The Experts below are selected from a list of 3024 Experts worldwide ranked by ideXlab platform

Tobias Melz - One of the best experts on this subject based on the ideXlab platform.

  • Fatigue life and cyclic material behavior of butt-welded high-strength steels in the LCF regime*
    Materials Testing, 2015
    Co-Authors: Benjamin Möller, Rainer Wagener, Heinz Kaufmann, Tobias Melz
    Abstract:

    Abstract Fatigue life approach methods based on general local concepts for welded joints assign universal material properties to geometrically well-defined weld toes or weld roots, in order to evaluate local stresses and strains, ignoring any metallurgical discrepancies. In this study, analysis of the main influences on these concepts, Linear Damage Accumulation and cyclic material behavior, of the high-strength and ultra-high-strength steels S960QL, S960M and S1100QL was performed for the base material and for butt-welded specimens. Results of stress-controlled tests under constant amplitude loading (CAL) and variable amplitude loading (VAL) show that a Linear Damage Accumulation with a Damage sum of Dal = 0.5 is conservative. Effects of the geometrical and metallurgical notch on the cyclic material behavior are shown by strain controlled testing of both base material and welded specimens. Cycles to crack initiation, presented in strain-life curves, are consequently reduced in the as-welded state. Cyclic...

  • Influence of the Transient Material Behaviour in the Fatigue Life Estimation Under Random Loading
    Procedia Engineering, 2015
    Co-Authors: Alessio Tomasella, Rainer Wagener, Tobias Melz
    Abstract:

    Abstract The estimation of the fatigue life under variable amplitude loading is a fundamental step in the design phase. To consider variable amplitudes in the fatigue design the Linear Damage Accumulation is applied, thus disregarding non Linearity. When materials show cyclic hardening/softening, the hypotheses from Palmgren and Miner are not valid and this causes appreciable errors in the fatigue life estimation. Fatigue tests were carried out on the steel HC340LA. The influence of strain softening and mean stress relaxation is shown. A simplified method for considering this transient phase is presented. More accurate results can be achieved by applying this method.

  • Fatigue Life of Welded High-strength Steels under Gaussian Loads☆
    Procedia Engineering, 2015
    Co-Authors: Benjamin Möller, Rainer Wagener, Jennifer Hrabowski, Thomas Ummenhofer, Tobias Melz
    Abstract:

    Within the scope of the investigation of welded high-strength steels for application in crane structures, a Gaussian-like test spectrum is derived from an analysis of recorded load time histories. In addition to stress-controlled fatigue tests under constant amplitude loading, the test spectrum is used for the experimental investigation of MAG-welded butt joints and tubular sample components under variable amplitude loading. A Linear Damage Accumulation using Palmgren-Miner-Elementary is conservative for a Damage sum of D = 0.5. Application of the theoretical Damage sum Dth = 1 results in a closer approximation of the Gasner-curve. For further improvement of this approximation, a rotation of the calculated Gasner-curve, i.e. a variable Damage sum, is suggested for both butt joints and sample components.

Abdolmajid Mosleh - One of the best experts on this subject based on the ideXlab platform.

  • A model of BGA thermal fatigue life prediction considering load sequence effects
    Materials, 2016
    Co-Authors: Weiwei Hu, Yaqiu Li, Yufeng Sun, Abdolmajid Mosleh
    Abstract:

    Accurate testing history data is necessary for all fatigue life prediction approaches, but such data is always deficient especially for the microelectronic devices. Additionally, the sequence of the individual load cycle plays an important role in physical fatigue Damage. However, most of the existing models based on the Linear Damage Accumulation rule ignore the sequence effects. This paper proposes a thermal fatigue life prediction model for ball grid array (BGA) packages to take into consideration the load sequence effects. For the purpose of improving the availability and accessibility of testing data, a new failure criterion is discussed and verified by simulation and experimentation. The consequences for the fatigue underlying sequence load conditions are shown.

Weiwei Hu - One of the best experts on this subject based on the ideXlab platform.

  • A model of BGA thermal fatigue life prediction considering load sequence effects
    Materials, 2016
    Co-Authors: Weiwei Hu, Yaqiu Li, Yufeng Sun, Abdolmajid Mosleh
    Abstract:

    Accurate testing history data is necessary for all fatigue life prediction approaches, but such data is always deficient especially for the microelectronic devices. Additionally, the sequence of the individual load cycle plays an important role in physical fatigue Damage. However, most of the existing models based on the Linear Damage Accumulation rule ignore the sequence effects. This paper proposes a thermal fatigue life prediction model for ball grid array (BGA) packages to take into consideration the load sequence effects. For the purpose of improving the availability and accessibility of testing data, a new failure criterion is discussed and verified by simulation and experimentation. The consequences for the fatigue underlying sequence load conditions are shown.

Benjamin Möller - One of the best experts on this subject based on the ideXlab platform.

