Dimpling process in cold roll metal forming by finite element modelling and experimental validation

The dimpling process is a novel cold-roll forming process that involves dimpling of a rolled flat strip prior to the roll forming operation. This is a process undertaken to enhance the material properties and subsequent products’ structural performance while maintaining a minimum strip thickness. In order to understand the complex and interrelated nonlinear changes in contact, geometry and material properties that occur in the process, it is necessary to accurately simulate the process and validate through physical tests. In this paper, 3D non-linear finite element analysis was employed to simulate the dimpling process and mechanical testing of the subsequent dimpled sheets, in which the dimple geometry and material properties data were directly transferred from the dimpling process. Physical measurements, tensile and bending tests on dimpled sheet steel were conducted to evaluate the simulation results. Simulation of the dimpling process identified the amount of non-uniform plastic strain introduced and the manner in which this was distributed through the sheet. The plastic strain resulted in strain hardening which could correlate to the increase in the strength of the dimpled steel when compared to plain steel originating from the same coil material. A parametric study revealed that the amount of plastic strain depends upon on the process parameters such as friction and overlapping gap between the two forming rolls. The results derived from simulations of the tensile and bending tests were in good agreement with the experimental ones. The validation indicates that the finite element analysis was able to successfully simulate the dimpling process and mechanical properties of the subsequent dimpled steel products

Finite Element Analysis of Cold-Formed Dimpled Steel Columns

Dimpled steel products are produced from the combination of an innovative dimpling process and a traditional forming process such as cold-roll forming or press-braking. The wider use of cold-formed dimpled steel members has promoted considerable interest in the local instability and strength of these members. Of particular interest is their buckling behaviour and ultimate strength capacity. However, the dimpling process produces cold-formed sections with a complex ‘dimpled’ surface topography and the ‘dimpled’ material is nonuniformly work hardened through the entire thickness. Owing to these complex issues, there are no existing methods to calculate the buckling strength of the dimpled products and validate against physical measurements. This paper presents a Finite Element analysis of the compressive behaviour of cold-formed dimpled steel columns. True stress-strain data obtained from physical tests were incorporated into nonlinear simulations of dimpled steel columns. The simulation results were compared with compression test results on dimpled channel and lipped channel columns and good agreements in both buckling and ultimate strength were obtained. It is demonstrated that the Finite Element analysis can therefore be used to analyse and design cold-formed dimpled steel columns

Down-Hole Heat Exchangers: Modelling of a Low-Enthalpy Geothermal System for District Heating

In order to face the growing energy demands, renewable energy sources can provide an alternative to fossil fuels. Thus, low-enthalpy geothermal plants may play a fundamental role in those areas—such as the Province of Viterbo—where shallow groundwater basins occur and conventional geothermal plants cannot be developed. This may lead to being fuelled by locally available sources. The aim of the present paper is to exploit the heat coming from a low-enthalpy geothermal system. The experimental plant consists in a down-hole heat exchanger for civil purposes and can supply thermal needs by district heating. An implementation in MATLAB environment is provided in order to develop a mathematical model. As a consequence, the amount of withdrawable heat can be successfully calculated

The Design and Development of New Cold Roll Formed Products by Finite Element Modeling and Optimisation

The design and development of new cold roll formed products can incur significant cost and the product may not be optimised for either performance or manufacture. This paper describes a new method to develop an optimum structural design of profile by cold roll forming using a combined approach of finite element analysis and optimisation techniques. To illustrate the concept, the design and development of a new channel beam and a new drain grating subjected to bending are presented. The two case studies, demonstrate how a roll formed profile may be optimised to improved structural performance through use of stiffeners and/or dimples. Improved performance of cold roll formed products is achieved by increasing the strength of the product without increasing the amount of the material used. The results of this paper clearly demonstrate an efficient and effective method and tool set to optimise design for performance and manufacture of cold roll formed products

A new trans-Ionian spider species for the Italian fauna: Habrocestum graecum Dalmas, 1920 (Araneae, Salticidae)

