High Fatigue Life Research Articles

Investigation on the electrochemical machining by using metal reinforced double insulating layer cathode

With the superior performance of high machining efficiency, no tool loss, machined surface possessing good quality, and high fatigue life, electrochemical machining (ECM) has been more and more used in difficult-to-machine materials (titanium alloy, high temperature alloy, etc.). However, there are some problems that may restrict the further development of ECM. For example, cathode insulating layer is easily damaged, and machining localization is not high enough. To solve these problems, a metal-reinforced double-insulating layer cathode (MRDILC) and unequal-height cathode (UEHC) are proposed. Firstly, the numerical simulations show that the localization of ECM current could be improved effectively by UEHC, so the machining localization would be improved. Then, experiments are carried out on titanium alloy TB6. The superiority of MARDILC is verified: the insulating layer is firm and durable; the insulating effect is remarkable. The machining localization could be improved by UEHC, which would be beneficial to improve machining accuracy. Finally, holes with good machining localization and small surface roughness (Ra ≤0.8 μm) are machined with the optimized parameters of h = 0.1 mm, v = 7 μm/s.

Static and fatigue performance of the bolt-connected structural jointed of deep corrugated steel plate member

Corrugated steel plate culvert bridge has been more commonly used as soil steel bridges because it is the cost-effective alternative for railway-highway crossings. The corrugated steel plate culvert bridge is considered the most suitable for quick rebuilding of bridges compared with the conventional bridges. This study intends to experimentally investigate the static and fatigue performance of the bolted connection of deep corrugated steel plate. Test variables are the thickness of deep corrugated steel plate and the types of bolted connection such as bolted-only, gasket, slot hole, and washer. For static test, the failure is mainly caused by a local buckling of deep corrugated steel plate member and bearing failure of bolts. Type of gasket and slot hole showed the largest stiffness so that they may be recommended for structural safety and redundancy under a static flexural behavior. For fatigue test, the bolted-only specimen exhibited no increase in the strain until failure and the highest fatigue life among the test variables. For structural safety under cyclic loading, bolted-only connection is recommended. According to AASHTO LRFD Bridge Design Specification, fatigue life category can be determined as category D level and the fatigue limit was estimated to be 48.3 MPa. The deep corrugated steel plate members tested in this study can provide a sufficient fatigue performance in compliance with the design specification.

The influence of cohesion and adhesion parameters on the fatigue life of hot mix asphalt

abstractFatigue cracking is one of the major distresses of hot mix asphalt (HMA) at moderate temperatures. Two of the main properties of asphalt mixtures affecting fatigue are the cohesive bond energy of asphalt binder and the adhesive bond energy between asphalt binder and aggregate. These two parameters were calculated using surface free energy (SFE) theory. Furthermore, the fatigue life of asphalt mixtures was measured by indirect tensile fatigue test. The results showed that asphalt mixtures with limestone aggregates, with the most specific surface area, and magnitude of adhesion had the highest fatigue life. Moreover, asphalt mixtures made with asphalt binder having the highest penetration had greater fatigue life than the other mixtures. The enhanced fatigue life was attributed to the greater cohesion energy and higher resistance to fatigue cracking in asphalt film. Also, these mixtures had the highest adhesion energy on the contact surface between asphalt binders and aggregates, which increased the energy required to separate the asphalt binder from the aggregate surface and the occurrence of adhesion rupture distress.

Assessment of specific contribution of residual stress generated near surface anomalies in the high temperature fatigue life of a René 65 superalloy

AbstractThis study evaluates the influence of residual stresses induced by the fabrication of surface anomalies on the fatigue crack growth in a nickel based superalloy. To separate the notch effect of the geometry from the residual stress field induced by fabrication of the surface flaws, two V‐type anomalies are considered: scratches and dents with equivalent morphology and size. A specially designed heat treatment has been used to reduce the magnitude of residual stresses around these anomalies in order to highlight their effects on the different stages of the crack propagation, under low cycle fatigue conditions at 400 °C. The crack initiation life is short for both anomalies but in the presence of compressive residual stresses, a decrease of the fatigue crack growth rate has been observed during the first stages of the crack propagation. Furthermore, the results showed that without residual stresses, scratches and dents exhibit the same behaviour. Thus, the residual stress field below surface anomalies is the main parameter controlling the fatigue life from surface anomalies.

