BS EN 302-4-2004 pdf download.Adhesive for load-bearing timber structures Test methods Part 4: Determination of the effects of wood shrinkage on the shear strength.
This part of EN 302 specifies a method for determining the extent to which wood shrinkage under drying conditions will weaken an adhesive bond.
It is suitable for the following applications:
a) for assessing the compliance of adhesives with EN 301;
b) for assessing the suitability and quality of adhesives for load-bearing timber structures;
C) for determining if the adhesive is capable of withstanding stresses due to wood shrinkage without unacceptable loss of strength.
This test is Intended primarily to obtain performance data for the classification of adhesives for load-bearing timber structures according to their suitability for use in defined climatic environments. This test is carried out on spruce (Picea abies L.).
This method is not intended for use to provide numerical design data and does not necessarily represent the performance of the bonded member in service. It is not intended to be used to assess the suitability of adhesives for the manufacture of wood-based panels.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
EN 301, Adhesives, phenolic and aminoplastic, for Ioad-beanng timber structures — Classification and performance requirements.
EN 13183-1, Moisture content of a piece of sawn timber — Part 1: Determination by oven thy method.
ISO 5893, Rubber and plastics test equipment Tensile, flexural and compression types (constant rate of
traverse) — Specification.
3 Principle
A crosswise double joint with a 0.5 mm thick glue line is submitted to a dry storage treatment and then
strained to failure by a compressive shear force.
4 Safety
b) a constant rate of traverse machine as described in ISO 5893.
5.2 Climatic cabinets
The cabinets shall be enclosures capable of maintaining the bonded assemblies under the following conditions:
a) (40 ± 2) ec and a relative humidity of (30 ± 2) % and an air speed of (0.6 to 0,8) m/s (air speed as measured in an empty cabinet);
b) (20 ± 2) °C and a relative humidity of (65 ± 5) %;
C) (20 ± 2) °C and a relative humidity of (75 to 80) %.
6 Method
6.1 Selection of timber
6.1.1 General
Use spruce (Picea abies L.) having a density of (425 ± 25) kg/rn3 measured at (12 ± 1) % moisture content as
determined by oven drying (according to EN 13183-1).
6.1.2 Preparation of cover pieces
From three boards with a length of at least 1 200 mm prepare three pairs of solid spruce cover pieces that are knot-free, straight grained and
a) 400 mm in length
b) 140 mm in width
C) (20 ± 0,5) mm in thickness
after conditioning, measurement of moisture content (oven dry method according to EN 13183-1) and final preparation, with growth rings that are approximately tangential to the face and have a radius of 60 mm to 140 mm. Each matching pair of cover pieces is intended for the production of a specimen.
6.1.3 Preparation of core pieces
Prepare three laminated spruce core pieces that are knot-free, straight-grained and with annual rings at an angle of 35° to 55° relative to the surface (see Figure 1).
6.2 Preparation of the bonded assemblies
Before bonding the specimens together, take a sample from each of the core and cover pieces for the wood moisture content determination, using the oven-dry method, according to EN 13183-1.
Calculate and record each specimen’s mean moisture content using the following formula:
where
tJm = the specimens mean moisture content in percent;
U = the moisture content of the first cover piece in percent:
U., = the moisture content of the second cover piece in percent;
U1 = the moisture content of the core piece in percent.
Prepare the bonded assemblies as shown In Figure 2 with the curvature of the growth rings of the cover pieces away from the surfaces to be bonded (Figure 2 c)). and the grain of the cover pieces at right angles to the grain of the core piece (Figures 2 a) and 2 b)). Fix two (0,5 ± 0,01) mm thick aluminium spacer frames (Figure 3), one spacer on the core piece and one spacer on the cover piece to limit the bond area to (100 ± 0,1) mm x (100 ± 0,1) mm and the nominal bond line thickness to 0,50 mm.
NOTE I If no other instructions are provided by the adhesive manufacturer, apply the adhesive on the surface of the core piece to be bonded as well as on the surface of the cover piece to be bonded, to ensure good surface wetting.
NOTE 2 To aid in the removal of the left over, hardened adhesive after bonding, it is recommended to use tape strips on the lateral sides of the core and cover pieces before bonding.
Bonding shall Lake place in a standard atmosphere of (20 ± 2) °C and (65 ± 5) % relative humidity. Apply a road of (7.7 ± 0,1) kN and maintain for 24 h. This load corresponds to a pressure of approximately 0,8 N/mm2 applied to the surface of the frame (9 600 mm2).
Remove the clamps and carefully remove any left-over hardened adhesive from the surfaces of the assembled specimen. Weigh and record each specimen’s weight to the nearest gram, which is now considered the initial weight of the specimen. Store the assemblies for seven days at (20 ± 2) °C and (65 ± 5) % relative humidity.BS EN 302-4-2004 pdf download.