Composites Part A-applied Science and Manufacturing, 2003
Purpose of the paper is to investigate the possibility of extending the interlaminar shear streng... more Purpose of the paper is to investigate the possibility of extending the interlaminar shear strength (ILSS) results obtained by four-point bend testing of unidirectional laminates to multidirectional laminates, such as cross-ply and quasi-isotropic, the testing of which is a common practice in the industry but has not been previously validated in the literature. An experimental database is gathered through the known modified version of the ASTM D2344 short beam test and the results show a surprising proximity of results for the three different fiber architectures for the same composite system. Various finite element analyses were developed using ANSYS w software, allowing for better insight on the mechanics of delamination in four-point bending, and showed extremely good agreement with the experimental values. The final and most accurate model partially confirmed observations made by other authors, and includes the 'skewed' profile of the shear stress through the thickness and its variation along the length, the distribution of the shear stress across the width, the location of delamination initiation and propagation and maximum ILSS and the shear stress contour. q
Recent research programs conducted on low-velocity impact events on composite structures have use... more Recent research programs conducted on low-velocity impact events on composite structures have used force as the sole governing parameter and based their damage resistance and tolerance considerations on the peak recorded value. Understanding of other available parameters, such as contact duration and coefficient of restitution, which are related to the effective structural stiffness of the target, is fundamental in the design of a methodology for assessing impact performance and can offer greater insight in the interpretation of future research programs. An experimental database is gathered through drop tower impact testing by means of a rigid striker on clamped circular plates, for a particular polymer composite system. Several researchers have presented data showing that a critical value of the impact force for the onset of damage exists. Structural properties are hereby studied in both the sub-and supercritical regimes, which means for impact energy values below and above the damage threshold. A modified approach to the classic spring-mass model, which employs the notions of damaged stiffness and dissipated energy, leads to the derivation of approximate formulas that describe the peak force-energy curve. In particular, the introduction of a dashpot to simulate the effect of damage greatly improves the accuracy of the model in the regime beyond the structural integrity threshold. A novel method to assess the residual performance of the damaged plate is developed, and it consists in low-energy, nondestructive impact testing, the results from which bear a striking resemblance with the curves obtained by compression after impact.
Carbon fibre composites can offer a great deal of weight saving and manufacturing flexibility in ... more Carbon fibre composites can offer a great deal of weight saving and manufacturing flexibility in the design of a high performance vehicle, while decades of research in metal science have produced manufacturing techniques that guarantee perfect surface finish, alloys that can withstand weathering agents during the lifetime of a vehicle and very reliable joining methods, these relatively new materials require constant evaluation in automotive applications to ensure equal if not greater performance than their metallic counterpart. This paper highlights the fundamental contributions of advanced composites in the production of the body panels and integrated chassis components for the Murcièlago and Murcièlago Roadster.
Composites Part A-applied Science and Manufacturing, 2010
An energy-absorbing composite sandwich structural concept, comprised of a deep honeycomb core wit... more An energy-absorbing composite sandwich structural concept, comprised of a deep honeycomb core with carbon/epoxy facesheets, is subject to through-thickness crushing and penetration using a cylindrical pole. With the aid of the building block approach, the response of the structure is predicted by analysis supported by test evidence. Experiments are conducted at various levels of complexity, from the coupon level used
