Thermal degradation of bending properties of structural wood and wood-based composites

Holzforschung ◽  
2011 ◽  
Vol 65 (2) ◽  
Author(s):  
Arijit Sinha ◽  
Rakesh Gupta ◽  
John A. Nairn
Keyword(s):  
Thermal Degradation ◽  
Exposure Time ◽  
Structural Integrity ◽  
Elevated Temperatures ◽  
Bending Strength ◽  
Oriented Strand Board ◽  
Thermal Exposure ◽  
Effect Of Temperature ◽  
Statistical Regression ◽  
Single Family

Abstract Wood and wood-based composites are being used extensi-vely in single-family residential dwellings. Therefore, it is important to categorize their response when exposed to elevated temperatures for a sustained period of time. In fire-resistant design for wood structures, the main goal is to ensure that enough structural integrity is maintained, during and after a fire, to prevent collapse and to maintain means of egress. Another goal is an ability to assess post-fire structural integrity and residual strength of an existing structure. The objectives of this study are: (a) to study the effect of temperature and exposure time on bending strength (MOR) and stiffness (MOE) of solid sawn lumber (SSL), laminated veneer lumber (LVL), oriented strand board (OSB) and plywood; and (b) to develop predictive relations between different temperatures and times of exposure and the thermal degradation of strength. A total of 1080 samples were tested in static bending under various heat treatments. The results indicated that exposure to elevated temperature caused significant degradation of bending strength and stiffness. A statistical regression-based model and a kinetics-based model were developed and evaluated for predicting the strength loss of wood and wood-based composites as a function of thermal exposure temperature and exposure time. The kinetics-based model fit the data better and predictions consistently matched the observed values, making the model preferred over the regression approach.

Effect of Elevated Temperature Exposures on Shear Properties of Sheathing Panels

2020 ◽  
Vol 70 (1) ◽  
pp. 115-121
Author(s):  
Rajendra Soti ◽  
Cody Knight ◽  
Shanmathi Mageshwar ◽  
Srikar D. Valluri ◽  
Arijit Sinha
Keyword(s):  
Shear Strength ◽  
Elevated Temperature ◽  
Shear Modulus ◽  
Exposure Time ◽  
Elevated Temperatures ◽  
Oriented Strand Board ◽  
Effect Of Temperature ◽  
Structural Wall ◽  
Timber Frame ◽  
Existing Structures

Abstract Structural wall sheathing such as oriented strand board (OSB) and plywood have been heavily used in residential and commercial timber frame construction. The response of these wood-based composites under elevated temperatures between 100°C and 200°C (herein referred to as elevated temperatures) and exposure time needs to be characterized to assess residual strength of the materials in the existing structures. The main objective of this work is to study the effect of temperature and exposure time on shear strength and shear modulus of plywood and OSB. A total of 110 test specimens was tested in shear after exposure to five different temperatures and two exposure durations, followed by cooling to ambient temperature. The results indicated that the plywood and OSB behaved differently after exposure to elevated temperatures and exposure duration. Plywood showed a consistent degradation of shear strength with elevated temperature and time, while OSB did not exhibit a clear picture of thermal degradation. The results further indicated that the shear modulus of plywood and OSB remained unaffected after exposure to elevated temperatures.

Thermal Degradation of Bending Properties of Structural Larch Wood

2012 ◽  
Vol 557-559 ◽  
pp. 1563-1566
Author(s):  
Hai Bin Zhou ◽  
Chuan Shuang Hu ◽  
Jian Hui Zhou
Keyword(s):  
Structural Integrity ◽  
Elevated Temperatures ◽  
Bending Strength ◽  
Effect Of Temperature ◽  
Clear Wood ◽  
Larch Wood ◽  
Timber Construction ◽  
Strength And Stiffness ◽  
Structure Collapse ◽  
In Fire

Wood is being used extensively in timber construction in China. It is important to understand its response when exposed to elevated temperatures. In fire-resistant design for timber construction, the main goal is to ensure that enough structural integrity is maintained during a fire to prevent structure collapse. To study the effect of temperature on bending strength (MOR) and stiffness (MOE) of solid clear wood from Chinese larch, a total of 108 samples with various target temperatures were tested in static bending under same temperatures to ensure the wood temperature to be sustained. The results indicated that exposure to sustained temperatures caused significant degradation of bending strength and stiffness. The degradation of chemical composition of larch wood happened after 170 °C and caused a serious drop in mechanical properties of larch wood after 225 °C. The bending strength and MOE of larch wood behaved negative linear relationship with temperatures before 100 °C.

