Process-adapted temperature application within a two-stage rivet forming process for high nitrogen steel

Mechanical joining technologies like self-piercing riveting are gaining importance with regard to environmental protection, as they enable multi-material design and lightweight construction. A new approach is the use of high nitrogen steel as rivet material, which allows to omit the usually necessary heat treatment and coating and thus leads to a shortening of the process chain. Due to the high strain hardening, however, high tool loads must be expected. Thus, appropriate forming strategies are needed. Within this contribution, the influence of applying different temperatures for each forming stage in a two-stage rivet forming process using the high nitrogen steel 1.3815 is investigated. The findings provide a basic understanding of the influence of the temperature management when forming high nitrogen steel. For this purpose, the rivets are not formed at the same temperature in each stage, but an elevated temperature is applied selectively. Different process routes are investigated. First, cups are manufactured in stage 1 at room temperature, followed by stage 2 at 200°C. Second, cups are formed in stage 1 at 200°C and used for stage 2 at room temperature. By comparing the findings with results when applying the same temperature in both stages, it is shown that the temperature during the first forming operation has an effect on the forming behaviour during the second forming stage. The required forming forces and the resulting rivet hardness can be influenced by process-adapted temperature application. Furthermore, the causes for the temperature impact on the residual cup thickness in stage 1 are evaluated by a cause and effect analysis, which provides a deeper process understanding. The thermal expansion of the tool and the billet as well as the improved forming behaviour at 200°C are identified as the main influencing causes on the achieved residual cup thickness.

An investigation of the Formability Behaviour of High Strength Aluminium Alloys Using Different Heat Assisted Forming Processes

The usage of ultra-high strength aluminium alloys (EN AW-7000 series) offers a great weight saving potential due to the high rigidity and specific strength values. Various heat assisted forming technologies have been developed in order to improve the limited formability at room temperature and thus to be able to increase the geometrical complexity of such sheet metal parts. In this study the forming behaviour of EN AW-7021 sheet metal alloy is described as a function of the forming process and the corresponding temperature profile. The forming limit curves (FLCs) are obtained by experimental Nakajima tests using the Warmforming, Hotforming, extended Hotforming and W-Temper process route. For this purpose, a Nakajima testing tool is designed according to ISO 12004 standard which allows operating temperatures of up to 200 °C.

Religiosity and Egyptian Muslim millennials’ views on offensive advertising

Purpose This paper explores reasons behind Muslim fervour, in response to advertisements that cause them offence – where marketing promotions and brands are seen to contradict or challenge the tenets of their religion (Islam) and culture. Design/methodology/approach The authors investigate Egyptian Muslim Millennials’ perceptions post 2011 Egyptian Arab Spring revolution qualitatively – through a series of iterative focus groups, diaries, and laddered coding procedures. Findings In contrast to the way in which media stories regularly highlight this phenomenon locally, internationally, and inside and outside of the Muslim world, we find that the landscape is more cultural, contextual, dynamic, politicised, and subtle. In addition, religiosity may not in fact be the determining factor and its presence is much more nuanced. The socially mobile, educated, and digitally connected Egyptian Muslim millennial demographic, that grabbed headlines during the Arab Spring for their influence, were found in this study to describe offence as being annoying or provocative advertisements where the message, theme or execution disregards their intelligence. Furthermore, parents, access to basic utilities, and having a stable living environment command a greater influence than religiosity for them. Finally, an environmental paradox exists, where restricted living conditions juxtaposed in parallel with escapism offered by social-media consumption, leads millennials towards being more accepting of advertising that could be classified as offensive. Practical implications This study is of value for researchers, educators, and professionals in the fields of advertising, marketing communications, consumer behaviour, and sociology. Social implications The observations raise questions concerning how the media reports stories, or advertisers conduct their campaigns – as to whether they are representative, motivated by sociopolitics or propaganda, an intended tactic, highlight unintended poor execution, ambivalence, or part of a wider phenomenon. Originality/value The authors present a new dual-process personality/religiosity conceptual model – designed to explain the stepwise process of Muslim opinion-forming, behaviour, and consumption of advertisements. Furthermore, we illustrate this with a supporting allegory the authors call a “Narnia paradigm”, drawing from C.S. Lewis’s fictional story “The Lion, the Witch and the Wardrobe”.

Experimental and numerical investigation on draping behaviour of woven carbon fabric

In the liquid composite moulding (LCM) process, fabric is draped over the mould surface and a resin is injected under pressure to develop a composite laminate. Wrinkling is one of the most common flaws that occurs during the draping of the fabric. Wrinkling of the fabric within the composite could severely reduce the quality of the finished composite laminate. Thus, to develop a high-quality composite laminate, exact prediction of fabric wrinkling behaviour is necessary. The aim of the paper is to investigate the draping behaviour of carbon fabric. Carbon fabric with an areal density of 245 g/m2 is used in the study. Both experimental and numerical investigations were performed. An experimental setup was developed to predict the draping behaviour of the carbon fabric used in the study. LS-DYNA/Explicit solver is used to achieve macro level draping simulation. Material model MAT_REINFORCED_THERMOPLASTIC [MAT_249] offers the possibility to simulate the forming behaviour of a thermoplastic material. To simulate dry fabrics using MAT_249, a very low properties are used for the matrix in the material model. To capture the forming behaviour of fabric, an intensive material characterization has been performed. Tensile and shear properties of the fabrics were determined using uniaxial and picture frame tests, respectively. Influence of the position of the integration points from the mid surface on bending behaviour is studied and calibrated using a simple test.

