JOURNAL OF
ADVANCED MATERIALS ISSN 1070-9789
Volume 36, No. 4, October 2004
An International Journal of Processing, Science, Characterization and Application of Advanced Materials 3
Experimental Investigation of Eddy Current Inspection Aircraft Materials
11
Automated VARTM Processing of Large-Scale Composite Structures
18 Investigation of Flexural Creep for High-Density Polyethylene Pipe 25 Effect of Creosote and Copper Naphtenate Preservative Treatments on Properties of FRP Composite Materials Used for Wood Reinforcement 34 The Effects of Strain Rate and Temperature on the Mechanical Properties of Ultra-High Molecular Weight Polyethylene Fiber 39 Transformation Mechanism Among Various Nano-Morphologies
43 Fundamental Investigations on Electrospun Fibers 48 Densification and Microstructure Characteristics of Mechanically Alloyed W-Ni-Fe Composite Powders 53 The Effect of the Microstructural Difference Between Surface and Center on the Hot Workability of AA 6063 Homogenized Ingot 60 61 62 63 64
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Society for the Advancement of Material and Process Engineering Volume 36, No. 4, October 2004
Effect of Creosote and Copper Naphthenate Preservative Treatments on Properties of FRP Composite Materials Used for Wood Reinforcement Benjamin Herzog, Barry Goodell, Roberto Lopez-Anido, Lech Muszyñski, Douglas Gardner University of Maine Orono, Maine E-Mail:
[email protected]
Cihat Tascioglu Abant Izzet Basal University Duzce, Turkey Received 06/05/03; Revised manuscript received 08/28/03
Abstract Structural timbers and FRP (Fiber Reinforced Polymer)-wood composites must be protected by preservative systems when used in high decay hazard environments. In this study, the mechanical properties of FRP materials treated with either creosote or a solvent-borne preservative were investigated. Undiluted creosote (coal tar distillate, a complex mixture of hydrocarbons) and 1% copper naphthenate (CuNap) in a mineral spirits carrier were the two preservatives selected for this study. The mechanical properties investigated included: interlaminar shear strength (Fzx), longitudinal elastic modulus (Ex) and longitudinal tensile strength (Fxt). The results showed that an FRP consisting of E-glass fiber, bonded with epoxy, fabricated by the continuous lamination method was adversely affected by a creosote-treatment with regard to interlaminar shear strength. Longitudinal tensile strength of a pultruded FRP composite flat-sheet (E-glass fiber, bonded with urethane) was adversely affected when treated with either preservative. The preservative treatments did not affect these properties for two FRP materials (E-glass fiber, bonded with vinyl ester and carbon fiber, bonded with vinyl ester) fabricated by the SCRIMP process. Similarly, longitudinal elastic modulus was not affected by treatment in any FRP material tested. The longitudinal tensile strength of E-glass/epoxy composite material was apparently improved by a CuNap treatment.
Introduction Background and Literature Review Wood as a traditional construction material has been widely used in transportation infrastructure. Wooden elements exposed to exterior environments are susceptible to biological deterioration from decay fungi, insect attack, and other environmental agents, which impact their mechanical properties, strength and durability.
