scholarly journals Biaxial tensile tests identify epidermis and hypodermis as the main structural elements of sweet cherry skin

AoB Plants ◽  
2014 ◽  
Vol 6 ◽  
Author(s):  
Martin Brüggenwirth ◽  
Heiko Fricke ◽  
Moritz Knoche
Keyword(s):  
Sweet Cherry ◽  
Tensile Tests ◽  
Structural Elements ◽  
Biaxial Tensile

scholarly journals Time to Fracture and Fracture Strain are Negatively Related in Sweet Cherry Fruit Skin

2016 ◽  
Vol 141 (5) ◽  
pp. 485-489 ◽  
Author(s):  
Martin Brüggenwirth ◽  
Moritz Knoche
Keyword(s):  
Tensile Test ◽  
Water Uptake ◽  
Sweet Cherry ◽  
Tensile Tests ◽  
Volume Increase ◽  
Biaxial Tensile Test ◽  
Biaxial Tensile ◽  
Rate Of Increase ◽  
Fruit Skin ◽  
Time To Fracture

Rain cracking of sweet cherry fruit (Prunus avium L.) is said to occur when the volume increase associated with water uptake, extends the fruit skin beyond its upper mechanical limits. Biaxial tensile tests recorded fracture strains (εfracture) in the range 0.17 to 0.22 mm2·mm−2 (equivalent to 17% to 22%). In these tests, an excised skin segment is pressurized from its inner surface and the resulting two-dimensional strain is quantified. In contrast, the skins of fruit incubated in water in classical immersion assays are fractured at εfracture values in the range 0.003 to 0.01 mm2·mm−2 (equivalent to 0.3% to 1%)—these values are one to two orders of magnitude lower than those recorded in the biaxial tensile tests. The markedly lower time to fracture (tfracture) in the biaxial tensile test may account for this discrepancy. The objective of our study was to quantify the effect of tfracture on the mechanical properties of excised fruit skins. The tfracture was varied by changing the rate of increase in pressure (prate) and hence, the rate of strain (εrate) in biaxial tensile tests. A longer tfracture resulted in a lower pressure at fracture (pfracture) and a lower εfracture indicating weaker skins. However, a 5-fold difference in εfracture remained between the biaxial tensile test of excised fruit skin and an immersion assay with intact fruit. Also, the percentage of epidermal cells fracturing along their anticlinal cell walls differed. It was highest in the immersion assay (94.1% ± 0.6%) followed by the long tfracture (75.3% ± 4.7%) and the short tfracture (57.3% ± 5.5%) in the biaxial tensile test. This indicates that the effect of water uptake on cracking extends beyond a mere increase in fruit skin strain resulting from a fruit volume increase. Instead, the much lower εfracture in the immersion assay indicates a much weaker skin—some other unidentified factor(s) are at work.

scholarly journals Mechanical Properties of Skins of Sweet Cherry Fruit of Differing Susceptibilities to Cracking

2016 ◽  
Vol 141 (2) ◽  
pp. 162-168 ◽  
Author(s):  
Martin Brüggenwirth ◽  
Moritz Knoche
Keyword(s):  
Mechanical Properties ◽  
Creep Strain ◽  
Water Uptake ◽  
Cell Walls ◽  
Plasma Membranes ◽  
Sweet Cherry ◽  
Tensile Tests ◽  
Cultivar Differences ◽  
Repeated Loading ◽  
Biaxial Tensile

Rain cracking of sweet cherry fruit (Prunus avium L.) may be the result of excessive water uptake and/or of mechanically weak skins. The objectives were to compare mechanical properties of the skins of two cultivars of contrasting cracking susceptibility using biaxial tensile tests. We chose ‘Regina’ as the less-susceptible and ‘Burlat’ as the more-susceptible cultivar. Cracking assays confirmed that cracking was less rapid and occurred at higher water uptake in ‘Regina’ than in ‘Burlat’. Biaxial tensile tests revealed that ‘Regina’ skin was stiffer as indexed by a higher modulus of elasticity (E) and had a higher pressure at fracture () than ‘Burlat’. There was little difference in their fracture strains. Repeated loading, holding, and unloading cycles of the fruit skin resulted in corresponding changes in strains. Plotting total strains against the pressure applied for ascending, constant, and descending pressures yielded essentially linear relationships between strain and pressure. Again, ‘Regina’ skin was stiffer than ‘Burlat’ skin. Partitioning total strain into elastic strain and creep strain demonstrated that in both cultivars most strain was accounted for by the elastic component and the remaining small portion by creep strain. Differences in E and between ‘Regina’ and ‘Burlat’ remained even after destroying their plasma membranes by a freeze/thaw cycle. This indicates that differences in skin mechanical properties must be accounted for by differences in the cell walls, not by properties related to cell turgor. Microscopy of skin cross-sections revealed no differences in cell size between ‘Regina’ and ‘Burlat’ skins. However, mass of cell walls per unit fresh weight was higher in ‘Regina’ than in ‘Burlat’. Also, the ratio of tangential/radial diameters of epidermal cells was lower in ‘Regina’ (1.86 ± 0.12) than in ‘Burlat’ (2.59 ± 0.15). The results suggest that cell wall physical (and possibly also chemical) properties account for the cultivar differences in skin mechanical properties, and hence in cracking susceptibility.

