Mechanical Behaviour of Unshelled Moringa oleifera Seeds at Varying Moisture Contents

The determination of mechanical properties of unshelled Moringa oleifera seeds was studied under compression test at varying orientations and moisture contents for postharvest equipment design. A completely randomized block design (CRBD) was applied in designing the experiment. The impact of varying moisture content levels of (10.25, 17.33, 24.47, and 32.34% dry basis) on the applied force at bio-yield and rupture, deformation, energy at rupture, crushing strength, and elastic modulus of the seed samples were investigated. Polynomial functions of the 2nd order with coefficients of correlation ranging between 0.642 ≤ R2 ≤ 0.999 gave the best fit and described the resulting relationships between the studied properties with respect to moisture levels at the two loading axes. Results obtained showed that the seed samples had maximum values of 80.3 N, 110 N and 257.2 J, for bio-yield force, rupture and rupture energy respectively at (10.25% d.b., in the horizontal orientation; whereas minimum values of 31.5 N, 54.9 N and 51.3 J for bio-yield force, rupture force and rupture energy occurred at (32.34% d.b.) respectively in the vertical orientation. Also, the maximum compressive strength of 5.8 N mm-2 in the horizontal orientation of the seed samples at 10.25% d.b. whereas the minimum compressive strength (2.5 N mm-2) occurred in the vertical orientation at 10.25% d.b. moisture content. The sample exhibited less resistive strength to crushing in the horizontal position as the moisture increased; whereas in the vertical position, the cell’s vertical edges provide some form of shield against external pressure which resulted in increased crushing resistance per contact area of the sample.

Study of Selected Physical-Mechanical Properties of Corn Grains Important from the Point of View of Mechanical Processing Systems Designing

Mechanical properties of corn grains are of key importance in a design of processing machines whose energy demand depends on these properties. The aim of this study is to determine the selected mechanical properties of corn grains and the rupture energy. The research problem was formulated as questions: (1) How much force and energy is needed to induce a rupture of corn grain maintaining good quality of the product of processing (mixing, grinding transport)? (2) Can empirical distributions of the studied physical-mechanical properties be described by means of probability distributions provided by the literature? (3) Is there a relationship between the corn grain size and the selected mechanical properties, as well as rupture energy? In order to achieve the goals, the selected physical properties (size, volume) of corn grains have been distinguished and a static compression test has been carried out on an Instron 5966 testing machine. The results indicate a significant scatter of the results in terms of size, grain shape, forces, energy, and deformation corresponding to the point of inflection, bioyiled point, and rupture point. It has also been indicated that empirical distributions of the analyzed properties can be described by means of distributions known from the literature, e.g., gamma, Weibull or lognormal distributions. It has been confirmed that mechanical properties such as force, energy, and stress that cause rupture depend on the grain size, more precisely, the grain thickness—there are negative relations between thickness and force, energy and stress in relation to the point of inflection, bioyiled point, and rupture point.

On the scale dependence in the dynamics of rupture

<p>Potential energy stored during the inter-seismic period by tectonic loading around faults can be released through earthquakes as radiated energy, heat and rupture energy. The latter is of first importance, since it controls both the nucleation and the propagation of the seismic rupture. On one side, the rupture energy estimated for natural earthquakes (also called Breakdown work) ranges between 1 J/m<sup>2</sup> and tens of MJ/m<sup>2</sup> for the largest events, and shows a clear slip dependence. On the other side, recent experimental studies highlighted that at the scale of the laboratory, rupture energy is a material property (energy required to break the fault interface), limited by an upper bound value corresponding to the rupture energy of the intact material (1 to 10 kJ/m<sup>2</sup>), independently of the size of the event, i.e. of the seismic slip.</p><p>To reconcile these contradictory observations, we performed stick-slip experiments, as an analog for earthquakes, in a bi-axial shear configuration. We analyzed the fault weakening during frictional rupture by accessing to the on-fault (1 mm away) stress-slip curve through strain-gauge array. We first estimated rupture energy by comparing the experimental strain with the theoretical predictions from both Linear Elastic Fracture Mechanics (LEFM) and the Cohesive Zone Model (CZM). Secondly, we compared these values to the breakdown work obtained from the integration of the stress-slip curve. Our results showed that, at the scale of our experiments, fault weakening is divided into two stages; the first one, corresponding to an energy of few J/m<sup>2</sup>, coherent with the estimated rupture energy (by LEFM and CZM), and a long-tailed weakening corresponding to a larger energy not observable at the rupture tip.</p><p>Using a theoretical analysis and numerical simulations, we demonstrated that only the first weakening stage controls the nucleation and the dynamics of the rupture tip. The breakdown work induced by the long-tailed weakening can enhance slip during rupture propagation and can allow the rupture to overcome stress heterogeneity along the fault. Additionally, we showed that at a large scale of observation the dynamics of the rupture tip can become controlled by the breakdown work induced by the long-tailed weakening, leading to a larger stress singularity at the rupture tip which becomes less sensitive to stress perturbations. We suggest that while the onset of frictional motions is related to fracture, natural earthquakes propagation is driven by frictional weakening with increasing slip, explaining the large values of estimated breakdown work for natural earthquakes, as well as the scale dependence in the dynamics of rupture.</p>

