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.

scholarly journals Factors Affecting Mechanical Properties of the Skin of Sweet Cherry Fruit

2016 ◽  
Vol 141 (1) ◽  
pp. 45-53 ◽  
Author(s):  
Martin Brüggenwirth ◽  
Moritz Knoche
Keyword(s):  
Mechanical Properties ◽  
Water Uptake ◽  
Cell Walls ◽  
Sweet Cherry ◽  
Prunus Avium ◽  
Biaxial Strain ◽  
Factors Affecting ◽  
Fruit Skin ◽  
Cell Turgor ◽  
Cell Layers

The skins of all fruit types are subject to sustained biaxial strain during the entire period of their growth. In sweet cherry (Prunus avium L.), failure of the skin greatly affects fruit quality. Mechanical properties were determined using a biaxial bulging test. The factors considered were the following: ripening, fruit water relations (including turgor, transpiration, and water uptake), and temperature. Excised discs of fruit skin were mounted in a custom elastometer and pressurized from their anatomically inner surfaces. This caused the skin disc to bulge outwards, stretching it biaxially, and increasing its surface area. Pressure (p) and biaxial strain (ε) due to bulging were quantified and the modulus of elasticity [E (synonyms elastic modulus, Young’s modulus)] was calculated. In a typical test, ε increased linearly with p until the skin fractured at pfracture and εfracture. Stiffness of the skin decreased in ripening late stage III fruit as indicated by a decrease in E. The value of pfracture also decreased, whereas that of εfracture remained about constant. Destroying cell turgor decreased E and pfracture relative to the turgescent control. The E value also decreased with increasing transpiration, while pfracture and (especially) εfracture increased. Water uptake had little effect on E, whereas εfracture and pfracture decreased slightly. Increasing temperature decreased E and pfracture, but had no effect on εfracture. Only the instantaneous elastic strain and the creep strain increased significantly at the highest temperatures. A decrease in E indicates decreasing skin stiffness that is probably the result of enzymatic softening of the cell walls of the skin in the ripening fruit, of relaxation of the cell walls on eliminating or decreasing turgor by transpiration and, possibly, of a decreasing viscosity of the pectin middle lamellae at higher temperatures. The effects are consistent with the conclusion that the epidermal and hypodermal cell layers represent the structural “backbone” of the sweet cherry fruit skin.

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 The mechanism of rain cracking of sweet cherry fruit

Italus Hortus ◽  
2019 ◽  
Vol 26 ◽  
pp. 59-65
Author(s):  
Moritz Knoche
Keyword(s):  
Water Uptake ◽  
Malic Acid ◽  
Cell Walls ◽  
Alternative Explanation ◽  
Sweet Cherry ◽  
Middle Lamella ◽  
Published Data ◽  
Tension Stress ◽  
Sequence Of Events ◽  
Fruit Cracking

