Fracture mechanics of carbon fibre reinforced plastics to Ti-alloy adhesive joints

Adhesive bonding has emerged as an appealing technique to join carbon fibre-reinforced plastics (CFRP) to other structural parts. The advantages that adhesive bonding offers include an even stress distribution, weight saving and superior fatigue resistance when compared to more traditional methods of joining. However, despite these advantages, the uncertainties regarding their durability have confined them largely to use in secondary structures. In the present work, a fracture mechanics methodology has been followed using both experimental and FE methods to predict the service-life of a CFRP-titanium alloy adhesive joint intended for use in a turbofan application. The methodology utilises the concept of the cohesive zone model to evaluate the performance of a simplified but representative structure, i.e. a Ti-to-CFRP tapered double-lap joint. The adhesive bondline was modelled by a layer of newly-developed cohesive elements, the kinematics and topology of which have been optimised to improve the mixed-mode behaviour and reduce the mesh-dependency. Their damage evolution has been enhanced to incorporate high-cycle fatigue degradation. Additionally, a simplified version of this formulation, specifically designed to predict only the fatigue threshold, has also been developed. To determine the various input parameters required for the models, a series of fracture mechanics specimens manufactured with a commercial film adhesive were tested quasi-statically in various modes and in mode I fatigue. Various data reduction schemes were evaluated and a version of corrected beam theory employing an effective crack length approach was found to be optimum for all tests. The fracture energies determined in the various modes were partitioned according to the theories proposed by Williams (Global) and by Davidson’s crack tip element singular field (CTE/SF) and non singular field (CTE-NSF) theories. The CTE-NSF partitioning strategy was found to be most suitable for the system under investigation. Fatigue tests were performed under wet and dry conditions, to investigate the effect of moisture on the joint performance. The fatigue results were fitted to a modified version of the Paris law and the required fatigue parameters were determined. The response of the various test specimens was simulated using the numerical scheme and good agreement with the experimental results was obtained. Significantly, the results obtained with a quadratic version of the cohesive element have been found to be independent of the element size, at least with respect to the global response. Finally, both the quasi-static and fatigue responses of the double lap joints were simulated using the cohesive element formulation and conservative predictions of the service life were obtained, in accordance with expectation, as only mode I fatigue data (lower bound Gc ) was inputted into the model

Microchannel cooling for the LHCb VELO Upgrade I

The LHCb VELO Upgrade I, currently being installed for the 2022 start of LHC Run 3, uses silicon microchannel coolers with internally circulating bi-phase \cotwo for thermal control of hybrid pixel modules operating in vacuum. This is the largest scale application of this technology to date. Production of the microchannel coolers was completed in July 2019 and the assembly into cooling structures was completed in September 2021. This paper describes the R\&D path supporting the microchannel production and assembly and the motivation for the design choices. The microchannel coolers have excellent thermal peformance, low and uniform mass, no thermal expansion mismatch with the ASICs and are radiation hard. The fluidic and thermal performance is presented.Comment: 31 pages, 27 figure

Prototyping of larger structures for the Phase-II upgrade of the pixel detector of the ATLAS experiment

For the high luminosity era of the Large Hadron Collider (HL-LHC) it is forseen to replace the current inner tracker of the ATLAS experiment with a new detector to cope with the occuring increase in occupancy, bandwidth and radiation damage. It will consist of an inner pixel and outer strip detector aiming to provide tracking coverage up to |η|<4. The layout of the pixel detector is foreseen to consist of five layers of pixel silicon sensor modules in the central region and several ring-shaped layers in the forward region. It results in up to 14 m² of silicon depending on the selected layout. Beside the challenge of radiation hardness and high-rate capable silicon sensors and readout electronics many system aspects have to be considered for a fully functional detector. Both stable and low mass mechanical structures and services are important. Within the collaboration a large effort is started to prototype larger detector structures for both the central and forward region of the detector. The aspect of system integration is tested with prototype components. In the paper the latest evaluation of mechanical and thermo-mechanical prototypes and fully electrical prototypes is presented. Important qualification steps of the system design are discussed

An environmental monitoring and control system for the ATLAS Outer Barrel QC and Integration

