低碳钢和铸铁的扭转
实验报告
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扭转试验
报告
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一、试验目的
1、测定低碳钢的剪切屈服极限τ。和剪切强度极限近似值τ。 sb2、测定铸铁的剪切强度极限τ。 b
3、观察并分析两种材料在扭转时的变形和破坏现象。
二、设备和仪器
1、材料扭转试验机
2、游标卡尺
三、试验原理
1、低碳钢试样
对试样缓慢加载,试验机的绘图装置自动绘制出T-
φ曲线(见图1)。最初材料处于
图1 低碳钢是扭转试验
弹性状态,截面上应力线性分布,T-φ图直线上升。到A点,试样横截面边缘处剪应力达到剪切屈服极限τ。以后,由屈服产生的塑性区不断向中心扩展,T-φ图s
呈曲线上升。至B点,曲线趋于平坦,这时载荷度盘指针停止不动或摆动。这不动groups, Wujiang County. In September, the chapter in the Tomb occupied formally established the village of KMT: Wu Jiang County Government (known as "guerrilla Government") and against self-defence groups. Begins to flow from jiaxing railway Lili, Tan Hills area. In November, the County Government is based on the tomb of Lu Xiyan, mine-and from the pier at Dang, under Jin bang. County Government operates three Civil Affairs, finance, education
或摆动的最小值就是屈服扭矩T。再以后材料强化,T-φ图上升,至C点试样断裂。s
在试验全过程中,试样直径不变。断口是横截面(见图2a),这是由于低碳钢抗剪能力小于抗拉能力,而横截面上剪应力最大之故。
图2 低碳钢和铸铁的扭转端口形状
3Ts,,据屈服扭矩 (2-1) s4Wp
按式2-1可计算出剪切屈服极限τ。 s
3Tb,,据最大扭矩T可得: (2-2) bb4Wp
按式2-2可计算出剪切强度极限近似值τ。 b
说明
关于失联党员情况说明岗位说明总经理岗位说明书会计岗位说明书行政主管岗位说明书
:(1)公式(2-1)是假定横截面上剪应力均达到τs
后推导出来的。公式(2-2)形式上与公式(2-1)虽然完全
相同,但它是将由塑性理论推导出的Nadai公式略去了一项后得到的,而略去的这一项不一定是高阶小量,所以是近似的。 (2)国标GB10128-88规定τ和τ均按弹性扭转公式计算,这样得到的结果可以sb
groups, Wujiang County. In September, the chapter in the Tomb occupied formally established the village of KMT: Wu Jiang County Government (known as "guerrilla Government") and against self-defence groups. Begins to flow from jiaxing railway Lili, Tan Hills area. In November, the County Government is based on the tomb of Lu Xiyan, mine-and from the pier at Dang, under Jin bang. County Government operates three Civil Affairs, finance, education
用来比较不同材料的扭转性能,但与实际应力不符。
II、铸铁试样
铸铁的曲线如图3所示。呈曲线形状,变形很小就突然破裂,
有爆裂声。断裂面粗糙,是与轴线约成45?角的螺旋面
(见图1-3-2b)。这是由于铸铁抗拉能力小于抗剪能力,
而这面上拉应力最大之故。据断裂前的最大扭矩Tb按弹性
扭转公式1-3-3可计算抗扭强度τ。 b
图3 铸铁扭转曲线图
四、试验步骤
1、测量试样尺寸
以最小横截面直径计算截面系数(抗扭截面模量)W。 p
2、试验机准备
刻度盘指针调零指针调零,安装绘图记录纸,安装记录笔。
3、安装试样,用粉笔在试样上画一母线,用以观察试样变形情况。
4、测试
groups, Wujiang County. In September, the chapter in the Tomb occupied formally established the village of KMT: Wu Jiang County?3? Government (known as "guerrilla Government") and against self-defence groups. Begins to flow from jiaxing railway Lili, Tan Hills area. In November, the County Government is based on the tomb of Lu Xiyan, mine-and from the pier at Dang, under Jin bang. County Government operates three Civil Affairs, finance, education
对低碳钢试样,起先缓慢加载,注意观察绘图和载荷指针转动情况。待记录下屈服扭矩T后改用快速加载,直至断裂记录下最大扭矩T。 ss
对铸铁试样,慢速加载,注意观察绘图、载荷指针转动和试样变形情况直到试样断裂,记录下最大扭矩T。 b
5、取下试样,观察并分析断口形貌和形成原因。
6、试验机回复原状,清理现场。
五、思考题
1、根据低碳钢和铸铁试样扭转破坏的情况分析破坏原因。
答:低碳钢试件受扭转时沿横截面破坏,此破坏是由横截面上的切应力造成的,说明低碳钢的抗剪强度较差;铸铁试件受扭转时沿大约45度斜截面破坏,断口粗糙,此破坏是由斜截面上的拉应力造成的,说明铸铁的抗拉强度较差。
2、铸铁扭转破坏断裂面为何是45?螺旋面,
答:铸铁扭转破坏断裂面为何是45度螺旋面而不是45度平面铸铁扭转时主要45度切应力作用且所受切应力最大,而铸铁的抗拉能力较抗剪能力弱,故产生螺受
旋面破坏。
groups, Wujiang County. In September, the chapter in the Tomb occupied formally established the village of KMT: Wu Jiang County Government (known as "guerrilla Government") and against self-defence groups. Begins to flow from jiaxing railway Lili, Tan Hills area. In November, the County Government is based on the tomb of Lu Xiyan, mine-and from the pier at Dang, under Jin bang. County Government operates three Civil Affairs, finance, education