Therefore, when used in exposed outdoor environments glulam timbers are normally treated with wood preservatives to prevent deterioration1, 2 . In the late 1970’s the American Institute of Timber Construction (AITC) developed recommendations requiring that all exterior-use laminated members be treated with preservatives 3 . The preservative treatments may be divided by nature of the carrier into oil-borne and waterborne. Both preservatives and the carriers may aggressively attack a number of structural materials. Comprehensive reviews of the history of glulam beam production, and the
history of wood preservative treatment with respect to glulams and other engineered wood products, have previously been published4. Glulam beams reinforced with FRP composites for exterior use must also be protected from biodeterioration. In fact, the production of preservative treated composite reinforced laminated timbers represents the latest stage of investigation and development in the structural wood products industry, and there is considerable interest by both the wood preserving and composite reinforced wood hybrid industry in the development of wood preservative Journal of Advanced Materials
compatible FRP composite systems. Treatment of the entire FRP reinforced wood elements (post-treatment), or alternatively bonding the FRP reinforcement to the pre-treated glulam member, often exposes the FRP reinforcement to long-term contact with aggressive chemicals. The effect of preservative treatments on bond integrity as well as the physical and mechanical properties of the glulam members is already well recognized5-8. However, there is limited knowledge of the treatment effect on physical and mechanical properties, and durability of different types of FRP reinforcements. While current thought is that the use of FRP composite systems provides longer lifetimes and lower maintenance than equivalent structures fabricated from conventional materials, actual data on the durability of wood/FRP composites is sparse, not well documented, and in cases where available, not easily accessible. There also is evidence that certain types of FRP degrade more rapidly than expected when exposed to certain environmental conditions9. Clearly, when FRP is bonded to glulam members, engineers need to consider the durability and degradation of the FRP, and also that of the wood. The increased strength of the FRP component may add to a member may simply negate the decreased strength of a deteriorated timber. Wood in exterior environments, and in many indoor environments where extended periods of moist or high humidity conditions are possible, will continue to need preservative treatment regardless of the benefits of FRP reinforcement. Few studies are available investigating the effect of preservative treatments on FRP composites. Tascioglu, et al.4 examined the effect of both water-borne and oil-borne preservatives on an E-glass/phenolic pultruded composite material. The results showed that although the longitudinal elastic modulus was unaffected by oil-borne treatment, some longitudinal strength losses were recorded for water-borne treated material. In this study it was also concluded that for preservative treatments, e.g. PCP in diesel fuel, CuNap in mineral spirits, or Volume 36, No. 4, October 2004
creosote, caused no statistically significant reduction in longitudinal tensile strength in the composite material regardless of the retention level. Creosote treatment, however, resulted in a statistically significant (10%) reduction in interlaminar shear strength (ILSS) while other oil-borne and CCA-C treatments had no effect on this strength property4. In our current work, the effects of oil and solvent borne preservative treatments (creosote and copper naphthenate solution in mineral spirits) and two preservative treatment carriers (represented by diesel fuel and mineral spirits) on the mechanical properties of four FRP composite material systems used for wood reinforcement were characterized. The properties studied were: longitudinal elastic modulus (Ex), longitudinal tensile strength (Fxt) and interlaminar shear strength (Fzx). A unified interpretation of the experimental results is provided with the intent of developing acceptance criteria and recommendations appropriate for development of performance based material specifications.
Objectives The objective of this paper is to characterize the effect of typical oil or solvent based wood preservative treatments used in glulam timber bridge construction on the mechanical properties of FRP composite materials for wood reinforcement.
Materials and Methods FRP Composite Materials Four FRP composite systems exhibiting exterior durability potential for glulam reinforcement were selected to validate a material qualification protocol developed as part of a larger project focused on the development of FRP reinforcement for timber bridge construction (See Acknowledgments). These reinforcement systems were selected based on a screening test matrix
of ten different combinations of FRP composite materials, primers and adhesives. The four FRP materials represent a broad spectrum of fiber reinforcement, polymer matrix and adhesive systems, as shown in Table 1 and specified below. Material Pultru-G-U is a pultruded E-glass/urethane (reinforcement/matrix) sheet bonded with one-part moist-cure urethane adhesive. Material ConLam-GE is an E-glass/epoxy sheet fabricated by a continuous lamination process bonded with epoxy. For the remaining materials, a variation of the Vacuum Assisted Resin Transfer Molding (VARTM) process, the licensed Seemann Composites Resin Infusion Process (SCRIMP), was used. This process has previously been applied at the University of Maine to reinforce glulam members and was used to fabricate Materials VARTM-G-VE (Eglass fibers) and VARTM-C-VE (Carbon fibers) using vinyl ester resin as the matrix. The longitudinal elastic modulus, longitudinal tensile strength and ILSS of the FRP composite materials (untreated controls) were determined according to ASTM D3039 and D2344 standard test procedures Table 2.
