树脂传递模塑成型工艺RTM工艺的主要原理是在模腔中铺放按性能和结构要求设计的增强材料预成形体，采用注射设备将专用树脂体系注入闭合模腔，模具具有周边密封和紧固以及注射及排气系统，以保证树脂流动流畅并排出模腔中的全部气体和彻底浸润纤维，还具有加热系统，可加热固化成形复合材料构件。

它是一种不采用预浸料，也不采用热压罐的成形方法。

因此，具有效率高、投资、绿色等优点，是未来新一代飞机机体有发展潜力的制造技术。

该方法的优点是环保、形成的层合板性能好且双面质量好，在航空中应用不仅能够减少本身劳动量，而且由于能够成形大型整体件，使装配工作量减少。

但是树脂通过压力注射进入模腔形成的零件存在着孔隙含量较大、纤维含量较低、树脂在纤维中分布不匀、树脂对纤维浸渍不充分等缺陷，因此该技术还有改进潜力。

该工艺还能帮助生产尺寸精确，表面工艺精湛的复杂零件。

树脂传递模塑工艺还有一个特点是，能够允许闭模前在预成型体中放入芯模填充材料，避免预成型体在合模过程中被挤压。

芯模在整个预成型体中所占的比重较低，大约在0-2%之间。

下表是一些常见RTM成型产品的缺陷问题和解决办法。

粗纱、硬度大再选牌号邹折玻璃纤维流动错位用对预成型坯粘结剂有效的粘结剂，减慢注入速度玻璃纤维类型质量不好选择质量好的玻纤挠曲变形脱模时固化不完全促进树脂固化，用补强材料提高刚度使用矫正夹具树脂固化收缩使用低收缩剂，使用填料RTM工艺成功事例：图：ASC – II桨叶通过美国联邦航空局的认证，成功运用于派珀飞机上（Piper Matrixaircraft），ASC – II桨叶同样适用于Cirrus的SR - 22和其他通用航空飞机。

来源：派珀飞机公司Hartzell公司使用自有设计软件--PROP Code和ANSYS公司开发的有限元分析（FEA）软件对桨叶上应力的分配进行分析和设计，然后用另一个内部开发程序来生成ASC - II复合层压结构。

汉克将这种泡沫夹芯三明治结构设计描述为单体横造结构。

制备原理是通过湿法手糊将碳纤维及芳纶纤维（单向或混编）与环氧树脂复合成型，然后在中间插入闭孔泡沫夹芯材料，形成一个桁条形状的完整复合材料桨叶。

碳纤维能保证桨叶具备高模量和高弯曲强度，而芳纶纤维则能有效提高整个桨叶的阻尼性能和增加其扭曲强度。

机翼外蒙皮是由玻璃纤维制造，表面附有一层铝材避雷网。

值得一提的是，该桨叶结构上不同位置所采用的层压材的层数及其纤维取向各有不同，因此产生了厚度分布的差异化。

虽然汉克没有透露过多的设计细节，比如桨叶是如何通过闭模不锈钢柄的复合材料界面连接到集线器上的？他只是说：“我们借助有限元分析软件，将复合材料桨叶连接到不锈钢柄上，实现了飞行阻力最小化。

”关于具体的材料和供应商是商业秘密，但汉克表示，选定的材料都是航天级的，桨叶上不同位置的厚度的差异化是专门针对不同负载而设计的。

桨叶的前三分之二部分是整个部分旋转速度最快的位置，因此设计上充分考虑这点，采用了高度耐用、易于拆卸和抗损坏材料---镍蚀条制造。

靠近集线器的三分之一则是采用聚氨酯条。

完成设计草图之后，Hartzell开始转向模塑成型工艺。

迪布罗回忆说：“原先的预浸料螺旋桨同样是一个优秀的解决方案，但预浸料的成本对于大多数一般的航空应用来说太昂贵了。

而降低成本正是我们设计ASC – II桨叶的初衷，我们需要的是一款既能让用户负担得起，又拥有最先进技术，同时还不能丧失原始设计的精华的一款复合材料螺旋桨叶。

”在制备工艺上，我们最终诉诸于树脂传递模塑（RTM）工艺认证包括一系列严格的地面试验，和雷击试验（20万安培）；循环疲劳试验；和离心力拔出测试（该测试模拟引擎超速飞行条件，利用一个测试夹具试图将桨叶从集线器上拔出来）。