Bioinspired Ternary Artificial Nacre Nanocomposites Based on Reduced Graphene Oxide and Nanofibrillar Cellulose.

Inspired by the nacre, we demonstrated the integrated ternary artificial nacre nanocomposites through synergistic toughening of graphene oxide (GO) and nanofibrillar cellulose (NFC). In addition, the covalent bonding was introduced between adjacent GO nanosheets. The synergistic toughening effects from building blocks of one-dimensional NFC and two-dimensional GO, interface interactions of hydrogen and covalent bonding together result in the integrated mechanical properties including high tensile strength, toughness, and fatigue life as well as high electrical conductivity. These extraordinary properties of the ternary synthetic nacre nanocomposites allow the support for advances in diverse strategic fields including stretchable electronics, transportation, and energy. Such bioinspired strategy also provides a new insight in designing novel multifunctional nanocomposites.

Fatigue Life of Welded Joints of High-Strength Structural Steel S960QL

The article presents the results of research on low cycle fatigue strength of welded joints of structural steel S960QL. Two types of butt welds were analysed: I-joints and V-joints. The tests were performed under load controlled using the total strain amplitude εac. Fatigue life analysis was conducted based on the Manson-Coffin-Basquin equation, which made it possible to determine fatigue parameters. High concordance was found of the adopted description model with experimental results. Studies have shown differences in the fatigue life of the various joints analysed, wherein I-joints showed about 20-50% higher fatigue life. Fractographic tests of fatigue fractures in joints revealed the details of fatigue cracking and differences in the propagation rate of fatigue cracks.

Clean preparation of tailored microcellular foams of polystyrene using nucleating agents and supercritical CO2

Microcellular foams are well-known polymeric materials since they present excellent properties: high impact strength, high toughness, high stiffness-to-weight ratio, high fatigue life as well as low dielectric constant and low thermal conductivity. Environment-friendly techniques are being proposed to prepare polymeric foams. In particular, supercritical CO2 (scCO2) has received great attention instead of traditional blowing agents (chlorofluorocarbon hydrochlorofluorocarbons or hydrocarbons) due to its low cost and mild impact on the environment. In the foaming process proposed in this work, mild working conditions (90 bar and 30 °C) were required thanks to the presence of CO2 and p-cymene, which benefits the nucleation and cell growth. The influence of inorganic particles (silica and montmorillonite) on the cell morphology was studied experimentally and theoretically in order to promote the simultaneous formation of the embryos, thereby reducing the average cell size and narrowing the cell size distribution. A great enhancement of the polystyrene foam homogeneity was observed, independent of the nucleating agent employed and under low temperature conditions.

Dissimilar friction stir welding of duplex stainless steel to low alloy structural steel

In the present study, 6 mm nominal thickness dissimilar steel plates were joined using friction stir welding. The materials used were duplex stainless steel and low alloy structural steel. The weld was assessed by metallographic examination and mechanical testing (transverse tensile and fatigue). Microstructural examination identified four distinct weld zones and a substantially hard region within the stir zone at the base of the weld tool pin. Fatigue specimens demonstrated high level fatigue life and identified four distinct fracture modes.

Fatigue life and fracture mechanics of unconstrained Ni–Mn–Ga single crystals in a rotating magnetic field

Fracture resistance and long fatigue life are required to commercialize Ni–Mn–Ga ferromagnetic shape memory alloys. While Ni–Mn–Ga achieves high fatigue life at low strains, there is little data on the fatigue life of samples that are actuated near the theoretical strain limit. Furthermore, constraints imposed by clamping samples impact their magneto-mechanical and fatigue properties. Here, 10M Ni–Mn–Ga single crystals were exposed to a rotating magnetic field while holding them with rubber O-rings so they were minimally constrained. Prior to testing, sample surfaces were prepared to various levels of finish. Fatigue life varied with some samples reaching more than 800,000 cyclic loads before fracturing and some samples failing after only 4000 cyclic loads. Long fatigue life and fracture resistance are achieved when avoiding crystal defects and surface imperfections. Short fatigue life was caused by high surface roughness and stress concentration at defects and notches.