The salticid spider Habrocestum graecum Dalmas, 1920, until now only known from Greece, is for the first time recorded in Italy. Observations on ecology and behavior are also reported and pictures of its habitus and genitalia are provided. Furthermore, the first DNA barcode sequence for H. graecum is produced and made publicly available. The species has been observed in Puglia, in South-Eastern Italy, and a trans-Ionian dispersal pattern is most likely the cause of its presence both in Greece and Southern Italy, as reported for other taxa with similar distribution in different animal groups

Compressive Strength Tests and Design of Cold-formed Plain and Dimpled Steel Columns

This paper presents the experiments and design formulae of cold-formed plain and dimpled steel columns. A series of compression tests on plain and dimpled channel columns were conducted over a range of different geometries and the strength of the columns were investigated. The change in strength of the dimpled columns resulting from the cold working associated with the dimpling process was considered. The results showed that the buckling and ultimate strengths of dimpled steel columns were up to 33% and 26% greater than plain steel columns, respectively. The test results were evaluated by comparing buckling and ultimate loads of plain and dimpled channel columns with the values predicted by theoretical and semi-empirical methods. It was found that the predicted buckling and ultimate loads correlated well with the experimental results. Based on the experimental results, expressions for determining buckling and ultimate strengths of component plate elements of plain and dimpled channel columns were formulated

Current LISA Spacecraft Design

The Laser Interferometer Space Antenna (LISA) mission. a space based gravitational wave detector. uses laser metrology to measure distance fluctuations between proof masses aboard three spacecraft. LISA is unique from a mission design perspective in that the three spacecraft and their associated operations form one distributed science instrument. unlike more conventional missions where an instrument is a component of an individual spacecraft. The design of the LISA spacecraft is also tightly coupled to the design and requirements of the scientific payload; for this reason it is often referred to as a "sciencecraft." Here we describe some of the unique features of the LISA spacecraft design that help create the quiet environment necessary for gravitational wave observations

Case Report: Could Hennebert's Sign Be Evoked Despite Global Vestibular Impairment on Video Head Impulse Test? Considerations Upon Pathomechanisms Underlying Pressure-Induced Nystagmus due to Labyrinthine Fistula

We describe a case series of labyrinthine fistula, characterized by Hennebert's sign (HS) elicited by tragal compression despite global hypofunction of semicircular canals (SCs) on a video-head impulse test (vHIT), and review the relevant literature. All three patients presented with different amounts of cochleo-vestibular loss, consistent with labyrinthitis likely induced by labyrinthine fistula due to different temporal bone pathologies (squamous cell carcinoma involving the external auditory canal in one case and middle ear cholesteatoma in two cases). Despite global hypofunction on vHIT proving impaired function for each SC for high accelerations, all patients developed pressure-induced nystagmus, presumably through spared and/or recovered activity for low-velocity canal afferents. In particular, two patients with isolated horizontal SC fistula developed HS with ipsilesional horizontal nystagmus due to resulting excitatory ampullopetal endolymphatic flows within horizontal canals. Conversely, the last patient with bony erosion involving all SCs developed mainly torsional nystagmus directed contralaterally due to additional inhibitory ampullopetal flows within vertical canals. Moreover, despite impaired measurements on vHIT, we found simultaneous direction-changing positional nystagmus likely due to a buoyancy mechanism within the affected horizontal canal in a case and benign paroxysmal positional vertigo involving the dehiscent posterior canal in another case. Based on our findings, we might suggest a functional dissociation between high (impaired) and low (spared/recovered) accelerations for SCs. Therefore, it could be hypothesized that HS in labyrinthine fistula might be due to the activation of regular ampullary fibers encoding low-velocity inputs, as pressure-induced nystagmus is perfectly aligned with the planes of dehiscent SCs in accordance with Ewald's laws, despite global vestibular impairment on vHIT. Moreover, we showed how pressure-induced nystagmus could present in a rare case of labyrinthine fistulas involving all canals simultaneously. Nevertheless, definite conclusions on the genesis of pressure-induced nystagmus in our patients are prevented due to the lack of objective measurements of both low-acceleration canal responses and otolith function