Material Preparation and Wood Preservative Treatments The two preservative systems selected were those determined by the Federal Highway Administration working-group as appropriate for use in timber bridges material. Plates of the four FRP composites were treated with preservative prior to being cut to final specimen (coupon) size for mechanical testing. For the ILSS test, the plates measured approximately 127 – 152 mm (in width) and 254 mm (in length), with thickness dependent upon the material. Material Pultru-G-U and Material ConLam-G-E had a thickness of about 6.35 mm, while the remaining two materials had a thickness of about 1.25 mm. For the tensile test, plates measured approximately 51 mm in width, 127 – 152 mm in length, and 6.35 mm in thickness. Undiluted creosote (coal tar distillate, a complex mixture of
Table 1. FRP composite systems: materials and processes.
Table 2. FRP composite control properties.
hydrocarbons) and copper naphthenate (CuNap [a.i. – naphthenic acid, copper salt 1.0%, mineral spirits 99%]) in a mineral spirits carrier were the two preservatives selected for use. The FRP plates (as described above) were submerged in the solutions prior to treatment. The method of treatment used was the “full-cell” process with a vacuum of approximately 215 kPa applied and held for five minutes followed by an applied pressure of 962 – 1013 kPa for 20 minutes10. All preservatives were maintained at ambient temperature and samples and controls were treated at ambient temperature. Treatment was followed by a conditioning period of one week (in a constant environment of approximately 24°C and a relative humidity of about 70%) before testing. All sample sets had corresponding solvent carrier controls as well as untreated controls. The treatment procedure was the same for both test samples.
Retention values were calculated using the methods outlined in the American Wood-Preservers’ Association Standard E1091. A modification of the standard was applied to calculate total solution uptake rather than active ingredient uptake as specified. Typical retention values of the preservative treatments in the FRP materials tested are reported in Table 3.
Longitudinal Tensile Test Initial problems with the preparation of the tensile samples became evident during the testing of Materials Pultru-G-U and ConLam-G-E (as described in the Results below). Initially, tabbing - attaching tapered fiberglass/epoxy tabs to reduce grip-induced failures of the tensile samples - was performed prior to preservative treatment. During testing, the tabs of these Journal of Advanced Materials
software package (Systat Software Inc., Richmond, CA). The independent factors used in the analysis were the FRP material type and the preservative treatment.
Table 3. Retention values of sample FRP materials tested.
Experimental Results Longitudinal Tensile Properties
materials, including untreated specimens, repeatedly slipped. Modifications were made; gripping pressures were tested and modified, and replicate samples were fabricated. The tabbing procedure was then modified so that tabs were applied post-preservative treatment using a polyurethane adhesive (Pliogrip, Ashland Specialty Chemical Company, Columbus, Ohio). After tab curing (24 hours), the tensile coupons were fabricated from the plates in accordance with ASTM D303911 to a specimen size of 12.7 mm in width and 2.54 mm in length (thickness varied depending on material). Six specimens were prepared for each of the five treatment regimens for every FRP composite material. All specimens were tested in accordance with ASTM D3039. The longitudinal tensile strength of the FRP composite material was calculated as: [1] where = ultimate tensile load prior to failure; b = width of tensile specimen; and d = thickness of tensile specimen. The tensile chord longitudinal elastic modulus was calculated as: [2] where,
= change in longitudinal stress;
= change in longitudinal strain.