A comparison of methods for predicting the fatigue life of gray cast iron at elevated temperatures

AbstractHigh temperature fatigue life tests were compared with various life assessment methods for gray cast iron in the cylinder liners of marine engines. The plastic strain range‐based methods such as the universal slopes method, Mitchell's method, Bäumel and Seeger's method, and Ong's method were not predicted well. A method employing tensile energy density, which is defined as the sum of the tensile area of the plastic energy and the elastic energy in the hysteresis loop, was suggested as an improved alternative to the plastic strain range‐based methods. The life estimation equation using tensile energy density predicted well within the 3X scatter band at various temperature ranges of the gray cast iron.

A combined critical distance and energy density model to predict high temperature fatigue life in notched single crystal superalloy members

The formation of short cracks at notched members of superalloy single crystals under high temperature low cycle fatigue is analysed. AM1 superalloy at 950°C is studied for [001] and [111] loading axis under fully reversed strain loading. An anomalous crack growth rate regime is observed that depends upon test frequency. Local strain gradient is computed using a finite element model and crystal viscoplasticity constitutive equations. A damage model based on viscoplastic strain energy density and dilation energy density is used to describe short crack growth and fatigue life of smooth specimens. Finite element results are used to identify a critical distance model for notched specimens. A good correlation between experimental results and model predictions is achieved for all test orientations and frequencies.

Evaluation of Mechanical Behaviour Aluminium Metal Matrix Composites

Technology is advancing, demand of the hour is increasing and to face that engineers are also ready. Maintaining the economic production with optimal use of resources is of prime concern for the engineers. Aluminum alloy materials or simply composites are combinations of materials. They are made up of combining two or more materials in such a way that the resulting materials have certain design properties on improved properties .The Aluminum alloy composite materials consist of high specific strength, high specific stiffness, more thermal stability, more corrosion and wear resistance, high fatigue life. Conventional materials like Steel, Brass, and Aluminum etc will fail without any indication. Cracks initiation, propagation will takes place within a short span. Now a day to overcome this problem, conventional materials are replaced by Aluminum alloy materials. Aluminum alloy materials found to the bestalternative with its unique capacity of designing the materials to give required properties. In this project tensile strength experiments have been conducted by varying mass fraction of SiC and fly ash magnesium with Aluminum. To attain maximum tensile strength various mechanical properties alloys are also to be investigated.

Current Issues and Challenges in Polypropylene Foaming: A Review

Thermoplastic foams have several advantages in comparison with unfoamed polymers such as lightweight, high strength to weight ratio, excellent insulation property, high thermal stability, high impact strength and toughness, as well as high fatigue life. These outstanding properties lead cellular plastics to various industrial applications in packaging, automotive parts, absorbents, and sporting equipment. Nowadays, polypropylene (PP), because of its outstanding characteristics such as low material cost, high service temperature, high melting point, high tensile modulus, low density, and excellent chemical resistance, is a major resin in the foaming industry. However, foaming of conventional PP is limited by its low melt strength leading to poor cell morphology, cell rupture/coalescence and limited density reduction. To improve PP melt strength, several strategies including particle addition as nucleating agent, introduction of long chain branching, blending with high melt strength polymers and crosslinking have been proposed. In this review, these issues are discussed and analyzed in terms of mechanical, thermal, and rheological characterizations.

