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High Dynamic Measurement of Strain and Acceleration Using a Multichannel Measuring System with Single Cable Serial Connection
Available online at www.sciencedirect.com
ScienceDirect Materials Today: Proceedings 3 (2016) 931 – 935
DAS 2015
High dynamic measurement of strain and acceleration using a multichannel measuring system with single cable serial connection M. Bartholmai*, M. Kammermeier, T. Wilk, and K.-D. Werner Federal Institute for Materials Research and Testing,12205 Berlin, Germany
Abstract Strain and acceleration measurement during high dynamic drop tests, e.g., of containments for dangerous goods is performed using high speed multichannel measuring systems. So far established and operated systems need a cable connection of every strain gauge and acceleration sensor with the measuring device, often counting up to a number of more than 100 cables, corresponding to the number of applied sensors. The result is a massive cable harness consisting of all single cables, which is difficult to handle and causes a number of practical problems. An innovative approach is proposed by using a single cable measuring system, consisting of measuring modules with data bus connection and local data acquisition. Promising results were presented in a previous study. This paper follows up with additional results from full-scale testing of a further enhanced single cable system for the application in drop tests. © 2015 Elsevier Ltd. All rights reserved. © 2016 Elsevier Ltd. All rights reserved. Selectionand andPeer-review Peer-review under responsibility of the Committee Members of DANUBIA 32nd DANUBIA SYMPOSIUM on Selection under responsibility of the Committee Members of 32nd ADRIAADRIA SYMPOSIUM on Experimental Mechanics (DAS 2015). AdvancedininExperimental Advanced Mechanics (DAS 2015) Keywords: Multichannel measuring; single cable serial connection; dangerous goods container; drop test; high impact testing
1. Introduction High dynamic measurement of strain and acceleration is an essential task during drop tests. The Federal Institute for Materials Research and Testing (BAM) holds a unique drop test facility on its test site for technical safety (Fig. 1). The drop test facility is extraordinary in its dimensions and test parameters [1]. Main objective and application is testing and approval of containers for transport and storage of dangerous goods, particularly radioactive materials.
* Corresponding author. Tel.: +49-30-8104-1912; fax: +49-30-8104-1919. E-mail address: [email protected]
2214-7853 © 2016 Elsevier Ltd. All rights reserved. Selection and Peer-review under responsibility of the Committee Members of 32nd DANUBIA ADRIA SYMPOSIUM on Advanced in Experimental Mechanics (DAS 2015) doi:10.1016/j.matpr.2016.03.023
932
M. Bartholmai et al. / Materials Today: Proceedings 3 (2016) 931 – 935
Casks up to 200 t can be tested from a maximum drop height up to 25 m. The impact area is built of an unyielding base featuring 2450 t of concrete mass, 103 t of steel reinforcement and 77 t of steel impact plates. These parameters turn the facility to one of a few, which are capable of testing state of the art containers in their original size. The handling of dangerous goods is controlled by laws and regulations, on international [2], [3] and national level. In Germany, BAM is the central authority for the evaluation and approval of certain containment systems, e.g. containers for the transport and storage of radioactive materials. In the scope of the evaluation procedures experimental testing of construction types is performed, e.g. drop tests, leak tightness and fire investigations [4]. Beside the evaluation of the tested container, the results are also used as input data for finite element simulation in the layout procedure for new or improved containers. To achieve most accurate and reliable results it is important to use state-of-the-art measuring methods and equipment.
Fig. 1. Drop test facility of BAM.
1.1. Limitations of the established equipment Generally, high speed multichannel measuring systems are used to perform measurements of strain and acceleration with high dynamic during container drop tests [1]. So far established and operated systems need a cable connection of every strain gauge and acceleration sensor with the measuring device, often counting up to a number of more than 100 cables, corresponding to the number of applied sensors. The result is a massive cable harness consisting of all single cables, which is difficult to handle and causes a number of practical problems (Fig.2). Cabling needs great effort, particularly modifications on the test object like cut-outs and lead-throughs must be applied, which can influence and falsify its mechanical behavior during the impact.
Fig. 2. Examples of complex cabling for drop test preparation.
