Key Engineering Materials Vols. 554-557

Abstract: The efficiency offorging processes is significantly influenced by the tool and scrap costs whichin their turn depend on the life time of forging dies. The tools used for hotforging are subject to process-related high mechanical, tribological, chemicaland thermal-cyclic loads which usually interact with each other. In comparisonto other manufacturing methods, the resulting load spectrum leads to extensivewear and thus to the failure of forging dies after a short tool life. Toincrease the wear resistance of forging dies, duplex treatments consisting ofplasma nitriding and plasma deposition techniques were used to improve thesurface properties and hence to increase the die life time. By basicinvestigation of the wear mechanisms the potentials of newly developed vanadiumdoped chromium nitride and boron containing titanium nitride coating systemswere investigated. Within the presented work it is demonstrated that vanadium-dopedchromium nitride layers have a high wear reduction potential for hot forgingdies.

Abstract: Titanium alloys are finding an increasing use in the aeronautical field, due to their characteristics of high mechanical properties, lightness and corrosion resistance. Moreover these alloys are compatible with the carbon fibre reinforced plastics that are also finding a wide use in the aeronautical field. On the other hand the use of these alloys implies some drawbacks, for example titanium alloys are often considered more difficult to form and generally have less predictable forming characteristics than other metallic alloys such as steel and aluminum. In this paper was studied both the microstructure evolution and the mechanical properties of a Ti-6Al-4V rolled bar after hot forging. The thermo-mechanical response of a Ti-6Al-4V alloy was studied in elevated temperature compression tests (CT). Furthermore numerical simulations were carried out in order to do a comparison between numerical data and experimental results. The simulations were carried out using an implicit commercial code able to conduct coupled thermo-mechanical-microstructural analysis of hot forming processes of metal alloys.

Abstract: Computer aided design of the manufacturing technology for anchors is presented in the paper. Evaluation of applicability of various materials for anchors, as well as analysis of the influence of process parameters on the in use properties of product, were the objectives of the research. In the material part, bainitic steels were considered as an alternative for the commonly used C-Mn steels. Possibility of elimination of the heat treatment was evaluated. Rheological models for the investigated steels were developed and implemented into the finite element code for simulations of drawing and multi stage forging. Criteria for the selection of the best manufacturing chain composed dimensional accuracy, tool life and product properties. Industrial trials were performed for the selected cycle and the efficiency of this cycle was evaluated. Finally, simulations of the in use behaviour of the anchor-concrete joint were performed. On the basis of the simulations the optimization task using strength of the joint as the objective function was formulated

Abstract: In this paper the compression behaviour after different pre-strain and different shear angle of steel and glass fibre knitted fabrics will be analysed. These types of materials are used during the production of automotive windshields and other glasses in a car. The production of a windshield involves a step whereby the glass is deformed to the desired shape by using a mould. It is important that during this forming step the glass is not damaged and that the optical quality of the glass falls within the specifications of the customer. A knitted steel fibre fabric covers the mould. Since this fabric comes in direct contact with the glass, it is a key factor that determines the quality of the formed windshield. Variation of the fabric thickness can affect the optical quality of the glass. Thus far fabric very often manufacturers operate on the basis of empirical trial and error results to design their products. The challenge of the present work is to establish an experimental procedure for identification of the material laws for knitted fabrics deformation resistance. The paper describes an experimental procedure for derivation of the fabric thickness dependence on its deformation, using biaxial tension, shear and compression tests. The compression tests are performed on an Instron mechanical testing machine. During the test, a load cell (1 kN) pushes down with a constant speed of 1 mm/min onto the sample, compressing it. The load cell is attached to a cylinder which has a diameter of 70mm. The knitted fabrics was tested in the relaxed state and after pre-tension on the biaxial tester with pre-strains of 5x5%, 10x10%, 15%x15%, 0x10%, 10x0%, 0x20%, 20x0% and they was also tested after different shear angle (5°, 10°, 15°, 25°). Difference of thickness of fabrics after pres-strain is till 90 µm and for 25°shear angle is about 30 µm. Acknowledgements The work was funded by the grant 631/MOB/2011 of the Polish Ministry of Science and High Education, with the support from K.U.Leuven and N.V. Bekaert S.A.

Abstract: This paper proposes a first attempt to define a two scales kinetic theory to describe concentrated suspensions involving short fibers, nano-fibers or nanotubes. In this case, fiber-fiber interactions can not be neglected and rich microstructures issued from these interactions can be observed, involving a diversity of fibers clusters or aggregates with complex kinematics, and different sizes and shapes. These clusters can interact to create larger clusters and also break because the flow induced hydrodynamic forces. In this paper we propose a double-scale model to describe such microstructure: at the finest scale we study the cluster kinematic based on the behaviour of the rods that constitute it, at a coarser scale, we use clusters distribution to derive the effect of the clusters presence on the suspensions properties.

