Submitted by Izabel Franco (izabel-franco@ufscar.br) on 2016-09-20T18:30:12Z No. of bitstreams: 1 DissJVAE.pdf: 4217973 bytes, checksum: 5bff49bb1884d56f5cb1d7e47edfd24f (MD5) / Approved for entry into archive by Ronildo Prado (ronisp@ufscar.br) on 2016-09-21T18:13:46Z (GMT) No. of bitstreams: 1 DissJVAE.pdf: 4217973 bytes, checksum: 5bff49bb1884d56f5cb1d7e47edfd24f (MD5) / Approved for entry into archive by Ronildo Prado (ronisp@ufscar.br) on 2016-09-21T18:13:57Z (GMT) No. of bitstreams: 1 DissJVAE.pdf: 4217973 bytes, checksum: 5bff49bb1884d56f5cb1d7e47edfd24f (MD5) / Made available in DSpace on 2016-09-21T18:23:53Z (GMT). No. of bitstreams: 1 DissJVAE.pdf: 4217973 bytes, checksum: 5bff49bb1884d56f5cb1d7e47edfd24f (MD5) Previous issue date: 2015-02-26 / Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) / The friction spot joining (FSpJ) emerges as an alternative and innovative technique for producing polymer-metal hybrid structures. This technique was developed and patented by HZG / Germany in 2012. The process uses a combination of tools that by friction generates heat leading to the formation of a polymer layer through the interface and mechanical interlocking between the joints partners. Previous studies have demonstrated the technical feasibility of producing hybrid joints by FSpJ, however, no studies have demonstrated the influence of the process parameters on the joints properties. This study aimed to produce hybrid joints of 6181-T4 aluminum alloy and carbon fiber reinforced poly(phenylene sulfide) laminate composite (CF-PPS) by FSpJ and investigate the influence of process and aluminum surface treatment on the structure and the mechanical strength of these joints. The proper combination of these parameters resulted in hybrid joints with single lap shear force of up to 1861 N (29 MPa) and 3522 N (55 MPa) for double lap joints. This level of shear strength is similar or superior to others metal / polymeric composite joints produced by conventional joining techniques, demonstrating the potential of the FSpJ. The rotational speed (RS) was the parameter with the greatest influence on the shear strength of the joints, followed by the joining time (JT), tool plunge depth (PD) and joining force (JF). Joints that had predominantly cohesive fracture showed higher shear strength. Joints that were cooled at lower rates showed higher joint shear strength, regardless the heat input, due to lower residual stress at the interface of these joints. Through simple aluminum surface treatment (griding followed by acid pickling) it was possible to achieve an increasing up to 160% in the shear strength of the joints. / A união pontual por fricção (“Friction Spot Joining – FSpJ”) desponta como uma técnica alternativa e inovadora para produzir estruturas híbridas metal-polímero. Esta técnica foi desenvolvida e patenteada pela HZG / Alemanha em 2012. O processo utiliza uma combinação de ferramentas que através da fricção sobre o metal gera calor levando a formação de camada polimérica na interface e de travamento mecânico entre as chapas. Estudos anteriores demonstraram a viabilidade técnica para produção de juntas híbridas, porém, não há estudos demonstrando efetivamente a influência dos parâmetros de união nas propriedades das juntas. Este estudo teve como objetivo produzir juntas híbridas de alumínio 6181-T4 e compósito laminado de poli(sulfeto de fenileno) e fibra de carbono (CF-PPS) por FSpJ, e investigar a influência de parâmetros de processo e tratamento superficial do alumínio sobre a estrutura e a resistência mecânica dessas juntas. A combinação apropriada desses parâmetros resultou em juntas híbridas com força máxima em cisalhamento de até 1861 N (29 MPa) na geometria junta pontual sobreposta simples e de 3522 N (55 MPa) na geometria de junta sobreposta dupla. Esse nível de resistência mecânica é similar ou superior ao de outras juntas metal-compósito polimérico produzidas por técnicas convencionais de união, demonstrando o potencial da técnica FSpJ. A velocidade rotacional (VR) foi o parâmetro com maior influência na resistência ao cisalhamento das juntas, seguida pelo tempo de união (TU), profundidade de penetração (PP) e força de união (FU). As juntas com falha predominantemente coesiva apresentaram resistência ao cisalhamento superior. Foi verificado que juntas produzidas em menores taxas de resfriamento apresentam maior desempenho mecânico, independentemente do aporte térmico utilizado, devido a menor tensão residual na interface dessas juntas. Através de tratamentos superficiais simples no alumínio (lixamento seguido de decapagem ácida) foi possível alcançar aumento de até 160% na resistência ao cisalhamento das juntas.

