Integration of sensors into various kinds of products and machines provides access to in-depth us... more Integration of sensors into various kinds of products and machines provides access to in-depth usage information as basis for product optimization. Presently, this large potential for more user-friendly and efficient products is not being realized because (a) sensor integration and thus usage information is not available on a large scale and (b) product optimization requires considerable efforts in terms of manpower and adaptation of production equipment. However, with the advent of cloud-based services and highly flexible additive manufacturing techniques, these obstacles are currently crumbling away at rapid pace. The present study explores the state of the art in gathering and evaluating product usage and life cycle data, additive manufacturing and sensor integration, automated design and cloud-based services in manufacturing. By joining and extrapolating development trends in these areas, it delimits the foundations of a manufacturing concept that will allow continuous and econo...
ABSTRACT The mechanical behaviour of stainless steel AISI 316L based syntactic foams containing e... more ABSTRACT The mechanical behaviour of stainless steel AISI 316L based syntactic foams containing either 40/60 vol.% of hollow glass microspheres (S60HS) or 40 vol.% of Fillite cenospheres were investigated. In these materials, the hollow particle shells as third phase besides matrix and voids can provide a strengthening effect with the potential of raising mechanical performance above that of conventional, two phase steel foams. Samples were produced by means of metal powder injection moulding (MIM) and subjected to characterization under compressive load, with special attention dedicated to strain-rate sensitivity. Four strain-rate levels were investigated, covering 6 orders of magnitude from 10-3 to 103 s-1. For the highest, a Hopkinson Bar apparatus was used. The influence of density on strength was determined for samples containing glass microspheres and described by a power law relationship. The foams mechanical strength was found to increase with strain-rate in accordance with the behaviour observed for the reference material without hollow particles. The data were compared with those obtained in a previous work, in which Fe99.7 matrix syntactic foams containing similar levels of glass microspheres were investigated. The higher strength of the AISI 316L materials is associated with differences in matrix properties. Differences in strain-rate dependence of mechanical properties between both materials can be explained qualitatively based on the fcc (AISI 316L) and bcc (Fe99.7) lattice structure. The introduction of Fillite cenospheres induced a further increase of specific strength. Under quasi-static conditions, samples of this type were found to reach the same yield strength as the reference material despite the reduction in density. The significantly lower strength of glass microsphere based AISI 316L foams can be related to the observed microstructures: due to the high processing temperature (1200°C), glass microspheres are destroyed during sintering, their remainders forming glass inclusions, whereas thermally more stable cenospheres remain intact and can thus stabilize the pores. Finally, an empirical strain-rate sensitive model was adopted to reproduce the experimental data: the fitting procedure used to obtain the model parameters was explained and the influence of the strain-rate discussed. The model allows property prediction for additive content and strain-rate levels further to those evaluated experimentally.
ABSTRACT The mechanical behaviour of stainless steel AISI 316L based syntactic foams containing e... more ABSTRACT The mechanical behaviour of stainless steel AISI 316L based syntactic foams containing either 40/60 vol.% of hollow glass microspheres (S60HS) or 40 vol.% of Fillite cenospheres were investigated. In these materials, the hollow particle shells as third phase besides matrix and voids can provide a strengthening effect with the potential of raising mechanical performance above that of conventional, two phase steel foams. Samples were produced by means of metal powder injection moulding (MIM) and subjected to characterization under compressive load, with special attention dedicated to strain-rate sensitivity. Four strain-rate levels were investigated, covering 6 orders of magnitude from 10-3 to 103 s-1. For the highest, a Hopkinson Bar apparatus was used. The influence of density on strength was determined for samples containing glass microspheres and described by a power law relationship. The foams mechanical strength was found to increase with strain-rate in accordance with the behaviour observed for the reference material without hollow particles. The data were compared with those obtained in a previous work, in which Fe99.7 matrix syntactic foams containing similar levels of glass microspheres were investigated. The higher strength of the AISI 316L materials is associated with differences in matrix properties. Differences in strain-rate dependence of mechanical properties between both materials can be explained qualitatively based on the fcc (AISI 316L) and bcc (Fe99.7) lattice structure. The introduction of Fillite cenospheres induced a further increase of specific strength. Under quasi-static conditions, samples of this type were found to reach the same yield strength as the reference material despite the reduction in density. The significantly lower strength of glass microsphere based AISI 316L foams can be related to the observed microstructures: due to the high processing temperature (1200°C), glass microspheres are destroyed during sintering, their remainders forming glass inclusions, whereas thermally more stable cenospheres remain intact and can thus stabilize the pores. Finally, an empirical strain-rate sensitive model was adopted to reproduce the experimental data: the fitting procedure used to obtain the model parameters was explained and the influence of the strain-rate discussed. The model allows property prediction for additive content and strain-rate levels further to those evaluated experimentally.
