Materials Testing

doi: 10.3139/120.016072pmid: N/A

Klein, Martin; Starke, Peter; Nowak, David; Boller, Christian; Walther, Frank

doi: 10.3139/120.110896pmid: N/A

AbstractA wide range of industries including energy, chemistry, pharmacy, textiles, food and drink, pulp and paper, etc. is using stainless steels. Metastable austenitic steels such as used in power plants and chemical industry are subjected to cyclic mechanical and thermal loading in air as well as under the influence of corrosive media. This paper provides an overview on different nondestructive and electrochemical measurement techniques, which allow differentiating fatigue damage effects in total strain controlled multiple and constant amplitude tests with respect to damage appearance on surface, in subsurface area as well as in volume of specimens or components microstructure. In addition to conventional mechanical stress-strain hysteresis curves, electrical resistance, magnetic and open circuit potential measurements have been applied to characterize the cyclic deformation behavior of the metastable austenitic steel AISI 348 (X10CrNiNb18-9) in laboratory air and in distilled water. Based on these results obtained, the paper provides an outlook on the possibility for an efficient (remaining) fatigue life evaluation approach, which is adapted to the needs of the application areas.

Merie, Violeta; Ţărmure, Viorica; Haragâş, Simion; Pop, Andreea

doi: 10.3139/120.110897pmid: N/A

AbstractBrackets, together with the arch wires, are widely used in orthodontics in order to align and to straighten teeth and also to position the teeth with regard to the patient bite. Different materials are employed for manufacturing such orthodontic devices. This paper is a study of two types of brackets. Commercial stainless steel and ceramic brackets were investigated by atomic force microscopy analyses. The tests were performed at room temperature with a relative humidity of 13 %. The topography and the friction parameters of the investigated brackets were determined at nanoscale. The results pointed out that the ceramic brackets are characterized by higher values of both topographical and frictional parameters (average roughness, friction force and friction coefficient) in comparison to the stainless steel brackets.

Frei, Julian; Suwala, Hubert; Gumenyuk, Andrey; Rethmeier, Michael

doi: 10.3139/120.110904pmid: N/A

KurzfassungDie stetig zunehmenden Anforderungen an Kraftstoffverbrauch, Schadstoffemission, sowie passive Sicherheit haben die Automobilindustrie vor Herausforderungen gestellt, die nur durch einen konsequenten Einsatz moderner hochfester Stahlwerkstoffe zu bewältigen sind. Obgleich eine generelle Eignung dieser Stähle für das Widerstandspunktschweißen (WPS) gegeben ist, kann es durch verschiedene externe Einflüsse im betrieblichen Umfeld zur Rissbildung in der Schweißverbindung kommen. Der Einfluss dieser Risse auf die mechanischen Eigenschaften ist derzeit nicht hinreichend genau erfasst, so dass häufig die Vorgabe einer rissfreien Schweißverbindung besteht. Die Kenntnis der Rissanfälligkeit der verarbeiteten Materialkombinationen sowie von ungünstigen Schweißparametern ist daher für viele Unternehmen von erheblicher wirtschaftlicher Bedeutung. Im Rahmen des FOSTA Projekts P921 „Entwicklung eines Verfahrens zur Bestimmung der Rissanfälligkeit von hochfesten Stählen beim Widerstandspunktschweißen“ wurde ein Ansatz zur Bestimmung der Rissanfälligkeit von WPS-Verbindungen hochfester Stähle entwickelt. Mittels einer hydraulischen Vorrichtung unter Zugbelastung wurden geschweißte, rissbehaftete Proben optisch ausgewertet. Das Verfahren ist geeignet, um ein Werkstoffranking bezüglich der Rissanfälligkeit beim Widerstandspunktschweißen für Werkstoffe aufzustellen.

Szlosarek, Robert; Karall, Thomas; Enzinger, Norbert; Hahne, Clemens; Meyer, Nils; Berger, André

doi: 10.3139/120.110905pmid: N/A

AbstractThis publication describes novel experimental and numerical investigations on the punching failure of carbon fiber-reinforced plastics. This kind of failure is relevant in joining processes as well as a characteristic failure type of mechanical fasteners between metals and carbon fiber-reinforced plastics like rivets or screws. So far, there is a lack of a precise phenomenological description of this failure mode. For this reason, this paper focuses on the experimental analysis of the damage and failure mechanism. As a result, the experiments show a failure evolution without any shearing of the fibers. This provides the basis for the accompanying simulation using the finite element method. Subsequently, the simulation of the experiments demonstrates that a modeling of a punching failure is possible by a combination of known fiber, inter-fiber and delamination failure criteria without extensions.

