Point Bending Fatigue Research Articles

Influence of Deposition Bias Voltage on Fatigue Cracking Behavior of Chromium Nitride Film Deposited on Steel

Three point bending fatigue tests were carried out to investigate the influence of bias voltage on fatigue behavior of medium carbon steel with chromium nitride film. The substrate material of the specimens was JIS S45C medium carbon steel. The chromium nitride films were coated at two different bias voltages (VB = -20V, -300V) for fatigue test by arc ion plating method. As a result, the fatigue limit was improved by coating at low bias voltage, while the fatigue limit of high bias voltage samples decreased by coating. In order to clarify the difference between high and low bias voltages, the tensile test was performed using the coated specimens. For this test, the chromium nitride films were deposited at four different bias voltages. It was found the cracking behavior clearly changed between -40V and -80V. For low bias voltage samples, short cracks were initiated in the films, while the long cracks were initiated at same strain for high bias voltage samples. These differences between low and high bias voltage sample may be due to the elastic modulus of the film and droplets distribution in the film.

Effects of Dynamic Ion Mixing Coating Condition for Fatigue Properties of Stainless Steel with TiN Film

Four point bending fatigue tests were carried out using martensitic stainless steel with TiN film deposited at five different deposition rates by dynamic ion mixing process in order to investigate the influence of deposition rate on the fatigue strength. As a result, the fatigue limit clearly increased by the deposition at appropriate conditions. However, the deposition by other conditions resulted in the degradation of fatigue strength. This is caused by the decrease of threshold stress intensity factor after TiN deposition and the difference of defect distribution in the film. In addition, the crack propagation rate was increased in low stress intensity factor range by the deposition of TiN film.

Quantitative Evaluation of Fatigue Strength at N=107 for Carburized Steels

The fatigue strength at N=107 for carburized steels, which indicates the fatigue strength for specimens whose fatigue origins are not at inner defects but at as-carburized surfaces in this study, is affected by a softened structure, oxidized intergranular, retained austenite and residual stress. In the early study, it was clarified that the fatigue strength at N=107 of the specimens containing the retained austenite in the structure was higher than that estimated by the √area parameter model.This study aims to quantitatively evaluate these complex influences mentioned above and predict the fatigue strength at N=107 with high accuracy. Therefore, rotating bending and three point bending fatigue tests with several stress ratios were conducted using carburized SCM420s. Since the fatigue crack of all the specimens, whose fatigue origin was at the as-carburized surface, emanated from oxidized intergranular at a non-martensitic structure, the oxidized intergranular was considered to be mechanically equivalent to a surface crack. The dependence of mean stress on the fatigue strength at N=107 was accurately arranged by the modified Goodman diagram. Furthermore, the hardness of a thin softened structure was estimated from the half value breadth of the structure. Based on these results, the prediction of the fatigue strength at N=107 for the carburized SCM420s was performed by applying the √area parameter model, and its fatigue strength was successfully estimated at an unquestionable level for practical use.

Fatigue Life Evaluation of Shot Peened Al-Alloys 5083 H11 T-Welded Joints by Experimental and Numerical Approaches

In this investigation, the fatigue life improvements of T-welded joints in aluminium alloy 5083 H11 by shot peening was evaluated. Use was made using both experimental and numerical approaches. The experimental assessment was conducted using four point bending fatigue tests at R = 0.5. The numerical method used in this study, to predict the nucleation fatigue life, was developed on the basis of a local approach, which took into account the stresses induced by the welding process and the residual stresses generated by the shot-peening treatment. The propagation fatigue life was calculated using fracture mechanics concepts. It was found that the numerical results were well correlated with the experimental ones.

THE EFFECTS OF DIFFERENT WAVE PATTERN AND REST PERIOD IN REPEATED LOAD ON THE FATIGUE BEHAVIOR OF THE ASPHALT MIXTURE

The four point bending fatigue tests were carried out for dense graded asphalt mixtures under various wave patterns in repeated loading: sinusoidal, triangular, twin peaks, sinusoidal with one second rest period, sinusoidal with ten second rest period. Analyzing the results using classical fatigue analysis, energy approach and ENTPE fatigue damage approach, it was found 1) that the fatigue damage subjected in asphalt mixtures differs significantly depending on the wave patterns of repeated loading, giving much difference in the number of load applications to failure, 2) that the number of load applications to failure is depending considerably on the rest period 3) that there are linear relations between the rate of stiffness change and the number of load applications to failure, showing approximately constant relations even if loading wave pattern and rest period are different.

