This present paper is devoted to the numerical and experimental investigation of the modal charac... more This present paper is devoted to the numerical and experimental investigation of the modal characteristics of composite laminates, with emphasis on damping. Complementing previous studies dedicated to conventional laminates, one considers variable-angle tow laminates, in which the fibers are deposited following curvilinear trajectories. The main objective is to characterize the influence of fiber steering on the damping levels, and evaluate the possibility of achieving increased damping. A dynamic model is derived by combining the semianalytical Rayleigh-Ritz approach, the Classical Lamination Theory, and the Strain Energy Method. This later enables to estimate the specific damping capacity of each vibration mode. Based on this model, analytical developments are performed aiming at putting in evidence the contribution of each strain component in each layer of the laminate to the specific damping capacities. The results of numerical simulations are presented, enabling to compare the values of specific damping capacities and vibration natural frequencies obtained for variableangle tow and conventional laminates in a variety of simulation scenarios. Some of the numerical results are validated by comparisons with experimental counterparts. The results confirm the effectiveness of design strategies intended to regulate and possibly increase the damping levels of composite laminates by exploring fiber steering.
IOP Conference Series: Materials Science and Engineering, 2018
This paper analyses the Mode II fatigue delamination growth onset for secondary bonded joints com... more This paper analyses the Mode II fatigue delamination growth onset for secondary bonded joints compared to co-cured joints. The materials used were composed by two carbon fiber reinforced sub-laminates joined by the secondary bonded and co-cured (without adhesive) methods. Mode II fatigue tests were performed using three-point bending End Notched Flexure test setup. The tests were performed under displacement control and a sinusoidal displacement applied at a frequency of 5 Hz with a Rd = 0.1, that mean, δmin = 0.1 δmax. The main objective of this study was to obtain the strain energy release rate (SEER) versus number of cycles (Nf) in order to evaluate the effect of the adhesive on fatigue life of bonded joints. A Closed form solution for 3-ENF setup was used in order to define the displacement amplitudes that were applied in the fatigue test. The results show that the use of adhesive causes a reduction on Mode II fatigue delamination growth onset SERR (Gth) for secondary-bonded compared to cocured joints. Finally, a scanning electron microscopy (SEM) was used to analyze the fracture surfaces of the Mode II secondary bonded specimens. The fractography images show no crack growth for the specimens tested below or at Gth loading levels, which indicated that the value corresponds to the threshold. Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.
This present paper is devoted to the numerical and experimental investigation of the modal charac... more This present paper is devoted to the numerical and experimental investigation of the modal characteristics of composite laminates, with emphasis on damping. Complementing previous studies dedicated to conventional laminates, one considers variable-angle tow laminates, in which the fibers are deposited following curvilinear trajectories. The main objective is to characterize the influence of fiber steering on the damping levels, and evaluate the possibility of achieving increased damping. A dynamic model is derived by combining the semianalytical Rayleigh-Ritz approach, the Classical Lamination Theory, and the Strain Energy Method. This later enables to estimate the specific damping capacity of each vibration mode. Based on this model, analytical developments are performed aiming at putting in evidence the contribution of each strain component in each layer of the laminate to the specific damping capacities. The results of numerical simulations are presented, enabling to compare the values of specific damping capacities and vibration natural frequencies obtained for variableangle tow and conventional laminates in a variety of simulation scenarios. Some of the numerical results are validated by comparisons with experimental counterparts. The results confirm the effectiveness of design strategies intended to regulate and possibly increase the damping levels of composite laminates by exploring fiber steering.
Recently, the success in new product development process has become one of the main competitive a... more Recently, the success in new product development process has become one of the main competitive advantages. Thus, many companies are looking for improving their new product development (NPD) process, to launching products as fast as possible with the required quality and low costs. To achieve such objectives, many organizations have designed phasedreview processes that cut across functional areas of the NPD. One such process with wide acceptance is the Phase Review Process. Phase Reviews are checkpoints that take place at key periods in the product development process to review the opportunity/development effort, assess it from a business and strategic perspective, and determine whether it is worthy to continue the development, redirect or kill it. New product development best practices usually include such processes, however little has been written on how to implement such practices. The available literature reports generic issues and recommendations, without describing a structured approach. This paper describes and analyzes a practical phase review implementation process, pointing out difficulties and stating recommendations to improve and support a successful implementation. The results, compiled after an industrial case study, show clearly the improvements achieved for the proposed implementation.