Damage is inflicted on carbon-fiber/epoxy composite plates using both simulated lightning strike ... more Damage is inflicted on carbon-fiber/epoxy composite plates using both simulated lightning strike and mechanical impact in the effort to understand the relative effect of the two damage mechanisms. A methodology is proposed to characterize the damage resistance and tolerance of unconfigured composite plates subjected to lightning strike in a fashion that is consistent with the extensive work previously done on low-velocity impact. Using current and voltage diagnostics, it is possible to extrapolate the amount of electromechanical energy absorbed by the plate during the strike and compare it to that absorbed during a mechanical impact. Damage resistance is characterized by means of ultrasonic C-scans and microscopy, whereas residual strength is measured by means of compression after impact testing. Results show that the energy dissipated in a specimen during the lightning strike is much greater than the strain energy introduced by mechanical impact, and hence a comparison based on energy is not recommended. However, based on the relative threat levels associated with the impact and the lightning strike events, the comparison yields insightful observations on both damage state and residual performance. In general, for the configurations tested, lightning strike damage seems to be less detrimental than the mechanical impact in terms of both damage area and residual strength. †
When modern saloon cars are re-engineered as convertibles (or roadsters) it is typical for them t... more When modern saloon cars are re-engineered as convertibles (or roadsters) it is typical for them to lose 50% or more of the body's torsional rigidity. Consequently the vehicles rarely handle quite as crisply, nor do they ride as well as the coupes from which they derived. This paper highlights the fundamental contributions of advanced composites in achieving the desired value of handling of the Murcièlago Roadster without penalizing the overall weight of the vehicle. To compensate for the absence of the roof structure, the vehicle was strongly redesigned by introducing new structural members and reinforcing existing critical components. A new all-carbon/epoxy composite sub-frame, which spans the entire engine bay, is comprised of elliptical tubular members, and it is the first of its kind in a production vehicle. Engineering of the sub-frame, from preliminary design to manufacturing decisions, is the focus of this paper, and is achieved through a Building Block approach that sets the program within the Integrated Product Development (IPD) strategy that the Advanced Composites Division of Automobili Lamborghini S.p.A. employs for its technology demonstrators. The strategy consists in a concurrent analytical and experimental development of the product, from the initial conceptual design and coupon testing, through the stages of element and subcomponent engineering, to final component manufacturing.
Solid carbon fiber/epoxy laminates manufactured by liquid resin infusion of twill fabric reinforc... more Solid carbon fiber/epoxy laminates manufactured by liquid resin infusion of twill fabric reinforcement are recycled in a bath of boiling sulfuric acid to separate the fibers from the matrix. The recycled reinforcement consists of long fibers arranged in a random, entangled mat. Using the same epoxy matrix and infusion materials and process, the recycled fibers are reutilized to manufacture solid laminates. The physical properties of the recycled laminates are evaluated by means of pulse-echo ultrasound, visual microscopy, and fiber volume content. The average fiber volume content of the recycled laminates is 33%, compared to the 62% of the twill laminates. The mechanical properties of the recycled composite include tension modulus and strength, compression modulus and strength, three-point bend flexure strength, and short beam shear strength. The properties are compared against the values of the twill reinforcement with quasiisotropic stacking sequence. Results show that the recycled material offers promising elastic properties and strength values, similar to those of advanced carbon fiber sheet molding compounds, and therefore can be used as structural material.
While previous researchers have conducted their study on the relative impact performance of compo... more While previous researchers have conducted their study on the relative impact performance of composite structures from a force or an energy standpoint only, this proposed Composite Structure Impact Performance Assessment Program (CSIPAP) suggests a multi-parameter methodology to gain further insight in the impact behavior of composite structures. These are peak and critical force; critical and dissipated energy; contact duration and coefficient of restitution (COR), which is direct indication of effective structural stiffness; and residual stiffness (normalized contact duration) which yields a plot that bears a striking resemblance with the normalized Compression After Impact (CAI) strength. Using a determinate impactor/target system as baseline configuration, the program is applied toward the understanding of the role played in an impact event by fundamental impactor and target parameters. The equations previously derived for the prediction of the force-energy and residual stiffness curves are shown to apply to the configurations tested, thus confirming their general validity. A modification to the existing effective structural stiffness formulation, which does not account for impactor characteristics, is proposed, and it comprises the impactor material, size and mass characteristics.