Experimental Investigation of Ti-6Al-4V with a Biaxial Tensile Test Setup at Elevated Temperature

2014 ◽  
Vol 622-623 ◽  
pp. 273-278 ◽  
Author(s):  
Marion Merklein ◽  
Sebastian Suttner ◽  
Adam Schaub
Keyword(s):  
Elevated Temperature ◽  
Elevated Temperatures ◽  
Tensile Tests ◽  
Advanced Materials ◽  
Uniaxial Tensile ◽  
Plastic Yielding ◽  
Characterization Methods ◽  
Specific Strength ◽  
Biaxial Tensile ◽  
Stress States

The requirement for products to reduce weight while maintaining strength is a major challenge to the development of new advanced materials. Especially in the field of human medicine or aviation and aeronautics new materials are needed to satisfy increasing demands. Therefore the titanium alloy Ti-6Al-4V with its high specific strength and an outstanding corrosion resistance is used for high and reliable performance in sheet metal forming processes as well as in medical applications. Due to a meaningful and accurate numerical process design and to improve the prediction accuracy of the numerical model, advanced material characterization methods are required. To expand the formability and to skillfully use the advantage of Ti-6Al-4V, forming processes are performed at elevated temperatures. Thus the investigation of plastic yielding at different stress states and at an elevated temperature of 400°C is presented in this paper. For this reason biaxial tensile tests with a cruciform shaped specimen are realized at 400°C in addition to uniaxial tensile tests. Moreover the beginning of plastic yielding is analyzed in the first quadrant of the stress space with regard to complex material modeling.

Design of a Flat Plate Specimen Suitable for Biaxial Tensile Tests on Polymer Materials

2015 ◽  
Vol 23 (9) ◽  
pp. 627-638 ◽  
Author(s):  
Nayeem Tawqir Chowdhury ◽  
John Wang ◽  
Wing Kong Chiu
Keyword(s):  
Flat Plate ◽  
Tensile Tests ◽  
Polymer Materials ◽  
Biaxial Tensile ◽  
Plate Specimen

Macroindentation of a soft polymer: Identification of hyperelasticity and validation by uni/biaxial tensile tests

2013 ◽  
Vol 64 ◽  
pp. 111-127 ◽  
Author(s):  
Zhaoyu Chen ◽  
Tobias Scheffer ◽  
Henning Seibert ◽  
Stefan Diebels
Keyword(s):  
Tensile Tests ◽  
Biaxial Tensile ◽  
Soft Polymer

scholarly journals Water on the Surface Aggravates Microscopic Cracking of the Sweet Cherry Fruit Cuticle

2006 ◽  
Vol 131 (2) ◽  
pp. 192-200 ◽  
Author(s):  
Moritz Knoche ◽  
Stefanie Peschel
Keyword(s):  
Outer Surface ◽  
Liquid Water ◽  
Sweet Cherry ◽  
Prunus Avium ◽  
Developmental Stages ◽  
Tensile Tests ◽  
Deionized Water ◽  
Cuticular Membrane ◽  
High Concentrations ◽  
Fruit Surface

The effect of surface water on the frequency of microcracks in the cuticular membrane (CM) of exocarp segments (ES) of developing sweet cherry fruit (Prunus avium L.) was studied. Strain of CM and ES on the fruit surface was preserved by mounting a stainless steel washer on the fruit surface in the cheek region using an ethyl-cyanacrylate adhesive. ES were excised by tangentially cutting underneath the washer. Frequency of microcracks in the CM of ES was determined following infiltration for 10 minutes with a 0.1% acridine orange solution by fluorescence microscopy before and after exposure to deionized water (generally 48 hours). Exposing the surface of ES of mature `Burlat' sweet cherry fruit to water resulted in a rapid increase in microcracks in the CM that approached an asymptote at about 30 microcracks/cm2 within 24 hours. There was no change in microcracks in the CM when the surface of the ES remained dry. Incubating ES in polyethylene glycol solution that was isotonic to fruit juice extracted from the same batch of fruit resulted in a greater increase in frequency of microcracks as compared to incubation in deionized water. The water-induced increase in microcracks was closely related to strain of the CM across different developmental stages within a cultivar [between 45 and 94 days after full bloom (DAFB); r2 = 0.96, P ≤ 0.001, n = 9] or across different cultivars at maturity (r2 = 0.92, P ≤ 0.0022, n = 6). Incubating ES of developing fruit in enzyme solution containing pectinase and cellulase such that the outer surface remained dry resulted in complete rupture and failure of the ES. Time to rupture and percentage of ruptured ES were closely related to the strain of the CM (r2 = 0.92, P ≤ 0.001, n = 9 and r2 = 0.68, P ≤ 0.0063, n = 9, respectively). Removal of epicuticular wax had no effect on frequency of water-induced microcracks. Also, temperature had no effect on frequency of water-induced microcracks, but frequency of microcracks increased exponentially when exposing the outer surface of ES to relative humidities above 75%. At 100% humidity the increase in frequency of microcracks did not differ from that induced by liquid water. Local wetting the surface of intact fruit in the pedicel cavity or stylar end region resulted in formation of macroscopically visible cracks despite of a net water loss of fruit. Uniaxiale tensile tests using dry and fully hydrated CM strips isolated from mature `Sam' sweet cherry fruit established that hydration increased fracture strain, but decreased fracture stress and moduli of elasticity. Our data demonstrate that exposure of the fruit surface to liquid water or high concentrations of water vapor resulted in formation of microcracks in the CM.

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