EFFECT OF WATER ON DUCTILITY AND FATIGUE STRENGTH OF AUSTEMPERED DUCTILE CAST IRON (ADI)

In order to study the mechanism of decreasing tensile strength and elongation of Austempered Ductile Cast Iron (ADI) in the wet condition, various tension tests and impact tests were carried out. Three point bending fatigue tests were carried out on ADI and annealed 0.55% carbon steel to clarify the influence of water on fatigue strength. The main conclusions are as follow. Embrittlement by water begins when plastic deformation starts in a tension test. The fatigue limit of ADI in water showed a lower value than that in air. The influence of a water environment on fatigue behaviour was similar to that of annealed 0.55% carbon steel. Embrittlement such as that in a tension test was not observed in a fatigue test.

1325 AIP法によりCrN薄膜を被覆したS45Cの疲労特性(S21-3 表面改質処理,S21 金属材料の疲労特性と破壊機構)

Three point bending fatigue tests were carried out using S45C steel with CrN film. The film was coated onto S45C steel by arc ion plating method. In order to investigate the effect of coating condition on the fatigue behavior, the films were coated under two different conditions. As a result, the fatigue strength was increased coated under low arc current and bias voltage, while the fatigue strength of high arc current and bias voltage. The change of the fatigue behavior was mainly caused by the difference of crack initiation.

1326 TiN薄膜被覆マルテンサイトステンレス鋼の疲労特性に与えるAIP成膜条件の影響(S21-3 表面改質処理,S21 金属材料の疲労特性と破壊機構)

In order to investigate the effect of coating condition on the fatigue properties of high strength steel, the four point bending fatigue tests were carried out for martensitic stainless steel with TiN film coated by arc ion plating (AIP) method. TiN film having 2μm thick was deposited onto the substrate surface under four kind of the bias voltage; V_B=0, -60, -160 and -260V. For V_B=0, -160V and -260V, the fatigue limit increased. The highest fatigue limit of σ_<max>=900MPa was obtained for V_B=-160V. For V_B=-60V and -260V with film delamination, the fatigue limit was decreased by coating. It appears that the fatigue properties of the coatings strongly depend on the crack initiation behavior. The fatigue crack initiated from subsurface in the substrate independent of bias voltages and the crack initiation life depended on the surface roughness, adhesive strength, residual stress, elastic modulus, and hardness of the films.

Thermal fatigue crack networks parameters and stability: an experimental study

A thermal fatigue device––called SPLASH––similar to the facility developed by Marsh [Fatigue crack initiation and propagation in stainless steels subjected to thermal cycling, International Conference on Mechanical Behaviour and Nuclear Applications of Stainless Steels at Elevated Temperature, 1981] has been built in CEA/SRMA in 1985. Since then, it was used mostly on austenitic stainless steels to assess the initiation and growth of thermal fatigue crack networks. In 1998, a leak appeared in an auxiliary loop of the primary circuit of a pressurized water nuclear plant in Civaux (France). Thermal fatigue was suspected and studies began on AISI 304 L type austenitic stainless steel. They were eventually compared to results obtained earlier on AISI 316 L(N). First, the initiation conditions were determined and the damage before initiation was qualitatively observed. Then, some crack networks parameters were chosen and quantitatively determined by image analysis. This part of the study was done at the surface, during crack growth, and at the end of the tests, in depth. Finally, the stability of the crack networks obtained by thermal fatigue was tested under isothermal load controlled four point bending fatigue test, and some conclusions were drawn on the mechanisms of propagating crack selection.

Mechanical and precorroded fatigue properties of coated aluminium aircraft skin system as function of various thermal spray processes

Aluminium coatings deposited on AA2024-T3 by the flame arc, atmospheric plasma and high velocity oxyfuel (HVOF) processes were evaluated using quantitative metallography, microhardness, adhesion, three point bend and conventional fatigue tests as well as fatigue tests on precorroded samples. Comparison of the microstructures, mechanical properties, and the fatigue and precorroded fatigue properties of samples with the three types of thermal spray coating, as well as samples of bare AA2024-T3 and Alclad AA2024-T3, revealed that HVOF is the most promising thermal spray process for the deposition of aluminium coatings, and, in particular, HVOF coatings greatly increase the fatigue and precorroded fatigue lifetimes of the AA2024-T3 substrate.