Composites Part A-applied Science and Manufacturing, 2009
Carbon/epoxy square tubes and channel sections have been used in modern automotive and aircraft s... more Carbon/epoxy square tubes and channel sections have been used in modern automotive and aircraft structures, respectively, as dedicated components designed to dissipate energy under controlled collapse. However, there are currently no specialized test methods for the characterization of Specific Energy Absorption (SEA) of composite materials. A systematic experimental investigation is conducted to evaluate the effect of geometric features on crush behavior. From a square tube, individual test segments are machined in order to isolate corner radii and flat sections of varying sizes, for a total of five different test geometries. Laminate thickness, material system, manufacturing process, and test methodology are kept constant throughout the study. For the material system and lay-up considered in this study, fiber tensile fracture and tearing at the corners is responsible for the vast percentage of the energy absorbed, while frond formation and splaying of the flat segments is responsible for a much lower percentage. An analytical expression is derived that accounts for the combined behavior of corner elements and flat segments in the crush behavior of more complex test articles, such as tubes.
Composites Part A-applied Science and Manufacturing, 2010
Recent composite technology research and development efforts have focused on discontinuous carbon... more Recent composite technology research and development efforts have focused on discontinuous carbon fiber/epoxy molding systems derived from chopped aerospace-grade unidirectional tape prepreg. Although the average elastic modulus of this material has been shown to be as high as that of the continuous tape quasi-isotropic benchmark, experimental measurement by means of strain gage or extensometer has shown variation as high as
Composites Part A-applied Science and Manufacturing, 2009
The elastic behavior and failure response of discontinuous carbon fiber/epoxy laminates produced ... more The elastic behavior and failure response of discontinuous carbon fiber/epoxy laminates produced by compression molding of randomly-oriented preimpregnated unidirectional tape is characterized. Commercial applications for this type of material form already exist, such as Hexcel HexMC Ò . Complex relationships between unnotched and notched tensile strengths are observed, and show this material to be particularly notch-insensitive. A parametric study on the effect of specimen thickness, width, diameter/ width ratio, and hole size yields fundamental information on the behavior of this material.
One of the key factors preventing the widespread adoption of composites in primary crash structur... more One of the key factors preventing the widespread adoption of composites in primary crash structures is the absence of specialized test methods for the characterization of specific energy absorption (SEA). Aside from thin-walled tubular specimens, a limited number of attempts have been made at developing test specimens that are easier to manufacture. The possibility to employ a self-stabilizing corrugated plate
Composites Part A-applied Science and Manufacturing, 2003
The present research examines analytically and experimentally the mixed mode interlaminar fractur... more The present research examines analytically and experimentally the mixed mode interlaminar fracture toughness of a resin film infused (RFI) carbon fiber/epoxy laminate, namely a IM7-AS4/3501-6 hybrid composite system. The inability to develop representative interlaminar failure in composites with current mixed mode test configurations motivated this particular investigation. The paper is part of a more extensive research effort concerned with the effects of stitching upon the mixed mode fracture toughness of a RFI composite.
Journal of Reinforced Plastics and Composites, 2008
Abstract This paper quantifies the elastic behavior and failure response of discontinuous carbon ... more Abstract This paper quantifies the elastic behavior and failure response of discontinuous carbon fiber/epoxy laminates produced by compression molding of randomly oriented preimpregnated unidirectional tape. Flat plates have been successfully molded using ...
This paper seeks to quantify the influence of fiber length on the mechanical properties of discon... more This paper seeks to quantify the influence of fiber length on the mechanical properties of discontinuous carbon fiber/ epoxy laminates produced by compression molding. New interest is being generated toward low-cost composite material forms for aerospace applications, as shown by the structural window frames on the Boeing 787 Dreamliner. The high-volume carbon fiber content, combined with aerospace-qualified epoxy resins, opens up opportunities for more aircraft parts to be made of non-metallic materials. This material-process combination is ideal for large volume production of three-dimensional parts, allowing for the molding of complex contours, thickness variations, and stiffening ribs. Interesting relationships between fiber length and tensile, compressive, and flexural moduli and strengths are observed.
Composites Part A-applied Science and Manufacturing, 2010
Recent composite technology research and development efforts have focused on discontinuous carbon... more Recent composite technology research and development efforts have focused on discontinuous carbon fiber/epoxy molding systems derived from chopped aerospace-grade unidirectional tape prepreg. This study analyzes in detail the meso-structure of this class ...