The Inner Tracker (ITk) will be one of the major upgrades that the ATLAS experiment will undergo during the long shutdown 3 of the LHC. The ITk Pixel detector will be composed by an Inner System (IS), two Endcaps (EC) and an Outer Barrel (OB). The OB itself will be composed of more than 4,000 pixel modules, arranged on modular "local support" structures (longerons and half rings). In total, 158 local support structures will compose the OB. QC testing will be performed at the different stages of production (modules standalone, module loaded on cells and modules integration to loaded local supports, and after integration of several loaded local supports). Dedicated environmental boxes will be developed for the purpose, providing the required connectivity to services (CO2 cooling, power and data connectivity), light tightness and safe operation area during testing. In order to ensure the safety of operation of several modules at the loaded local support QC testing and integration stage, a dedicated DCS and Interlock system was developed at CERN, based entirely on industrial PLC solutions and providing a Scada WinCC-OA interface. Such system is meant to be employed in a standalone configuration during QC tests, while at the integration stage it is foreseen to be coupled to the specific interlock crate of the ITk. The system is meant to be modular and adaptable to the several different test configurations which are foreseen at the QC and integration stage. The talk will give an overview of the system and its capabilities as well as describe the validation of its operation in a representative use case, with a system test setup currently operating at CERN

An environmental monitoring and control system for the ATLAS ITk Outer Barrel QC and Integration.

This paper describes the development of a system based on Programmable Logic Controllers (PLC) for safety interlocking and environmental monitoring during ITk Outer Barrel loaded local support QC and later integration. The system has been developed at CERN with a focus on scalability, maintainability and reliability, and is expected to be deployed at the different ITk OB loading and integration sites

The Gigatracker of the NA62 experiment at CERN

NA62 is a fixed-target experiment at the CERN SPS designed to measure the branching ratio of the very rare kaon decay $K^{+} \rightarrow \pi^{+}\nu \bar{\nu}$ with 10% precision. Measurements of time, momentum and direction of incoming beam particles are provided by a beam spectrometer called GigaTracker. The GigaTracker is made of three stations of hybrid silicon pixel detector installed in vacuum ($\sim10^{-6}$ mbar). Each station consists of 18000 pixels of $300\times300\mu m^{2}$ area each, arranged in a matrix of $200\times90$ elements corresponding to a total area of $62.8\times27mm^{2}$. The beam particles, flowing at 750 MHz, are tracked in 4-dimensions by means of time-stamping pixels with the single hit time resolution reaching 115 ps. This performance has to be maintained despite the beam irradiation amounting to a yearly fluence of $4.5\times 10^{14} 1MeV n_{eq}/cm^{2}/200\ days$. In order to limit multiple scattering and beam hadronic interactions, the station material budget is reduced to $0.5\%X_{0}$ by using micro channel cooling (first application in HEP). We will present the detector design and performances during the NA62 data taking periods

Microchannel cooling for the LHCb VELO upgrade I

The LHCb VELO Upgrade I, currently being installed for the 2022 start of LHC Run 3, uses silicon microchannel coolers with internally circulating bi-phase for thermal control of hybrid pixel modules operating in vacuum. This is the largest scale application of this technology to date. Production of the microchannel coolers was completed in July 2019 and the assembly into cooling structures was completed in September 2021. This article describes the R&D path supporting the microchannel production and assembly and the motivation for the design choices, together with the achieved fluidic and thermal performance. The Thermal Figure of Merit of the microchannel coolers is measured on the final modules to be between 1.5 and 3.5 K cm W, depending on glue thickness. The microchannel coolers constitute 18% of the total radiation length of the VELO and less than 2% of the material seen before the second measured point on the tracks. Microchannel cooling is well suited to the VELO implementation due to the uniform mass distribution, close thermal expansion match with the module components and resistance to radiation

Strategic R&D Programme on Technologies for Future Experiments - Annual Report 2020

This report summarises the activities and achievements of the strategic R&D programme on technologies for future experiments in the year 2020

Strategic R&D Programme on Technologies for Future Experiments - Annual Report 2021

This report summarises the activities and main achievements of the CERN strategic R&D programme on technologies for future experiments during the year 2021