@phdthesis{SanthanakrishnanBalakrishnan, author = {Santhanakrishnan Balakrishnan, Venkateswaran}, title = {Near-net-shape semi-finished products for the local reinforcement and repair of fibre reinforced plastics}, publisher = {BTU}, address = {Cottbus}, doi = {10.26127/BTUOpen-5266}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:co1-opus4-52667}, pages = {139}, abstract = {The European Parliament and Council has defined a mandatory specific emission target of 95 g CO2/km by 2020 for passenger cars. Vehicle weight is a significant factor contributing to fuel consumption. Reducing the weight of the vehicle can be one promising option for decreasing CO2 emissions, which becomes a top priority for the automotive industry. In this research, two approaches were used to address the need. One involved developing structural parts using fibre reinforced plastics (FRP), and the other involved designing and developing FRP-metal hybrid laminates, which were constructed by reinforcing FRP locally to the metal surface. Existing joining techniques such as riveting, bolting, adhesive joining, ultrasonic welding, and flow drill joining techniques require additional processing steps to perform the joining, which could considerably increase processing time, cost, and energy expenditure. The present work describes a method to join FRP and metals using the adhesion strength of the investigated polymers. The developed FRP-metal hybrid laminates combine the advantages of metal and FRP together. Steel hot-stamping is known to yield very high strength. Fibre reinforced plastic-metal hybrid laminates were developed using hot stamped steels to transfer their superior mechanical properties to the final structure. To utilize the complete lightweight potential of thermoset and thermoplastic polymers, FRPs and FRP-metal hybrid laminates were developed using both the polymers. Along with this increased demand for FRP structures, there is growing interest in a repair technique in the automotive industry. The second objective of this thesis consists of designing and developing a new repair technique, which regains the strength and stiffness properties of the damaged part. The existing scarf repair technique is not suitable for thin laminates, which have limited access to the damaged area. Perforation damages were introduced into the FRP structures using a low-velocity impact load. A modified injection repair technique is used to repair these damaged FRP structures. Non-destructive techniques were utilized to understand the damage and the effectiveness of the repair.}, language = {en} } @misc{SanthanakrishnanBalakrishnanObrosovKukeetal., author = {Santhanakrishnan Balakrishnan, Venkateswaran and Obrosov, Aleksei and Kuke, Felix and Seidlitz, Holger and Weiß, Sabine}, title = {Influence of metal surface preparation on the flexural strength and impact damage behaviour of thermoplastic FRP reinforced metal laminate made by press forming}, series = {Composites Part B: Engineering}, volume = {173}, journal = {Composites Part B: Engineering}, issn = {1359-8368}, doi = {10.1016/j.compositesb.2019.05.094}, abstract = {In this paper the relationship between surface energy and flexural strength of metal laminate made by reinforcing glass fibre reinforced polymer on steel surfaces was investigated. Sand blasting was performed on 22MnB5 steel surface. This steel was stacked together with layers of unidirectional glass/polyamide-6 prepreg, followed by pressing in a hot press. Influenced parameters are pressure, temperature and time. 3D profilometer analysis was used to investigate the roughness profile on the surface of the steel generated by the sand blasting. The surface energy of the steel surface was calculated from a set of contact angles measured by three different liquids. To identify the optimal surface treatment, the variation of surface energy, flexural strength and roughness of the steel surface was determined as function of the surface treatment. Surface roughness (Ra of 1.08 μm), results indicate that increasing surface roughness leads to improvement in flexural modulus. The increase further leads to decrease in flexural modulus. In addition, the influence of surface energy and flexural strength on the impact damage behaviour was investigated too. The results showed that the sample with highest flexural modulus had the lowest impact-induced damage area.}, language = {en} } @misc{SanthanakrishnanBalakrishnanHartRawungBuhletal., author = {Santhanakrishnan Balakrishnan, Venkateswaran and Hart-Rawung, Thawin and Buhl, Johannes and Seidlitz, Holger and Bambach, Markus}, title = {Impact and damage behaviour of FRP-metal hybrid laminates made by the reinforcement of glass fibers on 22MnB5 metal surface}, series = {Composites Science and Technology}, volume = {Vol. 187}, journal = {Composites Science and Technology}, issn = {1879-1050}, doi = {10.1016/j.compscitech.2019.107949}, pages = {15}, language = {en} } @misc{SanthanakrishnanBalakrishnanSeidlitzAmbrosioetal., author = {Santhanakrishnan Balakrishnan, Venkateswaran and Seidlitz, Holger and Ambrosio, Marcello and Schuhmann, Tilo}, title = {Study on the Quality of Quasi-Isotropic Composite Laminates Containing a Circular Hole}, series = {Journal of Materials Science Research}, volume = {6}, journal = {Journal of Materials Science Research}, number = {4}, issn = {1927-0593}, doi = {10.5539/jmsr.v6n4p67}, pages = {67 -- 78}, abstract = {Composite