خصوصیات برشی، خمشی و فشاری ساقه نیشکر در قسمت های مختلف ساقه

نوع مقاله: مقاله پژوهشی

نویسندگان

1 دانشیار گروه مهندسی بیوسیستم دانشگاه علوم کشاورزی و منابع طبیعی ساری

2 دانشجوی کارشناسی ارشد گروه مهندسی بیوسیستم دانشگاه علوم کشاورزی و منابع طبیعی گرگان

چکیده

ساقه نیشکر به هنگام برداشت و پس از آن در معرض بارهای مکانیکی مختلف قرار دارد. طراحی و بهینه سازی دستگاه های برداشت و فرآوری نیشکر نیاز به مطالعه خصوصیات مکانیکی و فیزیکی محصول و ارتباط آنها با ماشین دارد. در این تحقیق، خصوصیات برشی، فشاری و خمشی ساقه در سه قسمت از ساقه (پایین، وسط و بالا)  و در دو نقطه (روی گره و بین گره ها) در قالب آزمایش فاکتوریل بر پایه طرح کاملا تصادفی در سه تکرار تجزیه و تحلیل شدند. نتایج نشان داد که تیمارهای آزمایشی در قسمت های مختلف ساقه اختلاف معنی دار دارند. مقاومت برشی و نیز مدول الاستیسیته و تنش حاصل از بارگذاری خمشی در قسمت های پایین تر ساقه و نقاط روی گره  بیشتر از نقاط دیگر می باشند. انرژی برشی مخصوص در قسمت های بالایی ساقه و روی گره بیشتر بود؛ در حالی­که انرژی حاصل از بارگذاری فشاری و خمشی در این نقاط کمتر بود. مقاومت برشی ساقه، مدول الاستیسیته فشاری، تنش خمشی و مدول خمشی در قسمت پایین ساقه و روی گره به ترتیب مگاپاسکال 47/2، 3/215، 4/93 و 3/721 و در قسمت بالای ساقه و بین گره ها به ترتیب مگاپاسکال 53/1، 5/84، 2/79 و 7/636 به­دست آمد. همچنین، انرژی برشی مخصوص، انرژی فشاری و خمشی در قسمت پایین ساقه و روی گره به ترتیب  mJ.mm-2 8/41، 3/111 و 2/110 و در قسمت بالای ساقه و بین گره ها به ترتیب  mJ.mm-2 1/56، 1/44 و 4/72 به­دست آمد. به­طور کلی می توان گفت که قسمت های پایین ساقه دارای ساختار سلولی و فیبری محکم بوده و در نتیجه بافت خشبی و سفت تری دارند و در قسمت گره نیز سلول­ها به­صورت رشته های مارپیچی و درهم تنیده هستند. بنابراین، خصوصیات مکانیکی ساقه نیشکر در قسمت های مختلف تحت تاثیر ساختار سلولی ساقه قرار می گیرد.

کلیدواژه‌ها


عنوان مقاله [English]

Shearing, compression and bending properties of sugarcane at different portions

نویسندگان [English]

  • R. Tabatabaekoloor 1
  • R. Hadipour 2
چکیده [English]

Introduction Sugarcane is one of the most important crops for sugar production. Iran produces about 6800 tons of sugarcane from 88000 ha. Sugarcane is subjected to different loading during harvest and postharvest processes. In order to design and modify sugarcane harvesting and processing machines there is a need to study the physical and mechanical properties of crops and their relationship with the machines.
Materials and Methods In this study, the experiments were performed on the sugarcane variety of CP48 supplied from Bahnamir city in Mazandaran province, Iran. The physical properties such as moisture content, diameter and linear density were measured. The relationship between linear density and diameter of sugarcane stem was determined on the node and between nodes and also at different heights of stem. Three mechanisms were developed and assembled to a universal testing machine (ASTM50) to measure the shearing, bending and compressing forces of stem. Experiments were conducted on stem samples of 5 cm length. The sugarcane properties in shear, compression and bending were determined using the related equations. All experiments were conducted at three portions of stem (bottom, middle and up) and two points (node and inter nodes). Data were analyzed using a factorial test based on a completely randomized design.
Results and Discussion The results of analysis of variance showed that height (bottom, middle and up) and cutting place (on the node and inter nodes) had significant effects on the shear strength and specific shear energy. The shear strength at the bottom and on the node of stem was higher than other parts of stem, but in reverse specific shear energy at the top of stem was higher.  The lower parts of stem due to cellular structure and stiff and thick fibers had higher strength. The specific shearing energy at upper portion and on the node was higher than the bending and compression energy at these points. The maximum amount of shear strength was 2.47 Mpa at the bottom of stem and on the node. The specific shear energy was obtained from the area under force-displacement diagram and increased at the upper parts of stem. The maximum and minimum specific shear energy was 56.1 and 41.8 mJ.mm-2, respectively.  Analysis of variance showed a significant effect of height and cutting place on the bending stress, bending energy and bending modulus of elasticity for sugarcane stem. The variation range of bending stress from bottom to the top of the stem was 93.4-79.2 Mpa. The bending energy of sugarcane stem was changed from 72.4 to 110.2mJ.mm-2. It was significantly higher in the bottom of the stem than the upper part of the stem. Also, the bending module of elasticity was changed from 721.3 Mpa at the bottom of the stem to 636.7 Mpa at the top of the stem. The effect of height and cutting place on the compressive modulus of elasticity and compressive energy was significant. There was a difference between compressive forces at different parts of stem. The upper parts of stem had less pressure force due to cavity of inter cellular structures. It was 111.3 Mpa at the bottom of the stem and 44.1 Mpa at the top of the stem. The compressive energy at upper parts reduced significantly as the maximum was 215.3 Mpa on the node and the minimum was 84.5 Mpa between nodes. Modulus of elasticity and bending stress at the upper portion and on the node was higher than other points. The same behavior was observed for compressive energy. The compressive modulus of elasticity showed a significant difference at different parts of the stem but there was no meaningful difference between nodes and on the nodes of the stem.
Conclusion The results indicated that shear, compressive and bending properties of sugarcane stem were affected by height on the stem. Shear strength was obtained at the range of 1.53-2.47 Mpa at different parts of the stem. The compressive force at the lower parts of the stem was higher than top of the stem. The maximum compressive module of elasticity was 215.3 Mpa on the node and at the bottom of stem. Also, the maximum compressive energy at the bottom of the stem was 111.3 Mpa and at the top of the stem it was 44.1 Mpa. The range of bending stress was obtained from 79.2 to 93.4 Mpa. In general, the results indicated that the lower parts of the stem due to cellular structure and stiff and thick fibers and the nodes due to complex structure and intersection of fibers have more strength than other portions. Therefore, mechanical properties of sugarcane stem are the function of stem structure at different points.

کلیدواژه‌ها [English]

  • Sugarcane
  • Shear
  • Bending
  • Compression