Bridging the failure of surface asperities to the macroscopic rupture energy during the onset of frictional sliding

<p>The onset of sliding between two rough surfaces held in frictional contact arises through the nucleation and propagation of rupture fronts, whose dynamics has been shown to obey the elastodynamics of a shear crack. By analogy with the fracture energy controlling the growth of brittle crack in intact material, a frictional rupture is governed by an associated rupture energy. In the context of earthquakes, this rupture energy is expected to control the nucleation and the transition from an accelerating slip patch or localized perturbation to a propagating seismic rupture. The microscopic origin of this rupture energy and its relation to the microcontacts topography remain however unsettled.</p><p>In this context, this study aims at bridging the macroscopic description of friction to the failure of contacting asperities and frictional wear prevailing at smaller scales. Recent studies demonstrated how the failure of two contacting asperities arises either by plastic deformation or brittle failure of their apices depending on whether their contact junction is respectively smaller or larger than a characteristic length scale. In this study, we investigate numerically how the different failure mechanisms of microcontact asperities impact the nucleation and propagation of frictional rupture fronts.</p><p>At a macroscopic level, we study the ability of an interface to withstand a progressively applied shearing, i.e. its frictional strength, while at the microscopic scale, we observe how the failure process develops across the microcontact junctions. We highlight how the microcontacts topography significantly impacts the nucleation and frictional strength, even when comparing interfaces with identical macroscopic properties and rupture energy. We present how the characteristic length governing microcontacts failure can be used to select which details of the surface roughness are homogenized along the tip of a nucleating slip front. Combining the approach proposed in this work with models solving normal contact between rough surfaces will open up new prospects to study the strength and rupture energy of frictional interfaces at the onset of sliding.</p>

On energy relationships between explosive rupture and extraction processes at quarries

The article deals with the links between mineral extraction processes. The most universal characteristic of the process is its energy intensity. Production process cycles are considered in the relationship between their energy characteristics, taking into account the extraction in the working face over time. This approach has been largely determined by earlier studies in the direction of studying the energy intensity of technological processes. However, the relationship between explosive rupture energy and excavation has not been established, although the link between explosive preparation and the performance of the excavation equipment was stated in the technical literature multiple times. The presented material analyzed previously published materials on establishing relationships between drilling and explosive rupture processes of rock massif. The energy characteristics of excavation works and explosive rupture were considered. Prospective direction of technological links study was proposed. Attention is drawn to the fact that the approach to relationships definition between processes may not always be monotonous, because it is sometimes difficult to express physical meaning in a flat system.

The physical properties and strength characteristics of kenaf plants

This article reports some physical properties and strength characteristics of two kenaf (Hibiscus cannabinus) varieties in Nigeria at critical stages of harvest with a view of understanding the plant material reaction to the load and deformation. The kenaf samples were subjected to a uniaxial compression test between two parallel plates at a loading rate of 20 mm·min^–1 and a uniaxial bending test between two supports on each end at a loading rate of 50 mm·min^–1using a Universal Instron Testing Machine (Instron, USA). The results of the parameters studied revealed that Tianung 1 gave the higher stem height, stem diameter, compressive stress, bending stress, rupture load, rupture energy, Young’s modulus, and toughness, which were 293.10 cm, 18.45 mm, 8.70 MPa, 44.86 MPa, 191.51 N, 3.43 J·mm^–2, 350.81 MPa, and 6.85 N·mm^–1, respectively, at four months after planting. The parameters studied significantly increased with maturity for the two kenaf varieties. However, the moisture content significantly reduced with maturity.

Mechanical Behaviour of Common Bean (cv. Butter) Seeds as Affected by Maturation

In this study, the effects of maturation of bean seeds on some mechanical behaviours of common bean (cv. Butter) were investigated. The bean seeds were harvested at three maturity stages (15 DAPA, 22 DAPA and 29 DAPA), and their rupture force, rupture energy, specific deformation, toughness and rupture power were test. The bean seeds were quasi-statically loaded in along their three main axes (X-axis, Y-axis and Z-axis), at a loading speed of 25 mm/min. The results obtained revealed that the maturity stage and loading orientation had significant (p ≤0.05) effect on all the mechanical parameters investigated in this study. According to the results, all the parameters investigated increased linearly as the bean seeds matured from 15 DAPA to 29 DAPA. For all the mechanical parameters, the highest values were obtained when the seeds were compressed along the Z-axis, while the least values were obtained when the seeds were compressed along the Y-axis. The highest rupture energy (0.064 Nm) was obtained for bean seeds (harvested at 29 DAPA) loaded along the Z-axis, while the bean seeds harvested at 15 DAPA and loaded along the Y-axis required the least energy to rupture (0.028 Nm). From the results, at 29 DAPA, the mean rupture power of 0.277 W, 0.212 W, and 0.314 W were recorded, when the seeds were compressed along the X-axis, Y-axis and Z-axis respectively. These results will be useful in the design and development of bean seeds processing and handling equipment.