Fatigue Design of Leaf Spring Based on Proving Ground

The suspension system of vehicle is directly influenced to ride and handling. Therefore, suspension part should have enough endurance during its lifetime to protect passenger. Spring is one of major suspension part of vehicle. Thus, in this paper, a fatigue design method for leaf spring based on proving ground response was proposed. At first, stress and displacement of leaf spring are measured through the proving ground test. And next, the maximum load acting on leaf spring assembly under driving condition was defined from the road load response. On the base of these results, fatigue tests for leaf spring assembly and 3-point bending fatigue tests for material of leaf spring were carried out. From the above, the maximum load-fatigue life relation of leaf spring material and assembly was defined, and 3-point bending test result has good agreement with leaf spring assembly fatigue test result. Thus, it is expect that economical fatigue design criterion for leaf spring assembly can be determined from fatigue data of simple smooth specimen by 3 point bending fatigue tests.

AIP法によりTiN薄膜を被覆したGIN6の疲労特性(J17-1 表面改質とトライボロジー(I),J17 表面改質とトライボロジー)

Four point bending fatigue tests were carried out using martensitic stainless steel with TiN film. The film was coated 2.1μm onto stainless steel by arc ion plating method. In order to investigate the effect of bias voltage on fatigue behavior, the films were coated under three different bias voltage; V_B= -60, -160 and -260V. As a result, the fatigue limit was increased coated under V_B=- 160V and -60V. The highest fatigue limit was σ_<max>=1800MPa for V_B=160V. However, in the case of V_B=260V, the fatigue limit was decreased by coating. The change of fatigue behavior was caused by surface roughness, residual stress and hardness.

Investigation of fatigue crack growth in acrylic bone cement using the acoustic emission technique

Failure of the bone cement mantle has been implicated in the loosening process of cemented hip stems. Current methods of investigating degradation of the cement mantle in vitro often require sectioning of the sample to confirm failure paths. The present research investigates acoustic emission as a passive experimental method for the assessment of bone cement failure. Damage in bone cement was monitored during four point bending fatigue tests through an analysis of the peak amplitude, duration, rise time (RT) and energy of the events emitted from the damage sections. A difference in AE trends was observed during failure for specimens aged and tested in (i) air and (ii) Ringer's solution at 37°C. It was noted that the acoustic behaviour varied according to applied load level; events of higher duration and RT were emitted during fatigue at lower stresses. A good correlation was observed between crack location and source of acoustic emission, and the nature of the acoustic parameters that were most suited to bone cement failure characterisation was identified. The methodology employed in this study could potentially be used as a pre-clinical assessment tool for the integrity of cemented load bearing implants.

Corrosion - Fatigue Performance of Magnesium Alloys

To determine the effect of a coating on fatigue strength, three point bend fatigue tests of coated and un-coated AM50 and AZ91D magnesium high pressure die cast specimens were made and S-N curves determined. Environments used were air, tap water and natural seawater. A difference in corrosion fatigue performance has been found, between AZ91D and AM50 and for both alloys performance in air was superior to both water environments. AZ91D has better corrosion fatigue resistance in tap water than in seawater; conversely, AM50 has better corrosion fatigue resistance in seawater than tap water. The results showed that the fatigue life was not reduced in these water environments for coated specimens, as the coating usually provided protection from corrosion.

Fatigue Properties of Nitride Cr-Mo Steel with CrN Thin Film Deposited by Aip Method

In this study, we selected the nitride Cr-Mo Steel SCM435 as the substrate. Attention was focussed on the effect of film thickness. The Arc Ion Plating was performed using Cr cathode and N2 gas. The specimens were prepared for the film thickness 6, 12 and 18μm The three point bending fatigue tests were performed at room temperature in a laboratory environment. After the fatigue test, crack initiation sites were examined by using an optical microscope and a scanning electron microscope. The results obtained were as follows: (1) A high compressive residual stress generated in the film, and the compressive residual stress of 12μm film thickness was the greatest. (2) The fatigue strength of coated specimens for thin film was slightly lower than for substrate. (3) The film thickness hardly affected the fatigue strength of coated specimens.