The present work describes a methodology to compute equivalent volumes representing the microstru... more The present work describes a methodology to compute equivalent volumes representing the microstructure of 3D-printed continuous fiber-reinforced thermoplastics, based on a statistical characterization of the fiber distribution. In contrast to recent work, the methodology herein presented determines the statistically equivalent fiber distribution directly from cross-section micrographs, instead of generating random fiber arrangements. For this purpose, several regions, with different sizes and from different locations, are cropped from main cross-section micrographs and different spatial descriptor functions are adopted to characterize the microstructures in terms of agglomeration and periodicity of the fibers. Detailed information about the adopted spatial descriptors and the algorithm implemented to identify the fiber distribution, as well as to define the location of cropped regions, are given. From the obtained statistical characterization results, the minimum size of the equival...
The generalized vortex lattice method for oscillating lifting surfaces in subsonic flow is extend... more The generalized vortex lattice method for oscillating lifting surfaces in subsonic flow is extended to the supersonic planar regime.
The velocity potential formulation is used to study the behavior of lifting surfaces oscillating ... more The velocity potential formulation is used to study the behavior of lifting surfaces oscillating harmonically in supersonic flow. Here the basic singularity is a doublet of constant density, corresponding to quadrilateral panels distributed over the wing and wake. The advantage of the present method over others available in the literature is the unification of the solution for the subsonic and supersonic regimes. Steady-state results are presented for both rectangular and delta wings, and they compare very well with analytical results when the wing aspect ratio is varied. Unsteady results along the symmetry line for a pitching rectangular wing are also presented, and again the agreement is excellent with bidimensional values. Finally, generalized aerodynamic coefficients are calculated and compared with several results available in the literature.
The problem of panel flutter is considered in the case of a free-molecule flow, the effect of the... more The problem of panel flutter is considered in the case of a free-molecule flow, the effect of the aerodynamic shear stress being incorporated into the structural model through distributed longitudinal and bending moment loads. This kind of analysis is relevant in the case of hypersonic flight vehicles, like the NASP, especially because in these conditions the shear stress can be expected to be considerably larger that the pressure at a given point. The aerodynamic loading is derived assuming a quasi-steady approximation. Two important parameters are given by alpha-m, the 'momentum accommodation coefficient', and Theta, the temperature ratio between the panel temperature and the temperature of the undisturbed flow. For high enough values of Theta the variation of the linear flutter parameter with alpha-m is close to linear. Comparison with continuum theory, given by linear piston theory, depends on the values of Theta and alpha-m considered. Finally, it is shown that buckling...
Panel flutter is a form of dynamic aeroelastic instability resulting from the interaction between... more Panel flutter is a form of dynamic aeroelastic instability resulting from the interaction between motion of an aircraft structural panel and the aerodynamic loads exerted on that panel by air flowing past one of the faces. It differs from lifting surface flutter in the sense that it is not usually catastrophic, the panel's motion being limited by nonlinear membrane stresses produced by the transverse displacement. Above some critical airflow condition, the linear instability grows to a limit cycle . The present investigation studies panel flutter in an aerodynamic regime known as 'free molecule flow', wherein intermolecular collisions can be neglected and loads are caused by interactions between individual molecules and the bounding surface. After collision with the panel, molecules may be reflected specularly or reemitted in diffuse fashion. Two parameters characterize this process: the 'momentum accommodation coefficient', which is the fraction of the specularl...
Some alloys with fine-grain size can present, under certain conditions, a very high ductility and... more Some alloys with fine-grain size can present, under certain conditions, a very high ductility and large deformations before rupturing occurs; a condition known as superplasticity. Superplastic forming (SPF) is a technique that takes advantage of this material’s behavior and consists of heating a metallic blank up to a suitable temperature and blow forming it under gas pressure into a die. There is a growing interest in this manufacturing process in many different areas, such as aeronautical, automotive and medical, due to the possibility of manufacturing complex, lightweight geometries, and strong thin shell parts. In this study, analytical approach is used to predict the optimum gas pressure for forming the blank, in order to maintain a controlled strain rate, ensuring superplastic behavior. Two domes are formed using aluminum and titanium, to test the pressure curves and study the phenomena related to superplastic forming.