Interlaminar Shear Test FRP plates were cut into coupons immediately after treatment and before the conditioning period. The coupons were fabricated in accordance with ASTM D2344 12 to a size of 6.4 mm x 6.4 mm x 38.1 mm. Six coupons were prepared for each of the five treatment regimens (two preservative treatments, two carrier control treatments, one untreated control) for every FRP material. All specimens were tested in accordance with ASTM D2344. The ILSS was calculated, as follows:
[3]
Statistical Analysis In addition to average, standard deviation, and coefficient of variation values, an Analysis of Variance (ANOVA) was also performed for longitudinal tensile strength (Fxt), ILSS (Fzx), and longitudinal elastic modulus (Ex) values the SYSTAT Volume 36, No. 4, October 2004
Problems were encountered when Materials Pultru-G-U and ConLam-G-E were tensile tested. Even after modifications were made to the tabbing procedure, the dominant failure type encountered with these materials (regardless of treatment regimen and including untreated material) was failure at the grip area. This mode of failure is unacceptable in the ASTM standard. The results for these samples should therefore be viewed with caution. See Discussion for further analysis of this problem. No significant Ex differences between preservative treatments, carrier controls, and untreated samples for the four FRP materials tested were observed, as shown in Table 4. When an ANOVA was done on the individual materials (to determine whether treatments had a significant effect on the test results) the resulting p-values were: 0.955 (VARTMG-VE), 0.237 (Pultru-G-U), 0.396 (ConLam-GE), and 0.296 (VARTM-C-VE), indicating that the treatment type does not affect the modulus of elasticity in the longitudinal direction for any of the materials tested. There were, however, differences in Fxt values for Materials VARTM-G-VE, PultruG-U, and ConLam-G-E depending on treatment. The ANOVA p-value (0.036) for Material VARTM-G-VE implied significance at the 95% confidence level. A plot of the least square means (Figure 1) resulting from an ANOVA showed that differences between treatments are not readily apparent. Because the error bars represent two standard errors, however, the figure is conservative. For Material Pultru-G-U, differences exist between both preservative treatments and the control samples (Figure 2). The reported values for the treatment regimens are lower than that of the controls (p = 0.000), showing that preservative treatments adversely affect the strength of this material. Neither carrier is significantly different from untreated material. The results of Material ConLam-G-
Table 4. Longitudinal tensile strength and the tensile longitudinal elastic modulus.
Figure 1. Least square means resulting from ANOVA for Material VARTM-G-VE. Error bars represent two standard errors. Fxt is measured in MPa.
Figure 2. Least square means resulting from ANOVA for Material Pultru-G-U. Error bars represent two standard errors. Fxt is measured in MPa.
E show that there are significant differences between the control specimens and CuNap- or diesel-treated specimens (Figure 3). However, instead of an adverse effect, the results suggest that the preservative treatments increase the strength of this material. The exact reasons for this are currently unknown. The preservatives may have further polymerized a component of the FRP material during the treatment process, but this was not investigated. The results show that Material VARTM-C-VE had much greater Ex and Fxt values than the other materials as would be expected because carbon is a higher strength fiber than glass. Smith et al. (2000) found a similar relationship comparing two composite laminated panels and one composite sandwich panel fabricated using the VARTM process. Their E-glass panel had an Ex = 23.03 GPa and Fxt = 325 MPa whereas their carbon panel material had an Ex = 47.51 GPa and Fxt = 436 MPa13.
Figure 3. Least square means resulting from ANOVA for Material ConLam-G-E. Error bars represent two standard errors. Fxt is measured in MPa. Journal of Advanced Materials
Table 5. Interlaminar shear strength, Fzx.
When the remaining E-glass FRP materials were compared, there was overlap of Ex when average reported values were ranked. However, trends indicate that Material Pultru-G-U had a higher Fxt and Ex than Material ConLam-G-E, which in turn had higher values than Material VARTM-G-VE.
Material ConLam-G-E, regardless of treatment, possessed the highest ILSS values of the four FRP materials tested. This was followed by Material Pultru-G-U, VARTMC-VE, and VARTM-G-VE respectively. Interestingly, there was no overlap of materials when specific ILSS values were ranked. This suggests that the vinyl ester resin used in Materials VARTM-G-VE and VARTM-C-VE may imbue an FRP with a lower ILSS than the other resins used. Another possibility is that the SCRIMP fabrication process results in an FRP with a lower ILSS than those fabricated by pultrusion or continuous lamination processes.
