Most soft materials behave as if they were hardened when subjected to an impact force. The strain rate dependence of viscosity resistance is the reason for this behavior. The authors carried out drop impact tests on s...Most soft materials behave as if they were hardened when subjected to an impact force. The strain rate dependence of viscosity resistance is the reason for this behavior. The authors carried out drop impact tests on several types of soft materials under the condition of a flat frontal impact. The impact force waveform of soft materials was found to consist of a thorn-shaped waveform and a succeeding mountain-shaped waveform. Based on our experimental observations, we believe that a large viscosity resistance is rapidly changed to a small resistance in the course of the impact. In the present study, the cause of this distinct waveform is discussed based on a dynamics model. The study applies a standard linear solid (SLS) model in which the viscosity transient phenomenon is considered is applied. Three types of impact force waveforms of actual soft materials are simulated using the SLS model. Some features of the impact force waveform of soft materials can be explained using the SLS model.展开更多
The authors carried out drop impact tests for several soft materials under a flat frontal impact condition in which a drop hammer with a flat bottom surface strikes a plate-like soft material in the normal direction. ...The authors carried out drop impact tests for several soft materials under a flat frontal impact condition in which a drop hammer with a flat bottom surface strikes a plate-like soft material in the normal direction. The experimental results indicated that the impact force waveforms of soft materials consisted of a thorn-shaped waveform and a subsequent mountain-shaped waveform. The thorn-shaped waveform was strongly affected by the strain rate. In the present study, the occurrence mechanism of this distinctive waveform was discussed from the viewpoint of the viscosity transient phenomenon. A standard linear solid (SLS) model in which the viscosity transient phenomenon was considered was applied to the simulation. Some features of the impact force waveform of soft materials could be explained by the SLS model. Furthermore, the thorn-shape waveform could also be observed in the impact force waveforms of human skin and free-falling hollow balls.展开更多
In the impact tests of soft materials, we sometimes observe a thorn shape in the rising segment of the impact force waveform. However, the reason for the occurrence of the thorn shape has not been made clear. In this ...In the impact tests of soft materials, we sometimes observe a thorn shape in the rising segment of the impact force waveform. However, the reason for the occurrence of the thorn shape has not been made clear. In this study, thorn-shape waveforms of several soft materials are measured using compact drop test equipment under the condition of a flat frontal impact. A flat frontal impact is the condition where a drop hammer with a flat bottom surface strikes a plate-like soft material in the normal direction. Synchronized impact forces are measured using two sensors installed on both the drop hammer side and the floor side. The examined soft materials are a sponge sheet, sponge rubber sheet, gel sheet, rubber sheet, flat oil clay, low-rebound urethane foam, cork sheet, sliced ham, pork ham steak, and pork. Based on the test results, the features of the thorn-shape waveforms are discussed from a bird’s-eye view. Furthermore, the occurrence mechanism of the thorn-shape waveforms is discussed from the viewpoint of viscosity discontinuity and the double-strike phenomenon.展开更多
利用高速拉伸实验机在宽的应变率范围内(0.001—1200 s 1),研究了NiTi形状记忆合金的宏观力学性能随应变率的变化规律,并借助透射电子显微镜深入研究了微观结构在不同应变率下的演变机制.研究发现:NiTi合金马氏体(B19′相)孪晶的解孪晶...利用高速拉伸实验机在宽的应变率范围内(0.001—1200 s 1),研究了NiTi形状记忆合金的宏观力学性能随应变率的变化规律,并借助透射电子显微镜深入研究了微观结构在不同应变率下的演变机制.研究发现:NiTi合金马氏体(B19′相)孪晶的解孪晶应力随应变率的升高而近乎线性增大,表明NiTi合金解孪晶应力具有正向应变率相关性.在拉伸应变率为10 s 1的样品微观结构中发现了大量的解孪晶区域,而当应变率进一步增大到100 s 1和1200 s 1时,在样品中没有发现解孪晶区域的存在,样品微观组织以孪晶形式存在.该结果表明,NiTi合金的马氏体解孪晶速率应在10—100 s 1范围内.在高应变率下(10 s 1)均发现了热引发奥氏体相(B2)的存在,表明随应变率的增加,拉伸过程由等温过程逐渐变为绝热过程.此外,在1200 s 1的样品差示扫描热量曲线中还发现了一个小肩峰,表明相变过程由一步相变变为两步相变.展开更多
文摘Most soft materials behave as if they were hardened when subjected to an impact force. The strain rate dependence of viscosity resistance is the reason for this behavior. The authors carried out drop impact tests on several types of soft materials under the condition of a flat frontal impact. The impact force waveform of soft materials was found to consist of a thorn-shaped waveform and a succeeding mountain-shaped waveform. Based on our experimental observations, we believe that a large viscosity resistance is rapidly changed to a small resistance in the course of the impact. In the present study, the cause of this distinct waveform is discussed based on a dynamics model. The study applies a standard linear solid (SLS) model in which the viscosity transient phenomenon is considered is applied. Three types of impact force waveforms of actual soft materials are simulated using the SLS model. Some features of the impact force waveform of soft materials can be explained using the SLS model.
