Wire Fatigue Research Articles

Effect of the initial phase constitution in the low-cycle fatigue of NiTi wires

Vastly used due to their functional properties, NiTi shape memory alloys have mechanical properties and fatigue resistance known to be strongly affected by their thermomechanical state. In this work, the goal was to evaluate the fatigue resistance of near equiatomic Ni-rich NiTi heat treated wires in different tests temperature. In this manner, it was possible to evaluate the phase constitution effect on the fatigue resistance with a fixed thermomechanical condition. For that, a heat treatment at 500 °C for 30 min was performed in initially superelastic wires in an argon atmosphere. DSC tests were performed in order to obtain the transformation temperatures and there different fatigue test temperatures were chosen according to the phase stability ranges. Rotating-bending fatigue tests took place in proper equipment at 4% maximum strain, evaluating the properties of structures constituted by the R-phase, austenite and R-phase + austenite, in each selected test temperature. The results showed that the R-phase presents higher low-cycle fatigue resistance than austenite and a fatigue mechanism was proposed.

Strategy for Diagnosing the Aging of an IGBT Module by ON-State Voltage Separation

An insulated-gate bipolar transistor (IGBT) module has two aging modes: 1) bond wire fatigue and 2) solder fatigue, both of which have a significant impact on the reliability of power electronic systems. A good way to increase the service life of such systems is to apply different compensation strategies according to different aging modes. As one of the simplest parameters in online measurements, the ON-state voltage is influenced by both types of fatigue, but its changes are not due solely to the aging of the IGBT module. Considering how the collector current and junction temperature influence the ON-state voltage, this article separates the ON-state voltage into three parts for the purpose of diagnosing IGBT module fatigue. In this article, the package voltage was extracted, which reflects the bond wire fatigue influence on the ON-state voltage of the IGBT module directly. This supplements the existing diagnostic method and realizes fatigue diagnosis under different working conditions.

<italic>In situ</italic> Condition Monitoring of IGBTs Based on the Miller Plateau Duration

Aging precursor identification is crucial to achieving online condition monitoring and estimating the remaining lifetime of insulated-gate bipolar transistors (IGBTs). However, existing failure precursors are limited with respect to in situ monitoring. In this paper, the duration of the Miller plateau during the IGBT turn- on transition is proposed as an online precursor indicating two dominant types of failures. Based on the theoretical closed-form expressions, the adverse effects of package-related bond wire fatigue and chip-related gate oxide degradation on the Miller plateau duration are explained. By using a dedicated online measurement system that is implemented on the gate driver side, the proposed precursor is extracted during operation. Discrete IGBTs of two gate structures are employed during the accelerated aging tests. Negative and positive degradation trends of the Miller plateau duration under power cycling and high electric field stress, respectively, are revealed, thus illustrating the validity of the proposed method. Finally, the main differences in physics-of-failure between two types of aged devices are investigated using post-failure analysis. The innovation of applying the Miller plateau duration as a failure precursor involves its ability to accomplish real-time field monitoring and its sensitivity to multiple failure mechanisms.

Reliability model of bond wire fatigue for IGBT in MMC with system redundancy consideration

Reliability is a significant factor in the operation of the modular multilevel converter (MMC). Since the bond wire fatigue is one of the dominant failures of the insulated-gate bipolar transistor (IGBT) in the aging aspect, the wire bond lifetime related research has captured much attention in recent years. However, at system level, the redundancy of the system is seldom discussed in the reliability analysis of MMC. This paper proposes a reliability model for wire bond failure of IGBT with system redundancy consideration. The reliability model for IGBT at the component level is established based on the lifetime model. Also, the reliability model for the system with redundancy is built by the end-of-life cumulative distribution obtained from Monte Carlo method. The unreliability change of system level and component level are compared, and the influence of bridge arm redundancy on system reliability is also analyzed.

Reliability Criteria for Thick Bonding Wire.

Bonding wire is one of the main interconnection techniques. Thick bonding wire is widely used in power modules and other high power applications. This study examined the case for extending the use of traditional thin wire reliability criteria, namely wire flexure and aspect ratio, to thick wires. Eleven aluminum (Al) and aluminum coated copper (CucorAl) wire samples with diameter 300 μm were tested experimentally. The wire response was measured using a novel non-contact method. High fidelity FEM models of the wire were developed and validated. We found that wire flexure is not correlated to its stress state or fatigue life. On the other hand, aspect ratio is a consistent criterion of thick wire fatigue life. Increasing the wire aspect ratio lowers its critical stress and increases its fatigue life. Moreover, we found that CucorAl wire has superior performance and longer fatigue life than Al wire.