EFFECT OF STORAGE DURATION ON MECHANICAL PROPERTIES OF BELLO EGGPLANT FRUIT UNDER QUASI COMPRESSION LOADING

The mechanical properties of eggplant fruit (cv. Bello) harvested at physiological maturity stage were evaluated in three storage periods (3d, 6d and 9d). These mechanical parameters (rupture force, rupture energy and deformation at rupture point) were measured under quasi compression loading, using the Universal Testing Machine (Testometric model). The fruit’s toughness and rupture power were calculated from the data obtained from the rupture energy and deformation at rupture point. Results obtained showed that mechanical properties of the Bello eggplant fruit exhibited strong dependence on the storage period. The results showed that as the Bello fruit stored longer, its rupture force and rupture energy decreased from 812 N to 411 N, and 5.58 Nm to 3.11 Nm respectively. While the rupture power decreased from 1.095 W to 0.353 W. On the contrary, the toughness and deformation at rupture increased from 0.270 mJ/mm3 to 0.403 mJ/mm3, and 16.99 mm to 25.22mm respectively during the 9 days storage period. The knowledge of the mechanical properties of fruits is important for their harvest and post-harvest operations, therefore, information obtained from this study will be useful in the design and development of machines for the mechanization of eggplant production.

Moisture and Rupture Models for Corn (Zea mays) Seeds of Different Endosperm Types

Mechanization of postharvest handling and conditioning inflicts damage on the physical, physiological, and sanitary qualities of corn (Zea mays) seeds, resulting in significant economic loss. The mechanical damage is related to the compression strength and strain, and therefore to the moisture content (MC) and endosperm type. This study was conducted from 2012 to 2014 at the Montecillo and Chapingo agricultural institutes in Mexico, where physical properties such as volumetric weight; apparent density; rupture compression strength, strain, and energy; and endosperm type were evaluated for five corn seed cultivars (floury, semi-floury, floury-flint, semi-flint, and flint) at seven MC levels (8%, 12%, 16%, 20%, 24%, 28%, and 32% w.b.). The aim of this study was to develop moisture-strength, moisture-strain, and moisture-energy regression models for postharvest handling of corn to prevent quality loss due to mechanization. For three model groups, the relationship (1) between MC and rupture strain was linear and directly proportional for the five studied cultivars; (2) between MC and rupture strength was linear and directly proportional for the floury cultivar, inverse for the semi-flint and flint cultivars, and quadratic for the semi-floury and floury-flint cultivars; and (3) between MC and rupture energy was linear and directly proportional for the floury cultivar and quadratic for the semi-floury, floury-flint, semi-flint, and flint cultivars. The models obtained in this study might be used as a reference for better handling of corn seeds, as none of the five studied varieties had a uniformly superior rupture strength, strain, or energy at the studied MC levels. Floury endosperm types might be handled at high MC and flint endosperm types might be handled at low MC to avoid mechanical damage produced by static loads; both types of endosperm support greater energy loads, e.g., impact, at higher MC. Keywords: Compression, Corn quality, Flint endosperm, Floury endosperm, Moisture, Zea mays.

Physical Properties of Upper Midwest U.S.-Grown Hybrid Hazelnuts

Nuts from F1 hybrid hazelnuts grown in Wisconsin were harvested and dried to eight different moisture contents. Nut dimensions and mass were recorded. Nuts were then subjected to uniaxial compression to determine total deformation required for rupture, rupture force, and rupture energy for each of the three major nut axes. Kernel dimensions, shell thickness, shell mass, and kernel mass of each nut were recorded after rupture. Hybrid hazelnuts and kernels were found to be smaller than European varieties. Nut geometry was found to change with nut size. When a nut is loaded, an initial crack forms along a longitudinal line parallel to the direction of applied load and then rapidly propagates until it has extended along two longitudinal lines (both parallel to the applied load), causing the shell to split into two pieces. Under lateral (Y-axis and Z-axis) loadings, the shell is split into nearly identical halves. Loading along the X-axis required the lowest rupture force, rupture energy, and rupture strain of all loading axes. Rupture force, rupture energy, and stiffness were shown to be highly correlated with moisture content. At lower moisture contents, shells fractured into more pieces. Keywords: Hazelnut, Nut cracking, Nut geometry, Nut rupture force, Shelling, Shell thickness.