Comparison of Axial and Radial Compression Tests for Determining Elasticity Modulus of Potatoes

Figures & data

Figure 1 Schematic presentation of test techniques and model equations used for determining the tangent modulus of elasticity of cylindrical samples of potatoes: (a) axial compression (b) radial compression.

Table 1 Tangent modulus of elasticity (MPa) of potatoes based on axial and radial compression of cylindrical test samples (Loading rate = 50 mm/min).

		Axial compression			Radial compression
Diam. (mm)	L-D ratio	10%	20%	30%	10%	20%	30%
10	1.0	2.171^a	2.868^a	3.945^a	2.858^a	3.210^a	3.643^a
	1.5	2.613^b	3.195^a	4.080^a	2.690^a	2.741^a	2.942^b
	2.0	2.554^b	3.187^a	4.121^a	2.989^a	3.081^a	3.337^ab
15	1.0	2.792^b	3.334^b	4.385^b	3.104^b	2.949^c	3.132^b
	1.5	2.818^b	3.347^b	4.653^bc	2.610^b	2.585^b	2.727^c
	2.0	2.774^b	3.321^b	5.177^c	2.903^b	3.051^c	3.313^b
20	1.0	2.696^a	3.525^c	4.890^c	3.060^d	2.810^d	3.010^d
	1.5	2.997^b	3.941^c	4.898^c	3.004^d	2.851^d	2.919^d
	2.0	2.909^b	3.522^c	4.916^c	2.883^d	3.044^d	3.259^d
Note: Values in a column for a given diameter followed by different letters are significantly different at 0.05 level.

Figure 2 Typical force deformation plots in axial and radial compression testing of cylindrical samples of potatoes (D = 15 mm; L = 30 mm; LR = 50 mm/min).

Figure 3 Tangent modulus of elasticity as function of compression level in axial and radial compression testing (D = 15 mm; L = 30 mm; LR = 50 mm/min).

Table 2 Results of stepwise multiple regression for compression testing of cylindrical test samples of potatoes based on Eq. (5).

Tests	Predictors	a0	a1	a2	a3	R^2		SEE	F
Axial	∊	1.682	9.30E-02			0.831	0.824	0.36	122.52∗
	∊, D	0.755	9.30E-02	6.18E-02		0.922	0.916	0.25	142.05∗
	∊, D, L/D	0.443	9.30E-02	6.18E-02	0.208	0.933	0.924	0.23	105.93∗
Radial	∊	2.747	1.21E-02			0.182	0.149	0.22	5.56∗
	∊, D	2.855	1.21E-02	−7.24E-03		0.198	0.131	0.22	2.96
	∊, D, L/D	2.842	1.21E-02	−7.24E-03	9.02E-03	0.198	0.094	0.23	1.90
Note: ∗Significant (p < 0.05).

Table 3 Tangent modulus of elasticity (MPa) of potatoes based on axial and radial compression of cylindrical test samples (D = 15 mm; L = 30 mm).

	Axial compression			Radial compression
Loading rate (mm/min)	10%	20%	30%	10%	20%	30%
50	2.774^a	3.321^a	5.177^a	2.903^a	3.051^a	3.313^b
100	2.553^a	3.534^ab	4.821^a	3.006^a	2.892^a	2.938^a
200	2.796^a	3.690^abc	4.997^a	3.193^a	3.110^a	3.204^ab
300	2.867^ab	4.094^c	5.092^a	3.545^a	3.153^a	3.219^ab
400	3.159^b	3.925^bc	5.228^a	3.512^a	3.093^a	3.104^ab
Note: Values in a column followed by different letters are significantly different at 0.05 level.

Table 4 Results of stepwise multiple regression for compression testing of cylindrical test samples of potatoes based on Eq. (6).

Tests	Predictors	a0	a1	a2	R^2		SEE	F
Axial	∊	1.635	0.112		0.936	0.931	0.26	189.98∗
	∊, LR	1.374	0.112	1.24E-02	0.964	0.959	0.20	162.97∗
Radial	LR	2.957	9.22E-04		0.248	0.190	0.22	4.29
	LR, ∊	3.065	9.22E-04	−5.38E-03	0.282	0.163	0.22	2.36
Note: ∗Significant (p < 0.05).