Engineering topics

Cano, Roberto J.

Publications and source records attributed to Cano, Roberto J..

66 records · Page 4

NASA NTRS2001

Automated Fiber Placement of PEEK/IM7 Composites with Film Interleaf Layers

The incorporation of thin discrete layers of resin between plies (interleafing) has been shown to improve fatigue and impact properties of structural composite materials. Furthermore, interleafing could be used to increase the barrier properties of composites used as structural materials for cryogenic propellant storage. In this work, robotic heated-head tape placement of PEEK/IM7 composites containing a PEEK polymer film interleaf was investigated. These experiments were carried out at the NASA Langley Research Center automated fiber placement facility. Using the robotic equipment, an optimal fabrication process was developed for the composite without the interleaf. Preliminary interleaf processing trials indicated that a two-stage process was necessary; the film had to be tacked to the partially-placed laminate then fully melted in a separate operation. Screening experiments determined the relative influence of the various robotic process variables on the peel strength of the film-composite interface. Optimization studies were performed in which peel specimens were fabricated at various compaction loads and roller temperatures at each of three film melt processing rates. The resulting data were fitted with quadratic response surfaces. Additional specimens were fabricated at placement parameters predicted by the response surface models to yield high peel strength in an attempt to gage the accuracy of the predicted response and assess the repeatability of the process. The overall results indicate that quality PEEK/lM7 laminates having film interleaves can be successfully and repeatability fabricated by heated head automated fiber placement.

Hulcher, A. Bruce↗

NASA NTRS2001

Composite Structures and Materials Research at NASA Langley Research Center

A summary of recent composite structures and materials research at NASA Langley Research Center is presented. Fabrication research to develop low-cost automated robotic fabrication procedures for thermosetting and thermoplastic composite materials, and low-cost liquid molding processes for preformed textile materials is described. Robotic fabrication procedures discussed include ply-by-ply, cure-on-the-fly heated placement head and out-of-autoclave electron-beam cure methods for tow and tape thermosetting and thermoplastic materials. Liquid molding fabrication processes described include Resin Film Infusion (RFI) Resin Transfer Molding (RTM) and Vacuum-Assisted Resin Transfer Molding (VARTM). Results for a full-scale composite wing box are summarized to identify the performance of materials and structures fabricated with these low-cost fabrication methods.

Starnes, James H., Jr.↗

NASA NTRS2001

Polyimide Composites from 'Salt-Like' Solution Precursors

Four NASA Langley-developed polyimide matrix resins, LaRC(TM)-IA, LaRC(TM)-IAX, LaRC(TM)-8515 and LaRC(TM)-PETI-5, were produced via a 'saltlike' process developed by Unitika Ltd. The salt-like solutions (65% solids in NMP) were prepregged onto Hexcel IM7 carbon fiber using the NASA LaRC multipurpose tape machine. Process parameters were determined and composite panels fabricated. The temperature dependent volatile depletion rates, the thermal crystallization behavior and the resin rheology were characterized. Composite molding cycles were developed which consistently yielded well consolidated, void-free laminated parts. Composite mechanical properties such as the short beam shear strength; the longitudinal and transverse flexural strength and flexural modulus; the longitudinal compression strength and modulus; and the open hole compression strength and compression after impact strength were measured at room temperature and elevated temperatures. The processing characteristics and the composite mechanical properties of the four intermediate modulus carbon fiber/polyimide matrix composites were compared to existing data on the same polyimide resin systems and IM7 carbon fiber manufactured via poly(amide acid) solutions (30-35% solids in NMP). This work studies the effects of varying the synthetic route on the processing and mechanical properties of the polyimide composites.

Cano, Roberto J.↗

NASA NTRS2001

Hybrid Composites for LH2 Fuel Tank Structure

The application of lightweight carbon fiber reinforced plastics (CFRP) as structure for cryogenic fuel tanks is critical to the success of the next generation of Reusable Launch Vehicles (RLV). The recent failure of the X-33 composite fuel tank occurred in part due to microcracking of the polymer matrix, which allowed cryogen to permeate through the inner skin to the honeycomb core. As part of an approach to solve these problems, NASA Langley Research Center (LaRC) and Marshall Space Flight Center (MSFC) are working to develop and investigate polymer films that will act as a barrier to the permeation of LH2 through the composite laminate. In this study two commercially available films and eleven novel LaRC films were tested in an existing cryogenics laboratory at MSFC to determine the permeance of argon at room temperature. Several of these films were introduced as a layer in the composite to form an interleaved, or hybrid, composite to determine the effects on permeability. In addition, the effects of the interleaved layer thickness, number, and location on the mechanical properties of the composite laminate were investigated. In this initial screening process, several of the films were found to exhibit lower permeability to argon than the composite panels tested.