A new galling insect model enhances photosynthetic activity in an obligate holoparasitic plant

Insect-induced galls are microhabitats distinct from the outer environment that support inhabitants by providing improved nutrients, defence against enemies, and other unique features. It is intriguing as to how insects reprogram and modify plant morphogenesis. Because most of the gall systems are formed on trees, it is difficult to maintain them in laboratories and to comprehend the mechanisms operative in them through experimental manipulations. Herein, we propose a new model insect, Smicronyx madaranus, for studying the mechanisms of gall formation. This weevil forms spherical galls on the shoots of Cuscuta campestris, an obligate parasitic plant. We established a stable system for breeding and maintaining this ecologically intriguing insect in the laboratory, and succeeded in detailed analyses of the gall-forming behaviour, gall formation process, and histochemical and physiological features. Parasitic C. campestris depends on host plants for its nutrients, and usually shows low chlorophyll content and photosynthetic activity. We demonstrate that S. madaranus-induced galls have significantly increased CO2 absorbance. Moreover, chloroplasts and starch accumulated in gall tissues at locations inhabited by the weevil larvae. These results suggest that the gall-inducing weevils enhance the photosynthetic activity in C. campestris, and modify the plant tissue to a nutrient-rich shelter for them.

Virtual parameter identification of the forming behaviour of discontinuous fibre reinforced thermoplastic composite sheets

Fibre-reinforced thermoplastics (FRTP), such as organo sheets or laminates, are increasingly being used in large-scale automotive production. The high weight-saving potential, high specific strengths and stiffnesses as well as processing times suitable for large-scale production are some of the reasons for using these materials. However, the formability of such semi-finished products is severely limited by the fibre reinforcement, which can lead to fibre breakage, fibre displacement or wrinkling in complex-shaped components. In order to increase the formability, an FRTP semi-finished product is developed, which consists of discontinuous tapes. Due to the local sliding of the tape sections, a pseudo-plastic material behaviour is achieved. Experimental uniaxial tensile tests at elevated temperatures are used to investigate the forming behaviour of the material for different tape lengths and overlap lengths. Subsequently, this tensile test is numerically modelled in order to fit the pseudo-plasticity to the experimental data by a virtual parameter identification. With the help of the parameters determined from the numerical tensile test, the sliding behaviour of the tape sections can be used for forming simulations in order to achieve a higher prediction quality.

The effect of reinforcement, fibre, and matrix on the forming behaviour of continuous fibre reinforced thermoplastic composites

Forming simulations are a cost-effective solution to mitigate process-induced defects. The models developed to simulate the forming process require material property data for the dominant deformation mechanisms: intra-ply shear, bending, and inter-ply friction. These mechanisms are considered independent, and material property data has to be derived from experimental data for each mechanism separately. However, it is known that the material response to the deformation mechanisms is correlated, as the choice of matrix, fibre, and reinforcement influences the response to all mechanisms. Over the past years a large variety of thermoplastic composites have been characterised, covering a broad field of applications in automotive and aerospace industry. This makes it possible to start correlating the forming behaviour of thermoplastic composites. In this study, the effect of the constituents of a composite on the forming behaviour is analysed. To this end, a Bayesian cross-classified multilevel model with varying intercepts was applied, and the effects found by the model were analysed. Correlations were found between the effect of the constituents and their properties. The study confirms that the matrix material is an important indicator for the forming behaviour.

Investigation of the formability behaviour of optimized tufted and un-tufted multi-layer carbon preforms during the stamping process

The originality of this work consists of studying the stamping behaviour of tufted and un-tufted multi-layer carbon preforms. Several tufted preforms with different stratifications have been manufactured. The stamping test was carried out using a hemispherical punch and conducted at two blank-holder pressures (0.05 and 0.2 MPa). The experimental data show that the addition of tufting yarn, the number of layers and the blank-holder pressure significantly affected the forming behaviour: the tufted preform presents a higher punch force, lower material drawin and shear angles with significant structural defects than the un-tufted preform. The increase of the blank-holder pressure increases all these characteristics and emphasizes the structural defects on the fibrous reinforcements. Similarly, the transition from two layers to four layers lamination at the same blank-holder pressure is followed by an increase of the punch force, reducing the material draw-in and the shear angles especially those measured at the transient zone, and causes more structural defects on all stamped preforms. Therefore, two localized tufting configurations, Right Localized Tufted and Inclined Localized Tufted, at the stamping transition area have been proposed. The results show that these two configurations present a minimum punch force and a maximum material draw-in similar to those measured on the un-tufted structure. The shear angles are much greater than those recorded on the conventionally (fully) tufted preform. Thus, the localized tufting in the most stressed areas proves to be the most suitable solution for the stamped preforms.