M. Bartholmai et al. / Materials Today: Proceedings 3 (2016) 931 – 935
In the worst case, potentially interesting measuring positions cannot be instrumented. The drop down of the cable harness can influence the orientation of the test object, which can lead to deviation from the defined test specifications. During the drop test, especially at the impact the cable harness can be damaged and partially or rather completely destroyed, which results in a partial or complete failure of the measurement with immense consequences regarding costs and efforts. Generally, extensive cabling is accident-sensitive. From experiences at BAM the vast majority of measuring failures is due to cabling problems. 1.2. Innovative approach An innovative approach in the field of drop tests is the application of a decentralized measuring system [5]. In contrast to a central measuring unit, the decentralized multichannel device consists of a number of small selfsustaining measuring modules connected via a single cable in serial connection. Data acquisition is achieved autonomously by each single module, which consists of data memory and internal data processing, including amplifier, filter, analog digital converter, and power supply. For synchronous triggering, read-out subsequent to the measurement, and battery charge, all modules are connected through a data bus in serial (daisy-chain) connection using a single cable. After triggering, all modules operate autonomously and a cable damaging has no influence on the data. This technique offers high potential to optimize the accuracy and reliability of drop tests measuring with heavy load and/or high impact. Main objective of this approach is to decrease the failure rate caused by complex cabling and drop of the cable harness. This study presents the results of investigations, in which the M=Bus Pro measuring system (Messring Systembau GmbH, Germany) was adapted and validated for application in drop tests [5]. Messring Systembau GmbH develops and produces crash test facilities for the automobile industry. In 2005 its single cable data acquisition system M=BUS was introduced. The system was designed for in-dummy data acquisition and crash test walls. It is appropriate for measuring tasks using a great number of sensors at high dynamic load. The principle advantage of the technology is the minimization of cabling. Basis for the adapted system (Fig. 3) is the M=BUS Pro, which is the successor of the M=BUS system. It features a compact and robust form factor and should withstand dynamic impacts up to 10.000 g. Each module can connect up to 8 sensors, which can be strain gauges (350 ohm), accelerometers and thermocouples. A great advance in comparison to the former study is the increased sampling rate of 100 kHz, which is a common value in drop test data acquisition. The resolution is 16 bit. Low-pass Filtering can be applied in the range 10 to 50 kHz. Additionally to bridge sensor amplifiers also an interface for integrated electronics piezoelectric (IEPE) sensors is implemented. IEPE accelerometers are often applied in drop tests, because of their robustness and easy handling.
Fig. 3. Application of the single cable system on a container for drop test preparation.
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M. Bartholmai et al. / Materials Today: Proceedings 3 (2016) 931 – 935
2. Experiment - Drop test for validation of the single cable system For validation experiments the single cable system and a conventional multichannel measuring system as reference were applied. Test object was an experimental steel plate container with dimensions of 3.2 x 2.0 x 1.7 m 3 and a weight of 1.84 t. The drop was performed from a height of 5 m to one of the 3.2 m edges with an angle of 48°. Two measuring positions regarding strain and one position regarding acceleration were taken into account for comparable investigation of the systems. So for each system two strain gauges and one accelerometer were applied at the specified positions as close as possible to another (2 to 3 cm), to deliver preferably similar measuring results during the drop test. It must be taken into account that the single cable system was operated at 100 kHz in contrast to 200 kHz of the conventional system and equipped with a different type of accelerometer (H64C-2000-360 accelerometer, Humanetics Innovative Solutions, USA) than the conventional system (350C02, IEPE shock accelerometer, PCB Piezotronics, Inc., USA). All measured data is processed the same way. Signal offsets are corrected regarding the synchronized time point just before ground impact. All displayed signals are filtered using a 2 kHz low-pass Bessel filter, corresponding to the typical data processing for documentation. 2.1. Results of acceleration measurements Figure 4 (left) shows the results of the acceleration measurements. The main deceleration appears between 0 and 5 ms. During this time period the signals show maximal peak and fluctuation values. In comparison to each other, the measuring systems deliver high short term deviations and low similarity of signal sequence. For example the reference system shows no minimum comparable to the strong negative peak of the single cable system at 2 ms. In contrast, during the following time period starting from 5 ms the measured acceleration signals show considerably good similarities in curve progression with synchronous peaks. The reference system was instrumented on an angle piece, for orientating it vertically in drop direction, whereas the sensor used with the single cable system was instrumented flat on the container and orientation correction was processed subsequently. This could explain the different impulse transformation and acceleration behavior, particularly during the main impact between 0 and 5 ms. The velocity behavior of the container can be calculated by integration of the acceleration signals (Fig. 4, right). Despite some differences in the acceleration signal, the velocity curves are well comparable. Considering the drop height of 5 m a drop velocity of -9.9 m/s is given before impact on ground. Deceleration up to positive values indicate the main impact and rebound of the container, followed by a velocity close to zero, when the container stays connected to ground, but still in movement due to continuing vibrations.
Fig. 4. Results of acceleration measurements during the drop test (left) and results of calculated velocities (right).
