Experimental Methods

The s m a l l strain dynamic m e c h a n i c a l p r op er ti es of the foam s amp le s were m e a s u re d o ve r a f r e qu en c y range of 0.07-70Hz, using the m i c r o p r o c e s s o r c o n t r o l l e d dynamic mechanical spectrometer described in Chapter 2. For each test piece the s torage m o d u l u s and loss t angent were measured over the full frequency range at various levels of pre-compression, in the range 1-60$ of the undeformed sample height. The upper level of pre-compression could not be exce ed ed due to p r a c t i c a l l i m i t a t i o n s to the loading capability of the electromagnetic shaker in use with the spectrometer. In each case the amplitude of the dynamic d e f o r m a t i o n was set at 0.35nun» or 0 .5$ of the u nd e f o r m e d height of the sample, and r emained at this level throughout the frequency range. A typical example of the variation of the storage modulus and loss tangent with frequency and imposed pre-strain is shown in figure 4.3, in the form of a 3 - d i m e n s i o n a l graph. A l t h o u g h the test pieces were f i l l e d with air and the re fo re c o u l d be s u b j e c t to f l u i d f l o w d a m p i n g p r o c e s s e s , the h i g h permeabilities observed with these foams resulted in the contribution to the mechanical properties from motion of the air in the m at r ix being n e g l i g i b l e in the f r e q u e n c y range of interest

The properties of the test-pieces have been characterised u s i n g two o t h e r e x p e r i m e n t a l t e c h n i q u e s . F o r c e - d e f o r m a t i o n diagr ams such as that shown in figure 4«1 have b e e n g e n e r a t e d fo r e a c h f o a m s a m p l e . Th e

10 3 LU I03 ICT1-6 Frequency/ Hz pre -strain 0 5 0-5 _{i-o F r e q u e n c y /H z} pre-strain _O-Oi0*01 FIGURE 4 0

5-D Graph S h ow i ng a) E'(O^) and b) d(cO) as a F u n c t i o n of F r e q u e n c y and P r e - S t r a i n for a H i g h - R e s i 1 iency PU Test Piece .

Table 4«1 Parameters from the Rusch Shape Function FOAM a /1 0"2 b _{P q eb} /10“2 ^ (e ^min emin I VP1 0 6.4 1 .3 0.97 4.5 6.1 0.158 0.50 I VP1 2 6.0 2.0 0.96 5.5 4.0 0.152 0.48 I VP30 6.0 1 .0 0.91 3.7 4.0 0.1 56 O • CD I VP45 7.6 1.5 0.92 4.1 5.4 0.184 0.47 I VRT300 5.5 1 .2 0.93 4.4 4.0 0.143 0 • 00 I VRT400 4.3 0.9 0.97 3.9 3.3 0.125 0.47 II FHR26 9.3 1 .1 0.81 2.5 4.4 0.250 0.41 II FHR30 3.2 1 .0 0.85 3.3 1 .2 0.117 0.58 II FHR50 6.6 1 • 6 0.80 3.8 2.5 0.182 0 • 0 II FHR60 6.8 1 .4 0.85 3.5 3.2 0.189 0.40

measurements were made using an Instron Universal Testing Facility, model TT-CM with compression load-cell. Appart from non-standard environmental conditions of temperature r e l a t i v e h u m i d i t y and sa mp l e geometry, a l l t e st in g was performed to comply with BS4443 [65 ] and involved loading the sample at a fixed compression rate of 10cm/min, up to a m a x i m u m l e v e l of 70$. The load was then r educed at the same rate. Tests were p e r f or m ed on s a mp l e s h a v i n g a s tandard size of 240x80x75mm. The test p r o c e d u r e was repeated using the test piece g e o m et ry r eq ui re d by BS 4443. Once converted into stress-strain plots, the

500*— 400 z LU CL O LL. 300

200

Compressive F-D Curves for Flexible Test Pieces with the Same Geometry. S olid Line H i g h -R e s i 1 iency PU Foam, Broken Line; C o n v e n t i o n a l PU Foam. Arrows I nd ic at e Direction of Deformation.

di ff e re n ce b e t w e e n the r e s u l t s for the two d i ff er en t geometries was negligible. Figure 4*4 shows typical F-D curves for type I ( c o n v e n ti on al ) and type II (high- r e s i l i e n c y ) PU s a m p l e s h a v i n g the same t e s t - p i e c e geometry. From c u r ve s such as figure 4*4 the Rusch para me te rs a, h, p, q, e-^, em j_n and ^(e )min h a v e ^ een calculated. Table 4*1 sumarises the results for the foam types tested.

The final test method i n v o l v e d the use of an E l e c t r o S ervo H y d r a u l i c Te st i ng Machine, m a n u f a c t u r e d by ESH Testing Ltd. This facility has the capability of testing both d y n a m i c a l l y and q u a s i - s t a t i c a 1 ly [6 6 ]. In these tests the c o m p r e s s i v e d e f o r m a t i o n cycle was a h a l f sinusiod at an e f f e c t i v e f r e qu en cy of 0.07 Hz. The preset upper limit was v a r ie d in the range 5- 7 0 $ of the u n de f o r m e d sam pl e height, and f a m i l i e s of c u r v e s were drawn. Figure 4*5 shows f a m i l i e s of c urves for s a m pl e s of type I and type II. The data is p l o t t e d as force against deformation. These are related to the stress and the strain by the sample dimensions.

Test Pieces

T h e s a m e t e s t - p i e c e g e o m e t r y w a s u s e d f o r a l l measurements. The samples were a standard shape, forming a r e c t a n g u l a r p a r a l l e l e p i p e d w i t h edge d im e n s i o n s 240x80x75mm. The smallest dimension in each case applied to the t es t-pie ce height and formed the d i r e c t i o n of deformation. U n if or m load in g was a c h i e v e d by b o nd in g

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Boao

d

11

3

-Deformat i on Curve Fami l i es For a) Convent i onal and b) H i g h - R e a i l i e n c y F l e x i b l e am Test Pieces Having the Same Geometry.

flat aluminium plates to the loaded surfaces, by means of a suitable adhesive. The dimensions of each sample could then by measured using a micrometer gauge.

As no environmental control facilities were available, the tests were made at a mbient a t m o sp he ri c t em pe r a t u r e and humidity. In all cases the local temperature during the t e s t s l a y in the r a n g e 22+_3 °C. The r e l a t i v e h u m i d i t y of the e n v i r o n m e n t was checked and found to be in the range 45^.10 %. When not in use the t es t- p i e c e s were stored in a dark place.