Abstract The elastic modulus of discontinuous carbon fiber/epoxy laminates produced by compressio... more Abstract The elastic modulus of discontinuous carbon fiber/epoxy laminates produced by compression molding of chopped unidirectional prepreg tape is measured by several means. Commercial applications for this type of material form already exist, such as ...
Composites Part A-applied Science and Manufacturing, 2009
Damage is inflicted in a series of carbon fiber/epoxy composite specimens using a simulated light... more Damage is inflicted in a series of carbon fiber/epoxy composite specimens using a simulated lightning strike generator in the effort to understand the fundamental damage response of this material form. The strikes up to 50,000 A and 28,000 V are inflicted on both pristine specimens and specimens containing a Hilok stainless steel fastener. Damage area is evaluated via ultrasonic scanning, and advanced optical microscopy is used to gain further understanding in the morphology of damage. Subsequent mechanical testing to assess the residual tensile and compressive strength and modulus of the material is performed according to ASTM standards. Results show that residual tension strength counter intuitively increases after the infliction of damage, while residual compressive strength is much more dramatically and negatively affected. Furthermore, the presence of the fastener influences dramatically both the state of damage in the specimen and its residual strength by spreading throughout the thickness rather than limiting it to the specimen surface.
One of the key factors preventing the widespread adoption of composites in primary crash structur... more One of the key factors preventing the widespread adoption of composites in primary crash structures is the absence of specialized test methods for the characterization of specific energy absorption (SEA). Aside from thin-walled tubular specimens, a limited number of attempts have been made at using a plate specimen, which is easier to manufacture but requires complex anti-buckling fixtures. A new method, featuring a corrugated plate, which can be easily manufactured and is self-stabilizing and hence does not require a dedicated test fixture, is suggested here. A systematic investigation is performed to validate the possibility of using such specimen to screen candidate material systems and laminate designs, with the specific goal of isolating the sensitivity of the method to intrinsic specimen parameters.
Composites Part A-applied Science and Manufacturing, 2003
Purpose of the paper is to investigate the possibility of extending the interlaminar shear streng... more Purpose of the paper is to investigate the possibility of extending the interlaminar shear strength (ILSS) results obtained by four-point bend testing of unidirectional laminates to multidirectional laminates, such as cross-ply and quasi-isotropic, the testing of which is a common practice in the industry but has not been previously validated in the literature. An experimental database is gathered through the known modified version of the ASTM D2344 short beam test and the results show a surprising proximity of results for the three different fiber architectures for the same composite system. Various finite element analyses were developed using ANSYS w software, allowing for better insight on the mechanics of delamination in four-point bending, and showed extremely good agreement with the experimental values. The final and most accurate model partially confirmed observations made by other authors, and includes the 'skewed' profile of the shear stress through the thickness and its variation along the length, the distribution of the shear stress across the width, the location of delamination initiation and propagation and maximum ILSS and the shear stress contour. q
Recent research programs conducted on low-velocity impact events on composite structures have use... more Recent research programs conducted on low-velocity impact events on composite structures have used force as the sole governing parameter and based their damage resistance and tolerance considerations on the peak recorded value. Understanding of other available parameters, such as contact duration and coefficient of restitution, which are related to the effective structural stiffness of the target, is fundamental in the design of a methodology for assessing impact performance and can offer greater insight in the interpretation of future research programs. An experimental database is gathered through drop tower impact testing by means of a rigid striker on clamped circular plates, for a particular polymer composite system. Several researchers have presented data showing that a critical value of the impact force for the onset of damage exists. Structural properties are hereby studied in both the sub-and supercritical regimes, which means for impact energy values below and above the damage threshold. A modified approach to the classic spring-mass model, which employs the notions of damaged stiffness and dissipated energy, leads to the derivation of approximate formulas that describe the peak force-energy curve. In particular, the introduction of a dashpot to simulate the effect of damage greatly improves the accuracy of the model in the regime beyond the structural integrity threshold. A novel method to assess the residual performance of the damaged plate is developed, and it consists in low-energy, nondestructive impact testing, the results from which bear a striking resemblance with the curves obtained by compression after impact.