M. Bartholmai et al. / Materials Today: Proceedings 3 (2016) 931 – 935
935
2.2. Results of strain measurements Figure 5 shows the results of strain measurements at two different positions on the container. Typical deformation behavior for drop tests can be observed with strain rates up to 1000 μm/m during the main impact. The measurements at both positions deliver good results. Comparison of the two measurement systems shows very good similarity in curve progression, synchronicity and peak amounts. Reason for the small deviations between both systems is presumably rather the slight distance between the particular strain gauges than the different specifications and configurations of the measuring systems. Hence, concerning the strain measurements, no essential discrepancy could be observed between both systems in their qualitative and quantitative results.
Fig. 5. Results of strain measurements during the drop test.
3. Conclusions A single cable measuring system based on serial connection and decentralized data acquisition has principle advantages for the application in drop tests compared to conventional multichannel systems. The effort and costs of instrumentation can be essentially reduced, disturbing transverse forces can be minimized, and data storage in selfsustaining measuring modules makes the system nearly fail-proof. The single cable connection is substantially only used to trigger the measurement. First validation results demonstrate the applicability in high dynamic scenarios. Even in a Hopkinson bar experiment for investigating shock impact behavior, good results were achieved [5]. It could be proven that the measuring dynamics of the system allows its unlimited application for standard drop tests. Acknowledgements The authors thank the involved colleagues of BAM which contributed to the study, particularly to the drop test investigations, and our industry partner Messring Systembau GmbH. References [1] K. Mueller, T. Quercetti, B. Droste. Transport, Storage and Security of Radioactive Material 17 (2006) 4, 191-196. [2] UN Recommendations on the Transport of Dangerous Goods, Model Regulations. United Nations, 2005. [3] ISO 2919:1999: Radiation protection - Sealed radioactive sources - General requirements and classification. International Organisation for Standardization, 1999. [4] IAEA Safety Sandards Series No. TS-R-1: Regulations for the Safe Transport of Radioactive Material. International Atomic Energy Agency, 2005. [5] M. Bartholmai, K.-D. Werner, M. Kammermeier, E. Köppe, tm – Technisches Messen 76, 2009, 10, 447-454. [6] M. Bartholmai, M. Kammermeier, K.-D. Werner, T. Wilk, tm – Technisches Messen 80, 2013, 7-8, 249-255.
ScienceDirect Materials Today: Proceedings 3 (2016) 931 – 935
DAS 2015
High dynamic measurement of strain and acceleration using a multichannel measuring system with single cable serial connection M. Bartholmai*, M. Kammermeier, T. Wilk, and K.-D. Werner Federal Institute for Materials Research and Testing,12205 Berlin, Germany
Abstract Strain and acceleration measurement during high dynamic drop tests, e.g., of containments for dangerous goods is performed using high speed multichannel measuring systems. So far established and operated systems need a cable connection of every strain gauge and acceleration sensor with the measuring device, often counting up to a number of more than 100 cables, corresponding to the number of applied sensors. The result is a massive cable harness consisting of all single cables, which is difficult to handle and causes a number of practical problems. An innovative approach is proposed by using a single cable measuring system, consisting of measuring modules with data bus connection and local data acquisition. Promising results were presented in a previous study. This paper follows up with additional results from full-scale testing of a further enhanced single cable system for the application in drop tests. © 2015 Elsevier Ltd. All rights reserved. © 2016 Elsevier Ltd. All rights reserved. Selectionand andPeer-review Peer-review under responsibility of the Committee Members of DANUBIA 32nd DANUBIA SYMPOSIUM on Selection under responsibility of the Committee Members of 32nd ADRIAADRIA SYMPOSIUM on Experimental Mechanics (DAS 2015). AdvancedininExperimental Advanced Mechanics (DAS 2015) Keywords: Multichannel measuring; single cable serial connection; dangerous goods container; drop test; high impact testing
1. Introduction High dynamic measurement of strain and acceleration is an essential task during drop tests. The Federal Institute for Materials Research and Testing (BAM) holds a unique drop test facility on its test site for technical safety (Fig. 1). The drop test facility is extraordinary in its dimensions and test parameters [1]. Main objective and application is testing and approval of containers for transport and storage of dangerous goods, particularly radioactive materials.