ABSTRACT AlSi7 aluminum foams produced via the powder compact melting process suffer from deficie... more ABSTRACT AlSi7 aluminum foams produced via the powder compact melting process suffer from deficiencies in the pore structure that are linked to the mismatch between the decomposition temperature range of the common blowing agent TiH2 and the solidus and liquidus temperature of the matrix alloy. To alleviate these deficiencies, two main paths have been discussed in the past: One is the adaptation of the matrix alloy towards lower melting temperatures, the other the modification by heat treatment of the foaming agent itself, which leads to higher decomposition temperatures. The present paper compares the mechanical response of foams produced according to the second approach to that of the reference material, AlSi7 foamed using untreated TiH2 as blowing agent. Mechanical performance is evaluated based on uniaxial, quasi-static compression tests over a wide range of densities. In parallel, the pore and microstructure of the respective materials is characterized using metallographic sections and computed tomography for image acquisition, as well as image analysis to derive quantitative parameters. Foams based on thermally treated blowing agents show increased compressive strength at technically relevant density levels. The advantage is lost at very high porosities in excess of 85–90% only.
ABSTRACT AlSi7 aluminum foams produced via the powder compact melting process suffer from deficie... more ABSTRACT AlSi7 aluminum foams produced via the powder compact melting process suffer from deficiencies in the pore structure that are linked to the mismatch between the decomposition temperature range of the common blowing agent TiH2 and the solidus and liquidus temperature of the matrix alloy. To alleviate these deficiencies, two main paths have been discussed in the past: One is the adaptation of the matrix alloy towards lower melting temperatures, the other the modification by heat treatment of the foaming agent itself, which leads to higher decomposition temperatures. The present paper compares the mechanical response of foams produced according to the second approach to that of the reference material, AlSi7 foamed using untreated TiH2 as blowing agent. Mechanical performance is evaluated based on uniaxial, quasi-static compression tests over a wide range of densities. In parallel, the pore and microstructure of the respective materials is characterized using metallographic sections and computed tomography for image acquisition, as well as image analysis to derive quantitative parameters. Foams based on thermally treated blowing agents show increased compressive strength at technically relevant density levels. The advantage is lost at very high porosities in excess of 85–90% only.
Integration of sensors into various kinds of products and machines provides access to in-depth us... more Integration of sensors into various kinds of products and machines provides access to in-depth usage information as basis for product optimization. Presently, this large potential for more user-friendly and efficient products is not being realized because (a) sensor integration and thus usage information is not available on a large scale and (b) product optimization requires considerable efforts in terms of manpower and adaptation of production equipment. However, with the advent of cloud-based services and highly flexible additive manufacturing techniques, these obstacles are currently crumbling away at rapid pace. The present study explores the state of the art in gathering and evaluating product usage and life cycle data, additive manufacturing and sensor integration, automated design and cloud-based services in manufacturing. By joining and extrapolating development trends in these areas, it delimits the foundations of a manufacturing concept that will allow continuous and econo...
ABSTRACT The mechanical behaviour of stainless steel AISI 316L based syntactic foams containing e... more ABSTRACT The mechanical behaviour of stainless steel AISI 316L based syntactic foams containing either 40/60 vol.% of hollow glass microspheres (S60HS) or 40 vol.% of Fillite cenospheres were investigated. In these materials, the hollow particle shells as third phase besides matrix and voids can provide a strengthening effect with the potential of raising mechanical performance above that of conventional, two phase steel foams. Samples were produced by means of metal powder injection moulding (MIM) and subjected to characterization under compressive load, with special attention dedicated to strain-rate sensitivity. Four strain-rate levels were investigated, covering 6 orders of magnitude from 10-3 to 103 s-1. For the highest, a Hopkinson Bar apparatus was used. The influence of density on strength was determined for samples containing glass microspheres and described by a power law relationship. The foams mechanical strength was found to increase with strain-rate in accordance with the behaviour observed for the reference material without hollow particles. The data were compared with those obtained in a previous work, in which Fe99.7 matrix syntactic foams containing similar levels of glass microspheres were investigated. The higher strength of the AISI 316L materials is associated with differences in matrix properties. Differences in strain-rate dependence of mechanical properties between both materials can be explained qualitatively based on the fcc (AISI 316L) and bcc (Fe99.7) lattice structure. The introduction of Fillite cenospheres induced a further increase of specific strength. Under quasi-static conditions, samples of this type were found to reach the same yield strength as the reference material despite the reduction in density. The significantly lower strength of glass microsphere based AISI 316L foams can be related to the observed microstructures: due to the high processing temperature (1200°C), glass microspheres are destroyed during sintering, their remainders forming glass inclusions, whereas thermally more stable cenospheres remain intact and can thus stabilize the pores. Finally, an empirical strain-rate sensitive model was adopted to reproduce the experimental data: the fitting procedure used to obtain the model parameters was explained and the influence of the strain-rate discussed. The model allows property prediction for additive content and strain-rate levels further to those evaluated experimentally.