Sakthivel, Munisamy; Vijayakumar, Subramani

doi: 10.3139/120.110906pmid: N/A

AbstractFiber metal laminate (FML) composite materials are an economical alternative to engineering materials because of their superior properties. While assembling these composites, drilling is unavoidable. Drilling of such materials is a difficult task because of the drilling induced damage. Reducing this damage requires an optimization of the drilling parameters. The main focus on the optimization of the process parameters in drilling of fiber metal mesh laminate (FMML) composites lies in the application of the Taguchi procedure with Grey relational analysis (GRA). In the respective drilling experiments, coated drills were used for the FMML which was specially made with stainless steel wire mesh (SSWM) in the middle layer and woven glass fiber on top and on bottom layer using vacuum bag molding. The drilling parameters such as point angle, spindle speed and feed rate were optimized with concern of multiple performance characteristics, such as thrust force, delamination factor and roundness. The results of the GRA indicate that the feed rate is the most influential parameter. The experimental results illustrate that with the help of the optimal drilling conditions, the machining performance in the complete composite component production process can be improved.

Esme, Ugur; Kulekci, Mustafa Kemal; Ustun, Deniz; Buldum, Barış; Kazançoğlu, Yigit; Ocalır, Seref

doi: 10.3139/120.110907pmid: N/A

AbstractThe present study is aimed at finding an optimization strategy for the CNC pocket milling process based on regression analysis including differential evolution algorithm (DEA). Milling parameters such as cutting speed, feed rate and depth of cut have been designed using rotatable central composite design (CCD). The AISI 1050 medium carbon steel has been machined by a high speed steel (HSS) flat end cutter tool with 8 mm diameter using the zig-zag cutting path strategy under air flow condition. The influence of milling parameters has been examined. The model for the surface roughness, as a function of milling parameters, has been obtained using the response surface methodology (RSM). Also, the power and adequacy of the quadratic mathematical model have been proved by analysis of variance (ANOVA) method. Finally, the process design parameters have been optimized based on surface roughness using bio-inspired optimization algorithm, called differential evolution algorithm (DEA). The enhanced method proposed in this study can be readily applied to different metal cutting processes with greater and faster reliability.

Istif, Ilyas; Tuncel, Mehmet Tunc

doi: 10.3139/120.110895pmid: N/A

AbstractConventional aluminum (Al) and its alloys have been replaced by aluminum matrix composites (AMCs) due to their superior properties in the recent years. There are several attractive candidates as reinforcement for aluminum composites such as Al2O3, B4C and SiC. Nowadays, carbon based materials such as graphite, carbon nanotubes (CNTs) and graphene have attracted much attention owing to their above mentioned mechanical and physical properties. In this study, the wear behavior of Al graphene nanoplatelets (GNPs) composites reinforced with up to 2 wt.-% GNP were investigated. The addition of graphene up to 1 wt.-% decreased coefficient of friction. Experimental data were used to develop linear and nonlinear models. The experimental results are in good agreement with the results of the simulations based on the identified models.

Treffler, René; Dick, Thomas; Ladstätter, Elisabeth; Fröschl, Jürgen

doi: 10.3139/120.110898pmid: N/A

KurzfassungIm Vergleich zu metallischen Werkstoffen zeigen faserverstärkte Kunststoffe auch bei einfachen uniaxialen Beanspruchungen ein komplexes viskoelastisches Materialverhalten. Die Werkstoffmodelle sind schwer übertragbar und nur für eng eingeschränkte Werkstoffgruppen gültig. Der vorliegende Beitrag analysiert daher anhand von experimentellen Untersuchungen (Zug, Kriech-Erholung, Wöhler Tests) das mechanische Verhalten von carbonfaserverstärkten Sheet Molding Compounds (CF-SMC) in Abhängigkeit von Temperatur, Probendicke und zahlreichen weiteren Einflussfaktoren. Darüber hinaus wird der Fokus auf die Beschreibung des Schwingfestigkeitsverhaltens unter Berücksichtigung der Steifigkeitsdegradation gelegt. Auf Basis umfangreicher Prüfergebnisse werden unterschiedliche Ansätze zur Werkstoffmodellierung vorgestellt und diskutiert.

Bosch, Alexander; Vormwald, Michael; Langschwager, Kay; Scholz, Alfred; Oechsner, Matthias

doi: 10.3139/120.110899pmid: N/A

KurzfassungStumpfschweißverbindungen austenitischer Werkstoffe sind häufig Teil von Komponenten der Kraftwerkstechnik oder des chemischen Apparatebaus. In diesem Bereich unterliegen die Bauteile zyklischen mechanischen und thermischen Lasten. Vornehmlich bedingt durch hohe Temperaturschwingweiten, resultieren hohe elastisch-plastische Dehnungsschwingweiten. Die Bereiche Grundmaterial und Schweißnaht zeigen ein unterschiedliches plastisches Deformationsverhalten, die daraus resultierende metallurgische Kerbe kann versagensmaßgebend sein. Im Rahmen der begleitenden numerischen Untersuchungen wurde ein Modell entwickelt, um die metallurgische Kerbe abzubilden.