* Corresponding author. Tel.: +49-30-8104-1912; fax: +49-30-8104-1919. E-mail address: [email protected]
2214-7853 © 2016 Elsevier Ltd. All rights reserved. Selection and Peer-review under responsibility of the Committee Members of 32nd DANUBIA ADRIA SYMPOSIUM on Advanced in Experimental Mechanics (DAS 2015) doi:10.1016/j.matpr.2016.03.023
932
M. Bartholmai et al. / Materials Today: Proceedings 3 (2016) 931 – 935
Casks up to 200 t can be tested from a maximum drop height up to 25 m. The impact area is built of an unyielding base featuring 2450 t of concrete mass, 103 t of steel reinforcement and 77 t of steel impact plates. These parameters turn the facility to one of a few, which are capable of testing state of the art containers in their original size. The handling of dangerous goods is controlled by laws and regulations, on international [2], [3] and national level. In Germany, BAM is the central authority for the evaluation and approval of certain containment systems, e.g. containers for the transport and storage of radioactive materials. In the scope of the evaluation procedures experimental testing of construction types is performed, e.g. drop tests, leak tightness and fire investigations [4]. Beside the evaluation of the tested container, the results are also used as input data for finite element simulation in the layout procedure for new or improved containers. To achieve most accurate and reliable results it is important to use state-of-the-art measuring methods and equipment.
Fig. 1. Drop test facility of BAM.
1.1. Limitations of the established equipment Generally, high speed multichannel measuring systems are used to perform measurements of strain and acceleration with high dynamic during container drop tests [1]. So far established and operated systems need a cable connection of every strain gauge and acceleration sensor with the measuring device, often counting up to a number of more than 100 cables, corresponding to the number of applied sensors. The result is a massive cable harness consisting of all single cables, which is difficult to handle and causes a number of practical problems (Fig.2). Cabling needs great effort, particularly modifications on the test object like cut-outs and lead-throughs must be applied, which can influence and falsify its mechanical behavior during the impact.
Fig. 2. Examples of complex cabling for drop test preparation.
M. Bartholmai et al. / Materials Today: Proceedings 3 (2016) 931 – 935
In the worst case, potentially interesting measuring positions cannot be instrumented. The drop down of the cable harness can influence the orientation of the test object, which can lead to deviation from the defined test specifications. During the drop test, especially at the impact the cable harness can be damaged and partially or rather completely destroyed, which results in a partial or complete failure of the measurement with immense consequences regarding costs and efforts. Generally, extensive cabling is accident-sensitive. From experiences at BAM the vast majority of measuring failures is due to cabling problems. 1.2. Innovative approach An innovative approach in the field of drop tests is the application of a decentralized measuring system [5]. In contrast to a central measuring unit, the decentralized multichannel device consists of a number of small selfsustaining measuring modules connected via a single cable in serial connection. Data acquisition is achieved autonomously by each single module, which consists of data memory and internal data processing, including amplifier, filter, analog digital converter, and power supply. For synchronous triggering, read-out subsequent to the measurement, and battery charge, all modules are connected through a data bus in serial (daisy-chain) connection using a single cable. After triggering, all modules operate autonomously and a cable damaging has no influence on the data. This technique offers high potential to optimize the accuracy and reliability of drop tests measuring with heavy load and/or high impact. Main objective of this approach is to decrease the failure rate caused by complex cabling and drop of the cable harness. This study presents the results of investigations, in which the M=Bus Pro measuring system (Messring Systembau GmbH, Germany) was adapted and validated for application in drop tests [5]. Messring Systembau GmbH develops and produces crash test facilities for the automobile industry. In 2005 its single cable data acquisition system M=BUS was introduced. The system was designed for in-dummy data acquisition and crash test walls. It is appropriate for measuring tasks using a great number of sensors at high dynamic load. The principle advantage of the technology is the minimization of cabling. Basis for the adapted system (Fig. 3) is the M=BUS Pro, which is the successor of the M=BUS system. It features a compact and robust form factor and should withstand dynamic impacts up to 10.000 g. Each module can connect up to 8 sensors, which can be strain gauges (350 ohm), accelerometers and thermocouples. A great advance in comparison to the former study is the increased sampling rate of 100 kHz, which is a common value in drop test data acquisition. The resolution is 16 bit. Low-pass Filtering can be applied in the range 10 to 50 kHz. Additionally to bridge sensor amplifiers also an interface for integrated electronics piezoelectric (IEPE) sensors is implemented. IEPE accelerometers are often applied in drop tests, because of their robustness and easy handling.
Fig. 3. Application of the single cable system on a container for drop test preparation.
