Arif KARADEMİR, Sami İMAMOĞLU, Nihat Sami ÇETİN

Crack propagations and fatigue characteristics of some handmade papers

Bu çalışmada, dövme ve ağartma işlemi yapılmamış olan sırası ile kraft, rafinör mekanik ve pamuk linters kağıt hamurları kullanılarak bir takım standart laboratuar kağıtları yapılmış ve monoton yüklenme altında kağıtlarda oluşan çatlamalar izlenerek bunlar ile lifsel yapıların özellikleri arasındaki bağlar incelenmiştir. Uygulanan yük altında kağıtların durumunu daha iyi anlamak için, test edilen kağıt şeritlerde oluşan çatlamanın başlangıcı ve ilerlemesi de taramalı elektron mikroskobunda incelenmiştir. Kağıtların ayrıca yırtılma, çekme ve katlanma dirençleri gibi bazı mekaniksel özellikleri de test edilmiştir. Bu çalışmada esas amaç kağıtların devam eden kademeli yükleme altındaki yorulma sonuçlarını bulmak üzerine yoğunlaşmıştır. Test edilen kağıtların yorulma karakteristiklerini gösteren deneysel bir formül geliştirilmiştir. Kağıtların, bir hetorejen malzeme olarak, onu oluşturan bireysel lifler ve bu lifler arasındaki bağların durumuna göre uygulanan yüklenmelere karşı farklı davrandıkları bulunmuştur. Örneğin kraft hamurundan elde edilen standart elkağıtları en yüksek mekanik özellikler gösterirken bunu sırasıyla rafinör mekanik ve pamuk linters hamurundan yapılan standart elkağıtları izlemiştir. Genel olarak, geliştirilen formulasyonun, değişen yüklenmelere maruz kalan kağıtların yorulma değerlerini vermesi açısından iyi bir yöntem olduğu gösterilmiştir.

Bazı el kağıtlarına ait çatlama ve yorulma karakteristikleri

In this work, a number of handsheets made from unbeaten and unbleached kraft, refiner mechanical and cotton linter pulps and crack propagations on paper samples under monotonic loading, were analyzed and possible links with the properties of fibrous networks were investigated. Crack initiation and propagation on the tested paper strips were also investigated under a scanning electron microscope to determine visually the state of the paper matrix under applied loads. Furthermore, paper samples were subjected to a series of mechanical tests, such as tearing resistance, folding endurance and tensile strength. The primary goal of this study concentrated on determining the fatigue life responses of paper samples under cyclic loading. An empirical equation for the fatigue life responses of paper samples tested was developed. It was found that paper, being a heterogeneous composite material, responds differently to applied loads depending on the properties of its constituent individual fibers and the nature of interfiber bonding in its structure. Kraft handsheets, for instance, showed the highest mechanical properties, followed by samples made from refiner mechanical pulps and cotton linters respectively. Overall, the equation developed proved to be a good way of predicting the fatigue life of paper materials subjected to variable loads.

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