Sweet cherry (Prunus avium L.) cracking is a severe limitation in production worldwide. It is thought to be caused by excessive water uptake and a subsequent increase in turgor. When a critical threshold is exceeded (‘critical turgor’) the fruit is believed to crack. Experimental evidence supporting this wide spread concept is lacking. Instead, published data question the critical turgor hypothesis and an alternative explanation must be thought of. This mini review summarizes experimental research published in the last two decades that resulted in an alternative explanation of sweet cherry fruit cracking, the so called Zipper hypothesis. According to this hypothesis, cracking is the result of a series of events that ultimately propagate a crack through skin and flesh and ‘unzip’ the fruit. It is based on the following sequence of events: Tension (stress) develops in the skin during stage III growth and particularly in the cuticle due to a downregulation of genes involved in cutin and wax synthesis. Stress in the skin results in strain and microcracks in the cuticle. Furthermore, surface wetness on and high humidity above the strained cuticle aggravates microcracking. Microcracking impairs the cuticle’s barrier function and focuses water uptake in a particular region of the fruit surface. Water bypasses the cuticle, penetrates into the fruit and moves to sites where water potential is most negative. These are the large thin-walled parenchyma cells of the outer mesocarp that have a more negative osmotic potential than the small thick walled epidermal and hypodermal cells. Water uptake causes individual cells to burst. As a consequence, cell content leaks into the apoplast. Major constituents of sweet cherry such as glucose, fructose and malic acid now occur in the apoplast at comparable concentrations as in the symplast. The consequences are several fold: First, cell turgor decreases and is entirely lost when epidermal cells plasmolyse in the juice from the flesh. Second, malic acid extracts cell wall bound Ca, weakens cell walls and increases the permeability of plasma membranes causing a chain reaction of leakage of adjacent cells. The leakage of cells and the loss of the (low) turgor results in swelling of cell walls, in particular of the pectin middle lamella. Swollen cell walls have decreased stiffness, fracture tension and cell adhesion resulting in the separation of neighbouring cells along their cell walls. The tension generated by the strain of the skin is now sufficient to cause the cells to separate along their swollen walls and to rupture the skin. This process continues at the crack tip where the stress concentrates and causes the crack to elongate. The skin ‘unzips’ in the same way like a ‘zipper’ or a ‘ladder’ that propagates in a piece of knitted fabric.

Flatwise compression behavior of composite Nomex® honeycomb sandwich structure

2021 ◽  
pp. 109963622110354
Author(s):  
Wei Zhao ◽  
Ruodi Jia ◽  
Xin Li ◽  
Jian Zhao ◽  
Zonghong Xie
Keyword(s):  
Mechanical Properties ◽  
Cell Walls ◽  
Element Model ◽  
Tensile Tests ◽  
Numerical Results ◽  
Compression Behavior ◽  
Buckling Strength ◽  
Honeycomb Sandwich ◽  
Compressive Buckling ◽  
Honeycomb Sandwich Structure

In this paper, the mechanical properties of Nomex® paper coated with resin and composite Nomex® honeycomb sandwich structures (CNHSS) were obtained by tensile tests and flatwise tests respectively. The fundamental mechanical properties of the Nomex® paper were used as input materials parameters of finite element model generated at meso-scale level for the CNHSS, and the mechanical properties of CNHSSs were used to validate the numerical results. Based on the test and numerical results, the theoretical equations were modified to predict the flatwise compressive buckling strength and modulus of the CNHSS. The numerical and theoretical results clearly revealed that the CNHSS had two flatwise compressive elastic moduli. However, the flatwise test can only capture the second flatwise compressive elastic modulus due to manufacturing geometric defects of the cell walls. The numerical and test results showed that the manufacturing geometric defects of the cell walls showed little influence on the ultimate flatwise compressive strength. And the modified equation can predict the flatwise compressive buckling strength and modulus of the CNHSS with sufficient accuracy.

scholarly journals Synthesis, Properties, and Biodegradability of Thermoplastic Elastomers Made from 2-Methyl-1,3-propanediol, Glutaric Acid and Lactide

Life ◽  
2021 ◽  
Vol 11 (1) ◽  
pp. 43
Author(s):  
Lamya Zahir ◽  
Takumitsu Kida ◽  
Ryo Tanaka ◽  
Yuushou Nakayama ◽  
Takeshi Shiono ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Glass Transition ◽  
Transition Temperature ◽  
Glass Transition Temperature ◽  
Glutaric Acid ◽  
Triblock Copolymers ◽  
Tensile Tests ◽  
Thermoplastic Elastomers ◽  
Proteinase K ◽  
Synthesis Properties