An experimental investigation of the superelastic fatigue of NiTi SMA wires

Nickel–titanium shape memory alloys (NiTi SMA) working in superelastic regime have been applied in several fields, such as health (medicine and dentistry) and engineering, in a static or dynamic way. The aim of this paper is to study the behavior of these smart metals when subjected to dynamic mechanical stresses (fatigue). Cyclic stress-controlled tensile tests were performed to evaluate the functional and structural superelastic fatigue properties of NiTi SMA wires. The functional parameters were defined as energy dissipation, transformation stresses, residual strain, and superelastic strain, for peak stresses between 500 and 800 MPa, at frequencies of 1, 2, and 3 Hz. These frequencies were determined after a preliminary evaluation of self-heating of the NiTi wires. The number of cycles until failure (Nf) was plotted as a function of peak stresses (S) in an S–Nf fatigue curve, for each studied frequency. It was verified that both frequency and peak stress affected the functional behavior of the NiTi wires. However, the fatigue life was between 5.0 × 103 and 1.6 × 104 cycles, with a faster degradation in this range as higher is the applied peak stress, irrespective of the loading frequency.

Accelerated mechanical fatigue interconnect testing method for electrical wire bonds

Abstract Every new development in device performance and packaging design, can drastically affect the reliability of devices due to implementation of new materials and design changes. High performance and high reliability demands in power electronics over several decades and a short time to market development, raise the need for very fast reliability testing methods. In this study a mechanical fatigue testing method is presented for evaluating the interfacial fatigue resistance of heavy Al wire bonded interconnects in high power modules. By separating the concurrent thermal, mechanical and environmental failure mechanisms a selective investigation of the desired failure mode is possible. The setup is designed to reproduce the thermo-mechanical shear stresses by mechanical means, while provoking the same lift-off failure mode as in power cycling tests. With a frequency variable test setup of a few Hz up to several kHz, measurements from 103 up to 108 loading cycles and determining the influence of the testing frequency on the fatigue life are possible. A semi-automated bond wire fatigue tester operating at 60 kHz is presented which is suitable for rapid screening and qualification of a variety of wire bonds at the stages of development and during the production.

Integration of risk matrix and event tree analysis: a natural stone plant case

Machining has considerably increased with evolving technology and increasing demand in natural stone production facilities. Different types of accidents may occur in natural stone facilities during movement, dimensioning, cutting of blocks and surface processing. These accidents may be due to physical, chemical, ergonomic and mechanical conditions. Therefore, possible work accidents and occupational diseases should be investigated. In this study, an L-matrix analysis is conducted to analyze hazards and forecast risks in natural stone facilities. According to the L-matrix results, three major initiating events are identified. For each of these initiating events, event tree analysis is used to calculate risk scores. These initiating events are hoist rope fatigue and breaking, diamond wire fatigue and breaking, and electrical leakage due to old systems. These events and their results are classified according to the probabilities using event tree analysis.

Improved Functional Properties and Efficiencies of Nitinol Wires Under High-Performance Shape Memory Effect (HP-SME)

Martensitic Ti-rich NiTi intermetallics are broadly used in various cyclic applications as actuators, which exploit the shape memory effect (SME). Recently, a new approach for exploiting austenitic Ni-rich NiTi shape memory alloys as actuators was proposed and named high-performance shape memory effect (HP-SME). HP-SME is based on thermal recovery of de-twinned martensite produced by mechanical loading of the parent phase. The aim of the manuscript consists in evaluating and comparing the fatigue and actuation properties of austenitic HP-SME wires and conventional martensitic SME wires. The effect of the thermomechanical cycling on the actuation response and the changes in the electrical resistivity of both shape memory materials were studied by performing the actuation tests at different stages of the fatigue life. Finally, the changes in the transition temperatures before and after cycling were also investigated by differential calorimetric tests.

Effect of Applied Potential on Fatigue Life of Electropolished Nitinol Wires.

Nitinol is used as a metallic biomaterial in medical devices due to its shape memory and pseudoelastic properties. The clinical performance of nitinol depends on factors which include the surface finish, the local environment, and the mechanical loads to which the device is subjected. Preclinical evaluations of device durability are performed with fatigue tests while electrochemical characterization methods such as ASTM F2129 are employed to evaluate corrosion susceptibility by determining the rest potential and breakdown potential. However, it is well established that the rest potential of a metal surface can vary with the local environment. Very little is known regarding the influence of voltage on fatigue life of nitinol. In this study, we developed a fatigue testing method in which an electrochemical system was integrated with a rotary bend wire fatigue tester. Samples were fatigued at various strain levels at electropotentials anodic and cathodic to the rest potential to determine if it could influence fatigue life. Wires at potentials negative to the rest potential had a significantly higher number of cycles to fracture than wires held at potentials above the breakdown potential. For wires for which no potential was applied, they had fatigue life similar to wires at negative potentials.

