Fatigue Assessment of Tubular Automotive Components in Presence of Inhomogeneities

2004 ◽  
Author(s):  
Stefano Beretta ◽  
Herna´n Juan Desimone ◽  
Andrea Poli
Keyword(s):  
Fatigue Limit ◽  
Detrimental Effect ◽  
Fatigue Behavior ◽  
High Strength Steels ◽  
High Strength ◽  
Probability Of Failure ◽  
Integral Approach ◽  
Material Strength ◽  
Automotive Components ◽  
Tubular Components

Tubular automotive components, e.g. stabilizers and half shafts, are components subjected to fatigue. In order to assess fatigue behavior of such components, it is important to know both the real load conditions as well as the material strength against multi-axial fatigue. For the second point, a detrimental effect in the fatigue limit of high strength steels is given by the defects present in the component, coming from the material (such as microinclusions, microvoids, etc) or for the process (e.g. handling marks). An integral approach in order to assess fatigue limit of tubular components is proposed. The attention is focused onto planar inhomogeneities, which are the most common in tubular products, though the methodology can be extended to different defect-shapes. The method is applied together with a probabilistic model, in order to analyze the probability of failure. In particular, two different processes (in terms of inhomogeneities present in the final component) are compared, and the results allow to evaluate, for example, the admissible load for the desired (or design) level of failure probability for the component.

Usability Testing of Ultra High-Strength Steels

2012 ◽  
Author(s):  
Jouko A. Heikkala ◽  
Anu J. Väisänen
Keyword(s):  
Tensile Strength ◽  
Plate Thickness ◽  
Rolling Direction ◽  
High Strength Steels ◽  
High Strength ◽  
Structural Steels ◽  
Test Material ◽  
Material Strength ◽  
Machining Parameters ◽  
Usability Tests

New ultra high strength (UHS) steels have been developed in order to get advantages in machine design and construction. Following benefits can be obtained for example: - less material usage due to lighter constructions; - better payload and less fuel consumption in vehicle industry; - energy saving in material production. A rough distinction of structural steels can be defined to ductile steels, with tensile strength less than 300 MPa, and high strength steels, up to 700 Mpa. A steel material can be defined as UHS steel when the tensile strength exceeds 700 MPa. Steels with yield strength of 1500 Mpa have been developed so far. UHS steels can also be divided into structural steels and wear resistant steels. With the tensile strength also the hardness increases and the tensile strain decreases. That causes several difficulties when the material is processed into products. Especially mechanical processing like bending, machining and shearing gets difficult as the material strength increases. That causes problems for the construction material users to find the proper manufacturing methods in production. In Oulu University Production Technology Laboratory material processing tests have been performed during several years in co-operation with the local steel manufacturer. The usability tests comprise mainly of bending and machining tests. Shearing and welding tests have been made to a smaller extent. Also laser treatment has been used for local heat conditioning in order to improve the bending and shearing properties, but these techniques are not yet widely used in production. The bending tests are carried out with standard bending tools and test steel plates with standard dimensions. The plate thickness varies depending on the test material. The target is to determine the reliable minimum bending radiuses whereby the plate can be bent without failure, from both sides and along the rolling direction and orthogonally to that. Also the springback angle is measured and the bent surfaces are evaluated according to several criteria. When necessary, also the mechanical testing of the formed material is carried out. The machining tests are made mainly by drilling. Also some milling tests have been performed. Drilling is a convenient way of machining testing because a substantial amount of holes can be drilled in one test plate. The drilling power can be observed precisely by monitoring the spindle power. Also a variety of different tool types can be used, from uncoated HSS drills to boring tools with indexable inserts. The optimal machining parameters (feed and speed) will be defined according to maximum tool life and minimum machining costs.

Expulsion Intensity Monitoring and Modeling in Resistance Spot Welding Based on Electrode Displacement Signals

2020 ◽  
Author(s):  
Yu-Jun Xia ◽  
Yan Shen ◽  
Lang Zhou ◽  
Yong-Bing Li
Keyword(s):  
Resistance Spot Welding ◽  
Spot Welding ◽  
Low Carbon Steel ◽  
Sheet Thickness ◽  
High Strength Steels ◽  
High Strength ◽  
Material Strength ◽  
Low Carbon ◽  
Resistance Spot ◽  
Electrode Displacement

Abstract Weld expulsion is one of the most common welding defects during resistance spot welding (RSW) process especially for high strength steels (HSS). In order to control and eventually eliminate weld expulsion in production, accurate assessment of the expulsion severity should be the first step and is urgently required. Among the existing methods, real-time monitoring of RSW-related process signals has become a promising approach to actualize the online evaluation of weld expulsion. However, the inherent correlation between the process signals and the expulsion intensity is still unclear. In this work, a commonly used process signal, namely the electrode displacement and its instantaneous behavior when expulsion occurs are systematically studied. Based upon experiments with various electrodes and workpieces, a nonlinear relation between the weight of expelled metal and the sudden displacement drop accompanied by the occurrence of weld expulsion is observed, which is mainly influenced by electrode tip geometry but not by material strength or sheet thickness. The intrinsic relationship between this specific signal feature and the magnitude of expulsion is further explored through geometrical analysis, and a modified analytical model for online expulsion evaluation is finally proposed. It is shown that the improved model could be applied to domed electrodes with different tip geometries and varying workpieces ranging from low carbon steel to HSS. The error of expulsion estimation could be limited within ±20.4 mg (±2σ) at a 95% confidence level. This study may contribute to the online control of weld expulsion to the minimum level.

