃, 170℃ for 300, 600 and 900 hours. Thickness of the intermetallic compound layer was measured for each condition and the activation energy for their growth was computed. The fracture surfaces were analyzed using SEM (Scanning Electron Microscope) with EDS (Energy Dispersive Spectroscopy).

Mechanical fatigue test method for chip/underfill delamination in flip-chip packages

Underfill resin between Si chips and printed circuit boards is useful for improving the reliability of flip-chip packages. Generally, thermal cycle tests (TCTs) are applied to electronic packages under development in order to prove their reliability. At the early stage of development, however, a more effective test method is desirable, because TCTs are time-consuming. A new mechanical fatigue test for the underfill resin in flip-chip packages, namely the four points support test method, is proposed in this paper. The validity of the mechanical test method could be verified from the results of stress analyses and experiments. Considering the chip/underfill delamination statistically based on the assumption of Markov process, it was shown that the delamination probability during cyclic loads could be estimated with equations of the displacement range and number of cycles.

Effect of deformation and heat treatment on the structure and properties of quenched and aged alloy 36NTYu

Variation of the structure and mechanical properties of alloy 36NTYu after various kinds of treatment (quenching with aging at 750°C, deformation with degree e = 50 – 98%, annealing at 750°C) studied by mechanical tensile and fatigue tests is described. The changes in the dislocation structure and lamellar segregations of γ′-phase in the treatment process are determined. It is shown that the fatigue limit and the friction stress are well correlated.

843 Sn-Ag-Cu 系はんだ BGA 接合部の疲労強度評価

Three different sizes of BGA (Ball Grid Array) solder joints were subjected to mechanical fatigue testing. It was found that the fatigue life of these joints strongly depends on their size and can be expressed by Coffin-Manson's law. In addition, Sn-3Ag-0.5Cu, Sn-1Ag-0.7Cu, and conventional Sn-37Pb BGA solder joints were also subjected to mechanical fatigue testing. It was found that the Sn-3Ag-0.5Cu joints had a fatigue life close to that of the Sn-37Pb joints. In contrast, the Sn-1Ag-0.7Cu joints had a fatigue life half as long as that of the Sn-37Pb joints.

Thermal–mechanical fatigue behaviour of cast aluminium alloys for cylinder heads reinforced with 15 vol.% discontinous Al 2O 3 (Saffil) fibers

Thermal–mechanical fatigue (TMF) tests were done on the aluminium alloys AlSi10Mg0.3 and AlSi10Mg0.6, unreinforced and reinforced with 15 vol.% discontinous Al 2O 3 (Saffil) fibers. The tests were carried out with total strain constraint, triangular shaped temperature cycles, a minimum temperature of 50 °C and maximum temperatures from 200 to 400 °C. Both unreinforced alloys show nearly the same lifetime- and cyclic-deformation-behaviour. At all T max, the fiber reinforcement distinctly increases the lifetimes of AlSi10Mg0.3, whereas for AlSi10Mg0.6 this is only the case at T max≥300 °C. In the first cycle, higher peak stresses occur in the unreinforced alloys and the compound based on AlSi10Mg0.6 than in AlSi10Mg0.3+15% Saffil. All materials soften cyclically due to overageing of the peak aged matrix alloys. The rate of cyclic softening increases with T max and is higher in the unreinforced alloys and in AlSi10Mg0.6+15% Saffil than in AlSi10Mg0.3+15% Saffil. At T max≥300 °C, the initial difference between the peak stresses of the compounds vanishes within a tenth of the lifetime. So, nearly identical numbers of cycles to fracture occur at both materials. At T max≤250 °C, in AlSi10Mg0.6+15% Saffil higher peak stresses are acting until the fracture and lead to the lower lifetimes of this material. The age hardenability ofAlSi10Mg0.3 is reduced by the fiber reinforcement, whereas the fibers do not affect significantly the strength of AlSi10Mg0.6 in the T6 state. This was proven by microhardness measurements HV0.025 in the α-Al crystals of the fiber reinforced and the unreinforced alloys. In AlSi10Mg0.3+15% Saffil, an enrichment of magnesium in the fiber/matrix interfaces reduces the Mg content in the rest of the α-Al matrix below the necessary value for a full hardenability. In AlSi10Mg0.6+15% Saffil with its higher Mg-content, enough Mg for age hardening remains in the α-Al Matrix in spite of the Mg-enrichment near the fibers which also occurs in this material.

Effects of different thermomechanical treatments on fatigue of NiTi shape memory alloys

Fully recrystallized NiTi sheets were deformed in four different temperature ranges: fully transformed martensite (T 1/3 T m ). The types and distributions of defects produced in these materials depend on the deformation temperature. The characteristic defect structures resulting from the low temperature deformation lead to different microstructures even after annealing. The thermomechanically treated as compared to the fully recrystallized NiTi alloys were subjected to thermal, mechanical and thermomechanical fatigue tests. Their microstructural origin was interpreted by TEM investigations. In conclusion it is proposed that a low ratio of pseudo-yield stress to true yield stress is responsible for good fatigue resistance. Regarding fatigue it is better to increase the yield stress by a small grain size than by a high dislocation density (work hardening).

Fretting wear and cracking in sintered metal matrix composites

A methodology, involving fretting tests, to develop wear and crack resistant materials for tribological applications for automotive valve train parts (e.g. cams, tappets) has been recently reported for high speed steels. Modifications to one of these sintered steels, M3 Class 2, were effected by additions, singly and in combination, of 5 wt.% of wear resistant titanium carbide and of solid lubricant manganese sulphide. In our fretting tests alternate displacements were imposed between the test material (plane) and a chromium steel or alumina ball. Running conditions fretting and material response fretting maps were constructed for the four materials. Two types of fretting damage were detected and analysed: cracking or particle detachment and wear through the tribologicaly transformed structure (TTS). Crack initiation, associated with porosity and interfaces, was detected when the maximum tensile stress in the contact reached 1.2 GPa. Cracking analyses were also carried out using static and fatigue mechanical tests and replica scanning electron microscopy. Crack growth and propagation were influenced by details of the microstructure, e.g. TiC was observed to arrest crack growth, whereas MnS made it easier. Wear analysis included the determination after each test of the wear volume, which could be related to the coefficient of friction and the cumulative dissipation energy during the fretting test.

High-Cycle Thermal Fatigue Crack Initiation and Growth Behavior in a Semi-Infinite Plate Model

At a T-junction in piping system, hot and cold water mixes in a whirl. The vibrating mixing boundary between the hot and cold water causes a temperature fluctuation on the inner surface of the pipe just after the connection point at the T-junction, and this temperature fluctuation yields a cyclic thermal stress near the pipe surface, resulting in crack initiation. In this study, the thermal stress distribution was analyzed for a semi-infinite plate model. The allowable water temperature range for the fatigue crack initiation was determined based on the mechanical fatigue test results. The thermal fatigue crack arrest behavior was analyzed based on the distributions of the stress intensity factor. The arrested crack depth is found to be in proportion to the reciprocal root of the frequency of the temperature fluctuation and is 3.8 mm for the frequency of 1 Hz.