An innovative type of biodegradable thermoplastic elastomers with improved mechanical properties from very common and potentially renewable sources, poly(L-lactide)-b-poly(2-methyl-1,3-propylene glutarate)-b-poly(L-lactide) (PLA-b-PMPG-b-PLA)s, has been developed for the first time. PLA-b-PMPG-b-PLAs were synthesized by polycondensation of 2-methyl-1,3-propanediol and glutaric acid and successive ring-opening polymerization of L-lactide, where PMPG is an amorphous central block with low glass transition temperature and PLA is hard semicrystalline terminal blocks. The copolymers showed glass transition temperature at lower than −40 °C and melting temperature at 130–152 °C. The tensile tests of these copolymers were also performed to evaluate their mechanical properties. The degradation of the copolymers and PMPG by enzymes proteinase K and lipase PS were investigated. Microbial biodegradation in seawater was also performed at 27 °C. The triblock copolymers and PMPG homopolymer were found to show 9–15% biodegradation within 28 days, representing their relatively high biodegradability in seawater. The macromolecular structure of the triblock copolymers of PLA and PMPG can be controlled to tune their mechanical and biodegradation properties, demonstrating their potential use in various applications.

Comprehensive study on mechanical properties of coated biaxial warp-knitted fabrics

2021 ◽  
pp. 073168442110204
Author(s):  
Bin Yang ◽  
Yingying Shang ◽  
Zeliang Yu ◽  
Minger Wu ◽  
Youji Tao ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Failure Modes ◽  
Least Squares Method ◽  
Tensile Tests ◽  
Tensile Creep ◽  
Base Layer ◽  
Sustained Load ◽  
Uniaxial Tensile ◽  
Membrane Structures ◽  
Knitted Fabrics

In recent years, coated fabrics have become the major material used in membrane structures. Due to the special structure of base layer and mechanical properties, coated biaxial warp-knitted fabrics are increasingly applied in pneumatic structures. In this article, the mechanical properties of coated biaxial warp-knitted fabrics are investigated comprehensively. First, off-axial tensile tests are carried out in seven in-plane directions: 0°, 15°, 30°, 45°, 60°, 75°, and 90°. Based on the stress–strain relationship, tensile strengths are obtained and failure modes are studied. The adaptability of Tsai–Hill criterion is analyzed. Then, the uniaxial tensile creep test is performed under 24-h sustained load and the creep elongation is calculated. Besides, tearing strengths in warp and weft directions are obtained by tearing tests. Finally, the biaxial tensile tests under five different load ratios of 1:1, 2:1, 1:2, 1:0, and 0:1 are carried out, and the elastic constants and Poisson’s ratio are calculated using the least squares method based on linear orthotropic assumption. Moreover, biaxial specimens under four load ratios of 3:1, 1:3, 5:1, and 1:5 are further tensile tested to verify the adaptability of linear orthotropic model. These experimental data offer a deeper and comprehensive understanding of mechanical properties of coated biaxial warp-knitted fabrics and could be conveniently adopted in structural design.

scholarly journals Influence of Hydrostatic Extrusion on the Mechanical Properties of the Model Al-Mg Alloys

2021 ◽  
Author(s):  
Aleksandra Towarek ◽  
Wojciech Jurczak ◽  
Joanna Zdunek ◽  
Mariusz Kulczyk ◽  
Jarosław Mizera
Keyword(s):  
Mechanical Properties ◽  
Plastic Deformation ◽  
Tensile Strength ◽  
Microstructural Analysis ◽  
Tensile Tests ◽  
Hydrostatic Extrusion ◽  
Microstructure Formation ◽  
Initial State ◽  
Degree Of Deformation ◽  
Al Mg Alloys

AbstractTwo model aluminium-magnesium alloys, containing 3 and 7.5 wt.% of Mg, were subjected to plastic deformation by means of hydrostatic extrusion (HE). Two degrees of deformation were imposed by two subsequent reductions of the diameter. Microstructural analysis and tensile tests of the materials in the initial state and after deformation were performed. For both materials, HE extrusion resulted in the deformation of the microstructure—formation of the un-equilibrium grain boundaries and partition of the grains. What is more, HE resulted in a significant increase of tensile strength and decrease of the elongation, mostly after the first degree of deformation.

