# Selected Properties of Overlaid Magnesium Based Composite Panels for Flooring
## Materials and Methods  
Commercially produced two different types of samples having magnesium substrate with a total thickness of 12.00 mm having linoleum and oak wood veneer overlays were used for the tests as illustrated in Figure 1. Both linoleum and oak veneer had 2.00 mm thickness. A total of 60 samples, 30 for each type were tested employing a Comten Universal Testing Unit Model DMC-026S equipped with 1000 kg load cell based on ASTM standards to determine their modulus of elasticity (MOE), modulus of rupture (MOR) as well as internal bond strength (IB) (Figure 1) [11] Samples were centrally loaded on laminated and non-laminated sides of each sample to determine if there was any influence of loading direction on structural characteristics of the members. Figure 2 shows schematics of sample type in regard to their loading directions.  
A total of forty samples with dimension of 50 mm by 50 mm in panel thickness were used for internal bond (IB) strength test on Comten Testing Unit described above. Samples were glued to aluminum block using a hot-melt adhesive in the form of sandwich configuration and they were kept in climate room having a temperature of 20 \({}^{\circ}\)C and relative humidity of 65% for several days before tests were carried out [11]. Crosshead speed of 3 mm/min was used for both bending and IB tests on the Comten Unit. For both bending and internal bond tests dimensions and weights of each sample were measured at accuracy levels of 0.1 mm and 0.01 g, respectively to determine their average density which was found as 1.09 g/cm\({}^{3}\).  
Figure 1: Internal bond strength (IB) samples and IB test set-up showing the cross section of the sample. (Left is linoleum overlaid and the right one is oak veneered sample).  
Figure 2: Schematics of the samples based on loading direction.  
Dimensional stability plays a very important role during the service life of the flooring panels. Therefore 10 samples in 120 mm by 120 mm from each type panel were soaked in water to determine their thickness swelling as a result of 2-h and 24-h water exposure. The thickness of each sample was also measured at four corners after 2-h and 24-h soaking time at accuracy level of 0.1 mm to determine their thickness swelling values.  
Roughness of the flooring panels is important for application of varnish or any kinds of maintenance coatings. It is a fact that any rough surface would require higher amount of varnish increasing overall production cost. Roughness can be defined as measure of fine irregularities on a surface [4, 12]. Surface instability is somehow a latent condition and may never happen unless favorable environmental conditions exist. A total of 40, 50 mm by 50 mm samples were used for roughness measurements. After taking initial measurements at dry condition the samples were soaked in water for 24-h and their roughness measurements were retaken from the surface of each sample. A stylus type equipment SRT-6200 unit was employed for the measurements. The equipment consists of the main unit and pick-up with a skid type diamond stylus with a 5 um tip radius and 90\({}^{\circ}\) tip angle. Four random measurements were taken over 15 mm tracing length from the surface of each sample. Two roughness parameters, namely average roughness (R\({}_{\text{a}}\)) and mean peak-to-valley height (R\({}_{\text{z}}\)) were used to quantify the roughness of the specimens. Description and principles of these three roughness parameters are presented in past studies [12, 13, 14]. Only oak veneer surfaces were considered for roughness test since linoleum is being non-hygroscopic material and having very rough surface.  
Finally vertical density profiles of the samples were also tested using an x-ray type density profilometer to be able to compare densification of the face and core portion of the panels.