Discussion of Experimental Results
The ILSS data in Table 5 show that there were no significant affects on Materials VARTM-G-VE and VARTM-CVE when treated with the various preservative treatments and carrier controls. However, significant differences were apparent in the other two materials when tested with some preservatives. The resulting p-value of an ANOVA performed to determine treatment effects on Fzx of Material Pultru-G-U was 0.000, signifying overall that treatments significantly affected this material. While there was no difference between the creosote, diesel-, mineral spirits- and untreated samples, (Figure 4) shows that when this material is treated with CuNap, the resulting Fzx was significantly greater. Treatment with creosote and diesel fuel also adversely affected the Fzx of Material ConLam-G-E (p = 0.003) (Figure 5). There were no differences between the CuNap-, mineral spirits-, and untreated specimens.
Interpretation of the test results requires consideration of the preservative treatment conditions including the preservative retention or permanent solution uptake of the FRP composite plates after treatments. Relatively small amounts of CuNap (as well as mineral spirits) were taken up by the FRP materials when compared to the creosote (and its matched carrier, diesel) retention levels, as shown in Table 3. Clearly this can be attributed to the solutions, not the FRP composite, as this trend holds true for all the materials tested. The relatively low retention levels in the FRP materials, when compared to wood, is explained typically by the much lower void content for all the FRP materials in this study, and the absence of a significant system of pores compared to wood. Although it can be argued that the treatment of the FRP alone (in the absence of wood) represents a severe treatment exposure, other factors must also be considered. The treatment time used in this work, a 20 minute pressure cycle, is relatively short compared to the treatment cycle used with most wood products, particularly when impermeable wood species are treated. Pressure cycles can typically extend from one
Figure 4. Least square means resulting from ANOVA for Material Pultru-G-U. Error bars represent two standard errors. Fzx is measured in GPa.
Figure 5. Least square means resulting from ANOVA for Material ConLam-G-E. Error bars represent two standard errors. Fzx is measured in GPa.
Interlaminar Shear Properties
Volume 36, No. 4, October 2004
Figure 6. Typical modes of failure for tensile testing. Pictured are Material VARTM-G-VE specimens exposed to different treatments (from left to right: creosote, CuNap, mineral spirits, and diesel fuel).
Figure 7. Shown above are Material Pultru-G-U specimens after being subjected to tensile testing. The specimen on the right (shown in face view) displays evidence of tab slipping. The two left-most specimens (viewed from the side) display examples of failure at the grip area. The other specimen (located second from the right) is also viewed from the side and exhibits an acceptable mode of failure.
to several hours depending on wood species and product type. The solutions we used were also unheated, whereas typically in industrial processing, preservative solutions of this type are heated to provide for better penetration into the substrate. Finally, the conditioning period for the samples was only one week. Under normal exposure conditions, preservative treated wood products are expected to last for 35 years or longer. When wood is in direct contact with FRP as occurs in woodFRP composites, the higher retention of preservative in the wood would be expected to act as a reservoir, maintaining the preservative solution and solids in association with the FRP material. The effects of long-term exposure of FRP to the wood preservative chemicals tested in this work have not been studied. Problems were encountered with the tensile tests of Materials Pultru-G-U and ConLam-G-E. Originally, the FRP plates were tabbed prior to treatment. However, when tested, most specimens prepared that way failed due to the tabs slipping, and this data was discarded. The exact reason for the tab adhesive failure has not been determined, but may relate to adhesive-preservative interactions affecting the tabs. When Materials VARTM-G-VE and VARTM-C-VE were tested, the failure mode was acceptable. Therefore we hypothesize that the problem lies with the material(s) and not the process. One factor that separates the materials with acceptable failure and those with unacceptable failure modes is the thickness (and therefore, the volume) of the materials. Materials Pultru-G-U and ConLam-G-E were much thicker than the other two, which perhaps caused the unacceptable modes of failure when tested. The tensile strength results for these materials may well be lower than would have resulted with acceptable failure modes. In addition, the Ex values associated with these materials should be viewed with caution. The goal of