scholarly journals Effect of Water Ingress on the Mechanical and Chemical Properties of Polybutylene Terephthalate Reinforced with Glass Fibers

Materials ◽  
2021 ◽  
Vol 14 (5) ◽  
pp. 1261
Author(s):  
Catarina S. P. Borges ◽  
Alireza Akhavan-Safar ◽  
Eduardo A. S. Marques ◽  
Ricardo J. C. Carbas ◽  
Christoph Ueffing ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Water Absorption ◽  
Water Uptake ◽  
Significant Influence ◽  
Water Immersion ◽  
Water Diffusion ◽  
Polybutylene Terephthalate ◽  
Chemical Changes ◽  
Water Ingress ◽  
Effect Of Water

Short fiber reinforced polymers are widely used in the construction of electronic housings, where they are often exposed to harsh environmental conditions. The main purpose of this work is the in-depth study and characterization of the water uptake behavior of PBT-GF30 (polybutylene terephthalate with 30% of short glass fiber)as well as its consequent effect on the mechanical properties of the material. Further analysis was conducted to determine at which temperature range PBT-GF30 starts experiencing chemical changes. The influence of testing procedures and conditions on the evaluation of these effects was analyzed, also drawing comparisons with previous studies. The water absorption behavior was studied through gravimetric tests at 35, 70, and 130 °C. Fiber-free PBT was also studied at 35 °C for comparison purposes. The effect of water and temperature on the mechanical properties was analyzed through bulk tensile tests. The material was tested for the three temperatures in the as-supplied state (without drying or aging). Afterwards, PBT-GF30 was tested at room temperature following water immersion at the three temperatures. Chemical changes in the material were also analyzed through Fourier-transform infrared spectroscopy (FTIR). It was concluded that the water diffusion behavior is Fickian and that PBT absorbs more water than PBT-GF30 but at a slightly higher rate. However, temperature was found to have a more significant influence on the rate of water diffusion of PBT-GF30 than fiber content did. Temperature has a significant influence on the mechanical properties of the material. Humidity contributes to a slight drop in stiffness and strength, not showing a clear dependence on water uptake. This decrease in mechanical properties occurs due to the relaxation of the polymeric chain promoted by water ingress. Between 80 and 85 °C, after water immersion, the FTIR profile of the material changes, which suggests chemical changes in the PBT. The water absorption was simulated through heat transfer analogy with good results. From the developed numerical simulation, the minimum plate size to maintain the water ingress unidirectional was 30 mm, which was validated experimentally.

scholarly journals Temperature-Dependent Creep Behavior and Quasi-Static Mechanical Properties of Heat-Treated Wood

Forests ◽  
2021 ◽  
Vol 12 (8) ◽  
pp. 968
Author(s):  
Dong Xing ◽  
Xinzhou Wang ◽  
Siqun Wang
Keyword(s):  
Mechanical Properties ◽  
Creep Behavior ◽  
Cell Walls ◽  
Treated Wood ◽  
Crosslinking Reaction ◽  
Depth Sensing ◽  
Temperature Dependent ◽  
Heat Treated ◽  
Static Mechanical ◽  
Static Mechanical Properties

In this paper, Berkovich depth-sensing indentation has been used to study the effects of the temperature-dependent quasi-static mechanical properties and creep deformation of heat-treated wood at temperatures from 20 °C to 180 °C. The characteristics of the load–depth curve, creep strain rate, creep compliance, and creep stress exponent of heat-treated wood are evaluated. The results showed that high temperature heat treatment improved the hardness of wood cell walls and reduced the creep rate of wood cell walls. This is mainly due to the improvement of the crystallinity of the cellulose, and the recondensation and crosslinking reaction of the lignocellulose structure. The Burgers model is well fitted to study the creep behavior of heat-treated wood cell walls under different temperatures.

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