THE MIXED MODE FRACTURE CRITERION OF BRITTLE ROCK UNDER COMPRESSION-SHEAR STRESS STATE

In this paper the test results of mixed mode fracture of three kinds of brittle rock under two kinds of stress paths are reported. The fracture mechanism and failure patterns of brittle lock under different stress paths are discussed. Theory analysis and test results show that the Compression- Shear fracture criterion of brittle rock can be expressed:     

A STUDY ON FRACTURE MECHANICS OF BRITTLE MATERIAL WITH PER-CRACKS

In this paper the fracture process of specimen,with single crack, double cracks and triple cracks is observed and analysed. The experimental results show that the fracture process of specimen is different because of the differention of the number, the distance and the type of array of cracks. And the fracture propagation of specimen with triple cracks and double cracks is foundmentally the same.     

The occurrence and inheritance of a brittle rachis phenotype in Italian durum wheat cultivars

Italian and Tunisian durum wheats from different eras of breeding were assessed for the presence of a gene for brittle rachis. Nine of 15 Italian durum landraces had brittle rachides. Strampellis achievement was the release of the well-known variety, Senatore Cappelli, which was derived from a Tunisian landrace, Jenah Rhettifah, which has a brittle rachis. Rachides of two Tunisian landraces were also brittle. Since the 1950s, 16 accessions were released as selections from crosses or mutagenesis involving Senatore Cappelli. Seven of these accessions have brittle rachides. F₂ segregation in intercrosses of Senatore Cappelli with other durum accessions with brittle rachides indicated a common allele for brittle rachis. Segregation of the F₂ from Senatore Cappelli/ANW 10A and the F₂ of Senatore Cappelli/ANW 10B showed that the gene for brittle rachis of Senatore Cappelli was allelic to the brittle allele of the Br-B1 locus on chromosome 3B. Senatore Cappelli was presumably the only source of brittle rachis used in Italian breeding programmes. The genes for brittle rachis have been retained in the gene pool of durum wheat, suggesting that the brittle rachis character is not associated with an appreciable yield loss in modern farming systems in Mediterranean environments.     

NONLINEAR ELASTIC-DAMAGE CONSTITUTIVE EQUATION OF BRITTLE ROCK AND EXPERIMENAAL VERIFICATION

on the basis of the experimental studies of mechanical properties in brittle rock,the generalized elastic modulus,generalized elastic Poisson ratio,irreversible deformation Poisson ratio and damage deformation characteristic arediscussed.And then,a new damage variable is defined.A new nonlinear elastic-damage constitutive equation is built and the damage evolution equation is proposed.The nonlinear elastic-damage constitutive equation is verified in the uniaxialcompression test of quartz sandstone in Chongqing.The results show that reasonableagreement exists between the theoretical analysis and the experimental data.     

电力系统脆性源辨识初探

电力系统的脆性源是电力系统脆性激发的源头,基于直流潮流和分布因子法相结合,提出了快速找到系统脆性源的方法和步骤,并以三母线电力系统脆性源辨识为例,证明了此方法的有效性。     

碳纤维增强混凝土受弯构件正截面承载力设计

提出碳纤维筋的抗弯设计强度的确定方法 ,阐述了碳纤维筋增强混凝土受弯构件的设计方法和设计所需的注意事项     

水稻脆性突变体nbc(t)的主要特性和脆性基因的初步定位

对脆性突变体的表型、主要农艺性状和稻米品质进行了考查,并对脆性基因进行了初步定位。结果表明:脆茎水稻nbc(t)与野生亲本9311在株高等形态特征上无明显区别,仅在机械强度上有区别;nbc(t)的根、茎、叶、穗及种子都很脆,易折断,且表现全生育期脆性。脆茎突变体nbc(t)的主要农艺性状与9311相似,产量略低于9311,除了整精米率偏低以外,其他稻米品质性状与9311相似。脆茎突变体nbc(t)与广占63-4S所配组合的产量和稻米品质与扬两优6号相当。与9311相比,nbc(t)茎秆的抗折力相当,但抗张力明显降低,纤维素含量约降低17%。遗传分析表明,nbc(t)的脆茎特性可能由2个基因位点控制,初步定位在9号染色体上的2个区段,一个位于9号染色体上段SSR标记RM3700和RM24371之间,遗传距离分别为1.3cM和3.1cM;另一个位于9号染色体下段INDEL标记CL062和CL045外侧,遗传距离分别为1.6cM和6.0cM。     

Chromosome location of the gene for brittle rachis in the Tibetan weedrace of common wheat

The brittle rachis of the Tibetan weedrace (Triticum aestivum var. tibetanum) was found to be governed by a single dominant gene on the short arm of chromosome 3D. The new brittle rachis gene was designated Br₁. This study also discovered that the type of disarticulation is governed by many genes that may differ from brittle rachis genes. In other words, the same brittle rachis gene may exhibit various types of disarticulation in various genetic backgrounds. So, after the brittle rachis gene (barrel type) in Aegilops tauschii entered hexaploid wheat through the amphidiploid path, it might exhibit the wedge type of disarticulation.     

水稻脆秆突变体bc16的鉴定和基因精细定位

脆秆突变体是一类研究植物机械强度的重要材料。利用EMS(甲基磺酸乙酯)诱变粳稻品种日本晴,筛选获得一个脆秆突变体,命名为bc16(brittle culm16)。与野生型植株相比,bc16茎秆、叶片和根明显变脆,而株高、穗粒数降低,穗长和主根长变短。茎秆细胞壁成分分析表明,bc16纤维素含量显著低于野生型植株,半纤维素含量则显著增加,而木质素含量差异不显著。突变体bc16薄壁细胞形状无规则、排列紊乱,表皮层下厚壁细胞次生壁和薄壁细胞壁变薄。遗传分析表明bc16突变体由隐性单基因控制,位于水稻第2染色体长臂端InDel标记2-F和2-H间66.6kb的区间内。该区间共有7个候选基因,其中Os02g0738900是bc3脆秆基因的等位基因。测序结果表明,bc16突变体中的Os02g0738900基因从ATG开始第5113位,在第13内含子近末端发生了T→A的置换,导致转录过程中该内含子末端6个核苷酸被剪切到mRNA中,最终导致翻译提前终止。实时荧光定量PCR结果表明Os02g0738900基因在bc16脆秆突变体根、茎、叶中的表达量降低。bc16基因可能通过调控厚壁组织次生细胞壁和薄壁细胞初生壁的合成来影响水稻茎秆机械强度。