Carbon fibre composites can offer a great deal of weight saving and manufacturing flexibility in ... more Carbon fibre composites can offer a great deal of weight saving and manufacturing flexibility in the design of a high performance vehicle, while decades of research in metal science have produced manufacturing techniques that guarantee perfect surface finish, alloys that can withstand weathering agents during the lifetime of a vehicle and very reliable joining methods, these relatively new materials require constant evaluation in automotive applications to ensure equal if not greater performance than their metallic counterpart. This paper highlights the fundamental contributions of advanced composites in the production of the body panels and integrated chassis components for the Murcièlago and Murcièlago Roadster.
Composites Part A-applied Science and Manufacturing, 2010
An energy-absorbing composite sandwich structural concept, comprised of a deep honeycomb core wit... more An energy-absorbing composite sandwich structural concept, comprised of a deep honeycomb core with carbon/epoxy facesheets, is subject to through-thickness crushing and penetration using a cylindrical pole. With the aid of the building block approach, the response of the structure is predicted by analysis supported by test evidence. Experiments are conducted at various levels of complexity, from the coupon level used
Damage is inflicted on carbon-fiber/epoxy composite plates using both simulated lightning strike ... more Damage is inflicted on carbon-fiber/epoxy composite plates using both simulated lightning strike and mechanical impact in the effort to understand the relative effect of the two damage mechanisms. A methodology is proposed to characterize the damage resistance and tolerance of unconfigured composite plates subjected to lightning strike in a fashion that is consistent with the extensive work previously done on low-velocity impact. Using current and voltage diagnostics, it is possible to extrapolate the amount of electromechanical energy absorbed by the plate during the strike and compare it to that absorbed during a mechanical impact. Damage resistance is characterized by means of ultrasonic C-scans and microscopy, whereas residual strength is measured by means of compression after impact testing. Results show that the energy dissipated in a specimen during the lightning strike is much greater than the strain energy introduced by mechanical impact, and hence a comparison based on energy is not recommended. However, based on the relative threat levels associated with the impact and the lightning strike events, the comparison yields insightful observations on both damage state and residual performance. In general, for the configurations tested, lightning strike damage seems to be less detrimental than the mechanical impact in terms of both damage area and residual strength. †
When modern saloon cars are re-engineered as convertibles (or roadsters) it is typical for them t... more When modern saloon cars are re-engineered as convertibles (or roadsters) it is typical for them to lose 50% or more of the body's torsional rigidity. Consequently the vehicles rarely handle quite as crisply, nor do they ride as well as the coupes from which they derived. This paper highlights the fundamental contributions of advanced composites in achieving the desired value of handling of the Murcièlago Roadster without penalizing the overall weight of the vehicle. To compensate for the absence of the roof structure, the vehicle was strongly redesigned by introducing new structural members and reinforcing existing critical components. A new all-carbon/epoxy composite sub-frame, which spans the entire engine bay, is comprised of elliptical tubular members, and it is the first of its kind in a production vehicle. Engineering of the sub-frame, from preliminary design to manufacturing decisions, is the focus of this paper, and is achieved through a Building Block approach that sets the program within the Integrated Product Development (IPD) strategy that the Advanced Composites Division of Automobili Lamborghini S.p.A. employs for its technology demonstrators. The strategy consists in a concurrent analytical and experimental development of the product, from the initial conceptual design and coupon testing, through the stages of element and subcomponent engineering, to final component manufacturing.