Abstract: In this paper, a non-orthogonal constitutive model [1] is used to investigate the effect of sample misalignment due to ‘tow meander’, across the initial blank sheet on the shear compliance of a woven glass fabric, as measured using the biaxial bias extension test with various transverse loads applied [2]. The same statistical distribution and spatial correlations of shear angles observed in the woven glass fabric have been automatically reproduced using ‘VarifabGA’ [3]. The effect of realistic tow directional variability is investigated by generating blanks using VarifabGA and then simulating the biaxial bias extension test using the finite element software, Abaqus ExplicitTM. In order to assign the initial fiber orientation to each element in the mesh, a unique element set is assigned to each element. A MatlabTM code 'InitialAngle.m' has been written to produce two input files; the first 'Mat.inp' includes the material property parameters of each element and the second 'Sec.inp' includes the sections of those elements. Finally, a comparison between the experimental and predicted shear compliance shows the effect of tow directional variabilityorientation to each element in the mesh, a method is introduced which involves assigning a unique element set to each element in the mesh. A Matlab code 'InitialAngle' has been written to produce two input files; the first input file 'Mat.inp' includes the material property parameters of each element and the second input file 'Sec.inp' includes the sections of those elements. Finally, a comparison between the experimental and predicted shear compliance shows the effect of tow misalignment on the shear compliance.

Abstract: The forming simulation of woven reinforcements allows accessing to information such as fibre position after forming but also deformation state as well as predicting defects such as wrinkles, yarn sliding, and fibre/yarn fracture. The proposed model consists in a mesoscopic description of the reinforcement. It is simple enough to render the simulation of the forming preform possible but describes also properly the main phenomena occurring during the forming. A geometrical model where each yarn is modelled using shell elements in contact-friction with its neighbours is proposed. A hypoelastic behaviour specific of the yarn is used. Identification and validation of the model are done using standard characterisation tests for fabrics. Forming simulations illustrate the capabilities of the proposed approach. A main interest of such modelling is the possibility for the simulation to exhibit large sliding between warp and weft yarns when the tensile loads are too important.

Abstract: In order to be able to properly evaluate the in-use mechanical properties of high performance composite materials, it is useful to identify all the critical operations of the forming process which can degrade the row materials (i.e. the yarns for continuous fibre reinforcements). Those degradations begin during the weaving process which is the main topic of the present paper. The weaving operation has been proved to be particularly critical, especially when the weaving parameters are not correctly tuned. For glass fibre reinforcements, the travel followed by both the warp and weft yarns inside the weaving loom is observed and several zones are identified as particularly critical: the contact between warp yarns and heddles, between yarns and the beater, between yarns … For each zone, the loading has been reproduced in laboratory devices in order to quantify its effect on the final resistance of the yarn. In parallel, the friction parameters have been measured for several friction configurations: friction between yarns in several directions, friction between yarns and various metallic parts of the loom. The objective is the identification of a forming window in terms of yarn tension, the shed opening, the beater for… This work is realised with the financial support of the French National Agency for Research (ANR) in the framework of project ANR- 09-MAPR-0018 (NUMTISS)

Abstract: In several fields of engineering the use of carbon fibre reinforced material (CFRP) is increasing. Minimized weight due to CFRPs could lead to lower consumption of raw materials especially in the automotive area. The goal within the research project TC² is the decrease of costs and production time for composite materials. To achieve better performance to weight ratio and to get acceptable production conditions the draping of dry unidirectional textiles and a following RTM process is investigated. Due to the high degree of complexity of automotive structures the forming process is challenging. Gapping in the textile could appear at corners as well as wrinkling or flexion of the fibres. To be able to define the amount and direction of layers or patches it is necessary to know the limits of forming for unidirectional material and to be able to predict the behaviour of the textile during the forming process. For the definition of the process limits several draping strategies are performed on different corner blend geometries. The goal of that work is to define the critical gradient of the flange to get first failures such as wrinkling or gapping. It is also important to understand the influence of different draping strategies. Parallel to the experimental tests a mesoscopic simulation method using an approach with roving and sewing thread is developed and presented. It is able to predict the material behaviour in critical areas (gapping, wrinkling). Different Young’s moduli and failure criteria can be implemented for the two main directions as well as for the bending of the textile. A validation with the experimental results is performed with the aim to enable the prediction of the textile behaviour using simulation methods.

Abstract: see enclosed file