structures used in modern engineering applications are often subjected to circular holes in order to join with metal components via riveting, bolting or pinning joints. These design based holes will interrupt the force flux in the direction of the fibers and create high stress concentrations near the notched area. Objective of the project is to understand the quality of the quasi-isotropic composite laminates ([45°, -45°, 0°, 90°]S) containing circular hole. To achieve this objective, a 3-phase portal milling machine and a 5kW continuous wave (cw) CO2 laser system were used to produce the circular holes in the composite laminates. The processing parameters for both the processes are varied to understand its influence. The quality of the circular hole produced by these methods are further investigated and compared in order to arrive at the optimum processing parameters for the given quasi-isotropic composite laminates. The hole qualities were evaluated by means of delamination factor caused by milling; cone angle, matrix evaporation for cw-CO2 laser system. For further comparisons, the optimal parameter combinations of both methods were selected for a tensile test according to the standard ASTM D5766-2002.}, language = {en} } @misc{SanthanakrishnanBalakrishnanSeidlitz, author = {Santhanakrishnan Balakrishnan, Venkateswaran and Seidlitz, Holger}, title = {Potential repair techniques for automotive composites: A review}, series = {Composites Part B: Engineering}, journal = {Composites Part B: Engineering}, number = {145}, issn = {1359-8368}, doi = {10.1016/j.compositesb.2018.03.016}, pages = {28 -- 38}, abstract = {Composite materials have gained popularity in automotive industries due to its lightweight potential, good damping behaviour as well as high strength and stiffness properties. Based on the increase in usage of composites, there is a growing interest for a repair technique in the automotive industry. Along with these raise in demand there comes a need for an all-inclusive review article and the objective of this article is to address this need. Two repair techniques, namely scarfing repair and injection repair, have the potential to be used in automotive industry. This paper compiles the various research work done in this field of repairing along with various processing steps associated with it. Further this paper reviews the non-destructive technique that can be used for damage identification and repair assessment.}, language = {en} } @misc{SanthanakrishnanBalakrishnanSeidlitzWeiss, author = {Santhanakrishnan Balakrishnan, Venkateswaran and Seidlitz, Holger and Weiß, Sabine}, title = {Layup Configuration Effect on Notch Residual Strength in Composite Laminates}, series = {Materials}, volume = {11}, journal = {Materials}, number = {2}, issn = {1996-1944}, doi = {10.3390/ma11020308}, pages = {12}, abstract = {The current trend shows an increasing demand for composites due to their high stiffness to weight ratio and the recent progress in manufacturing and cost reduction of composites. To combine high strength and stiffness in a cost-effective way, composites are often joined with steel or aluminum. However, joining of thermoset composite materials is challenging because circular holes are often used to join them with their metal counterparts. These design based circular holes induce high stress concentration around the hole. The purpose of this paper is to focus on layup configuration and its impact on notch stress distribution. To ensure high quality and uniformity, the holes were machined by a 5 kW continuous wave (cw) CO2 laser. The stress distribution was evaluated and compared by using finite element analysis and Lekhnitskii's equations. For further understanding, the notch strength of the laminates was compared and strain distributions were analyzed using the digital image correlation technique.}, language = {en} } @misc{SanthanakrishnanBalakrishnanSeidlitzWartigetal., author = {Santhanakrishnan Balakrishnan, Venkateswaran and Seidlitz, Holger and Wartig, Kevin and Tsombanis, Nikolas}, title = {Influence of processing parameters on the impact behaviour of glass/polyamide-6 composite}, series = {Composites Part B: Engineering}, volume = {159}, journal = {Composites Part B: Engineering}, issn = {1359-8368}, doi = {10.1016/j.compositesb.2018.09.064}, pages = {292 -- 299}, abstract = {This study aims to investigate the low-velocity impact response and post-impact flexural behaviour of glass/polyamide-6 (G/PA-6) composite. G/PA-6 composites with a layup configuration of [02,902]s were prepared via press-forming technique. Composite samples were developed using four different processing conditions, by modifying compression pressure and heating temperature. Local variations of fiber volume and porosity fraction were noticed for samples developed in each processing conditions. On the investigated samples, damages were induced by using 35 joule of drop weight impact to investigate the impact resistance of samples with respect to different processing conditions. The damage behaviour and residual flexural strength was characterized using a micro-CT and three-point bending tests respectively. Furthermore, the influence of porosity fraction on the residual flexural strength were investigated. This paper will provide necessary fundamental knowledge for future selection of processing parameters in order to have enhanced impact performance.}, language = {en} }