Solid carbon fiber/epoxy laminates manufactured by liquid resin infusion of twill fabric reinforc... more Solid carbon fiber/epoxy laminates manufactured by liquid resin infusion of twill fabric reinforcement are recycled in a bath of boiling sulfuric acid to separate the fibers from the matrix. The recycled reinforcement consists of long fibers arranged in a random, entangled mat. Using the same epoxy matrix and infusion materials and process, the recycled fibers are reutilized to manufacture solid laminates. The physical properties of the recycled laminates are evaluated by means of pulse-echo ultrasound, visual microscopy, and fiber volume content. The average fiber volume content of the recycled laminates is 33%, compared to the 62% of the twill laminates. The mechanical properties of the recycled composite include tension modulus and strength, compression modulus and strength, three-point bend flexure strength, and short beam shear strength. The properties are compared against the values of the twill reinforcement with quasiisotropic stacking sequence. Results show that the recycled material offers promising elastic properties and strength values, similar to those of advanced carbon fiber sheet molding compounds, and therefore can be used as structural material.
While previous researchers have conducted their study on the relative impact performance of compo... more While previous researchers have conducted their study on the relative impact performance of composite structures from a force or an energy standpoint only, this proposed Composite Structure Impact Performance Assessment Program (CSIPAP) suggests a multi-parameter methodology to gain further insight in the impact behavior of composite structures. These are peak and critical force; critical and dissipated energy; contact duration and coefficient of restitution (COR), which is direct indication of effective structural stiffness; and residual stiffness (normalized contact duration) which yields a plot that bears a striking resemblance with the normalized Compression After Impact (CAI) strength. Using a determinate impactor/target system as baseline configuration, the program is applied toward the understanding of the role played in an impact event by fundamental impactor and target parameters. The equations previously derived for the prediction of the force-energy and residual stiffness curves are shown to apply to the configurations tested, thus confirming their general validity. A modification to the existing effective structural stiffness formulation, which does not account for impactor characteristics, is proposed, and it comprises the impactor material, size and mass characteristics.
Composites Part A-applied Science and Manufacturing, 2009
Carbon/epoxy square tubes and channel sections have been used in modern automotive and aircraft s... more Carbon/epoxy square tubes and channel sections have been used in modern automotive and aircraft structures, respectively, as dedicated components designed to dissipate energy under controlled collapse. However, there are currently no specialized test methods for the characterization of Specific Energy Absorption (SEA) of composite materials. A systematic experimental investigation is conducted to evaluate the effect of geometric features on crush behavior. From a square tube, individual test segments are machined in order to isolate corner radii and flat sections of varying sizes, for a total of five different test geometries. Laminate thickness, material system, manufacturing process, and test methodology are kept constant throughout the study. For the material system and lay-up considered in this study, fiber tensile fracture and tearing at the corners is responsible for the vast percentage of the energy absorbed, while frond formation and splaying of the flat segments is responsible for a much lower percentage. An analytical expression is derived that accounts for the combined behavior of corner elements and flat segments in the crush behavior of more complex test articles, such as tubes.
Composites Part A-applied Science and Manufacturing, 2010
Recent composite technology research and development efforts have focused on discontinuous carbon... more Recent composite technology research and development efforts have focused on discontinuous carbon fiber/epoxy molding systems derived from chopped aerospace-grade unidirectional tape prepreg. Although the average elastic modulus of this material has been shown to be as high as that of the continuous tape quasi-isotropic benchmark, experimental measurement by means of strain gage or extensometer has shown variation as high as
Composites Part A-applied Science and Manufacturing, 2009
The elastic behavior and failure response of discontinuous carbon fiber/epoxy laminates produced ... more The elastic behavior and failure response of discontinuous carbon fiber/epoxy laminates produced by compression molding of randomly-oriented preimpregnated unidirectional tape is characterized. Commercial applications for this type of material form already exist, such as Hexcel HexMC Ò . Complex relationships between unnotched and notched tensile strengths are observed, and show this material to be particularly notch-insensitive. A parametric study on the effect of specimen thickness, width, diameter/ width ratio, and hole size yields fundamental information on the behavior of this material.