In this article, the structural behavior of co-cured composite joint (CC), co-bonded composite jo... more In this article, the structural behavior of co-cured composite joint (CC), co-bonded composite joint (CB), and secondary-bonded composite joint (SB) under Mode II fatigue loading was evaluated. Fatigue performance was evaluated in sub-critical strain energy release rate (SERR) associated with Mode II fatigue induced delamination growth onset. Fatigue tests were carried out using the three-point bending End Notched Flexure test setup for different energy ratios. The experimental results are presented in terms of SERR versus number of cycles, and the SERR threshold for no growth is determined (Gth). Fractographic analyses were performed in order to identify the main failure mechanisms related to each joining technology under Mode II. The results indicated an initial cohesive failure followed by an adhesive failure promoted by crack propagation at the interface between the adhesive and the composite adherend on SB and CB samples, through the coalescence of microcracks that promote the ...
The International Journal of Advanced Manufacturing Technology
The search for lighter and more resistant structures contributed to the development of effective ... more The search for lighter and more resistant structures contributed to the development of effective welding methods. Among them, friction stir welding, a recent technique patented in 1991, in which welding is performed by the friction between a rotating tool and the materials to be welded, has widely been studied in the last decades. Among the advantages the technique provides, are the possibility of welding aluminum alloys series 2xxx and 7xxx, and the possibility of welding materials of different chemical compositions. The industry is still cautious about using this technique, yet several studies have been performed to improve knowledge on it. This research investigated the three dissimilar junctions between aluminum alloys 2024-T4 and 7475-T6 with titanium alloy Ti6Al4V. The aluminum alloys were positioned on the top portion of the welding creating a butt weld. The titanium alloy was placed on the bottom portion of the weld creating a lap welding with the aluminum alloy. The parameters of rotation, welding speed, and tilt were varied, following a central composite experimental design. Through the response surface analysis, it was possible to identify the correlation between the input and output parameters. This correlation is used to identify main influence between the parameters and can be used to optimization of the process. The influences of these parameters were evaluated on the welding surface by measuring residual stress and microhardness. The residual stress was analyzed by the hole drilling method on the aluminum side and by X-ray diffraction on the titanium side. The microhardness was analyzed by the Vickers test. On the aluminum side, residual stress and microhardness show a strong relation; high value of residual stress resulted in low value of microhardness. On the titanium side, residual stress shows a relation with temperature; the high value of temperature resulted in low value of stress. The tensile test was used to compare joint efficiency between different welding parameters and the base metal. It was possible to reach parameters in which the welding ultimate tensile stress exceeded the AA2024 value.
32nd Structures, Structural Dynamics, and Materials Conference
The panel flutter phenomenon is studied assuming free-molecule flow. This kind of analysis is rel... more The panel flutter phenomenon is studied assuming free-molecule flow. This kind of analysis is relevant in the case of hypersonic flight vehicles traveling at high altitudes, especially in the leeward portion of the vehicle. In these conditions the aerodynamic shear can be expected to be considerably larger than the pressure at a given point, so that the effects of such a loading are incorporated into the structural model. This is accomplished by introducing distributed longitudinal and bending moment loads. The former can lead to buckling of the panel, with the second mode in the case of a simply-supported panel playing a important role, and becoming the dominant mode in the solution. The presence of equivalent springs in the longitudinal direction at the panel's ends also becomes of relative importance, even for the evaluation of the linear flutter parameter. Finally, the behavior of the system is studied in the presence of applied compressive forces, that is, classical buckling.