Fatigue Damage Study of Helical Wires in Catenary Unbonded Flexible Riser Near Touchdown Point

This study presents an analytical model of flexible riser and implements it into finite-element software abaqus to investigate the fatigue damage of helical wires near touchdown point (TDP). In the analytical model, the interlayer contact pressure is simulated by setting up springs between adjacent interlayers. The spring stiffness is iteratively updated based on the interlayer penetration and separation conditions in the axisymmetric analysis. During the bending behavior, the axial stress of helical wire along the circumferential direction is traced to determine whether the axial force overcomes the interlayer friction force and thus lead to sliding. Based on the experimental data in the literature, the model is verified. The present study implements this model into abaqus to carry out the global analysis of the catenary flexible riser. In the global analysis, the riser–seabed interaction is simulated by using a hysteretic seabed model in the literature. The effect of the seabed stiffness and interlayer friction on the fatigue damage of helical wire near touchdown point is parametrically studied, and the results indicate that these two aspects significantly affect the helical wire fatigue damage, and the sliding of helical wires should be taken into account in the global analysis for accurate prediction of fatigue damage. Meanwhile, different from the steel catenary riser, high seabed stiffness may not correspond to high fatigue damage of helical wires.

Condition Monitoring IGBT Module Bond Wires Fatigue Using Short-Circuit Current Identification

Finding and replacing the defective insulated-gate bipolar transistor (IGBT) module timely by monitoring the ageing state of IGBT can improve the reliability of a power converter and reduce the loss caused by IGBT failure. A method for detecting the condition of bond wires in IGBT module by identifying the short-circuit current of IGBT module is presented in this paper. It is based on the fact that parasitic parameters of IGBT module are affected by the local damage induced by ageing over time, and these changes can be easily detected by monitoring the difference of short-circuit current. The study results indicate that short-circuit current of IGBT module decreases with module ageing over time, and the difference of short-circuit current caused by junction temperature is much smaller than that caused by bond wires fatigue on a specific gate driving voltage. Therefore, the IGBT module in the power converter can be diagnosed by detecting the difference of short-circuit current without considering the effects of junction temperature. Finally, a confirmatory experiment is carried out, and the correctness of the method proposed in this paper is verified.

Online Condition Monitoring for Both IGBT Module and DC-Link Capacitor of Power Converter Based on Short-Circuit Current Simultaneously

Insulated-gate bipolar transistor (IGBT) modules and dc-link capacitors are important parts in the majority of power electronic converters which contribute to cost, size, and failure rate on a considerable scale. This paper presents an online condition monitoring method for both IGBT modules and dc-link capacitors of power converters based on short-circuit current of an IGBT module, which is a good condition indicator according to the theory analysis. The failure prediction of dc-Link capacitor is realized by equivalent series resistance, which can be calculated by short-circuit current and a step voltage, and the bond wires fatigue can also be identified by the short-circuit current. The proposed method is capable for detecting small changes in the failure indicators of IGBT modules and electrolytic capacitors, and its effectiveness is validated by a confirmatory experiment. The novelty of the proposed method is that the degradations of IGBT modules and capacitors can be identified simultaneously, and has the merits of low cost and circuit simplicity

Fatigue and fracture of wires and cables for biomedical applications

Fine wires and cables play a critical role in the design of medical devices and subsequent treatment of a large array of medical diagnoses. Devices such as guide wires, catheters, pacemakers, stents, staples, functional electrical stimulation systems, eyeglass frames and orthodontic braces can be comprised of wires with diameters ranging from 10s to 100s of micrometres. Reliability is paramount as part of either internal or external treatment modalities. While the incidence of verified fractures in many of these devices is quite low, the criticality of these components requires a strong understanding of the factors controlling the fracture and fatigue behaviour.1,2 Additionally, optimisation of the performance and reliability of these devices necessitates characterisation of the fatigue and fracture properties of its constituent wires. A review of cable architecture and stress states experienced during testing is followed by an overview of the effects of changes in material composition, microstructure, processing and test conditions on fracture and fatigue behaviour of wire and cable systems used in biomedical applications. The review concludes with recommendations for future work.

Probabilistic analysis for the functional and structural fatigue of NiTi wires

The present work aims to investigate the functional and structural fatigue of Ni49·8Ti50.2 (at.%) shape memory alloy (SMA) wires subjected to thermal cycling under a constant stress. More than 70 specimens were tested under 7 stress levels ranging from 140MPa to 200MPa. Probabilistic analysis of the fatigue life were performed, including analysis of final plastic strain and recovery strain, the evolution of the plastic strain and recovery strain through the whole life span. Corresponding probabilistic curves under the reliability of 0.5, 0.9, 0.99, and 0.999 were given. Moreover, the influence of the stress level on fatigue life, plastic and recovery strains were discussed. Finally, fracture surface analysis was also performed to determine the effect of stress level on behavior of the crack nucleation and propagation.