超微粒子超硬合金の曲げ疲労特性

As micrograin carbide alloys with average WC grain size below 1μm have been widely used for cutting tools and wear resistant tools, it is very important to acquire knowledge on bending fatigue characteristics of the alloys in order to estimate and improve a tool life. Therefore, in this study, the characteristics of three points bending fatigue in micrograin WC-6-15 mass%Co-0.4-1.2mass%Cr3C2 alloys with grain size of 0.8μm which were treated by HIP or Sinter-HIP process was mainly investigated in relation to a fracture origin.The results obtained were as follows: (1) As regarding the effects of Co content on bending fatigue of the HIP-treated alloys, the fatigue life was almost same in 6-12mass%Co alloys, but it decreased in 15 mass% Co alloy. (2) The fracture origin observed on the fractured surface after bending fatigue test in the HIP-treated alloys was Co pool with the step-shaped form in all cases. (3) There was some correlation between the size of Co pool origin and the fatigue life under same applied stress. In the Sinter-HIP treated alloys, the fatigue life was considerably improveddue to the decrease of the size of Co pool defect in the microstructure.

Effects of inclusions and tempering temperature on the life of a powder compacting punch

Effects of nonmetallic inclusions and tempering temperature on the mechanical properties and failure life of the powder metallurgical (P/M) high-speed steel (1.28% C, 4.20% Cr, 6.40% W, 5.00% Mo, 3.1% V, bal. Fe) were investigated. Small amounts of non-metallic inclusions in the specimen did not greatly affected impact energy and transverse rupture strength (TRS). But, failure lives of the three point bend fatigue specimens and powder compacting punch were drastically decreased by crack initiation around non-metallic inclusions under the cyclic load. On the other hand, as tempering temperature increased, the volume fraction and average size of carbides (MC or M 6C) did not significantly change, while hardness of specimen decreased. The failure lives of the three point bend tested specimens and powder compacting punch drastically increased with increasing tempering temperature due to increased resistance to fatigue crack propagation by the softening of the matrix.

Effects of processing conditions and test temperature on fatigue crack growth and fracture toughness of Be–Al metal matrix composites

The effects of changes in processing conditions and test temperature on the tension behavior, fatigue crack growth and fracture toughness of a Be–Al metal matrix composite (MMC) containing 70% by volume Be and 30% by volume Al have been determined. Prealloyed Be–Al powders were either hot isostatically pressed (HIP) or CIP/extruded to full density. Testing was conducted in uniaxial tension, three point bend fatigue, and both notched and fatigue precracked toughness, at temperatures ranging from −125 to 225°C. The fatigue crack growth experiments were conducted at R=0.1, 0.4, and 0.6. Significant effects of processing conditions, test temperature, and R, on the balance of properties were obtained. Tensile and fracture toughness properties of the extruded material were higher than the HIP material. Increasing the test temperature from −125 to 225°C decreased the strength and fracture toughness of both the HIP and extruded materials. Fracture surface observations revealed clear differences between the fracture morphologies in the HIP and extruded materials as well as those at low vs. high temperatures. These differences were used to rationalize the tensile and toughness behavior exhibited. In general, the materials tested exhibited fatigue behavior that is consistent with that of metals, despite the presence of the large volume fraction of Be, a semi-brittle constituent. Values for the Paris law slope and fatigue threshold were in the range of those exhibited by metals. However, changes in test temperature from 225 to −125°C produced significant increases in the Paris law slope for both materials. The results obtained on the Be–Al composite are also compared to that of the constituents (i.e. Be, Al) in order to illustrate some of the benefits obtained by creating the composite structure.

A Note on Fatigue Bending Tests Using a Haversine Loading

ABSTRACT Four point bending fatigue tests under haversine and pure sinusoidal loading is discussed from a theoretical point of view. In this discussion the material is considered to be visco-elastic rather than linear elastic. The differences between the two types of loading in force control are easily understood, but for deformation controlled tests the effect of different signals is less obvious. Tests that were performed to verify the theoretical considerations seem to indicate that the effect is different for different mixtures. The implication is that the results of fatigue tests under different loading signals cannot readily be compared.

A Note on Fatigue Bending Tests Using a Haversine Loading

ABSTRACT Four point bending fatigue tests under haversine and pure sinusoidal loading is discussed from a theoretical point of view. In this discussion the material is considered to be visco-elastic rather than linear elastic. The differences between the two types of loading in force control are easily understood, but for deformation controlled tests the effect of different signals is less obvious. Tests that were performed to verify the theoretical considerations seem to indicate that the effect is different for different mixtures. The implication is that the results of fatigue tests under different loading signals cannot readily be compared.