Friction Bit Joining (FBJ) is a recently developed spot joining technology capable of joining dissimilar metals. A consumable bit cuts through the upper layer of metal to be joined, then friction welds to the lower layer. The bit then snaps off, leaving a flange. This research focuses on FBJ using DP980 or DP590 steel as the lower layer, AZ31 magnesium alloy as the top layer, and 4140 or 4130 steel as the bit material. In order to determine optimal settings for the magnesium/steel joints, experimentation was performed using a purpose-built computer controlled welding machine, varying factors such as rotational speeds, plunge speed, cutting and welding depths, and dwell times. It was determined that, when using 1.6 mm thick coupons, maximum joint strengths would be obtained at a 2.03 mm cutting depth, 3.30 mm welding depth, and 2500 RPM welding speed. At these levels, the weld is stronger than the magnesium alloy, resulting in failure in the AZ31 rather than in the FBJ joint in lap shear testing.

In this study, the dissimilar metals 5754 aluminum and DP980 ultra-high strength steel were joined using the friction bit joining (FBJ) process. The friction bits were made using one of three steels: 4140, 4340, or H13. Experiments were performed in lap shear, T-peel, and cross tension configurations, with the 0.070" thick 5754 aluminum alloy as the top layer through which the friction bit cut, and the 0.065" thick DP980 as the bottom layer to which the friction bit welded. All experiments were performed using a computer controlled welding machine that was purpose-built and provided by MegaStir Technologies. Through a series of designed experiments (DOE), weld processing parameters were varied and controlled to determine which parameters had a significant effect on weld strength at a 95% confidence level. The parameters that were varied included spindle rotational speeds, Z-command depths, Z-velocity plunge rates, dwell times, and friction bit geometry. Maximum lap shear weld strengths were calculated to be 1425.4lbf and were to be obtained using a bit tip length at 0.175", tip diameter at 0.245", neck diameter at 0.198", cutting and welding z-velocities at 2.6"/min, cutting and welding RPMs at 550 and 2160 respectively, cutting and welding z-commands at -0.07" and -0.12" respectively, cooling dwell at 500 ms, and welding dwell at 1133.8 ms. These parameters were further refined to reduce the weld creation time to 1.66 seconds. These parameters also worked well in conjunction with an adhesive to form weld bonded samples. The uncured adhesive had no effect on the lap shear strengths of the samples. Using the parameters described above, it was discovered that cross tension and T-peel samples suffered from shearing within the bit that caused the samples to break underneath the flange of the bit during testing. Visual inspection of sectioned welds indicated the presence of cracking and void zones within the bit.