Grimsley, Brian W.↗

NASA NTRS2001

Flow and Compaction During the Vacuum Assisted Resin Transfer Molding Process

The flow of an epoxy resin and compaction behavior of carbon fiber preform during vacuum- assisted resin transfer molding (VARTM) infiltration was measured using an instrumented tool. Composite panels were fabricated by the VARTM process using SAERTEX(R)2 multi-axial non- crimp carbon fiber fabric and the A.T.A.R.D. SI-ZG-5A epoxy resin. Resin pressure and preform thickness variation was measured during infiltration. The effects of the resin on the compaction behavior of the preform were measured. The local preform compaction during the infiltration is a combination of wetting and spring-back deformations. Flow front position computed by the 3DINFIL model was compared with the experimental data.

Grimsley, Brian W.↗

NASA NTRS1999

Fabrication Of Carbon-Boron Reinforced Dry Polymer Matrix Composite Tape

Future generation aerospace vehicles will require specialized hybrid material forms for component structure fabrication. For this reason, high temperature composite prepregs in both dry and wet forms are being developed at NASA Langley Research Center (LaRC). In an attempt to improve compressive properties of carbon fiber reinforced composites, a hybrid carbon-boron tape was developed and used to fabricate composite laminates which were subsequently cut into flexural and compression specimens and tested. The hybrid material, given the designation HYCARB, was fabricated by modifying a previously developed process for the manufacture of dry polymer matrix composite (PMC) tape at LaRC. In this work, boron fibers were processed with IM7/LaRC(TradeMark)IAX poly(amide acid) solution-coated prepreg to form a dry hybrid tape for Automated Tow Placement (ATP). Boron fibers were encapsulated between two (2) layers of reduced volatile, low fiber areal weight poly(amide acid) solution-coated prepreg. The hybrid prepreg was then fully imidized and consolidated into a dry tape suitable for ATP. The fabrication of a hybrid boron material form for tow placement aids in the reduction of the overall manufacturing cost of boron reinforced composites, while realizing the improved compression strengths. Composite specimens were press-molded from the hybrid material and exhibited excellent mechanical properties.

Belvin, Harry L.↗

NASA NTRS1997

Composite Properties of Polyimide Resins Made From "Salt-Like" Solution Precursors

Recent work in high temperature materials at NASA Langley Research Center (LaRC (trademark)) have led to the development of new polyimide resin systems with very attractive properties. The majority of the work done with these resin systems has concentrated on determining engineering mechanical properties of composites prepared from a poly(amide acid) precursor. Three NASA Langley-developed polyimide matrix resins, LaRC (trademark) -IA, LaRC (trademark) -IAX, and LaRC (trademark) -8515, were produced via a salt-like process developed by Unitika Ltd. The 'salt-like' solutions (sixty-five percent solids in NMP) were prepregged onto Hexcel IM7 carbon fiber using the NASA LaRC Multipurpose Tape Machine. Process parameters were determined and composite panels fabricated. Mechanical properties are presented for these three intermediate modulus carbon fiber/polyimide matrix composites and compared to existing data on the same polyimide resin systems and IM7 carbon fiber manufactured via poly(amide acid) solutions (thirty-five percent solids in NMP). This work studies the effects of varying the synthetic route on the processing and mechanical properties of polyimide composites.

Cano, Roberto J.↗

NASA NTRS1994

Effect Of Molecular Weight On Adhesive Properties Of The Phenylethynyl-Terminated Polyimide LARC(sup TM)-PETI-5

Future civilian aircraft will require the use of advanced adhesive systems with high temperature capabilities. One such material has been developed at the NASA Langley Research Center, a phenylethynyl-terminated polyimide given the designation LARC(sup TM)-PETI-5. Recent work has shown the advantages of similar phenylethynyl-terminated polyimides as films, moldings, adhesives, and composite matrix resins. Phenylethynyl-terminated oligomers provide greater processing windows than materials which incorporate simple ethynyl endcaps. Since these low molecular weight, low melt viscosity oligomers thermally cure without the evolution of volatile by-products, they provide an excellent means of producing polymers with high glass transition temperatures, excellent solvent resistance, and high mechanical properties. Three different versions of LARC(sup TM)-PETI-5 with theoretical number average molecular weights (M(sub n)s) of 250, 5000, and 10000 g/mol were synthesized in this work. Differential Scanning Calorimetry (DSC) measurements were performed on the dry powder form of these materials to establish cure conditions which result in high glass transition temperatures (T(sub g)s). Lap shear specimens were prepared from adhesive tape made from each material and with the thermal cure conditions determined from the DSC data. The tensile shear data established processing conditions which provided the best adhesive strengths. Further testing was performed to establish the properties of LARC(sup TM)-PETI-5 as an adhesive material and to determine its solvent resistance.