ABSTRACT The mechanical behaviour of stainless steel AISI 316L based syntactic foams containing e... more ABSTRACT The mechanical behaviour of stainless steel AISI 316L based syntactic foams containing either 40/60 vol.% of hollow glass microspheres (S60HS) or 40 vol.% of Fillite cenospheres were investigated. In these materials, the hollow particle shells as third phase besides matrix and voids can provide a strengthening effect with the potential of raising mechanical performance above that of conventional, two phase steel foams. Samples were produced by means of metal powder injection moulding (MIM) and subjected to characterization under compressive load, with special attention dedicated to strain-rate sensitivity. Four strain-rate levels were investigated, covering 6 orders of magnitude from 10-3 to 103 s-1. For the highest, a Hopkinson Bar apparatus was used. The influence of density on strength was determined for samples containing glass microspheres and described by a power law relationship. The foams mechanical strength was found to increase with strain-rate in accordance with the behaviour observed for the reference material without hollow particles. The data were compared with those obtained in a previous work, in which Fe99.7 matrix syntactic foams containing similar levels of glass microspheres were investigated. The higher strength of the AISI 316L materials is associated with differences in matrix properties. Differences in strain-rate dependence of mechanical properties between both materials can be explained qualitatively based on the fcc (AISI 316L) and bcc (Fe99.7) lattice structure. The introduction of Fillite cenospheres induced a further increase of specific strength. Under quasi-static conditions, samples of this type were found to reach the same yield strength as the reference material despite the reduction in density. The significantly lower strength of glass microsphere based AISI 316L foams can be related to the observed microstructures: due to the high processing temperature (1200°C), glass microspheres are destroyed during sintering, their remainders forming glass inclusions, whereas thermally more stable cenospheres remain intact and can thus stabilize the pores. Finally, an empirical strain-rate sensitive model was adopted to reproduce the experimental data: the fitting procedure used to obtain the model parameters was explained and the influence of the strain-rate discussed. The model allows property prediction for additive content and strain-rate levels further to those evaluated experimentally.
ABSTRACT AlSi7 aluminum foams produced via the powder compact melting process suffer from deficie... more ABSTRACT AlSi7 aluminum foams produced via the powder compact melting process suffer from deficiencies in the pore structure that are linked to the mismatch between the decomposition temperature range of the common blowing agent TiH2 and the solidus and liquidus temperature of the matrix alloy. To alleviate these deficiencies, two main paths have been discussed in the past: One is the adaptation of the matrix alloy towards lower melting temperatures, the other the modification by heat treatment of the foaming agent itself, which leads to higher decomposition temperatures. The present paper compares the mechanical response of foams produced according to the second approach to that of the reference material, AlSi7 foamed using untreated TiH2 as blowing agent. Mechanical performance is evaluated based on uniaxial, quasi-static compression tests over a wide range of densities. In parallel, the pore and microstructure of the respective materials is characterized using metallographic sections and computed tomography for image acquisition, as well as image analysis to derive quantitative parameters. Foams based on thermally treated blowing agents show increased compressive strength at technically relevant density levels. The advantage is lost at very high porosities in excess of 85–90% only.
ABSTRACT AlSi7 aluminum foams produced via the powder compact melting process suffer from deficie... more ABSTRACT AlSi7 aluminum foams produced via the powder compact melting process suffer from deficiencies in the pore structure that are linked to the mismatch between the decomposition temperature range of the common blowing agent TiH2 and the solidus and liquidus temperature of the matrix alloy. To alleviate these deficiencies, two main paths have been discussed in the past: One is the adaptation of the matrix alloy towards lower melting temperatures, the other the modification by heat treatment of the foaming agent itself, which leads to higher decomposition temperatures. The present paper compares the mechanical response of foams produced according to the second approach to that of the reference material, AlSi7 foamed using untreated TiH2 as blowing agent. Mechanical performance is evaluated based on uniaxial, quasi-static compression tests over a wide range of densities. In parallel, the pore and microstructure of the respective materials is characterized using metallographic sections and computed tomography for image acquisition, as well as image analysis to derive quantitative parameters. Foams based on thermally treated blowing agents show increased compressive strength at technically relevant density levels. The advantage is lost at very high porosities in excess of 85–90% only.
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Papers by Dirk Lehmhus