Superplastic forming (SPF) is a technique that takes advantage of metallic alloys with fine grain... more Superplastic forming (SPF) is a technique that takes advantage of metallic alloys with fine grain size presenting very high ductility and large deformations before rupture under certain conditions. There is a growing interest in this manufacturing process in different areas, such as: aeronautical, automotive and medical, due to the possibility of fabricating complex geometry, lightweight, and strong thin shell parts. The researchers employed an industrial size superplastic hot press and, aiming to start investigations in the field of superplastic forming, finite element simulation and material analysis. This paper presents one of a first works in this field: developing a numerical model and forming a titanium alloy dome. A finite element model was developed to obtain the pressure curve, used as input in the superplastic forming machine control and for thickness prediction. Results and comparisons between the formed part and numerical calculations are presented, as well as the main d...
Many components for aerospace and automotive industries are currently manufactured using superpla... more Many components for aerospace and automotive industries are currently manufactured using superplastic forming, being the fine-grained aluminum alloy AA5083 widely used for this proposes. However, the development of cavitation voids is inherent in this process and reduces the ductility of the alloy. Back pressure can be used to diminish the growth of cavitation void. The experimental conditions used in this work are in the best condition for nucleation and grow of cavitation, because of the coarse grain size (81 µm), large second phase particles (9 µm) and elevated test temperature (570ºC) in a AA 5083. Domes were formed at 570ºC and at a strain rate of 5x10-5 s-1 by blow forming with and without back-pressure. They were compared in terms of their final shape, thickness distribution, and quantity of cavitation voids. The effectiveness of the usage of back pressure to reducing the quantity of cavitation void was analyzed.
The present work expands the application of Puck and Schürmann Inter-Fiber Fracture criterion to ... more The present work expands the application of Puck and Schürmann Inter-Fiber Fracture criterion to fiber reinforced thermoplastic 3D-printed composite materials. The effect of the ratio between the transverse compressive strength and the in-plane shear strength is discussed and a new transition point between the fracture conditions under compressive loading is proposed. The recommended values of the inclination parameters, as well as their effects on the proposed method, are also discussed. Failure envelopes are presented for different 3D-printed materials and also for traditional composite materials. The failure envelopes obtained here are compared to those provided by the original Puck and Schürmann criterion and to those provided by Gu and Chen. The differences between them are analyzed with the support of geometrical techniques and also statistical tools. It is demonstrated that the Expanded Puck and Schürmann is capable of providing more suitable failure envelopes for fiber reinf...
This present paper is devoted to the numerical and experimental investigation of the modal charac... more This present paper is devoted to the numerical and experimental investigation of the modal characteristics of composite laminates, with emphasis on damping. Complementing previous studies dedicated to conventional laminates, one considers variable-angle tow laminates, in which the fibers are deposited following curvilinear trajectories. The main objective is to characterize the influence of fiber steering on the damping levels, and evaluate the possibility of achieving increased damping. A dynamic model is derived by combining the semianalytical Rayleigh-Ritz approach, the Classical Lamination Theory, and the Strain Energy Method. This later enables to estimate the specific damping capacity of each vibration mode. Based on this model, analytical developments are performed aiming at putting in evidence the contribution of each strain component in each layer of the laminate to the specific damping capacities. The results of numerical simulations are presented, enabling to compare the values of specific damping capacities and vibration natural frequencies obtained for variableangle tow and conventional laminates in a variety of simulation scenarios. Some of the numerical results are validated by comparisons with experimental counterparts. The results confirm the effectiveness of design strategies intended to regulate and possibly increase the damping levels of composite laminates by exploring fiber steering.
IOP Conference Series: Materials Science and Engineering, 2018
This paper analyses the Mode II fatigue delamination growth onset for secondary bonded joints com... more This paper analyses the Mode II fatigue delamination growth onset for secondary bonded joints compared to co-cured joints. The materials used were composed by two carbon fiber reinforced sub-laminates joined by the secondary bonded and co-cured (without adhesive) methods. Mode II fatigue tests were performed using three-point bending End Notched Flexure test setup. The tests were performed under displacement control and a sinusoidal displacement applied at a frequency of 5 Hz with a Rd = 0.1, that mean, δmin = 0.1 δmax. The main objective of this study was to obtain the strain energy release rate (SEER) versus number of cycles (Nf) in order to evaluate the effect of the adhesive on fatigue life of bonded joints. A Closed form solution for 3-ENF setup was used in order to define the displacement amplitudes that were applied in the fatigue test. The results show that the use of adhesive causes a reduction on Mode II fatigue delamination growth onset SERR (Gth) for secondary-bonded compared to cocured joints. Finally, a scanning electron microscopy (SEM) was used to analyze the fracture surfaces of the Mode II secondary bonded specimens. The fractography images show no crack growth for the specimens tested below or at Gth loading levels, which indicated that the value corresponds to the threshold. Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.
