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常材料硬度的测定法有哪三种？它们主要适应于检验什么材料？

答案

参考答案：

（1）硬度（HB）测定法：布氏硬度测定是用一定直径D（mm）的钢球或硬质合金球为压头，施以一定的试验力F(kgf或N)，将其压入试样表面，经规定保持时间t(s)后卸除试验力，试样表面将残留压痕。测量压痕球形面积A（mm2）。布氏硬度（HB）就是试验力F除以压痕球形面积A所得的商。布氏硬度试验特别适用于测定灰铸铁、轴承合金等具有粗大晶粒或组成相的金属材料的硬度为钢件退火、正火和调质后的硬度。 

（2）洛式硬度（HR）试验：洛式硬度是以测量压痕深度来表示材料的硬度值。洛式硬度试验所用的压头有两种。一种是圆锥角ɑ＝120°的金钢石圆锥体；另一种是一定直径的小淬火钢球。常的三种洛式硬度如表2.1-2所示。洛氏硬度试验常用于检查淬火后的硬度。 

标尺符号压头类型总试验力F(N)测量硬度范围应用举例 ：

AHRA金钢石圆锥5.88422-88硬质合金、表面薄层硬化钢 

BHRB￠1.558钢球980.720-100低碳钢、铜合金、铁素体可锻铸铁 

CHRC钢金石圆锥147120-70淬火钢、高硬铸件、珠光体可锻铸铁 

（3）维氏硬度（HV）试验：维氏硬度试验适用于常规材料，其压头是两对面夹角ɑ＝136°的金钢石四棱锥体。压头在试验力F（N）的作用下，将试样表面压出一个四方锥形的压前，经一定保持时间后，卸除试验力，测量出压痕对角线平均年度并计算压痕的表面积A（mm2），得到HV＝0.1891F÷d2。

单项选择题

关于精神分裂症青春型的描述，错误的是（）

A．主要为联想散漫

B．片断幻觉、妄想，行为紊乱

C．发病多在青年期

D．治疗效果差

E．起病呈急性或亚急性
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单项选择题

Rising Prices Cause House "Apartheid"


涨价导致房屋的“种族隔离”


The Government has admitted that soaring house prices have left people on average incomes, such as teachers and nurses, locked out of buying their first homes across large parts of southern England, including London and most of the South East.
A spokeswoman for the Deputy Prime Minister, John Prescott, admitted last night that there was now an effective "housing apartheid", with people in their own homes pulling further and further away from those yet to get on the property ladder.
With house prices rising at between 15 and 20 percent a year, incomes, which are rising at between 5 and 10 percent a year, cannot keep up.
"Increasing housing supply is a national priority. In large areas of the wider South East, house purchase remains out of reach for families with average household incomes," the official said．
A new report out tomorrow will reveal the full scale of the housing crisis. The study by Cambridge University for the housing charity Shelter reveals that the Government will need to spend ￡3.5 billion a year to solve the housing problem.
More than 50,000 new homes are needed every year to help people on lower incomes to have their own homes. By 2014 a city the size of Leeds will need to be built.
Critics point out that, without the money, millions of people employed in the public sector will be unable to move to the South East to fill vacancies.
Without a new influx of staff, many hospitals and schools say that they will struggle to maintain standards. The Government is now expected to announce a package of measures in the Budget to try to help first-time buyers. The Treasury is considering raising the point at which people have to pay stamp duty, a tax paid on every house purchase.
The present threshold of ￡60,000 has remained unchanged since 1993, despite house prices increasing by 160 percent in that time.
Gordon Brown, the Chancellor, faces being accused of maintaining the threshold as a way of raising more tax because as house prices rise more and more people are dragged into paying the surcharge. More than 75 percent of all first-time buyers now pay the tax.
"The Government has to act," said Adam Sampson , the director of Shelter. The lack of affordable housing has a destabilising effect on the economy and its cost in human terms is massive.
"Successive governments have spoken about the growing housing crisis. It has now got to the point where it cannot be ignored any longer. Housing should be given the same priority as the other key areas of public life, health and education. "
The report says that more than three-quarters of all new homes are needed in the South of England, with about 20 percent in the North and the Midlands.
Shelter’s figures on housing demand will form the basis of a Treasury review of housing to be published at the time of the Budget next week. The review, by Kate Barker, is likely to say that tens of thousands of new houses are needed and that planning restrictions should be relaxed so that housing developments can be built more easily.
She will also criticise a culture of nimbyism which has crept into many, particularly rural, towns. Many local communities block new housing even though it is desperately needed．
A study released this weekend by the Halifax revealed that first-time buyers cannot get on to the property ladder in 80 percent of towns and cities across the country. The bank said that areas were classed as "unaffordable" if first-time buyers needed to borrow more than 4.27 times the local average salary to buy a home.
By that calculation, 100 percent of towns and cities in East Anglia were out of reach of first- time buyers, while 98 percent of towns and cities in the South West were unaffordable.
The Government is set to announce large amounts of extra funding for house building in the Budget. By 2006 the amount spent will have increased by ￡900 million, or 25 percent.
There will also be a ￡5 billion pot of money provided for affordable housing by 2006.

How many percent of new homes are needed in the south of England

A．About 20%.
B．More than 98%.
C．About 80%.
D．More than 45%.
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