this study was to compare the effects of various preservative treatments and not to define the exact Ex or Fxt of the materials. The authors justify the comparative value of the results, as nearly all of the non-standard failure in these two FRPs were of the same failure mode. The two mechanical tests conducted in this work were chosen because the results from these tests are related to several different properties of an FRP composite. The mechanical properties evaluated, Ex, Fxt and Fzx, are used as performance indicators to determine residual properties of FRP composite materials exposed to wood preservative treatments. Once relevant performance indicators are identified associated performance limits can be determined. It is assumed that the interlaminar shear strength (Fzx) is a matrix-dominated property, while the longitudinal elastic modulus (Ex) and longitudinal tensile strength (Fxt) are fiber-dominated properties. When thought of in this manner, some trends become readily apparent. The results suggest that creosote and/or CuNap preservative treatment affects, either positively or negatively, glass fiber and urethane or epoxy resins significantly more than it does carbon fiber and vinyl ester resin. The results of the tensile testing indicated that, Fxt was affected for Materials VARTM-G-VE, Pultru-G-U, and ConLam-G-E - all with glass fiber as the reinforcement – while the material with carbon fiber (VARTM-C-VE) was not affected. In addition, the two affected Journal of Advanced Materials
Figure 8. Untreated Materials ConLam-G-E (top) and Pultru-G-U (bottom) specimens after ILSS testing. After the pressure is released, shear failure is readily apparent. materials from the ILSS tests were PultruG-U and ConLam-G-E. The two materials with a vinyl ester matrix (VARTM-G-VE and VARTM-C-VE) were not affected. It is possible that the mechanical properties of these and other FRP materials could be affected if the solution uptake of creosote, CuNap, and the carriers were greater than we were able to achieve in this study, or when FRP materials are exposed to preservative treatments over longer periods of time as discussed above. Only long-term testing of preservative treated FRPs with wood will resolve this question. The question is important because previous workers have specifically designed FRPs intended for use with wood products to have a more permeable surface layer under the assumption that the greater permeability would improve bonding resin penetration14, 15, 16. For exterior use FRP composites that must be preservatively treated, this design may work to disadvantage. Volume 36, No. 4, October 2004
Conclusions and Recommendations Based on this research, the following conclusions are drawn: 1. Neither of the two preservative treatments, nor the two carriers, had an effect on the interlaminar shear strength of Materials VARTM- GVE or VARTM-C-VE. 2. Material ConLam-G-E, when creosote- or diesel fuel-treated, resulted in significantly reduced interlaminar shear strength. This indicates that hydrocarbons adversely affect epoxy resin. Ehrenstein et al. (1990) has determined that epoxide resins have limited resistance (dependent on temperature and concentration) to aromatic solvents17. 3. Longitudinal tensile strength was not significantly altered in VARTMC-VE when treated with the two pre-
servative chemicals or the two carrier treatments. This suggests that the carbon fiber used in this material may be resistant to chemical degradation by these treat-ments. 4. The longitudinal tensile strength of Materials VARTM-G-VE and PultruG-U, when treated with either of the preservative chemicals, was significantly lowered. The apparent strength of Material ConLam-G-E was increased when treated with either of the preservative chemicals or the two carriers. 5. The longitudinal elastic modulus was not significantly compromised in any of the tested materials when treated with the two preservative chemicals (or the two carrier treatments). The following commentary and practical recommendations are proposed: 1. In this study, our treatment times and levels were selected based upon previous experience with wood preser-
2.
vative treatments but did not explore the full range of preservative treatments for severe exposure conditions or for use with impermeable wood species. Practically, preservative treatment should follow the schedule required for the protection of wood that will be integrally associated with FRP materials in composite laminates. However, in future work, to accurately test the effects of chemical treatment on the FRP materials, solution uptake would need to be standardized. This may or may not be possible depending upon the porosity of the material. An analysis of how the tensile failure mode affects the resultant Ex and Fxt is also recommended. If a relationship and/or model is possible to calculate, the results presented here regarding Materials Pultru-G-U and ConLam-G-E) could be corrected for failure type.
