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1.
利用高温电子万能试验机和具有高温同步自组装功能的Hopkinson压杆对二维C/SiC复合材料 进行了应变率为10-4~103s-1,温度为293~1273K下的单轴压缩力学性能测试。实验结果表明:二维C/ SiC复合材料破坏时并未表现出典型的脆性破坏,而是在应力达到压缩强度时出现了显著的应变软化,在经 历了较大的变形后才最终破坏,同时材料还表现出良好的高温承载能力及一定的温度和应变率依赖性。随着 温度的升高,复合材料的压缩强度呈降低的趋势。与准静态下室温压缩时相比,材料在1273K 时的压缩强 度的降低程度不超过30%,但压缩强度对应变率的敏感性随着温度的升高而增大。由于高温下试样氧化,C/ SiC复合材料压缩强度对应变率的敏感性在温度为1073K时显著增大。  相似文献   

2.
连续纤维增韧的碳化硅复合材料(以下简称C/SiC),作为超高速飞行器热结构使用时,有可能在高温环境下受到高速撞击的作用,因此,掌握其在极端环境(高温、高应变率)下的力学性能是进行结构安全设计的基础。本文采用具有高温实验能力的分离式Hopkinson杆,在293~1273K温度范围内进行了动态压缩力学性能测试,研究了环境温度和加载速率对材料力学性能的影响。结果表明:C/SiC复合材料的高温压缩力学性能主要受应力氧化损伤和残余应力的共同影响。实验温度低于873K时,应力氧化损伤的影响很小,而由于增强纤维和基体界面残余应力的释放使界面结合强度增大,复合材料的压缩强度随温度的升高而增大;当实验温度高于873K时,应力氧化损伤加剧,其对压缩强度的削弱超过残余应力释放对强度的贡献,材料的压缩强度随温度的升高逐渐降低。由于应力氧化损伤受应变率的影响很大,当温度由873K升高至1273K时,高应变率下压缩强度降低的程度要比应变率为0.0001/s时低得多。  相似文献   

3.
采用分离式霍普金森压杆装置,测试了高应变率下ZrB2-20%SiC陶瓷复合材料的动态压缩力学性能,应变率范围为900s^-1~3000s^-1。结果表明:ZrB2-20%SiC陶瓷复合材料的动态压缩强度与临界应变均随应变率的增大而增加,2950s^-1时压缩强度与临界应变比981s^-1时分别增大了88.72%和148.85%;应变率对ZrB2-20%SiC陶瓷复合材料的动态压缩应力-应变曲线与破坏机理影响显著,应变率为1134s^-1时,ZrB2-20%SiC陶瓷复合材料破坏模式以裂纹扩展为主,应变率为2861s^-1时,多裂纹扩展为该材料的主要破坏机理;应变率越高,试件的损伤程度越大,压缩试件碎片尺寸越小,压缩应力-应变曲线的非线性越明显。  相似文献   

4.
分别在电子万能实验机和SHPB(split Hopkinson press bar)实验装置上对2D-C/SiC复合材料进行了静态、动态实验,探讨了该材料在10-4~2.8103 s-1的应变率范围内的层向压缩力学性能。实验结果表明,在动态加载条件下,2D-C/SiC复合材料的应力应变呈非线性关系。随着应变率的提高,破坏强度提高、失效应变减小,弹性模量增加。弹性模量与对数应变率基本呈线性关系。提出了一个含有与应变率相关的损伤变量的动态本构方程,该方程与实验结果吻合较好。  相似文献   

5.
为分析基体性质和纤维铺设方式对碳纤维树脂基复合材料(CFRP)压缩性能的影响,设计两种基体(耐高温环氧树脂基体和PA6 基体) 和两种碳纤维铺设方式[[45/0/-45/90]s和[45/-45]2s],共4 类盒型碳纤维试件.采用轴向压缩实验,研究低应变速率下碳纤维复合材料的极限载荷、压缩量和刚度等力学性能.研究表明试件的失效形式主要由基体性质决定,损伤区域及裂纹方向主要由碳纤维铺设方式决定.利用X射线显微镜(XRM)对试件典型的损伤区域进行三维扫描,并对扫描图像进行重构与渲染,获得破坏区域的内部损伤细节.根据损伤扫描结果,得到材料内部的损伤类型及破坏程度.归纳所获得的损伤测试特征,分析不同类型试件压缩时的损伤规律与失效机理.  相似文献   