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M. Bartholmai et al. / Materials Today: Proceedings 3 (2016) 931 – 935
2. Experiment - Drop test for validation of the single cable system For validation experiments the single cable system and a conventional multichannel measuring system as reference were applied. Test object was an experimental steel plate container with dimensions of 3.2 x 2.0 x 1.7 m 3 and a weight of 1.84 t. The drop was performed from a height of 5 m to one of the 3.2 m edges with an angle of 48°. Two measuring positions regarding strain and one position regarding acceleration were taken into account for comparable investigation of the systems. So for each system two strain gauges and one accelerometer were applied at the specified positions as close as possible to another (2 to 3 cm), to deliver preferably similar measuring results during the drop test. It must be taken into account that the single cable system was operated at 100 kHz in contrast to 200 kHz of the conventional system and equipped with a different type of accelerometer (H64C-2000-360 accelerometer, Humanetics Innovative Solutions, USA) than the conventional system (350C02, IEPE shock accelerometer, PCB Piezotronics, Inc., USA). All measured data is processed the same way. Signal offsets are corrected regarding the synchronized time point just before ground impact. All displayed signals are filtered using a 2 kHz low-pass Bessel filter, corresponding to the typical data processing for documentation. 2.1. Results of acceleration measurements Figure 4 (left) shows the results of the acceleration measurements. The main deceleration appears between 0 and 5 ms. During this time period the signals show maximal peak and fluctuation values. In comparison to each other, the measuring systems deliver high short term deviations and low similarity of signal sequence. For example the reference system shows no minimum comparable to the strong negative peak of the single cable system at 2 ms. In contrast, during the following time period starting from 5 ms the measured acceleration signals show considerably good similarities in curve progression with synchronous peaks. The reference system was instrumented on an angle piece, for orientating it vertically in drop direction, whereas the sensor used with the single cable system was instrumented flat on the container and orientation correction was processed subsequently. This could explain the different impulse transformation and acceleration behavior, particularly during the main impact between 0 and 5 ms. The velocity behavior of the container can be calculated by integration of the acceleration signals (Fig. 4, right). Despite some differences in the acceleration signal, the velocity curves are well comparable. Considering the drop height of 5 m a drop velocity of -9.9 m/s is given before impact on ground. Deceleration up to positive values indicate the main impact and rebound of the container, followed by a velocity close to zero, when the container stays connected to ground, but still in movement due to continuing vibrations.
Fig. 4. Results of acceleration measurements during the drop test (left) and results of calculated velocities (right).
M. Bartholmai et al. / Materials Today: Proceedings 3 (2016) 931 – 935
935
2.2. Results of strain measurements Figure 5 shows the results of strain measurements at two different positions on the container. Typical deformation behavior for drop tests can be observed with strain rates up to 1000 μm/m during the main impact. The measurements at both positions deliver good results. Comparison of the two measurement systems shows very good similarity in curve progression, synchronicity and peak amounts. Reason for the small deviations between both systems is presumably rather the slight distance between the particular strain gauges than the different specifications and configurations of the measuring systems. Hence, concerning the strain measurements, no essential discrepancy could be observed between both systems in their qualitative and quantitative results.
Fig. 5. Results of strain measurements during the drop test.
3. Conclusions A single cable measuring system based on serial connection and decentralized data acquisition has principle advantages for the application in drop tests compared to conventional multichannel systems. The effort and costs of instrumentation can be essentially reduced, disturbing transverse forces can be minimized, and data storage in selfsustaining measuring modules makes the system nearly fail-proof. The single cable connection is substantially only used to trigger the measurement. First validation results demonstrate the applicability in high dynamic scenarios. Even in a Hopkinson bar experiment for investigating shock impact behavior, good results were achieved [5]. It could be proven that the measuring dynamics of the system allows its unlimited application for standard drop tests. Acknowledgements The authors thank the involved colleagues of BAM which contributed to the study, particularly to the drop test investigations, and our industry partner Messring Systembau GmbH. References [1] K. Mueller, T. Quercetti, B. Droste. Transport, Storage and Security of Radioactive Material 17 (2006) 4, 191-196. [2] UN Recommendations on the Transport of Dangerous Goods, Model Regulations. United Nations, 2005. [3] ISO 2919:1999: Radiation protection - Sealed radioactive sources - General requirements and classification. International Organisation for Standardization, 1999. [4] IAEA Safety Sandards Series No. TS-R-1: Regulations for the Safe Transport of Radioactive Material. International Atomic Energy Agency, 2005. [5] M. Bartholmai, K.-D. Werner, M. Kammermeier, E. Köppe, tm – Technisches Messen 76, 2009, 10, 447-454. [6] M. Bartholmai, M. Kammermeier, K.-D. Werner, T. Wilk, tm – Technisches Messen 80, 2013, 7-8, 249-255.