Cano, Roberto J.↗

NASA NTRS1993

Effects of temperature and humidity cycling on the strengths of textile reinforced carbon/epoxy composite materials

Results are presented from an experimental evaluation of the combined effects of temperature and humidity cycling on AS4/3501-6 composites (unstitched, Kevlar 29 stitched, and S-2 glass stitched uniweave fabric) and AS4/E905L composites (2-D, S-2 glass stitched 2-D, and 3-D braided fabric). The AS4/3501-6 uniweave material had a quasi-isotropic layup, whereas the AS4/E905L materials were braided in a (+/-30 deg/0 deg)(sub s) orientation. Data presented include compression strengths and compression-compression fatigue results for uncycled composites and cycled composites (160, 480, 720, and 1280 cycles from 140 deg F at 95 percent relative humidity to -67 deg F). To observe the presence of microcracking within the laminates, photomicrographs were taken of each material type at the end of each cycling period. Microcracks were found to be more prevalent within stitched laminates, predominantly around individual stitches. The glass stitched laminates showed significant microcracking even before cycling. Less microcracking was evident in the Kevlar stitched materials, whereas the unstitched uniweave material developed microcracks only after cycling. The 3-D braid did not develop microcracks. The static compression strengths of the unstitched and Kevlar stitched uniweave materials were degraded by about 10 percent after 1280 temperature/humidity cycles, whereas the reduction in compression strength for the glass stitched uniweave was less than 3 percent. The reduction in compression strength for the glass stitched 2-D braid was less than 8 percent. The unstitched 2-D and 3-D braids did not lose strength from temperature/humidity cycling. The compression-compression fatigue properties of all six material types were not affected by temperature/humidity cycling.

Cano, Roberto J.↗

NASA NTRS1992

Properties of five toughened matrix composite materials

The use of toughened matrix composite materials offers an attractive solution to the problem of poor damage tolerance associated with advanced composite materials. In this study, the unidirectional laminate strengths and moduli, notched (open-hole) and unnotched tension and compression properties of quasi-isotropic laminates, and compression-after-impact strengths of five carbon fiber/toughened matrix composites, IM7/E7T1-2, IM7/X1845, G40-800X/5255-3, IM7/5255-3, and IM7/5260 have been evaluated. The compression-after-impact (CAI) strengths were determined primarily by impacting quasi-isotropic laminates with the NASA Langley air gun. A few CAI tests were also made with a drop-weight impactor. For a given impact energy, compression after impact strengths were determined to be dependent on impactor velocity. Properties and strengths for the five materials tested are compared with NASA data on other toughened matrix materials (IM7/8551-7, IM6/1808I, IM7/F655, and T800/F3900). This investigation found that all five materials were stronger and more impact damage tolerant than more brittle carbon/epoxy composite materials currently used in aircraft structures.

Cano, Roberto J.↗

NASA NTRS1992

Evaluation of the mechanical properties and damage tolerance of five new toughened matrix composite materials

Notched and unnotched tension and compression properties of quasi-isotropic laminates are presently evaluated, in conjunction with compression-after-impact (CAI) strengths, for the cases of five different carbon fiber-reinforced/toughened matrix composites. For a given impact energy, CAIs were dependent on impact velocities. When compared with other matrix-toughened materials, the five presently considered were more damage-tolerant than such aircraft primary structure composite systems as T300/5208.

Cano, Roberto J.↗

NASA NTRS1991

Characterization of multiaxial warp knit composites

The objectives were to characterize the mechanical behavior and damage tolerance of two multiaxial warp knit fabrics to determine the acceptability of these fabrics for high performance composite applications. The tests performed included compression, tension, open hole compression, compression after impact and compression-compression fatigue. Tests were performed on as-fabricated fabrics and on multi-layer fabrics that were stitched together with either carbon or Kevlar stitching yarn. Results of processing studies for vacuum impregnation with Hercules 3501-6 epoxy resin and pressure impregnation with Dow Tactix 138/H41 epoxy resin and British Petroleum BP E905L epoxy resin are presented.

Dexter, H. Benson↗