[pt] A indústria de transporte tem enfrentado rigorosas políticas econômicas e ambientais para a redução do consumo de combustível e consequentemente redução na emissão de CO2. Uma solução promissora para suprir tais exigências encontra-se na redução do peso da estrutura de carros e aviões através do uso de estruturas híbridas. Técnicas de união convencionais geralmente são inadequadas para produzir juntas híbridas de metal e polímero. Sendo assim, tecnologias de junção inovadoras estão sendo desenvolvidas para surprir tais limitações, como por exemplo: União pontual por fricção (FSpJ), rebitagem por fricção (FricRiveting) e união por energia ultra-sônica (U-Joining). Esta dissertação de mestrado foi desenvolvida para avaliar juntas híbridas produzidas com baixo (BAE) e alto aporte energético (AAE). O monitoramento da temperatura, a análise microestrutural, a resistência mecânica e os respectivos modos de falhas das juntas foram avaliados para as três técnicas de fricção. Neste contexto, técnicas de microscopia, microtomografia de raio-x e ensaios de resistência mecânica foram escolhidas para tal finalidade. Juntas de AAE produzidas por união pontual de fricção apresentaram 43 porcento maior resitência mecânica comparado com juntas de BAE e ambas falharam no centro da área de junção. Juntas de AAE produzidas por rebitagem apresentaram 46 porcento maior resitência mecânica e falha do rebite metálico fora da placa polimérica, comparado com juntas de BAE que teve o rebite metálico arrancado da placa polimérica. A resitência ao cisalhamento das juntas de AAE (fratura da placa polimérica) produzidas por energia ultra-sônica foi 85 porcento maior que as juntas de BAE (fratura dos pinos combinado com falhas coesivas e adesivas). / [en] The transportation industry has been facing stringent environmental regulations to decrease fuel consumption and CO2 emissions. A promising solution to fulfill these demands is decreasing the structural weight of vehicles and airplanes by combining lightweight alloys and fiber-reinforced polymers in hybrid structures. Conventional joining technologies are usually inadequate to produce high performance joints. To overcome these limitations, advanced joining technologies are under development such as: Friction Spot Joining (FSpJ), Friction Riveting (FricRiveting) and Ultrasonic Joining (U-Joining). This master dissertation was devised to evaluate FSp, FricRiveting and U-Joining joints produced with different heat input levels (low and high) in terms of process temperature development, microstructural features, quasi-static mechanical performance and the respective failure mechanisms. In this context, microscopy techniques (i.e. optical, confocal laser and scanning electron), X-Ray micro-computed tomography (microCT), lap shear and T-Pull testing were chosen for this purpose. FSp joints produced under HHI joining condition achieved an ultimate lap shear force (ULSF) 43 percent higher than LHI joints, whereas HEI joints produced by FricRiveting process achieved ultimate tensile force (UTF) 46 percent higher than LEI joints. The lap shear strength of ultrasonically joined joints produced under HEI joining condition was up to 85 percent higher than LEI joints. FSp joints failured in the center of the overlap area while friction-riveted joints failured through the rivet (HEI) and full rivet pull-out (LEI). Ultrasonically joined joints failured through the polymer (HEI), whereas LEI joints failured through a combination of shearing of the metallic pins and a mixed cohesive (CF) and adhesive (AF) failure.

Friction bit joining (FBJ) is a new solid-state spot joining technology developed in cooperation between Brigham Young University of Provo Utah, and MegaStir Technologies of West Bountiful Utah. Although capable of joining several different material combinations, this research focuses on the application of FBJ to joining 5754 aluminum to DP 980 steel, two alloys commonly used in automotive applications. The thicknesses of the materials used were 0.070 inches (1.78 mm) and 0.065 inches (1.65 mm), respectively. The FBJ process employs a consumable 4140 steel bit and is carried out on a purpose built research machine. In the first stage of the weld cycle the bit is used to drill through the aluminum top sheet to be joined. After this, spindle speed is increased so that the bit tip effectively forms a friction weld to the steel bottom sheet. Momentary stoppage of the spindle facilitates weld cooling before the spindle is restarted, shearing the bit tip from the bit shank, and retracted. Incorporated into the bit tip geometry is a flange that securely holds the aluminum in place after joint formation is complete. This research consists of several developmental steps since the technology only recently began to be formally studied. Initial joint strengths observed in lapshear tensile testing averaged only 978.5 pounds (4.35 kN), with a relatively high standard deviation for the data set. Final lapshear tensile test results were improved to an average of 1421.8 pounds (6.32 kN), with a significantly lower, and acceptable, standard deviation for the data set. Similar improvements were realized during the development work in cross tension tensile test results, as average strengths increased from 255.8 pounds (1.14 kN) to 566.3 pounds (2.52 kN). Improvements were also observed in the standard deviation values of cross tension data sets from initial evaluation to the final data set presented in this work.