Fatigue-Corrosion of High Strength Steels in Synthetic Seawater under Cathodic Protection

2020 ◽  
Vol 841 ◽  
pp. 294-299
Author(s):  
Sergio Lorenzi ◽  
Cristian Testa ◽  
Marina Cabrini ◽  
Francesco Carugo ◽  
Luigi Coppola ◽  
...  
Keyword(s):  
Cathodic Protection ◽  
Fatigue Behavior ◽  
High Strength Steels ◽  
High Strength ◽  
Loading Frequency ◽  
Offshore Pipelines ◽  
Synthetic Seawater ◽  
Steel Grades ◽  
Protection Potential ◽  
Fatigue Corrosion

The paper is aimed to the study of the corrosion-fatigue behavior of high strength steels for offshore pipelines. Tests have been performed in order to study fatigue crack growth in synthetic seawater under cathodic protection. The tests have been carried out on three different steel grades from 65 to 85 ksi with tempered martensite and ferrite-bainite microstructures. The effect of stress intensity factor, cathodic protection potential and cyclic loading frequency is shown.

Study of Fatigue Behavior for Spot Welded Tensile Shear Specimens of Advanced High Strength Steels

2012 ◽  
Vol 83 (10) ◽  
pp. 988-994 ◽  
Author(s):  
Gert Weber ◽  
Stephan Brauser ◽  
Holger Gaul ◽  
Michael Rethmeier
Keyword(s):  
Fatigue Behavior ◽  
High Strength Steels ◽  
High Strength ◽  
Tensile Shear ◽  
Advanced High Strength Steels ◽  
Spot Welded

313 Effect of Stress Ratio on Long-Life Fatigue Behavior in High Strength Steels

2005 ◽  
Vol 2005 (0) ◽  
pp. 197-198
Author(s):  
Kazuaki SHIOZAWA ◽  
Seiichi NISHINO ◽  
Takayuki HASEGAWA ◽  
Yasuyuki YACHI
Keyword(s):  
Stress Ratio ◽  
Fatigue Behavior ◽  
High Strength Steels ◽  
High Strength ◽  
Long Life

Expulsion Intensity Monitoring and Modeling in Resistance Spot Welding Based on Electrode Displacement Signals

2020 ◽  
Vol 143 (3) ◽  
Author(s):  
Yu-Jun Xia ◽  
Yan Shen ◽  
Lang Zhou ◽  
Yong-Bing Li
Keyword(s):  
Resistance Spot Welding ◽  
Spot Welding ◽  
Low Carbon Steel ◽  
Sheet Thickness ◽  
High Strength Steels ◽  
High Strength ◽  
Material Strength ◽  
Low Carbon ◽  
Resistance Spot ◽  
Electrode Displacement

Abstract Weld expulsion is one of the most common welding defects during the resistance spot welding (RSW) process, especially for high strength steels (HSS). In order to control and eventually eliminate weld expulsion in production, accurate assessment of the expulsion severity should be the first step and is urgently required. Among the existing methods, real-time monitoring of RSW-related process signals has become a promising approach to actualize the online evaluation of weld expulsion. However, the inherent correlation between the process signals and the expulsion intensity is still unclear. In this work, a commonly used process signal, namely, the electrode displacement and its instantaneous behavior when expulsion occurs are systematically studied. Based upon experiments with various electrodes and workpieces, a nonlinear correlation between the weight of expelled metal and the sudden displacement drop accompanied by the occurrence of weld expulsion is observed, which is mainly influenced by electrode tip geometry but not by material strength or sheet thickness. The intrinsic relationship between this specific signal feature and the magnitude of expulsion is further explored through geometrical analysis, and a modified analytical model for online expulsion evaluation is finally proposed. It is shown that the improved model could be applied to domed electrodes with different tip geometries and varying workpieces ranging from low carbon steel to HSS. The error of expulsion estimation could be limited within ±20.4 mg (±2σ) at a 95% confidence level. This study may contribute to the online control of weld expulsion to the minimum level.

Low Cycle Notched Fatigue Behavior and Life Predictions of A723 High Strength Steels.

1995 ◽  
Author(s):  
E. Troiano ◽  
J. H. Underwood ◽  
D. Crayon ◽  
R. T. Abbott
Keyword(s):  
Fatigue Behavior ◽  
High Strength Steels ◽  
High Strength ◽  
Life Predictions

Fatigue Designing of High Strength Steels Components Considering Aggressive Fuel Environment and Very High Cycle Fatigue Effects

2014 ◽  
Vol 783-786 ◽  
pp. 1845-1850
Author(s):  
Stephan Issler ◽  
Manfred Bacher-Hoechst ◽  
Steffen Schmid
Keyword(s):  
High Cycle Fatigue ◽  
Fuel Injection ◽  
Fatigue Testing ◽  
High Strength Steels ◽  
High Strength ◽  
Cycle Fatigue ◽  
Fatigue Reliability ◽  
Automotive Components ◽  
Very High Cycle Fatigue ◽  
Very High

Automotive components for injection systems are subjected to load spectra with up to 1E9 load cycles during the expected service life. However, fatigue testing with such a large number of cycles using original components is extremely time-consuming and expensive. A contribution for fatigue reliability assessment is available by the application of specimen testing and the transfer of the results to components including the verification by component spot tests.In this contribution very high cycle fatigue results in laboratory air and in ethanol fuel using notched specimens of high strength stainless steel are discussed. The influence of testing frequency was studied using ultrasonic and conventional test techniques. The validation and transfer of these accelerated testing results to components is one of the main challenges for a reliable fatigue designing.KeywordsVery High Cycle Fatigue (VHCF), automotive components, fuel injection, bio-fuels, corrosion fatigue, testing concepts, fatigue design concepts

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