其次是仪器的飞行测试。

Design decisions with digital helpTo achieve these goals, the company used its own proprietary design software called PROP Code. This aerodynamic program, notes Hanke, interfaces seamlessly with ANSYS finite element analysis (FEA) software from ANSYS Inc. (Canonsburg, Pa.) for determination of stresses and their distribution in the blades. Hartzell designers then used another internally developed program to generate the ASC-II's laminate architecture.The result was a foam-cored sandwich design that Hanke describes as a monocoque structure. A combination of carbon and aramid fibers (in both woven hybrid and unidirectional forms) wet out with epoxy enclose a closed-cell foam insert to form an integral composite spar that runs the length of the blade. A second, shaped foam insert fills the trailing edge. Carbon fiber provides the spar's high modulus and high bending strength, while aramid supplies excellent torsion and damping performance through the whole blade. The continuous outer skin is formed from fiberglass and an aluminum lightning protection mesh. The number of plies and their orientation varies throughout the blade span, resulting in a variable-thickness part.Although Hanke won't reveal how the composite interfaces with the comolded stainless steel shank that connects the blade to the hub, he does say, "We connected thecomposite material to the shank in such a way as to minimize stresses, a result we achieved through FEA analysis." Specific materials and suppliers are trade secrets, but Hanke revealed that the materials selected were aerospace-grade and that the laminate thickness was optimized at different locations along the blade span, to meet varying loads. Along the outer two-thirds of the blade's leading edge — the segment that travels at the highest speed — a highly durable, removable nickel erosion strip provides damage protection. Urethane tape protects the third closest to the hub.A revised design in hand, Hartzell turned to the molding process. "The legacy prepreg propeller was an excellent solution, but the prepreg and layup costs made it too expensive for most general aviation applications," Disbrow recalls. "The design goal for the ASC-II was to make an affordable advanced propeller that didn’t sacrifice any of the benefits of the earlier designs." This led to the adoption of resin transfer molding (RTM).The company produces its own lay-up kits, which contain the appropriate number of dry composite materials and metal parts, permitting quick layup in two-part steel molds, designed in-house. The blade parts are comolded and infused with epoxy resin at multiple workstations, each equipped with an automated RTM cell. Part production is fast and overall labor costs are lower as well, the company says.Because Hartzell chose to market the ASC-II to FAA-certified piston aircraft, like those built by Cirrus and Piper, rather than limit it to uncertified experimental planes, the blade had to be type-certified, which is "a huge, demanding task," Disbrow stresses. A series of stringent ground tests included a 4-lb/1.8 kg bird strike at the critical flight regime of full power at take-off rotation; lightning strike trials (200,000 amps); cyclic fatigue tests; and pull-out tests, in which a test fixture tried to pull the blade from the hub, simulating an engine overspeed condition. These were followed by instrumented flight testing. Disbrow points out that the expense and time required by FAA's test regime is one big reason "why there are so few composite propellers on the market for certified aircraft." Yet, overall, he says, "We determined it was worth the effort."Lower weight, longer life, less costWorth the effort, it was: The ASC-II blade saves 16 lb/7.3 kg in three-blade configuration on the Cirrus SR-22, over a comparable aluminum-bladed prop. Beyond weight savings, Hanke and Disbrow explain that the ASC-II has the potential to last 50,000 flight hours — unheard of for a metal blade — because of its repairability.When a metal blade is damaged (usually by gravel or debris), repair involves grinding down the surface to remove potential stress risers and restore the damaged area. Over time, repeated grinding results in an undersized propeller. In contrast, the ASC-II's erosion strip can be removed and replaced, and if the composite itself is damaged, material can be replaced at the damage site, so undersizing isn't an issue. Other advantages include a shank design geometrically similar to that used for aluminum blades, so that composite blades can be substituted readily for metal blades on a propeller. De-icing systems also are compatible, for aircraft so equipped.ASC-II is marketed to piston aircraft with 180- to 350-hp engines, and to turbine aircraft that generate between 400 and 1,800 hp. One arena in which the propeller excels, Hanke reports, is the diesel-powered aircraft niche. Diesel compression ratios are very high, resulting in large excitation pulses. Aluminum props fatigue too quickly, but the ASC-II blades have successfully managed the extreme fatigue regime.More than 500 propellers have been manufactured and shipped so far. The company is currently adapting the two- and three-blade design to additional aircraft and is working on a four-blade ASC-II design. Concludes Disbrow: "The ASC-II gives us a competitive advantage, since the composite materials allow us to balance weight, durability, performance and cost."。