Effect of Intermetallic Compounds on the Thermomechanical Fatigue Life of Three-Dimensional Integrated Circuit Package Microsolder Bumps: Finite Element Analysis and Study

Currently, intermetallics (IMCs) in the solder joint are getting much attention due to their higher volume fraction in the smaller thickness interconnects. They possess different mechanical properties compared to bulk solder. Large volume fraction of IMCs may affect the mechanical behavior, thermomechanical and mechanical fatigue life and reliability of the solder interconnects due to very brittle nature compared to solder material. The question that this study is seeking to answer is how degrading IMCs are to the thermomechanical reliability of the microbumps used in three-dimensional (3D) integrated circuits (ICs) where the microsolder bumps have only a few microns of bond thicknesses. Several factors such as “squeezed out” solder geometry and IMC thickness are studied through a numerical experiment. Fatigue life is calculated using Coffin–Manson model. Results show that, though undesirable because of high likelihood of creating short circuits, squeezed out solder accumulates less inelastic strains under thermomechanical cyclic load and has higher fatigue life. The results show that with the increase of IMCs thickness in each model, the inelastic strains accumulation per cycle increases, thus decreasing the fatigue life. The drop in fatigue life tends to follow an exponential decay path. On the other hand, it was observed that plastic strain range per cycle tends to develop rapidly in Cu region with the increase in IMC thickness which calls for a consideration of Cu fatigue life more closely when the microbump contains a higher volume fraction of the IMCs. Overall, by analyzing the results, it is obvious that the presence of IMCs must be considered for microsolder bump with smaller bond thickness in fatigue life prediction model to generate more reasonable and correct results.

Fatigue life of multilayer hard-faced specimens

Specimens and the method for experimental evaluation of the fatigue life of multilayer hard-faced metal subjected to cyclic mechanical loading are described. The tests were carried out by three-point bending with cyclic non-zero loading in the centre of the specimen, which reproduces, with certain assumptions, the force loading characteristics of rolling rolls, the rolls of continuous casting installations and other tools and equipment for deformation of metals and alloys which are subjected in service to the simultaneous effect of cyclic mechanical and thermal loads. The proposed method is then used to investigate the durability of the specimens of 40Kh steel, hard faced with PP-Np-25Kh5FMS flux-cored wire with and without a ductile sublayer. The sublayer was deposited using Sv-08A solid wire or the PP-Np-25Kh5MF flux-cored wire. The experimental results show that the deposition of the ductile sublayer with Sv-08A and PP-Np-25Kh5MF wires increases the fatigue life of the deposited specimens 1.3 and 1.6 times, respectively. PP-Np-123Kh1MF wire, which produces a deposited metal with higher mechanical properties in comparison with the Sv-08A wire, results in a higher fatigue life of multilayer hard-faced specimens.

Fatigue performance of biodegradable magnesium–calcium alloy processed by laser shock peening for orthopedic implants

Permanent orthopedic implants made from titanium, stainless steel, or cobalt–chromium alloys cause stress shielding and lead to secondary surgery. Biodegradable magnesium–calcium (MgCa) alloys have the potential to minimize stress shielding as well as eliminate the need for secondary surgery. The critical technical challenge is that magnesium degrades rapidly in the human body. In order to slow the corrosion rate, surface treatments such as laser shock peening (LSP), shot peening, or burnishing have been reported in literature. Each of these surface treatments uniquely alters the surface integrity and consequent fatigue life. Even though surface treatments may be effective at slowing corrosion rates, it is important to ensure that they do not shorten fatigue life. The purpose of this study was to (1) develop a laser shock peening (LSP) surface treatment of a curved surface that adjusts the surface integrity of a MgCa alloy by varying the peening overlap ratio and (2) determine the effect of LSP on the fatigue life. Surface integrity was characterized by topography, microstructure, and microhardness. Fatigue life of laser peened and unpeened samples were measured by rotating bending fatigue tests. It was found that LSP increased the fatigue life of the peened MgCa samples. Implementing LSP at high overlap ratios reduced the surface pile-up which resulted in a higher fatigue life. The fractured surfaces of the peened samples exhibited striation patterns which were more pronounced at higher peening overlap ratios.