This present paper is devoted to the numerical and experimental investigation of the modal charac... more This present paper is devoted to the numerical and experimental investigation of the modal characteristics of composite laminates, with emphasis on damping. Complementing previous studies dedicated to conventional laminates, one considers variable-angle tow laminates, in which the fibers are deposited following curvilinear trajectories. The main objective is to characterize the influence of fiber steering on the damping levels, and evaluate the possibility of achieving increased damping. A dynamic model is derived by combining the semianalytical Rayleigh-Ritz approach, the Classical Lamination Theory, and the Strain Energy Method. This later enables to estimate the specific damping capacity of each vibration mode. Based on this model, analytical developments are performed aiming at putting in evidence the contribution of each strain component in each layer of the laminate to the specific damping capacities. The results of numerical simulations are presented, enabling to compare the values of specific damping capacities and vibration natural frequencies obtained for variableangle tow and conventional laminates in a variety of simulation scenarios. Some of the numerical results are validated by comparisons with experimental counterparts. The results confirm the effectiveness of design strategies intended to regulate and possibly increase the damping levels of composite laminates by exploring fiber steering.
Recently, the success in new product development process has become one of the main competitive a... more Recently, the success in new product development process has become one of the main competitive advantages. Thus, many companies are looking for improving their new product development (NPD) process, to launching products as fast as possible with the required quality and low costs. To achieve such objectives, many organizations have designed phasedreview processes that cut across functional areas of the NPD. One such process with wide acceptance is the Phase Review Process. Phase Reviews are checkpoints that take place at key periods in the product development process to review the opportunity/development effort, assess it from a business and strategic perspective, and determine whether it is worthy to continue the development, redirect or kill it. New product development best practices usually include such processes, however little has been written on how to implement such practices. The available literature reports generic issues and recommendations, without describing a structured approach. This paper describes and analyzes a practical phase review implementation process, pointing out difficulties and stating recommendations to improve and support a successful implementation. The results, compiled after an industrial case study, show clearly the improvements achieved for the proposed implementation.
The present work describes a methodology to compute equivalent volumes representing the microstru... more The present work describes a methodology to compute equivalent volumes representing the microstructure of 3D-printed continuous fiber-reinforced thermoplastics, based on a statistical characterization of the fiber distribution. In contrast to recent work, the methodology herein presented determines the statistically equivalent fiber distribution directly from cross-section micrographs, instead of generating random fiber arrangements. For this purpose, several regions, with different sizes and from different locations, are cropped from main cross-section micrographs and different spatial descriptor functions are adopted to characterize the microstructures in terms of agglomeration and periodicity of the fibers. Detailed information about the adopted spatial descriptors and the algorithm implemented to identify the fiber distribution, as well as to define the location of cropped regions, are given. From the obtained statistical characterization results, the minimum size of the equival...
The generalized vortex lattice method for oscillating lifting surfaces in subsonic flow is extend... more The generalized vortex lattice method for oscillating lifting surfaces in subsonic flow is extended to the supersonic planar regime.
The velocity potential formulation is used to study the behavior of lifting surfaces oscillating ... more The velocity potential formulation is used to study the behavior of lifting surfaces oscillating harmonically in supersonic flow. Here the basic singularity is a doublet of constant density, corresponding to quadrilateral panels distributed over the wing and wake. The advantage of the present method over others available in the literature is the unification of the solution for the subsonic and supersonic regimes. Steady-state results are presented for both rectangular and delta wings, and they compare very well with analytical results when the wing aspect ratio is varied. Unsteady results along the symmetry line for a pitching rectangular wing are also presented, and again the agreement is excellent with bidimensional values. Finally, generalized aerodynamic coefficients are calculated and compared with several results available in the literature.