  • Fatigue life and cyclic material behavior of butt-welded high-strength steels in the LCF regime*
    Materials Testing, 2015
    Co-Authors: Benjamin Möller, Rainer Wagener, Heinz Kaufmann, Tobias Melz
    Abstract:

    Abstract Fatigue life approach methods based on general local concepts for welded joints assign universal material properties to geometrically well-defined weld toes or weld roots, in order to evaluate local stresses and strains, ignoring any metallurgical discrepancies. In this study, analysis of the main influences on these concepts, Linear Damage Accumulation and cyclic material behavior, of the high-strength and ultra-high-strength steels S960QL, S960M and S1100QL was performed for the base material and for butt-welded specimens. Results of stress-controlled tests under constant amplitude loading (CAL) and variable amplitude loading (VAL) show that a Linear Damage Accumulation with a Damage sum of Dal = 0.5 is conservative. Effects of the geometrical and metallurgical notch on the cyclic material behavior are shown by strain controlled testing of both base material and welded specimens. Cycles to crack initiation, presented in strain-life curves, are consequently reduced in the as-welded state. Cyclic...

  • Fatigue Life of Welded High-strength Steels under Gaussian Loads☆
    Procedia Engineering, 2015
    Co-Authors: Benjamin Möller, Rainer Wagener, Jennifer Hrabowski, Thomas Ummenhofer, Tobias Melz
    Abstract:

    Within the scope of the investigation of welded high-strength steels for application in crane structures, a Gaussian-like test spectrum is derived from an analysis of recorded load time histories. In addition to stress-controlled fatigue tests under constant amplitude loading, the test spectrum is used for the experimental investigation of MAG-welded butt joints and tubular sample components under variable amplitude loading. A Linear Damage Accumulation using Palmgren-Miner-Elementary is conservative for a Damage sum of D = 0.5. Application of the theoretical Damage sum Dth = 1 results in a closer approximation of the Gasner-curve. For further improvement of this approximation, a rotation of the calculated Gasner-curve, i.e. a variable Damage sum, is suggested for both butt joints and sample components.

Rainer Wagener - One of the best experts on this subject based on the ideXlab platform.

  • Fatigue life and cyclic material behavior of butt-welded high-strength steels in the LCF regime*
    Materials Testing, 2015
    Co-Authors: Benjamin Möller, Rainer Wagener, Heinz Kaufmann, Tobias Melz
    Abstract:

    Abstract Fatigue life approach methods based on general local concepts for welded joints assign universal material properties to geometrically well-defined weld toes or weld roots, in order to evaluate local stresses and strains, ignoring any metallurgical discrepancies. In this study, analysis of the main influences on these concepts, Linear Damage Accumulation and cyclic material behavior, of the high-strength and ultra-high-strength steels S960QL, S960M and S1100QL was performed for the base material and for butt-welded specimens. Results of stress-controlled tests under constant amplitude loading (CAL) and variable amplitude loading (VAL) show that a Linear Damage Accumulation with a Damage sum of Dal = 0.5 is conservative. Effects of the geometrical and metallurgical notch on the cyclic material behavior are shown by strain controlled testing of both base material and welded specimens. Cycles to crack initiation, presented in strain-life curves, are consequently reduced in the as-welded state. Cyclic...

  • Influence of the Transient Material Behaviour in the Fatigue Life Estimation Under Random Loading
    Procedia Engineering, 2015
    Co-Authors: Alessio Tomasella, Rainer Wagener, Tobias Melz
    Abstract:

    Abstract The estimation of the fatigue life under variable amplitude loading is a fundamental step in the design phase. To consider variable amplitudes in the fatigue design the Linear Damage Accumulation is applied, thus disregarding non Linearity. When materials show cyclic hardening/softening, the hypotheses from Palmgren and Miner are not valid and this causes appreciable errors in the fatigue life estimation. Fatigue tests were carried out on the steel HC340LA. The influence of strain softening and mean stress relaxation is shown. A simplified method for considering this transient phase is presented. More accurate results can be achieved by applying this method.

  • Fatigue Life of Welded High-strength Steels under Gaussian Loads☆
    Procedia Engineering, 2015
    Co-Authors: Benjamin Möller, Rainer Wagener, Jennifer Hrabowski, Thomas Ummenhofer, Tobias Melz
    Abstract:

    Within the scope of the investigation of welded high-strength steels for application in crane structures, a Gaussian-like test spectrum is derived from an analysis of recorded load time histories. In addition to stress-controlled fatigue tests under constant amplitude loading, the test spectrum is used for the experimental investigation of MAG-welded butt joints and tubular sample components under variable amplitude loading. A Linear Damage Accumulation using Palmgren-Miner-Elementary is conservative for a Damage sum of D = 0.5. Application of the theoretical Damage sum Dth = 1 results in a closer approximation of the Gasner-curve. For further improvement of this approximation, a rotation of the calculated Gasner-curve, i.e. a variable Damage sum, is suggested for both butt joints and sample components.