文摘The authors carried out drop impact tests for several soft materials under a flat frontal impact condition in which a drop hammer with a flat bottom surface strikes a plate-like soft material in the normal direction. The experimental results indicated that the impact force waveforms of soft materials consisted of a thorn-shaped waveform and a subsequent mountain-shaped waveform. The thorn-shaped waveform was strongly affected by the strain rate. In the present study, the occurrence mechanism of this distinctive waveform was discussed from the viewpoint of the viscosity transient phenomenon. A standard linear solid (SLS) model in which the viscosity transient phenomenon was considered was applied to the simulation. Some features of the impact force waveform of soft materials could be explained by the SLS model. Furthermore, the thorn-shape waveform could also be observed in the impact force waveforms of human skin and free-falling hollow balls.
文摘In the impact tests of soft materials, we sometimes observe a thorn shape in the rising segment of the impact force waveform. However, the reason for the occurrence of the thorn shape has not been made clear. In this study, thorn-shape waveforms of several soft materials are measured using compact drop test equipment under the condition of a flat frontal impact. A flat frontal impact is the condition where a drop hammer with a flat bottom surface strikes a plate-like soft material in the normal direction. Synchronized impact forces are measured using two sensors installed on both the drop hammer side and the floor side. The examined soft materials are a sponge sheet, sponge rubber sheet, gel sheet, rubber sheet, flat oil clay, low-rebound urethane foam, cork sheet, sliced ham, pork ham steak, and pork. Based on the test results, the features of the thorn-shape waveforms are discussed from a bird’s-eye view. Furthermore, the occurrence mechanism of the thorn-shape waveforms is discussed from the viewpoint of viscosity discontinuity and the double-strike phenomenon.
文摘利用高速拉伸实验机在宽的应变率范围内(0.001—1200 s 1),研究了NiTi形状记忆合金的宏观力学性能随应变率的变化规律,并借助透射电子显微镜深入研究了微观结构在不同应变率下的演变机制.研究发现:NiTi合金马氏体(B19′相)孪晶的解孪晶应力随应变率的升高而近乎线性增大,表明NiTi合金解孪晶应力具有正向应变率相关性.在拉伸应变率为10 s 1的样品微观结构中发现了大量的解孪晶区域,而当应变率进一步增大到100 s 1和1200 s 1时,在样品中没有发现解孪晶区域的存在,样品微观组织以孪晶形式存在.该结果表明,NiTi合金的马氏体解孪晶速率应在10—100 s 1范围内.在高应变率下(10 s 1)均发现了热引发奥氏体相(B2)的存在,表明随应变率的增加,拉伸过程由等温过程逐渐变为绝热过程.此外,在1200 s 1的样品差示扫描热量曲线中还发现了一个小肩峰,表明相变过程由一步相变变为两步相变.