The problem of panel flutter is considered in the case of a free-molecule flow, the effect of the... more The problem of panel flutter is considered in the case of a free-molecule flow, the effect of the aerodynamic shear stress being incorporated into the structural model through distributed longitudinal and bending moment loads. This kind of analysis is relevant in the case of hypersonic flight vehicles, like the NASP, especially because in these conditions the shear stress can be expected to be considerably larger that the pressure at a given point. The aerodynamic loading is derived assuming a quasi-steady approximation. Two important parameters are given by alpha-m, the 'momentum accommodation coefficient', and Theta, the temperature ratio between the panel temperature and the temperature of the undisturbed flow. For high enough values of Theta the variation of the linear flutter parameter with alpha-m is close to linear. Comparison with continuum theory, given by linear piston theory, depends on the values of Theta and alpha-m considered. Finally, it is shown that buckling...
Panel flutter is a form of dynamic aeroelastic instability resulting from the interaction between... more Panel flutter is a form of dynamic aeroelastic instability resulting from the interaction between motion of an aircraft structural panel and the aerodynamic loads exerted on that panel by air flowing past one of the faces. It differs from lifting surface flutter in the sense that it is not usually catastrophic, the panel's motion being limited by nonlinear membrane stresses produced by the transverse displacement. Above some critical airflow condition, the linear instability grows to a limit cycle . The present investigation studies panel flutter in an aerodynamic regime known as 'free molecule flow', wherein intermolecular collisions can be neglected and loads are caused by interactions between individual molecules and the bounding surface. After collision with the panel, molecules may be reflected specularly or reemitted in diffuse fashion. Two parameters characterize this process: the 'momentum accommodation coefficient', which is the fraction of the specularl...
Some alloys with fine-grain size can present, under certain conditions, a very high ductility and... more Some alloys with fine-grain size can present, under certain conditions, a very high ductility and large deformations before rupturing occurs; a condition known as superplasticity. Superplastic forming (SPF) is a technique that takes advantage of this material’s behavior and consists of heating a metallic blank up to a suitable temperature and blow forming it under gas pressure into a die. There is a growing interest in this manufacturing process in many different areas, such as aeronautical, automotive and medical, due to the possibility of manufacturing complex, lightweight geometries, and strong thin shell parts. In this study, analytical approach is used to predict the optimum gas pressure for forming the blank, in order to maintain a controlled strain rate, ensuring superplastic behavior. Two domes are formed using aluminum and titanium, to test the pressure curves and study the phenomena related to superplastic forming.
In this article, the structural behavior of co-cured composite joint (CC), co-bonded composite jo... more In this article, the structural behavior of co-cured composite joint (CC), co-bonded composite joint (CB), and secondary-bonded composite joint (SB) under Mode II fatigue loading was evaluated. Fatigue performance was evaluated in sub-critical strain energy release rate (SERR) associated with Mode II fatigue induced delamination growth onset. Fatigue tests were carried out using the three-point bending End Notched Flexure test setup for different energy ratios. The experimental results are presented in terms of SERR versus number of cycles, and the SERR threshold for no growth is determined (Gth). Fractographic analyses were performed in order to identify the main failure mechanisms related to each joining technology under Mode II. The results indicated an initial cohesive failure followed by an adhesive failure promoted by crack propagation at the interface between the adhesive and the composite adherend on SB and CB samples, through the coalescence of microcracks that promote the ...
The International Journal of Advanced Manufacturing Technology
The search for lighter and more resistant structures contributed to the development of effective ... more The search for lighter and more resistant structures contributed to the development of effective welding methods. Among them, friction stir welding, a recent technique patented in 1991, in which welding is performed by the friction between a rotating tool and the materials to be welded, has widely been studied in the last decades. Among the advantages the technique provides, are the possibility of welding aluminum alloys series 2xxx and 7xxx, and the possibility of welding materials of different chemical compositions. The industry is still cautious about using this technique, yet several studies have been performed to improve knowledge on it. This research investigated the three dissimilar junctions between aluminum alloys 2024-T4 and 7475-T6 with titanium alloy Ti6Al4V. The aluminum alloys were positioned on the top portion of the welding creating a butt weld. The titanium alloy was placed on the bottom portion of the weld creating a lap welding with the aluminum alloy. The parameters of rotation, welding speed, and tilt were varied, following a central composite experimental design. Through the response surface analysis, it was possible to identify the correlation between the input and output parameters. This correlation is used to identify main influence between the parameters and can be used to optimization of the process. The influences of these parameters were evaluated on the welding surface by measuring residual stress and microhardness. The residual stress was analyzed by the hole drilling method on the aluminum side and by X-ray diffraction on the titanium side. The microhardness was analyzed by the Vickers test. On the aluminum side, residual stress and microhardness show a strong relation; high value of residual stress resulted in low value of microhardness. On the titanium side, residual stress shows a relation with temperature; the high value of temperature resulted in low value of stress. The tensile test was used to compare joint efficiency between different welding parameters and the base metal. It was possible to reach parameters in which the welding ultimate tensile stress exceeded the AA2024 value.