6.
为了获得一种碳纤维二维正交平纹机织布增强树脂基复合材料在一维应变状态下的强度准则,在已完成的准静态和动态压缩实验的基础上,拟合出了单轴压缩下三个主方向上的计及应变率的应力-应变关系式,进而得到初始屈服应力和压缩破坏强度与应变率相关性表达式。依据该表达式,得到了该复合材料在一维应变下考虑应变率效应的Tsai-Hill屈服强度和破坏强度准则方程。通过计算,考察了Tsai-Hill屈服强度和破坏强度准则随应变率的变化规律。结果表明,本文中研究的复合材料的强度性能,不但存在应变率效应,而且这种效应是各向异性的。  相似文献   

7.
PTFE/Al含能复合材料的压缩行为研究   总被引:2,自引:0,他引:2  
金属/氟聚合物含能复合材料是一类新型的高级含能材料.研究了室温下Al含量和应变率对PTFE/Al含能复合材料压缩性能和反应性能的影响,所加载的应变率为6×10-3s-1~8×103s-1.材料压缩性能的应变率效应明显:与静态加载相比,动态加载下材料模量和强度明显提高,但应变降低.材料的损伤过程主要包括塑性变形、开裂和反应3部分.随着Al含量的增加,材料准静态和动态压缩强度均呈先升后降的趋势,在Al含量为35%时达到最高值102.6 MPa和154 MPa;引发反应所需加载的应变率增加,但对应的应力值差别不明显,基本在165 MPa左右,材料引发后反应完全性降低.  相似文献   

8.
冰在低温下的单轴压缩力学行为和破坏机制   总被引:1,自引:0,他引:1  
利用带有低温装置的Instron5848材料实验机和分离式Hopkinson压杆装置(SHPB),在-10℃、-20℃和-30℃温度下,对多晶冰进行了应变率为10-4~102S-1范围内的单轴压缩力学性能实验,分析了实验结果的可靠性和有效性。研究发现:冰的压缩强度具有明显的温度和应变率敏感性,随应变率的增大、温度的降低而提高;压缩强度与应变率对数呈线性关系,应变率的升高会增强降温对压缩强度的强化效应。在研究的应变率和温度范围内,冰主要有径向膨胀、纵向劈裂和整体破碎三种破坏模式,裂尖能量得不到及时释放、冰体内氢键强度和裂纹滑移摩擦阻力增大是导致冰破坏模式不同和压缩强度增大的原因。  相似文献   

9.
利用带有波形整形器的Split Hopkinson Pressure Bar(SHPB)技术测试了碳布叠层/碳复合材料在应变率为500、1 500 s-1时的动态压缩性能。研究结果表明:利用轧制紫铜作为整形器材料不仅可以有效地实现对碳布叠层/碳复合材料的常应变率压缩加载,而且有助于改善试样两端的应力平衡,从而保证测试数据的可靠性;此外,与准静态压缩相比较,在动态压缩载荷下,碳布叠层/碳复合材料的压缩强度有较强的应变率效应,且复合材料压缩强度的动态增加函数可以用Cowper-Symonds幂函数的形式来表示。  相似文献   

10.
利用材料试验机装置开展了三维正交机织Kevlar/乙烯基树脂复合材料力学实验,实验表明面内经向拉伸和厚度z方向压缩时,材料具有一定的应变率效应,厚度z方向压缩强度远大于面内压缩强度,而面内经向和纬向的拉伸强度则相当.结合纤维的编织方式,对这些现象做了必要的定性分析.最后,本文基于三维正交机织复合材料的结构特点,推导了一组可用于估算三维正交机织复合材料弹性模量的公式,估算结果和实验值接近.  相似文献   