Detection of Compositional Fluctuations in High Temperature Exposed Waspaloy

2001 ◽  
Vol 699 ◽  
Author(s):  
Xiaodong Zou ◽  
Tariq Makram ◽  
Rosario A. Gerhardt
Keyword(s):  
Exposure Time ◽  
Structural Integrity ◽  
Thermal Exposure ◽  
X Ray Diffraction ◽  
X Ray ◽  
Gamma Prime ◽  
Distribution Shape ◽  
The Matrix ◽  
Quantitative Stereology ◽  
Nickel Base

AbstractWaspaloy is a nickel base super-alloy used in aircraft engines. When this alloy is placed in service, it is subjected to long term exposure at high temperatures, which can cause the reinforcing gamma prime precipitate population to fluctuate and thus affect its structural integrity. The population fluctuates as a result of coarsening, dissolution or re-precipitation. Samples exposed to 1200° F for times ranging from 0 to 12626 hours were characterized using impedance spectroscopy, microhardness measurements, x-ray diffraction and quantitative stereology. Two important parameters were derived from the impedance measurements: (1) the imaginary admittance peak magnitude (Ymax) and (2) the associated relaxation frequency (fmax). As the distribution, shape and size of the precipitates change with exposure time, these parameters were also found to vary. In addition to the changes in precipitate geometry, lattice constant changes detected by analyzing x-ray diffraction data suggest that there are compositional shifts in the matrix as well as the gamma prime precipitates. Furthermore, the preferred orientation of the precipitates can also be seen to change with exposure time. These changes in composition, size and shape as a function of thermal exposure time are accompanied by changes in the volume fractions of primary and secondary gamma prime particles present. Using effective medium models, it is possible to predict that the measured properties are related to the gamma prime population. The grain boundary carbides do not appear to play any role at the conditions presented.

scholarly journals Thermal Degradation of Bonding Strength of Aspen Plywood

2020 ◽  
Vol 71 (2) ◽  
pp. 185-192
Author(s):  
Pavlo Bekhta ◽  
Nataliya Bekhta
Keyword(s):  
Exposure Time ◽  
Bonding Strength ◽  
Elevated Temperatures ◽  
Phenol Formaldehyde ◽  
Mass Density ◽  
Urea Formaldehyde ◽  
Statistical Regression ◽  
Colour Difference ◽  
Initial Strength ◽  
Shear Strength Test

The objective of this research was to study the effect of exposure time on the bonding strength of aspen plywood at elevated temperatures. The plywood samples were manufactured under laboratory conditions using two types of adhesive: urea-formaldehyde (UF) and phenol-formaldehyde (PF). The plywood samples were tested after exposure to three different temperatures (150 °C, 200 °C and 250 °C) and three exposure time levels (1, 2 and 3 hours) at each temperature. Additionally, a set of control samples was tested at room temperature. The quality of bonding was assessed by shear strength test in compliance with the requirements of the standard EN 314-1. The mass and density losses as well as colour changes of the plywood samples were also determined. The findings of this study indicated that exposure of plywood panels to elevated temperature caused significant degradation of their bonding strength. PF plywood samples lost 63.2 % of their initial strength after 3 h of exposure at 250 °C, while UF samples lost 65.9 % of their initial strength already after 3 h of exposure at the temperature of 200 °C. Statistical regression-based models were also developed for predicting the loss of plywood bonding strength as functions of mass and density losses and total colour difference. As the mass/density losses or total colour difference of panels increased, the losses in bonding strength increased too.

Effect of Temperature, Velocity Gradient and I.V. Heparin on in Vitro Blood Coagulation and Platelet Aggregation

1967 ◽  
Vol 17 (01/02) ◽  
pp. 112-119 ◽  
Author(s):  
L Dintenfass ◽  
M. C Rozenberg
Keyword(s):  
Blood Coagulation ◽  
Velocity Gradient ◽  
Elevated Temperatures ◽  
Morphological Changes ◽  
Effect Of Temperature ◽  
Clotting Time ◽  
Progressive Change ◽  
Aggregation Of Platelets ◽  
Microscopic Techniques

SummaryA study of blood coagulation was carried out by observing changes in the blood viscosity of blood coagulating in the cone-in-cone viscometer. The clots were investigated by microscopic techniques.Immediately after blood is obtained by venepuncture, viscosity of blood remains constant for a certain “latent” period. The duration of this period depends not only on the intrinsic properties of the blood sample, but also on temperature and rate of shear used during blood storage. An increase of temperature decreases the clotting time ; also, an increase in the rate of shear decreases the clotting time.It is confirmed that morphological changes take place in blood coagula as a function of the velocity gradient at which such coagulation takes place. There is a progressive change from the red clot to white thrombus as the rates of shear increase. Aggregation of platelets increases as the rate of shear increases.This pattern is maintained with changes of temperature, although aggregation of platelets appears to be increased at elevated temperatures.Intravenously added heparin affects the clotting time and the aggregation of platelets in in vitro coagulation.

