The fatigue behavior of several wood composites was investigated in this study as a possible basis for determining allowable design stresses for these materials. Particleboard, MDF, OSB and plywood were included in the study. Specimens were tested both in static bending and fatigue. Five applied stress levels expressed as percentages of the materials' ultimate strength (MOR), were used in the fatigue tests.Results indicated that all the materials tested were able to survive a fatigue life of over 1 million cycles at stress levels equal to 30% of average MOR. Fatigue failures occurred in some materials as stress levels increased to 40% of average MOR. In general, fatigue life descreased as stress level increased and vice versa. A non-linear, power relationship appeared to adequately relate stress level and fatigue life. For furniture designs in which cyclic loading must be taken into account, it appears that allowable design stresses maybe based on some percentage of MOR in order to satisfy safety and service requirements. In particular, design stress values ranging from 30% to 40% of the average MOR may provide base values for determining allowable design stresses.
Dauerstandfestigkeit und zulassige Beanspruchung einiger Holzwerkstoffe for die Mo'belherstellungDas Langzeitverhalten einiger Holzwerkstoffe wurde untersucht als m~Sgliche Grundlage zur Ermittlung zul~issiger Beanspruchungen. Spanplatten, MDF, OSB und Sperrholz wurden sowohl mittels statischem Biegetest als auch im Dauerstandversuch gepriift. Dabei wurden ft~nf Laststufen, ausgedrfickt als Prozent der Bruchfestigkeit bzw. des MOR, eingesetzt. Alle geprtiften Materialien waren in der Lage, iiber 1 Million Belastungszyklen bei 30% der Bruchlast zu tiberstehen. Bei einigen Materialien fiihrte erst die Erh6hung auf40% der durchschnittlichen Bruchlast zum Versagen. Mit Erh6hung der Last verringerte sich die Dauerfestigkeit, wobei eine nicht lineare (exponentielle) Beziehung zwischen Belastungsstufe und Dauerstandfestigkeit besteht. Fiir M6bel, bei denen zyklische Belastungen zu erwarten sing scheint eine zul/~ssige Beanspruchung yon einigen Prozent der Bruchlast auszureichen, um die Anforderungen an Sicherheit und Haltbarbeit zu gew~rleisten. [nsbesondere Werte zwischen 30 und 40% des durchschnittlichen MOR k6nnen als Grundlage zur Absch~itzung der zul~issigen Beanpruchung herangezogen werden.
In order to solve the problem of the strong ore pressure in the mining process of a shallow buried coal seam working face, the ore pressure law of a shallow buried coal seam working face was observed. According to the observation results of ore pressure, the law and characteristics of ore pressure on the working face of shallow buried coal seam are analyzed, the basic law and parameters of roof movement and the roof plate falling situation on the end face on the working face are obtained, and the rationality of the support is studied.
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