Johan Ahlström - Academia.edu (original) (raw)
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Papers by Johan Ahlström
IOP Conference Series: Materials Science and Engineering
MATEC Web of Conferences, 2019
A significant challenge for railway infrastructure managers is to know when and how to maintain r... more A significant challenge for railway infrastructure managers is to know when and how to maintain rails. Often, the critical missing information is the current health status, in particular information about rail cracks. Therefore, a new method for rail crack detection is proposed. By utilizing a train-mounted camera system, a single measurement train can monitor a large rail network. The system uses Digital Image Correlation (DIC) to measure the strain fields due to rail bending caused by the measurement train. Promising results are obtained under laboratory conditions. The identified cracks are correlated to the actual crack network, characterized by serial-sectioning microscopy. Furthermore, finite element simulations show the method's high sensitivity to crack depths. Knowing the crack depths enable infrastructure managers to optimize the rail maintenance.
Materials
As the use of continuous fiber polymer matrix composites expands into new fields, there is a grow... more As the use of continuous fiber polymer matrix composites expands into new fields, there is a growing need for more sustainable manufacturing processes. An integrated computational material design framework has been developed, which enables the design of tailored manufacturing systems for polymer matrix composite materials as a sustainable alternative to achieving high-quality components in high-rate production. Trapped rubber processing achieves high pressures during polymer matrix composite processing, utilizing the thermally induced volume change of a nearly incompressible material inside a closed cavity mold. In this interdisciplinary study, the structural analysis, material science and manufacturing engineering perspectives are all combined to determine the mold mechanics, and the manufacturing process in a cohesive and iterative design loop. This study performs the coupled thermo-mechanical analysis required to simulate the transients involved in composite manufacturing and the...
Materials
The electrification of automotive powertrains in recent years has been driving the development of... more The electrification of automotive powertrains in recent years has been driving the development of internal combustion engines towards reduced volumes with higher power outputs. These changes place extreme demands on engine materials. Engineers employ the computer-aided engineering approach to design reliable and cost-effective engines. However, this approach relies on accurate knowledge of the material deformation and fatigue characteristics during service-like loading. The present study seeks to investigate the effect of dwell times on the deformation and fatigue behaviour of the A356-T7 + 0.5 wt.% Cu alloy used to cast cylinder heads. In particular, we study the effect of dwell time duration at various temperatures. A combined fatigue-dwell testing procedure, with the dwell at the maximum compressive strain, replicates the service conditions. It is found that the material exhibits a stress relaxation behaviour with a decreasing relaxation rate. At lower temperatures, the load leve...
European Journal of Mechanics - A/Solids
Materials
Aggressive downsizing of the internal combustion engines used as part of electrified powertrains ... more Aggressive downsizing of the internal combustion engines used as part of electrified powertrains in recent years have resulted in increasing thermal loads on the cylinder heads and consequently, the susceptibility to premature thermo-mechanical fatigue failures. To enable a reliable computer aided engineering (CAE) prediction of the component lives, we need more reliable material deformation and fatigue performance data. Material for testing was extracted from the highly loaded valve bridge area of specially cast cylinder heads to study the monotonic and cyclic deformation behaviour of the A356–T7 + 0.5% Cu alloy at various temperatures. Monotonic tensile tests performed at different temperatures indicate decreasing strength from 211 MPa at room temperature to 73 MPa at 300 °C and a corresponding increase in ductility. Completely reversed, strain controlled, uniaxial fatigue tests were carried out at 150, 200 and 250 °C. A dilatometric study carried out to study the thermal expansio...
IOP Conference Series: Materials Science and Engineering
Materials
The continuous drive towards higher specific power and lower displacement engines in recent years... more The continuous drive towards higher specific power and lower displacement engines in recent years place increasingly higher loads on the internal combustion engine materials. This necessitates a more robust collection of reliable material data for computational fatigue life prediction to develop reliable engines and reduce developmental costs. Monotonic tensile testing and cyclic stress and strain-controlled testing of A356-T7 + 0.5 wt.% Cu cast aluminium alloys have been performed. The uniaxial tests were performed on polished test bars extracted from highly loaded areas of cast cylinder heads. The monotonic deformation tests indicate that the material has an elastic-plastic monotonic response with plastic hardening. The strain controlled uniaxial low cycle fatigue tests were run at multiple load levels to capture the cyclic deformation behaviour and the corresponding fatigue lives. The equivalent stress-controlled fatigue tests were performed to study the influence of the loading ...