Dielectric Breakdown in Printed Circuit Boards at Elevated Temperatures

1996 ◽  
Author(s):  
P. Singh ◽  
G.T. Galyon ◽  
J. Obrzut ◽  
W.A. Alpaugh
Keyword(s):  
Experimental Data ◽  
Thermal Degradation ◽  
Printed Circuit Boards ◽  
Printed Circuit Board ◽  
Elevated Temperatures ◽  
Dielectric Breakdown ◽  
Circuit Board ◽  
Circuit Boards ◽  
Printed Circuit ◽  
Data Matching

Abstract A time delayed dielectric breakdown in printed circuit boards, operating at temperatures below the epoxy resin insulation thermo-electrical limits, is reported. The safe temperature-voltage operating regime was estimated and related to the glass-rubber transition (To) of printed circuit board dielectric. The TG was measured using DSC and compared with that determined from electrical conductivity of the laminate in the glassy and rubbery state. A failure model was developed and fitted to the experimental data matching a localized thermal degradation of the dielectric and time dependency. The model is based on localized heating of an insulation resistance defect that under certain voltage bias can exceed the TG, thus, initiating thermal degradation of the resin. The model agrees well with the experimental data and indicates that the failure rate and truncation time beyond which the probability of failure becomes insignificant, decreases with increasing glass-rubber transition temperature.

scholarly journals Chlorine-Functional Silsesquioxanes (POSS-Cl) as Effective Flame Retardants and Reinforcing Additives for Rigid Polyurethane Foams

Molecules ◽  
2021 ◽  
Vol 26 (13) ◽  
pp. 3979
Author(s):  
Anna Strąkowska ◽  
Sylwia Członka ◽  
Karolina Miedzińska ◽  
Krzysztof Strzelec
Keyword(s):  
Flame Retardants ◽  
Elevated Temperatures ◽  
Bending Strength ◽  
Reaction System ◽  
Fire Retardant ◽  
Polyurethane Foams ◽  
Polymerization Reaction ◽  
Three Point Bending ◽  
One Step

The subject of the research was the production of silsesquioxane modified rigid polyurethane (PUR) foams (POSS-Cl) with chlorine functional groups (chlorobenzyl, chloropropyl, chlorobenzylethyl) characterized by reduced flammability. The foams were prepared in a one-step additive polymerization reaction of isocyanates with polyols, and the POSS modifier was added to the reaction system in an amount of 2 wt.% polyol. The influence of POSS was analyzed by performing a series of tests, such as determination of the kinetics of foam growth, determination of apparent density, and structure analysis. Compressive strength, three-point bending strength, hardness, and shape stability at reduced and elevated temperatures were tested, and the hydrophobicity of the surface was determined. The most important measurement was the determination of the thermal stability (TGA) and the flammability of the modified systems using a cone calorimeter. The obtained results, after comparing with the results for unmodified foam, showed a large influence of POSS modifiers on the functional properties, especially thermal and fire-retardant, of the obtained PUR-POSS-Cl systems.

scholarly journals The Synergistic Effect of Temperature and Loading Rate on Deformation for Thermoplastic Fiber Metal Laminates

Materials ◽  
2021 ◽  
Vol 14 (15) ◽  
pp. 4210
Author(s):  
Kai Jin ◽  
Shanyong Xuan ◽  
Jie Tao ◽  
Yujie Chen
Keyword(s):  
Melting Point ◽  
Softening Point ◽  
Bending Strength ◽  
Loading Rate ◽  
Synergistic Effects ◽  
Effect Of Temperature ◽  
Resin Matrix ◽  
Tension Stress ◽  
Fiber Metal Laminates ◽  
Fiber Metal

The glass fiber reinforced polypropylene/AA2024 hybrid laminates (short for Al/Gf/PP laminates) as structural materials were prepared and formed by hot pressing. The synergistic effects of temperature and loading speed on the laminate deformation under tensile and bending conditions were investigated and analyzed in this study. In tension, stress–strain curves presented bimodal types effected by tensile rates and temperatures. The state of PP resin determines the mechanical behavior of the FMLs. The tensile rate has no effect on FML deformation without heating or over the melting point of PP resin (about 170 °C). The softening point of PP resin (about 100 °C) is characteristic temperature. When the temperature exceeds the softening point but does not reach the melting point, the tensile strength and elongation will demonstrate coordinated growth at a relatively high tensile speed. The efficiency of fiber bridging is affected significantly since the resin is the medium that transfers load from the metal to the fiber. Under bending, the curves presented a waterfall decrement with temperature increment. The softening point of resin matrix is the key in a bending process. When the temperature is near the softening point, deformation is sensitive to both the temperature and the loading speed to a certain extent. If temperature is lower than softening point, deformation is mainly guided by temperature. If the temperature is beyond the softening point, loading speed is in a leading position of deformation. The bending strength gradually increases with loading rate. By using these deformation characteristics, the deformation of the thermoplastic laminates can be controlled in stamping or other plastic forming processes for thermoplastic fiber metal laminates.

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