Currently requirements of thin-walled tube with small bending radius cause the defects such as wrinkling, overthinning and cross-section distortion more prone to occur in bending process. Based on the analysis of the ...Currently requirements of thin-walled tube with small bending radius cause the defects such as wrinkling, overthinning and cross-section distortion more prone to occur in bending process. Based on the analysis of the forming characteristics by analytical and experimental methods, a complete 3D elastic-plastic FEM model of the process was developed using ABAQUS/Explicit code, including bending process, balls retracting and unloading process, and thus the plastic deformation characteristics with small bending radius were investigated. The main results show that: 1) The utmost deformation feature of the NC bending process is its continuous progressive deformation. 2) The occurring conditions of the defects such as wrinkling and tension instability in the process are obtained. The wrinkling is traditional on the double compressive stresses state and the tension instability is on the double tension stresses state. 3) The enhanced non-uniform deformation in thin-walled tube with small bending radius is demonstrated by comparing the stress/ strains distributions under the 1.5D and 1D bending conditions. 4) For ID small bending process, a new method-'stepped mandrel retraction' is proposed to improve the bending quality in experiment according to the FE simulation. The simulation results are verified by experiment.展开更多
以内蒙古白音华提质褐煤煤粉为研究对象,通过有粘结剂冷压成型方法研究了成型工艺因素与褐煤型煤强度的关系,并采用傅里叶红外光谱仪和扫描电子显微镜对粘结剂成型机理进行分析。试验结果表明:当1#提质褐煤煤粉与2#提质褐煤煤粉的配比为...以内蒙古白音华提质褐煤煤粉为研究对象,通过有粘结剂冷压成型方法研究了成型工艺因素与褐煤型煤强度的关系,并采用傅里叶红外光谱仪和扫描电子显微镜对粘结剂成型机理进行分析。试验结果表明:当1#提质褐煤煤粉与2#提质褐煤煤粉的配比为3∶2,水分为20%,成型压力为25 MPa时,所得型煤抗压强度可达10.45 k N/个,落下强度为91.34%。在成型过程中,提质褐煤煤粉与添加剂中的—OH和—COOH缔合的羟键和化学键,使煤粒与粘结剂的作用力更大;同时,在成型压力作用下,煤粒之间的机械啮合力增大,型煤强度增大。展开更多
以油茶壳炭粉为原料,纤维素和氧化淀粉为添加剂,采用万能试验机研究成型温度、成型压力、原料含水率对燃料成型品质的影响。研究发现,成型温度在60~100℃时成型燃料的品质较好,提高成型温度对燃料的松弛密度影响不明显,但比能耗增加,对...以油茶壳炭粉为原料,纤维素和氧化淀粉为添加剂,采用万能试验机研究成型温度、成型压力、原料含水率对燃料成型品质的影响。研究发现,成型温度在60~100℃时成型燃料的品质较好,提高成型温度对燃料的松弛密度影响不明显,但比能耗增加,对径向抗压强度影响与添加剂种类有关。提高成型压力,成型燃料的松弛密度、比能耗和径向抗压强度都随之增大,成型压力在6~8 k N时成型燃料品质较好。提高原料含水率对降低能耗有显著作用,但原料含水率过大不利于成型,原料含水率在15%~20%时成型燃料品质较好。对成型燃料燃烧特性研究发现,纤维素和氧化淀粉的加入,着火温度能分别降低至362.5℃和324.5℃,添加氧化淀粉后燃料品质和燃烧特性最好;添加纤维素的混合成型燃料热值降低更少,且品质受成型因素影响较小。展开更多
基金Projects(59975076, 50175092) supported by the National Natural Science Foundation of China Project(50225518) by the National Science Found of China for Distinguished Young Scholars Project by the Teaching and Research Award Program for Outstanding Young Teachers in Higher Education Institutions of MOE, PRC Project(20020699002) by the Specialized Research Fund for the Doctoral Program of Higher Education of MOE, PRC Project (04H53057) by Aviation Science Foundation
文摘Currently requirements of thin-walled tube with small bending radius cause the defects such as wrinkling, overthinning and cross-section distortion more prone to occur in bending process. Based on the analysis of the forming characteristics by analytical and experimental methods, a complete 3D elastic-plastic FEM model of the process was developed using ABAQUS/Explicit code, including bending process, balls retracting and unloading process, and thus the plastic deformation characteristics with small bending radius were investigated. The main results show that: 1) The utmost deformation feature of the NC bending process is its continuous progressive deformation. 2) The occurring conditions of the defects such as wrinkling and tension instability in the process are obtained. The wrinkling is traditional on the double compressive stresses state and the tension instability is on the double tension stresses state. 3) The enhanced non-uniform deformation in thin-walled tube with small bending radius is demonstrated by comparing the stress/ strains distributions under the 1.5D and 1D bending conditions. 4) For ID small bending process, a new method-'stepped mandrel retraction' is proposed to improve the bending quality in experiment according to the FE simulation. The simulation results are verified by experiment.
文摘以内蒙古白音华提质褐煤煤粉为研究对象,通过有粘结剂冷压成型方法研究了成型工艺因素与褐煤型煤强度的关系,并采用傅里叶红外光谱仪和扫描电子显微镜对粘结剂成型机理进行分析。试验结果表明:当1#提质褐煤煤粉与2#提质褐煤煤粉的配比为3∶2,水分为20%,成型压力为25 MPa时,所得型煤抗压强度可达10.45 k N/个,落下强度为91.34%。在成型过程中,提质褐煤煤粉与添加剂中的—OH和—COOH缔合的羟键和化学键,使煤粒与粘结剂的作用力更大;同时,在成型压力作用下,煤粒之间的机械啮合力增大,型煤强度增大。
文摘以油茶壳炭粉为原料,纤维素和氧化淀粉为添加剂,采用万能试验机研究成型温度、成型压力、原料含水率对燃料成型品质的影响。研究发现,成型温度在60~100℃时成型燃料的品质较好,提高成型温度对燃料的松弛密度影响不明显,但比能耗增加,对径向抗压强度影响与添加剂种类有关。提高成型压力,成型燃料的松弛密度、比能耗和径向抗压强度都随之增大,成型压力在6~8 k N时成型燃料品质较好。提高原料含水率对降低能耗有显著作用,但原料含水率过大不利于成型,原料含水率在15%~20%时成型燃料品质较好。对成型燃料燃烧特性研究发现,纤维素和氧化淀粉的加入,着火温度能分别降低至362.5℃和324.5℃,添加氧化淀粉后燃料品质和燃烧特性最好;添加纤维素的混合成型燃料热值降低更少,且品质受成型因素影响较小。