11.
A series of uniaxial compression specimens were tested over a range of applied ram displacement rates of 8.9 × 10−4 to 8.9 mm/sec to elucidate the effects of loading rate on the uniaxial compressive fracture stress of Witwatersrand quartzite. It was demonstrated that even within standard loading rate ranges, considerable scatter in the fracture strength (under uniaxial compression) existed in this particular quartzite rock. Nevertheless, a definite trend of increasing fracture resistance with increasing monotonic loading rate was evident inasmuch that increasing the loading rate (strain rate) by four orders of magnitude increase the fracture strength by almost 2.8 times. Prior fatigue loading also produced a significant strain strengthening as the uniaxial compressive fracture stress tended to increase in a sigmoidal fashion with increasing number of fatigue cycles prior to testing. Indeed, the fracture strength of quartzite was almost doubled in value after 10 cycles. Plane strain fracture toughness tests utilising three point bend specimens were conducted and an average of Klc = 1.7 MPa√m was realized. In both the uniaxial compression tests and the fracture toughness tests, failure occurred by crack extension predominantly by a transgranular flat cleavage-like mode through pure quartzite (silica) regions. However, crack extension was also observed to occur in an intergranular “ductile-like” mode through areas associated with inclusions prevalent in the quartzite.  相似文献   

12.
进行了混凝土在应变速率分别为10-5/s、10-4/s、10-3/s的条件下,经历极限抗压强度分别为0、40%、60%、75%和85%的单调荷载作用的动态单轴压缩试验,在此基础上分析了经历不同单调加载历史和应变速率下混凝土的峰值应力、峰值应变和弹性模量的变化规律。试验结果表明,随着应变速率的提高,动态单轴抗压强度明显增加;当单调加载应力水平高于某一应力阈值时,混凝土极限抗压强度明显降低;混凝土弹性模量随着应变速率的提高而增加,随着单调加载幅值的增加表现出先增大后减小的趋势;混凝土峰值应变随着应变速率的提高而增加,随着单调加载幅值的增加而减少。  相似文献   

13.
为探究Al2O3陶瓷的宏观力学响应与破坏机理,分别利用材料试验机和分离式霍普金森压杆对其进行准静态和动态压缩实验,同时通过原位光学成像观测试样的破坏过程,并利用同步辐射CT和扫描电镜(SEM)对回收碎片的尺寸和形状以及微观破坏模式进行表征分析。宏观强度数据表明,Al2O3陶瓷的抗压强度符合Weibull分布,且与加载应变率呈现指数增长关系。原位光学成像和SEM回收分析共同揭示了动静态加载下裂纹成核与扩展模式存在明显差异。准静态加载时材料微观上更易发生沿晶断裂,宏观表现为劈裂裂纹较少,且倾向于沿加载方向传播并贯穿整个试样;而动态加载时穿晶断裂占主导地位,劈裂裂纹明显增加并发生相互作用,因此在传播过程中容易分叉而形成大量次生裂纹,提高了试样内裂纹密度。这与碎片的CT表征结果一致,即碎片平均球形度和伸长、扁平指数等均随应变率对数线性增加。破坏模式的改变最终导致高应变率下陶瓷材料应变率敏感性显著增强。  相似文献   

14.
The goal of this study is to design a novel annular pulse shaping technique for large-diameter Kolsky bars for investigating the dynamic compressive response of concretes. The purpose of implementing an annular pulse shaper design is to alleviate inertia-induced stresses in the pulse shaper material that would otherwise superpose unwanted oscillations on the incident wave. This newly developed pulse shaping technique led to well-controlled testing conditions enabling dynamic stress equilibrium, uniform deformation, and constant strain-rate in the testing of a chosen concrete material. The observed dynamic deformation rate of the concrete is highly consistent (8 % variation) with the stress in the specimen well equilibrated confirming the validity of this new technique. Experimental results at both quasi-static (10?4 s?1) and dynamic (100 s?1, 240 s?1) strain rates showed that the failure strength of this concrete is rate-sensitive.  相似文献   

15.
The study on the compressive behavior of ptfe/al energetic composite   总被引:1,自引:0,他引:1  
金属/氟聚合物含能复合材料是一类新型的高级含能材料. 研究了室温下Al含量和应变 率对PTFE/Al含能复合材料压缩性能和反应性能的影响,所加载的应变率为6\times 10^{-3}s^{-1}\sim8\times 10^{3}s^{ -1}. 材料压缩性能的应变 率效应明显:与静态加载相比,动态加载下材料模量和强度明显提 高,但应变降低. 材料的损伤过程主要包括塑性变形、开裂和反应3部分. 随着Al含量的增 加,材料准静态和动态压缩强度均呈先升后降的趋势,在 Al含量为35\%时达到 最高值102.6 MPa和154 MPa; 引发反应所需加载的应变率增加,但对应的应力值 差别不明显,基本在165 MPa左右, 材料引发后反应完全性降低.  相似文献   