Influence of inelastic buckling on low-cycle fatigue degradation of reinforcing bars

The effect of inelastic buckling on low-cycle high amplitude fatigue life of reinforcing bars is investigated experimentally. Ninety low-cycle fatigue tests on reinforcing bars varied in amplitudes and buckling lengths are conducted. Using scanning electron microscope the fractography of fractured surfaces are studied. The results show that the inelastic buckling, bar diameter and surface condition are the main parameters affecting the low-cycle fatigue life of reinforcing bars. Through nonlinear regression analyses of the experimental data a new set of empirical equations for fatigue life prediction of reinforcing bars as a function of the buckling length and yield strength are developed. Finally, these empirical models have been implemented into a new phenomenological hysteretic material model for reinforcing bars. The new material model is able to simulate the nonlinear stress–strain behaviour of reinforcing bars with the effect of inelastic buckling and low-cycle fatigue degradation. The results of simulation using the analytical model show a good agreement with the observed experimental results.

Behavior of NiTi Wires for Dampers and Actuators in Extreme Conditions

Shape memory alloys are considered smart materials because of their singular thermo-mechanical properties, due to a thermoelastic martensitic transformation, enabling possible uses as actuators (because of mechanical recovery induced from temperature changes) and as dampers (because of hysteresis). NiTi wires for dampers in Civil Engineering had been characterized and tested in facilities. Guaranteed performance needs to know behavior during fatigue life and knowledge of effects in the event of extreme conditions, as eventual overstraining. In this work, we check the possibilities to absorb mechanical energy on the fatigue life depending on stress level and explore the consequences of overstraining the material during installation, the possibilities of partial healing by moderate heating, and some effects of over-stressing the wires. The mechanical energy absorbed by the unit weight of damper wire might be very high during its lifetime if maximum stresses remain relatively low allowing high fatigue life. We show also some results on NiTi wire working as an actuator. The lifetime mechanical work performed by an actuator wire can be very high if applied stresses are limited. The overstraining produces relevant “residual” deformation, which can be to some extent reversed by moderate heating at zero stress. The reason for the observed characteristics seems to be that when external high stresses are applied to an NiTi wire, it undergoes some plastic deformation, leaving a distribution of internal stresses that alter the shape and position of the macroscopic stress-strain transformation path.

Impact of corrosion on low-cycle fatigue degradation of reinforcing bars with the effect of inelastic buckling

The combined effect of inelastic buckling and chloride induced corrosion damage on low-cycle high amplitude fatigue life of embedded reinforcing bars in concrete is investigated experimentally. A total of forty-eight low-cycle fatigue tests on corroded reinforcing bars varied in percentage mass loss, strain amplitudes and buckling lengths are conducted. The failure modes and crack propagation are investigated by fractography of fracture surfaces using scanning electron microscope. The results show that the inelastic buckling, percentage mass loss and nonuniform corrosion pattern are the main parameters affecting the low-cycle fatigue life of reinforcing bars. It was found that the fatigue life of corroded reinforcing bars combined with inelastic buckling has a significant path dependency. The results show that in some cases the number of cycles to failure of corroded bars under constant amplitude fatigue test is increased.

Fatigue behavior of calcium containing AZ91 magnesium alloys*

Abstract The low density of magnesium alloys makes them attractive for light weight constructions. However, important aspects are the rather poor mechanical properties of the most commonly used Mg alloy AZ91 (approximately 9 wt.-% Al, 1 wt.-% Zn), which limits its use in, e. g., power train applications. Alloying AZ91 with Ca leads to a significant improvement of creep resistance. To investigate the influence of the Ca addition on the fatigue behavior, symmetric push pull tests have been performed on AZ91 alloys with an addition of 0, 1 and 3 wt.-% of Ca, respectively. At relatively high amplitudes, the Ca containing alloys show a decrease in fatigue life compared to Ca-free AZ91. However, with a decrease in amplitude, the fatigue life of the alloy with 3 wt.-% Ca are comparable with the Ca-free AZ91 alloy and with a further decrease in amplitude the alloy with an addition of 3 wt.-% Ca has an even higher fatigue life than the Ca-free alloy. All alloys contain pores due to the casting process.