One of the key factors preventing the widespread adoption of composites in primary crash structur... more One of the key factors preventing the widespread adoption of composites in primary crash structures is the absence of specialized test methods for the characterization of specific energy absorption (SEA). Aside from thin-walled tubular specimens, a limited number of attempts have been made at developing test specimens that are easier to manufacture. The possibility to employ a self-stabilizing corrugated plate
Composites Part A-applied Science and Manufacturing, 2003
The present research examines analytically and experimentally the mixed mode interlaminar fractur... more The present research examines analytically and experimentally the mixed mode interlaminar fracture toughness of a resin film infused (RFI) carbon fiber/epoxy laminate, namely a IM7-AS4/3501-6 hybrid composite system. The inability to develop representative interlaminar failure in composites with current mixed mode test configurations motivated this particular investigation. The paper is part of a more extensive research effort concerned with the effects of stitching upon the mixed mode fracture toughness of a RFI composite.
Journal of Reinforced Plastics and Composites, 2008
Abstract This paper quantifies the elastic behavior and failure response of discontinuous carbon ... more Abstract This paper quantifies the elastic behavior and failure response of discontinuous carbon fiber/epoxy laminates produced by compression molding of randomly oriented preimpregnated unidirectional tape. Flat plates have been successfully molded using ...
This paper seeks to quantify the influence of fiber length on the mechanical properties of discon... more This paper seeks to quantify the influence of fiber length on the mechanical properties of discontinuous carbon fiber/ epoxy laminates produced by compression molding. New interest is being generated toward low-cost composite material forms for aerospace applications, as shown by the structural window frames on the Boeing 787 Dreamliner. The high-volume carbon fiber content, combined with aerospace-qualified epoxy resins, opens up opportunities for more aircraft parts to be made of non-metallic materials. This material-process combination is ideal for large volume production of three-dimensional parts, allowing for the molding of complex contours, thickness variations, and stiffening ribs. Interesting relationships between fiber length and tensile, compressive, and flexural moduli and strengths are observed.
Composites Part A-applied Science and Manufacturing, 2010
Recent composite technology research and development efforts have focused on discontinuous carbon... more Recent composite technology research and development efforts have focused on discontinuous carbon fiber/epoxy molding systems derived from chopped aerospace-grade unidirectional tape prepreg. This study analyzes in detail the meso-structure of this class ...
Abstract The elastic modulus of discontinuous carbon fiber/epoxy laminates produced by compressio... more Abstract The elastic modulus of discontinuous carbon fiber/epoxy laminates produced by compression molding of chopped unidirectional prepreg tape is measured by several means. Commercial applications for this type of material form already exist, such as ...
Composites Part A-applied Science and Manufacturing, 2009
Damage is inflicted in a series of carbon fiber/epoxy composite specimens using a simulated light... more Damage is inflicted in a series of carbon fiber/epoxy composite specimens using a simulated lightning strike generator in the effort to understand the fundamental damage response of this material form. The strikes up to 50,000 A and 28,000 V are inflicted on both pristine specimens and specimens containing a Hilok stainless steel fastener. Damage area is evaluated via ultrasonic scanning, and advanced optical microscopy is used to gain further understanding in the morphology of damage. Subsequent mechanical testing to assess the residual tensile and compressive strength and modulus of the material is performed according to ASTM standards. Results show that residual tension strength counter intuitively increases after the infliction of damage, while residual compressive strength is much more dramatically and negatively affected. Furthermore, the presence of the fastener influences dramatically both the state of damage in the specimen and its residual strength by spreading throughout the thickness rather than limiting it to the specimen surface.
One of the key factors preventing the widespread adoption of composites in primary crash structur... more One of the key factors preventing the widespread adoption of composites in primary crash structures is the absence of specialized test methods for the characterization of specific energy absorption (SEA). Aside from thin-walled tubular specimens, a limited number of attempts have been made at using a plate specimen, which is easier to manufacture but requires complex anti-buckling fixtures. A new method, featuring a corrugated plate, which can be easily manufactured and is self-stabilizing and hence does not require a dedicated test fixture, is suggested here. A systematic investigation is performed to validate the possibility of using such specimen to screen candidate material systems and laminate designs, with the specific goal of isolating the sensitivity of the method to intrinsic specimen parameters.
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Papers by Paolo Feraboli