32nd Structures, Structural Dynamics, and Materials Conference
The panel flutter phenomenon is studied assuming free-molecule flow. This kind of analysis is rel... more The panel flutter phenomenon is studied assuming free-molecule flow. This kind of analysis is relevant in the case of hypersonic flight vehicles traveling at high altitudes, especially in the leeward portion of the vehicle. In these conditions the aerodynamic shear can be expected to be considerably larger than the pressure at a given point, so that the effects of such a loading are incorporated into the structural model. This is accomplished by introducing distributed longitudinal and bending moment loads. The former can lead to buckling of the panel, with the second mode in the case of a simply-supported panel playing a important role, and becoming the dominant mode in the solution. The presence of equivalent springs in the longitudinal direction at the panel's ends also becomes of relative importance, even for the evaluation of the linear flutter parameter. Finally, the behavior of the system is studied in the presence of applied compressive forces, that is, classical buckling.
Superplastic forming (SPF) is a technique that takes advantage of metallic alloys with fine grain... more Superplastic forming (SPF) is a technique that takes advantage of metallic alloys with fine grain size presenting very high ductility and large deformations before rupture under certain conditions. There is a growing interest in this manufacturing process in different areas, such as: aeronautical, automotive and medical, due to the possibility of fabricating complex geometry, lightweight, and strong thin shell parts. The researchers employed an industrial size superplastic hot press and, aiming to start investigations in the field of superplastic forming, finite element simulation and material analysis. This paper presents one of a first works in this field: developing a numerical model and forming a titanium alloy dome. A finite element model was developed to obtain the pressure curve, used as input in the superplastic forming machine control and for thickness prediction. Results and comparisons between the formed part and numerical calculations are presented, as well as the main d...
Many components for aerospace and automotive industries are currently manufactured using superpla... more Many components for aerospace and automotive industries are currently manufactured using superplastic forming, being the fine-grained aluminum alloy AA5083 widely used for this proposes. However, the development of cavitation voids is inherent in this process and reduces the ductility of the alloy. Back pressure can be used to diminish the growth of cavitation void. The experimental conditions used in this work are in the best condition for nucleation and grow of cavitation, because of the coarse grain size (81 µm), large second phase particles (9 µm) and elevated test temperature (570ºC) in a AA 5083. Domes were formed at 570ºC and at a strain rate of 5x10-5 s-1 by blow forming with and without back-pressure. They were compared in terms of their final shape, thickness distribution, and quantity of cavitation voids. The effectiveness of the usage of back pressure to reducing the quantity of cavitation void was analyzed.
The present work expands the application of Puck and Schürmann Inter-Fiber Fracture criterion to ... more The present work expands the application of Puck and Schürmann Inter-Fiber Fracture criterion to fiber reinforced thermoplastic 3D-printed composite materials. The effect of the ratio between the transverse compressive strength and the in-plane shear strength is discussed and a new transition point between the fracture conditions under compressive loading is proposed. The recommended values of the inclination parameters, as well as their effects on the proposed method, are also discussed. Failure envelopes are presented for different 3D-printed materials and also for traditional composite materials. The failure envelopes obtained here are compared to those provided by the original Puck and Schürmann criterion and to those provided by Gu and Chen. The differences between them are analyzed with the support of geometrical techniques and also statistical tools. It is demonstrated that the Expanded Puck and Schürmann is capable of providing more suitable failure envelopes for fiber reinf...
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