International Journal of Solids and Structures
Fatigue & Fracture of Engineering Materials & Structures
Proceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering
Materials Science and Engineering: A
International Journal of Fatigue
International Journal of Fatigue
Journal of Applied Physics, 2016
IOP Conference Series: Materials Science and Engineering
MATEC Web of Conferences, 2019
A significant challenge for railway infrastructure managers is to know when and how to maintain r... more A significant challenge for railway infrastructure managers is to know when and how to maintain rails. Often, the critical missing information is the current health status, in particular information about rail cracks. Therefore, a new method for rail crack detection is proposed. By utilizing a train-mounted camera system, a single measurement train can monitor a large rail network. The system uses Digital Image Correlation (DIC) to measure the strain fields due to rail bending caused by the measurement train. Promising results are obtained under laboratory conditions. The identified cracks are correlated to the actual crack network, characterized by serial-sectioning microscopy. Furthermore, finite element simulations show the method's high sensitivity to crack depths. Knowing the crack depths enable infrastructure managers to optimize the rail maintenance.
Materials
As the use of continuous fiber polymer matrix composites expands into new fields, there is a grow... more As the use of continuous fiber polymer matrix composites expands into new fields, there is a growing need for more sustainable manufacturing processes. An integrated computational material design framework has been developed, which enables the design of tailored manufacturing systems for polymer matrix composite materials as a sustainable alternative to achieving high-quality components in high-rate production. Trapped rubber processing achieves high pressures during polymer matrix composite processing, utilizing the thermally induced volume change of a nearly incompressible material inside a closed cavity mold. In this interdisciplinary study, the structural analysis, material science and manufacturing engineering perspectives are all combined to determine the mold mechanics, and the manufacturing process in a cohesive and iterative design loop. This study performs the coupled thermo-mechanical analysis required to simulate the transients involved in composite manufacturing and the...
Materials
The electrification of automotive powertrains in recent years has been driving the development of... more The electrification of automotive powertrains in recent years has been driving the development of internal combustion engines towards reduced volumes with higher power outputs. These changes place extreme demands on engine materials. Engineers employ the computer-aided engineering approach to design reliable and cost-effective engines. However, this approach relies on accurate knowledge of the material deformation and fatigue characteristics during service-like loading. The present study seeks to investigate the effect of dwell times on the deformation and fatigue behaviour of the A356-T7 + 0.5 wt.% Cu alloy used to cast cylinder heads. In particular, we study the effect of dwell time duration at various temperatures. A combined fatigue-dwell testing procedure, with the dwell at the maximum compressive strain, replicates the service conditions. It is found that the material exhibits a stress relaxation behaviour with a decreasing relaxation rate. At lower temperatures, the load leve...
European Journal of Mechanics - A/Solids
Materials
Aggressive downsizing of the internal combustion engines used as part of electrified powertrains ... more Aggressive downsizing of the internal combustion engines used as part of electrified powertrains in recent years have resulted in increasing thermal loads on the cylinder heads and consequently, the susceptibility to premature thermo-mechanical fatigue failures. To enable a reliable computer aided engineering (CAE) prediction of the component lives, we need more reliable material deformation and fatigue performance data. Material for testing was extracted from the highly loaded valve bridge area of specially cast cylinder heads to study the monotonic and cyclic deformation behaviour of the A356–T7 + 0.5% Cu alloy at various temperatures. Monotonic tensile tests performed at different temperatures indicate decreasing strength from 211 MPa at room temperature to 73 MPa at 300 °C and a corresponding increase in ductility. Completely reversed, strain controlled, uniaxial fatigue tests were carried out at 150, 200 and 250 °C. A dilatometric study carried out to study the thermal expansio...
IOP Conference Series: Materials Science and Engineering
Materials
The continuous drive towards higher specific power and lower displacement engines in recent years... more The continuous drive towards higher specific power and lower displacement engines in recent years place increasingly higher loads on the internal combustion engine materials. This necessitates a more robust collection of reliable material data for computational fatigue life prediction to develop reliable engines and reduce developmental costs. Monotonic tensile testing and cyclic stress and strain-controlled testing of A356-T7 + 0.5 wt.% Cu cast aluminium alloys have been performed. The uniaxial tests were performed on polished test bars extracted from highly loaded areas of cast cylinder heads. The monotonic deformation tests indicate that the material has an elastic-plastic monotonic response with plastic hardening. The strain controlled uniaxial low cycle fatigue tests were run at multiple load levels to capture the cyclic deformation behaviour and the corresponding fatigue lives. The equivalent stress-controlled fatigue tests were performed to study the influence of the loading ...
International Journal of Solids and Structures
Fatigue & Fracture of Engineering Materials & Structures
Proceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering
Materials Science and Engineering: A
International Journal of Fatigue
International Journal of Fatigue
Journal of Applied Physics, 2016