Position-Controlled Data Acquisition Embedded System for Magnetic NDE of Bridge Stay Cables

This work presents a custom-tailored sensing and data acquisition embedded system, designed to be integrated in a new magnetic NDE inspection device under development at Empa, a device intended for routine testing of large diameter bridge stay cables. The data acquisition (DAQ) system fulfills the speed and resolution requirements of the application and is able to continuously capture and store up to 2 GB of data at a sampling rate of 27 kS/s, with 12-bit resolution. This paper describes the DAQ system in detail, including both hardware and software implementation, as well as the key design challenges and the techniques employed to meet the specifications. Experimental results showing the performance of the system are also presented

Mechanical performance of cold-curing epoxy adhesives after different mixing and curing procedures

This paper presents strength, stiffness, and porosity characteristics of commercially available cold-curing epoxy adhesives for structural engineering applications in the field of externally bonded and/or near-surface mounted composite strip reinforcements. Depending on specific requirements, accelerated curing of the adhesive under high temperatures might be necessary. Experimental investigations aimed at assessing the possible differences in strength and stiffness between samples cured at elevated temperatures for a defined time span and the ones cured at room temperature. It could be demonstrated that for the same specimen age, nominal tensile strength and stiffness are lower after an initial accelerated curing process at elevated temperatures. Furthermore, it could be shown that the specimens after an accelerated curing at elevated temperatures exhibited an increased porosity. The development of a numerical code for image analysis allowed a detailed inspection of several fracture surfaces and subsequently to assess the level of decrease in available cross-section due to an increased overall porosity. Cross-section area losses in the range of 10–15% compared to the reference specimens could be deduced. The subsequent derivation of the actual tensile strength exhibits smaller differences between the room and high temperature exposed specimens while curing. Regardless of the short-term material strength, the observed porosity might be subject of important durability issues on a long-term and needs further investigation.FEDER funds through the Operational Program for Competitiveness Factors - COMPETE and National Funds through FCT - Portuguese Foundation for Science and Technology under the projects FRPreDur FCOMP- 01-0124-FEDER-028865 (FCT no. PTDC/ECM-EST/2424/2012)The authors want to express their gratitude to Max Heusser and Milos Dimic (Empa, CH) for their assistance in the experimental investigation. Marcel Rees, Iurii Burda and Andrea Battisti (Empa, CH) are kindly acknowledged for their assistance with the vacuum mixer and the sample preparation for porosity assessment. Eventually, Esther Strub (Empa, CH) is acknowledged for the instructions about the miscroscope utilization. Distributors S&P Clever Reinforcement AG (CH) and Sika (CH) are also acknowledged for their material provision. This work is also supported by FEDER funds through the Operational Program for Competitiveness Factors - COMPETE and National Funds through FCT - Portuguese Foundation for Science and Technology under the projects FRPreDur FCOMP- 01-0124-FEDER-028865 (FCT no. PTDC/ECM-EST/2424/2012)

Test Method for Thermal Characterization of Li-Ion Cells and Verification of Cooling Concepts

Temperature gradients, thermal cycling and temperatures outside the optimal operation range can have a significant influence on the reliability and lifetime of Li-ion battery cells. Therefore, it is essential for the developer of large-scale battery systems to know the thermal characteristics, such as heat source location, heat capacity and thermal conductivity, of a single cell in order to design appropriate cooling measures. This paper describes an advanced test facility, which allows not only an estimation of the thermal properties of a battery cell, but also the verification of proposed cooling strategies in operation. To do this, an active measuring unit consisting of a temperature and heat flux density sensor and a Peltier element was developed. These temperature/heat flux sensing (THFS) units are uniformly arranged around a battery cell with a spatial resolution of 25 mm. Consequently, the temperature or heat flux density can be controlled individually, thus forming regions with constant temperature (cooling) or zero heat flux (insulation). This test setup covers the whole development loop from thermal characterization to the design and verification of the proposed cooling strategy

New Experimental Approach for the Determination of the Heat Generation in a Li-Ion Battery Cell

With regard to safety, efficiency and lifetime of battery systems, the thermal behavior of battery cells is of great interest. The use of models describing the thermoelectric behavior of battery cells improves the understanding of heat generation mechanisms and enables the development of optimized thermal management systems. In this work, a novel experimental approach is presented to determine both the irreversible heat due to ohmic losses and the reversible heat due to entropy changes directly via heat flow measurements. No additional information about thermal properties of the battery cell, such as heat capacity or thermal conductivity, are required. Thus, the exothermic and endothermic nature of reversible heat generated in a complete charge/discharge cycle can be investigated. Moreover, the results of the proposed method can potentially be used to provide an additional constraint during the identification process of the equivalent circuit model parameters. The described method is applied to a 23 Ah lithium titanate cell and the corresponding results are presented

Test Method for Thermal Characterization of Li-Ion Cells and Verification of Cooling Concepts

Temperature gradients, thermal cycling and temperatures outside the optimal operation range can have a significant influence on the reliability and lifetime of Li-ion battery cells. Therefore, it is essential for the developer of large-scale battery systems to know the thermal characteristics, such as heat source location, heat capacity and thermal conductivity, of a single cell in order to design appropriate cooling measures. This paper describes an advanced test facility, which allows not only an estimation of the thermal properties of a battery cell, but also the verification of proposed cooling strategies in operation. To do this, an active measuring unit consisting of a temperature and heat flux density sensor and a Peltier element was developed. These temperature/heat flux sensing (THFS) units are uniformly arranged around a battery cell with a spatial resolution of 25 mm. Consequently, the temperature or heat flux density can be controlled individually, thus forming regions with constant temperature (cooling) or zero heat flux (insulation). This test setup covers the whole development loop from thermal characterization to the design and verification of the proposed cooling strategy