Acknowledgment The research work presented in this paper was sponsored through the FHWA Contract DTFH61-99-C-00064- FRP Reinforced Glulams for Bridge Applications, which is sponsored by the Federal Highway Administration. The authors would like to acknowledge the assistance of Yong Hong, Leopold Eisenheld, and Anca Pirvu (graduate research assistants, Advanced Engineered Wood Composite Laboratory, University of Maine, Orono, Maine), and the support of the University of Maine, Wood Utilization Research Program. The third author was partially supported by the National Science Foundation through the Grant No. CMS0093678. This is paper No. 2656 of the Maine Agricultural and Forest Experiment Station.
Notation The following symbols are used in this paper: Ex =Longitudinal elastic modulus, GPa (psi) Exchord =Tensile chord longitudinal elastic modulus, GPa (psi)
Fxt Fzx b d
=Longitudinal tensile strength, MPa (psi) =Interlaminar shear strength, N/m2 (or psi) =Width of specimen, m (or in.) =Thickness of specimen, m (or in.) =Breaking point, N (or lbf)
=Maximum load prior to failure, N (lbf) =Difference in applied tensile stress between 1000 and 3000 microstrains =Difference between the strain points (nominally 0.002) AI =Active Ingredient
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sion of Epoxy and Other Thermosetting Adhesives to Wood,” Wood Adhesives Proceedings No. 7296, Madison, WI, Forest Products Society, p. 47-55, (1995). 9. V.M. Karbhari, Civil Engineering Research Foundation, “Gap Analysis for Durability of Fiber Reinforced Polymer Composites in Civil Infrastructure,” American Society of Civil Engineers, (2001). 10. AWPA. AWPA, “Standard for Preservative Treatment of Structural Glued Laminated Members and Lamination Before Gluing of Southern Pine, Coastal Douglas Fir, Hemfir and Western Hemlock by Pressure Processes,” AWPA, C28-99, (1999). 11. ASTM, “ASTM D3039/D3039M-00 Standard Test Method for Tensile Properties of Polymer Matrix Composite Materials,” Annual book of ASTM Standards,” West Conshohocken, PA, American Society of Testing and Materials, (2000). 12. ASTM, “ASTM D2344/D2344M00e1 Standard Test Method for ShortBeam Strength of Polymer Matrix Composite Materials and Their Laminates,” Annual book of ASTM Standards, West Conshohocken, PA, American Society of Testing and Materials, (2000). 13. S.A. Smith, L.L. Emmanwori, R.L. Sadler, K.N. Shivakumar, “Evaluation of Composite Sandwich Panels Fabricated Using Vacuum Assisted Resin Transfer Molding,” 45 th International SAMPE Symposium and Exhibition, Long Beach, CA, p. 981-989, (2000). 14. H. Dagher, B. Abdel-Magid, S.M. Shaler, “Resin Starved Impregnated Panels, Wood Composites Utilizing Said Panels and Methods of Making the Same,” US Patent No. 6281148, (1996). 15. D.A. Tingley, “Surface Treated Synthetic Reinforcement for Structural Wood Members,” US Patent No. 5498460, (1996). 16. D.A. Tingley “Aligned Fiber Reinforcement Panel for Structural Wood Members,” US Patent No. 5362545, (1994). 17. G.W. Ehrenstein, A. Schmiemann, A. Bledzki, and R. Spaude, “Corrosion Phenomena in Glass-Fiber-Reinforced Thermosetting Resins,” N.P. Cheremisinoff, editor. Handbook of Ceramics and Composites, NY, Marcel Dekker, Inc., (1990). Copyright 2004© Society for the Advancement of Material and Process Engineering (SAMPE)
Journal of Advanced Materials