16.
A model is developed for brittle failure under compressive loading with an explicit accounting of micro-crack interactions. The model incorporates a pre-existing flaw distribution in the material. The macroscopic inelastic deformation is assumed to be due to the nucleation and growth of tensile “wing” micro-cracks associated with frictional sliding on these flaws. Interactions among the cracks are modeled by means of a crack-matrix-effective-medium approach in which each crack experiences a stress field different from that acting on isolated cracks. This yields an effective stress intensity factor at the crack tips which is utilized in the formulation of the crack growth dynamics. Load-induced damage in the material is defined in terms of a scalar crack density parameter, the evolution of which is a function of the existing flaw distribution and the crack growth dynamics. This methodology is applied for the case of uniaxial compression under constant strain rate loading. The model provides a natural prediction of a peak stress (defined as the compressive strength of the material) and also of a transition strain rate, beyond which the compressive strength increases dramatically with the imposed strain rate. The influences of the crack growth dynamics, the initial flaw distribution, and the imposed strain rate on the constitutive response and the damage evolution are studied. It is shown that different characteristics of the flaw distribution are dominant at different imposed strain rates: at low rates the spread of the distribution is critical, while at high strain rates the total flaw density is critical.  相似文献   

17.
A dynamic damage growth model applicable to brittle solids subjected to biaxial compressive loading is developed. The model incorporates a dynamic fracture criterion based on wing-crack growth model with a damage evolution theory based on a distribution of pre-existing microcracks in a solid. Influences of lateral confinement pressure (dynamic or static) as well as frictional coefficient on the rate dependence of fracture strength of basalt-rock are investigated systematically. It is found that the failure strength, damage accumulation and wing-crack growth rate are strongly influenced by the nature and the magnitude of confinement pressure. It is also verified that the effect of strain rate on fracture strength of brittle solids is independent of confinement pressure in a certain range of strain rate.  相似文献   

18.
Li  X.  Wang  S.  Xia  K.  Tong  T. 《Experimental Mechanics》2021,61(3):461-468
Background

Understanding the dynamic tensile response of microwave damaged rock is of great significance to promote the development of microwave-assisted hard rock breakage technology. However, most of the current research on this issue is limited to static loading conditions, which is inconsistent with the dynamic stress circumstances encountered in real rock-breaking operations.

Objective

The objective of this work is to investigate the effects of microwave irradiation on the dynamic tensile strength, full-field displacement distribution and average fracture energy of a granitic rock.

Methods

The split Hopkinson pressure bar (SHPB) system combined with digital image correlation (DIC) technique is adopted to conduct the experiments. The overload phenomenon, which refers to the strength over-estimation phenomenon in the Brazilian test, is validated using the conventional strain gauge method. Based on the DIC analysis, a new approach for calculating the average fracture energy is proposed.

Results

Experimental results show that both the apparent and true tensile strengths increase with the loading rate while decreasing with the increase of the irradiation duration; and the true tensile strength after overload correction is lower than the apparent strength. Besides, the overload ratio and fracture energy also show the loading rate and irradiation duration dependency.

Conclusions

Our findings prove clearly that microwave irradiation significantly weakens the dynamic tensile properties of granitic rock.

  相似文献   

19.
采用新型Ⅱ型动态断裂测试技术,对高强钢40Cr在高加载速率下的Ⅱ型动态断裂特性进行了测试研究。基于新设计的Ⅱ型动态断裂试样和分离式霍普金森压杆(split Hopkinson pressure bar, SHPB)技术,通过实验-数值方法确定了裂尖在加载过程中的应力强度因子曲线。采用应变片法确定了试样的起裂时间,最终得到40Cr的Ⅱ型动态断裂韧性值,并对其加载速率相关性和材料的失效机理进行了研究。结果表明,在1.08~5.53 TPa·m1/2/s的加载速率范围内,40Cr的Ⅱ型动态断裂韧性基本表现为与加载速率成正相关的变化趋势。通过对试样断口形貌的分析,确定了材料的失效模式及机理,发现随着加载速率的增加,存在拉伸型失效向绝热剪切型失效模式转变的现象。  相似文献   

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