Effect of specimen geometry on axial compressive strength variability in Oriental beech (Fagus orientalis Lipsky) and common hornbeam (Carpinus betulus L.) wood

Öz

The parallel-to-grain compressive strength of solid wood is significantly influenced by specimen geometry, slenderness ratio (the ratio of specimen length to characteristic cross-sectional dimension), and loading boundary conditions, alongside its heterogeneous and anisotropic structure. In this study, the combined effect of different specimen dimensions and slenderness ratios specified in international standards on the compressive strength of Oriental beech (Fagus orientalis Lipsky) and common hornbeam (Carpinus betulus L.) wood was investigated using a multidisciplinary approach. Experimental data were analysed using Weibull statistics, Bažant’s Size Effect Law (SEL), Carpinteri’s Multifractal Scaling Law (MFSL), and a three-dimensional orthotropic finite element method (FEM). Statistical findings revealed that the species × size interaction was highly significant (p < 0.001) in governing the mechanical response. Hornbeam wood exhibited a consistent loss of strength with increasing specimen volume, displaying a scaling behaviour compatible with Weibull and MFSL approaches. In contrast, beech wood displayed maximum strength at low slenderness ratios, generating a non-linear size effect. Whilst the Bažant SEL model showed a poor fit with the beech data, it failed to yield physically meaningful scaling parameters for hornbeam despite demonstrating a high regression fit. FEM-based stress analyses revealed the three-dimensional stress distribution within the specimens under experimental ultimate loads, enabling a mechanical assessment of the effects of slenderness ratios on stress concentrations and load transfer. Consequently, the findings demonstrate that explaining the compressive strength of solid wood solely through volumetric defect distribution may be insufficient; thus, in reliable engineering designs, the statistical size effect should be evaluated in an integrated manner with geometry- and contact-induced deterministic mechanisms.

Anahtar Kelimeler

• Compressive strength
• Fracture mechanics
• Finite element analysis
• Weibull distribution

Doğu kayını (Fagus orientalis Lipsky) ve adi gürgen (Carpinus betulus L.) odunlarında numune geometrisinin basınç dayanımı değişkenliği üzerindeki etkisi

Öz

Masif odunun liflere paralel basınç dayanımı, heterojen ve anizotropik yapısının yanı sıra numune geometrisi, narinlik oranı (numune uzunluğunun karakteristik kesit boyutuna oranı) ve yükleme sınır koşullarından önemli ölçüde etkilenmektedir. Bu çalışmada, Doğu kayını (Fagus orientalis Lipsky) ve adi gürgen (Carpinus betulus L.) odunlarında uluslararası standartlardaki farklı numune boyutları ve narinlik oranlarının basınç dayanımı üzerindeki birleşik etkisi çok disiplinli bir yaklaşımla araştırılmıştır. Deneysel veriler, Weibull istatistikleri, Bažant’ın Boyut Etkisi Yasası (SEL), Carpinteri’nin Çoklu-Fraktal Ölçekleme Yasası (MFSL) ve üç boyutlu ortotropik sonlu elemanlar yöntemi (FEM) ile analiz edilmiştir. İstatistiksel bulgular, tür × boyut etkileşiminin mekanik özellikler üzerinde son derece belirleyici olduğunu (p < 0,001) göstermiştir. Gürgen odunu, numune hacmi arttıkça istikrarlı bir dayanım kaybı sergileyerek Weibull ve MFSL yaklaşımlarıyla uyumlu bir ölçeklenme davranışı sunmuştur. Buna karşın kayın odunu, düşük narinlik oranlarında maksimum dayanım sergileyerek doğrusal olmayan bir boyut etkisi oluşturmuştur. Bažant SEL modeli kayın verileriyle zayıf bir uyum gösterirken, gürgende yüksek regresyon uyumuna rağmen fiziksel olarak anlamlı ölçekleme katsayıları üretememiştir. FEM analizleri, deneysel nihai yükleme koşullarında numune içerisindeki üç boyutlu gerilme dağılımını ortaya koymuş ve farklı geometrik narinlik oranlarının gerilme yığılmaları ile yük aktarımı üzerindeki etkisinin mekanik olarak değerlendirilmesine olanak sağlamıştır. Sonuç olarak bulgular, masif odunun basınç dayanımının yalnızca hacimsel kusur dağılımıyla açıklanmasının yetersiz kalabileceğini, güvenilir mühendislik tasarımlarında istatistiksel boyut etkisinin, geometri ve temas kaynaklı fiziksel mekanizmalarla entegre biçimde değerlendirilebileceğini göstermektedir.

Anahtar Kelimeler

• Basınç dayanımı
• Kırılma mekaniği
• Sonlu elemanlar analizi
• Weibull dağılımı

Etik Beyan

Etik kurul onayı gerekmemektedir.

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