Residual stress redistribution induced by fatigue in cold-drawn prestressing steel wires

In this paper the evolution of diverse residual stress states (similar to the ones produced after a cold drawing process) during several fatigue loading schemes is analysed. Thus, numerical simulations by finite element method were carried out applying diverse fatigue loading schemes to several cold drawn wires with a residual stress state associated. Numerical results reveal the key role of plastic strains produced by fatigue loading causing a redistribution of the residual stress when tensile stresses are placed at the wire surface. However, a negligible effect is obtained for wires with a compressive residual stress associated.

A phenomenological model for the simulation of functional fatigue in shape memory alloy wires

In this contribution, a modelling framework for functional fatigue in shape memory alloy wires is introduced. The approach is in particular designed to reproduce the effective response determined by experiments as published in, e.g., Eggeler et al. (Mat Sci Eng A 378:24–33, 2004). In this context, the decrease of transformation stresses, the increase of irreversible strains, and the occurrence of “characteristic points” with respect to the stress-strain relation is explicitly covered in the model formulation. The modelling approach for the phase transformations itself offers a large potential for further micromechanically well-motivated model extensions.

Fatigue of NiTi shape memory wires

In the present work, an innovative methodology for characterizing structural fatigue of NiTi superelastic wires is proposed. It consists in, firstly, performing low speed nearly isothermal pseudoelastic cycles in a limited region of the wire specimen. This results in the stabilization of the pseudooelastic behavior accompanied by a decrease in the stresses for forward and reverse transformations which allows obtaining an equivalent to a geometric dog-bone shaped specimen due to the reduced transformation stresses in the pre-cycled region. In a second stage, by limiting the transformation active zone to the pre-cycled region, the deformation speed can be increased to practical values avoiding any transformation activity outside that region. In that way, grip induced failures resulting in artificially shorter fatigue lives might be completely avoided thus allowing an accurate characterization of the true structural fatigue. Additionally, strain controlled experiments on wires in fully austenite and fully martensite states have been performed. Resulting fatigue lives in these cases were at least two orders of magnitude higher compared with the pseudoelastic fatigue indicating the decisive role played by the stress induced transformation in determining fatigue life. The influence of testing temperature and deformation rate on fatigue life has also been evaluated

Fatigue of superelastic NiTi wires with different plateau strain

Microstructures and thermomechanical responses of Ni-rich superelastic wires can be tuned in relatively large extent by varying the degree of cold work and heat treatment. What frequently remains unknown is the superelastic fatigue performance of the wires – whether and/or how it depends on the heat treatment. In this study, five superelastic NiTi wires (d=0.051mm) having similar transformation stresses but different microstructures and transformation strains (3.1, 3.9, 4.7, 5.6, 6.7 %) were produced from one spool of a hot worked NiTi wire by applying different cold work/heat treatments to investigate the influence of the wire microstructure (transformation strain) on its structural and functional fatigue performance. The wires were cycled in tension beyond the end of superelastic plateau at constant temperature in strain rate controlled mode until failure. It is found that various cold work/heat treatments do affect the superelastic fatigue performance of NiTi wires in a defined manner. As concerns the transformation strain dependence, the wires exhibiting large transformation strain show decreasing fatigue performance with increasing transformation strain, the wires exhibiting low transformation strain show opposite trend. On average, the furnace treated NiTi wires (recovered and precipitation hardened microstructure) showed better fatigue performance than the electropulse treated wires (nanosized but partially recrystallized microstructure).

Comparing Rotary Bend Wire Fatigue Test Methods at Different Test Speeds

Given its relatively simple setup and ability to produce results quickly, rotary bend fatigue testing is becoming commonplace in the medical device industry and is the subject of a new standard test method ASTM E2948-14. Although some research has been conducted to determine if results differ for different rotary bend fatigue test setups or test speeds, these parameters have not been extensively studied together. In this work, we investigate the effects of these two parameters on the fatigue life of three commonly used medical device alloys (ASTM F2063 nitinol, ASTM F138 stainless steel, and ASTM F1058 cobalt chromium). Results with three different rotary bend fatigue test setups revealed no difference in fatigue life among those setups. Increasing test speed, however, between 100 and 35,000 RPM led to an increased fatigue life for all three alloys studied (average number of cycles to fracture increased between 2.0 and 5.1 times between slowest and fastest test speed). Supplemental uniaxial tension tests of stainless steel wire at varying strain rates showed a strain rate dependence in the mechanical response which could in part explain the increased fatigue life at faster test speeds. How exactly strain rate dependence might affect the fatigue properties of different alloys at different alternating strain values requires further study. Given the difference in loading rates between benchtop fatigue tests and in vivo deformations, the potential for strain rate dependence should be considered when designing durability tests for medical devices and in extrapolating results of those tests to in vivo performance.